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Home My WebLink AboutMahoney Lake Hydroelectric Project Initial Consulation Document 1994City of Saxman, Alaska Mahoney Lake Hydroelectric Project FERC Project No. 11393-000 Initial Consultation Document TABLE OF CONTENTS Initial Consultation Document Section 1.0 Introduction 1 2.0 General Engineering Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. 0 Operational Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.0 Environmental and Regulatory Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Environmental Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Regulatory Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5.0 Stream Flow and Water Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Derivation of Long Tenn Daily Flow Database . . . . . . . . . . . . . . . . . . . . . 25 Flood Frequency Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.0 PURPA Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 7. 0 Licensing Study Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Water Quality and Quantity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Fisheries and Aquatic Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Wildlife and Botanical Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Historic and Archeological Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Recreational Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Aesthetic Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Erosion and Sediment Control Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 8.0 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 9.0 Consultation Document Mailing List . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 March 1994 i Mahoney Lake HydrMlectric Project FERC No. 11393 Initial Consultation Document TABLE OF CONTENTS CContinuedl LIST OF FIGURES 1-1 Project Location Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2-1 Project Site, Plan and Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2-2 Upper Tunnel and Lake Tap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2-3 Shaft and Tunnel Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2-4 Powerhouse, Plan and Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2-5 Powerhouse Site Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2-6 Access Road and Transmission Line . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5-1 Flow Duration Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 LIST OF TABLES 2-1 Principle Project Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3-1 Average Annual Energy Generation -Year 2000 . . . . . . . . . . . . . . . . . . . . 15 3-2 Average Annual Energy Generation -Year 2005 and Beyond . . . . . . . . . . . . 16 5-1 Upper Mahoney Lake, Average Monthly Flow . . . . . . . . . . . . . . . . . . . . . 26 APPENDICES A. Alternative Project Configuration Discussion B. 1982 U.S. Fish and Wildlife Service Coordination Act Report C. Agency Correspondence D. Temperature Infonnation E. Geotechnical Infonnation F. Hydrology Infom1ation March 1994 ii Mahoney Lake Hydroelectric Project FERC No. 11393 ADFG ADGC ADNR Beck CFR CFS COB DEIS ESCP FERC KPU NMFS NPS PDEIS PURPA SHPO USFS USFWS USGS March 1994 IJST OF ACRONYMS Alaska Department of Fish and Game Alaska Division of Governmental Coordination Alaska Department of Natural Resources R. W. Beck and Associates Code of Federal Regulations Cubic Feet Per Second U.S. Army Corps of Engineers Draft Environmental Impact Statement Erosion and Sediment Control Plan Federal Energy Regulatory Commission Ketchikan Public Utilities National Marine Fisheries Service National Park Service Initial Consultation Document Preliminary Draft Environmental Impact Statement Public Utility Regulatory Policies Act State Historic Preservation Officer U.S. Forest Service U.S. Fish and Wildlife Service U.S. Geological Survey iii Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document 1.0 INTRODUCTION The City of Saxman, Alaska, is investigating the development of a 9.6 megawatt (MW) hydroelectric generating plant located at Mahoney Lake near Ketchikan, Alaska. Cape Fox Corporation, an Alaskan corporation established under the Alaska Native Claims Settlement Act as the village corporation for the Native village of Saxman, has been retained by the City of Saxman as the development agent for the Project. The proposed Mahoney Lake Hydroelectric Project is located five miles northeast of Ketchikan, Alaska and about four miles north of an existing project, Lake Silvis/Beaver Falls Hydroelectric Project, which is owned and operated by the City of Ketchikan d/b/a Ketchikan Public Utilities (KPU). The Mahoney Lake Hydroelectric Project location is shown on Figure 1-1 and is located on lands owned by the Cape Fox Corporation and the U.S. Forest Service (USFS). Hydroelectric development at Mahoney Lake has been studied since the 1970's. A considerable amount of data has been gathered in the Project area on water quantity and quality, fisheries and geology, and an environmental impact statement was prepared for a project at this site in 1983. The Project presently proposed has been revised from previous alternatives studied to reduce environmental impacts and to make it more cost effective. The Federal Energy Regulatory Commission (FERC) issued a Preliminary Permit (No. 11393-000) to the City of Saxman in June 1993 to allow them to study the Project. This permit expires in June 1996. The FERC regulations require the Applicant to follow a three-stage agency consultation process in the preparation of a hydropower license application for the Project. The Applicant must contact all appropriate federal/state/local agencies, Native Americans, and public citizens who are interested in the Project. The reason for this is to obtain input on concerns about the proposed Project, to identify environmental or other issues surrounding the Project development, and to provide clear communication about the proposal and its possible impacts to all interested parties. This Initial Consultation Document has been prepared to provide a general overview of the proposed Project design, operation, and potential impacts. Also included is a description of the studies that are proposed in order to gain more detailed knowledge about potential impacts. After review of this document, agency and public hearings will be held in Ketchikan. Following these hearings, the agencies and the public are invited to submit written comments about the proposed Project and the proposed study plans. The plans will then be revised to incorporate comments received. A fmal version of the Consultation Document will be issued that contains fmalized study plans and copies of all consultation correspondence. This three-stage consultation process will lead to the submittal to the FERC of a license application for a Major Unconstructed Project (18 CFR 4.41) that has been developed utilizing the results of the agreed-to studies. March 1994 1 Mahoney Lake Hydroelectric Project FERC No. 11393 D I -' ~ ;, J r J J ~ j n ~ L " u ' i '· t GRAVINA (/ ISLAND ~ vJ -' (\ \ ~~f ( ' \<;1' ,~:~ \ LAKE r REVILLAGIGEDO , ISLAND ,() I ' ,f v~\'\ \ "-, ~~ R E VI LLAGIGEDO CHANNEL VICINITY MAP (> ~ ' ~ ~ IS ~ ,.. ~ " ARCTIC OCEAN r ;:J I I \ ALASKA \ !-'. ANCHORAGE I ~( r-~0n ~~~ ~) L::~~:/~tfij:-r \ j ~ .JJ~EAU ~~ o cuL of sr<"~.(-h._\ {{} A L A }u~<@ ~~TCHIKAN ~ -VY ~:~~ c:/;:::e-_,.. ' ' ~ ~ Vg •ll.. "'» pACIFIC 0 C £AN ~ LOCATION MAP HDR En CITY OF SAXMAN, ALASKA APPUCA TION fOR LICENSE MAHONEY LAKE HYDROELECTRIC PROJECT FERC PROJECT NO. 11393 PROJECT LOCATION MAPS fiGURE 1-1 Inc. Initial Consultation Document 2.0 GENERAL ENGINEERING DESIGN Several detailed environmental studies have been conducted at Mahoney Lake previously by the U.S. Anny Cotps of Engineers (COE) and R. W. Beck and Associates (Beck) on behalf of KPU. Because of southeast Alaska's dependency on diesel fuel for electrical generation and impacts caused by the oil crisis during the mid-1970's, Congress directed the COE to conduct feasibility studies of hydropower sites to serve Ketchikan, as well as other areas of southeast Alaska. An Appraisal Report for KPU was prepared by Beck in June 1977 for the Swan Lake, Lake Grace, and Mahoney Lake Hydroelectric Projects. A Preliminary Interim Feasibility Report on Hydroelectric Power and Related Puzposes for Ketchikan Area, Alaska and a Preliminary Draft Environmental Impact Statement (PDEIS) for the Proposed Mahoney Lakes Hydropower Project was prepared by the COE in 1978. More studies were conducted and another version of these documents were compiled and distributed in July 1983 as a Draft Interim Feasibility Report and Environmental Impact Statement; Hydroelectric Power for Sitka, Petersburg/Wrangell, and Ketchikan, Alaska (DEIS). These previous studies were reviewed in detail. A site visit in June 1993 was conducted to review present conditions and identify potential development sites as well as potential problems. The Project area was surveyed to develop accurate and detailed maps. A feasibility study was then performed to review alternative Project arrangements, select the best development alternative, and to estimate energy production and development cost for -the proposed Project. Refer to the attached figures that show the selected Project arrangement. The proposed Project will use a "lake tap", which will tunnel into Upper Mahoney Lake about 75 feet below its surface and then use a series of tunnels to convey water from Upper Mahoney Lake to the powerhouse located near Lower Mahoney Lake at the base of a large waterfall (Figure 2-1). No dam will be constructed. The normal water surface elevation of Upper Mahoney Lake is El. 1959. The centerline of the turbine runner in the powerhouse will be set at El. 150, thereby providing a gross head differential of 1,809 feet. As shown on Figure 2-1 , a 3, 350-foot long, 8-foot high by 8-foot wide horseshoe-shaped tunnel, will be constructed from the powerhouse into the hillside. Portions of the tunnel will be lined with shotcrete, and supported by rock bolts and steel sets as required. The tunnel will provide permanent access to a 32-inch diameter welded steel pipe supported on concrete saddles within the tunnel. The tunnel invert will slope at a 10% grade to the powerhouse. March 1994 3 Mahoney lAJce Hydroelectric Project FERC No. 11393 .... lll ~ t ~ I! t 5 I ~ I I I I ~ .~ I ~ .... 0 li I I~ ~ ... li i 3 li 2 I . ,1: ~<t..:-:...r,$'" .. '"~. -~~~ -~ -~1. .-. ;: . ~=~:_,:<· '·~ ~~ ·;: :-. ;Y, "'•~-·· ~~-........ ~· . : ·>-<,,,. 4_ ·:... ..... ·:...· LAKE TAP . ' i~' . 'I'~ • . ' ' . •' ~I ~· . ,~ ~· . 7 . / I · I I UPP£R WAHONEY LAI<£ NORMAL W.S.EL 1959.0 1800 1600 1400 _JlQQ_ .... ~ z 1000 o--- 1= ~ w d ~ ..§Q!L ~ ..1QQ_ ... _ o __ 0+00 12+00 16+00 I · . ' I / I :f ~ ~~~ .~., ' "'• ........ ~6: ;: . I ,· •. ~ ...... ""'!"' ,.-···-.·~.'__...· .............. SHAFT .# ,.~ .. D . ~ .. -.... • .,,,.;. \..I, ~. ·., $ .. ·."'"") # '\:-\ot ... ~ ";"~,...._, ... -< ,_ 20+00 24+00 ,, ;j ."~)::/ \ .. -{+ ... . I ; !./ I . •. . . ; ·.I ~ l -~,/ ~--A. ~ ': L i p~·:.r ; ~ n-11 . :'.;~. · r ,: ,·r //·/ '·;"j ~ ,, ' ~ : / : (" /· ~ .·· ._;[:'"' \ " ': .I \, •• } .. , . ~-.. '-; ~; /}_/!/. .... .... ~ '···~--":··,··t~·~y. -~i;.>··.,;.·-.. · j ·' ., I I: ( ' /: l .. _:H.s. ~ f t' :' i ;' ! -.· ; ... ) ~-j --~;/ /.jf · .. · .. ~ ~~~ ~--~ .. ~-~-..f~:;~ . .;ol!,~--· .. -?-.. :'. I . ;;:.' ~-~:.;~.y / .; ... ·I ···~ l . .... / , ·r · . .......... ~--. ... l ' ··'"7";. ,=-; ~ I: t• .... .,.~·. ·. ~;~· . ' _... ' . IJIIItNAEO ~~ • • ......-'-••• ' · · II"" ~ " -·;:-: . > <· -· <~ : /.'\~ ..... ~;~ . : ·~A .> /::··~ ..... .. -:~ -· ......... ··~~ .. . ...... ·~ ~ .. -. . ... ~. PLAN SCAL£""7":'" 200' •. 28+00 J2+00 PROFILE ~ ,. -200' ...... ,-;··:.· .. J6+oo 40+00 , < ; > . ' ! !'!--.... . ~-?-!-'\·-~ ._, / . :.~( .. :~ ~-...... :···:· . .,, ,, ':t:_ ':...,.:._ ·..;. ""\ ",\ ............ .. · ;. '!:· ., ; . \ .. '\. . .··.~ ·,: -~ ... '\.'1. ... .,.~ ..... ">. ~~:\,1-.... .1, " ... ~.t.. ..... ../~ ..... ,...,.~_.,....., ....... .·.~ J~;.:~;~ ""\. ·; ..... ~ , f .•, : .. ¢• ,.., t . ... ~ '• ) .... _ ... , •.. ('~ ~'OJr ~-Dow..,,.. Qlo' ' . -:~ ... 1IQ., II.~ "Oifts r ~ · · .. ·-:.. ~ .. ..... :..\.>::. 44+00 48+00 52+00 • -. 'Y' I' •. ~ of ~ • .. :; "":i: ~~t~];;;;,; :, .. , ... .. ~ .•• ,'!,...··. / ··""':· ~-'· _,_.... .. . ~ ..,- ".-~' .... .l~~...... ..,..,.. .,r • ·~ "-"'!. . ..... ....... POWERHOUSE ,. '•. t , i ~ ~· ., .. .... I ........ \ I' ·-~~~~-.. _ ...lQQQ_ ~ ·,600 ~ ...llQQ_ ... ~ 1000 z ---o ...!!QQ._ ...!Q2_ ~ ~ _o __ I= ~ w ... ... HOREn . -:.. ACCESS ROI\0 AHO BURIED lRANSMISSION LINE II AHONE Y LAKE W.S.EL 88.0% 200 0 200 400 600 1..-1 __1__ I · t I--I SCALE IN fEET OTY Of SAXMAN, ALASKA APPUCA 110N FOR UCEN SE MAHONEY LAKE HYDROELECTRIC PROJECT FERC PROJECT NO. 11.393 PROJECT SITE PLAN AND PROFILE FIGURE 2-1 I II Initial Consultation Document At the upstream end of the 8-foot tunnel, a I ,370-foot long rock-lined vertical shaft will be constructed, as shown on Figures 2-1 and 2-3, that will reach the ground surface in a flat area about I ,500 feet downstream of the upper lake. Following excavation of the vertical shaft, construction will proceed on the "upper" tunnel and lake tap. Plan and section views of the tunnel and lake tap are shown on Figure 2-2. The upper tunnel will be an 8-foot horseshoe- shaped tunnel, about 1,480 feet in length. Tunnel walls will be left unlined except in areas requiring additional support. Maximum velocity at full turbine flow will be 1.4 feet per second (fps) through the tunnel, which is well below accepted standards for safe velocities in unlined tunnels. The upstream end of the tunnel will pierce the submerged rock walls of Upper Mahoney Lake at a depth of about 75 feet. A lake tap deeper than this level would provide more draw down capability, but hydrologic analysis shows that further draw down may not allow the lake to be re-filled completely each year. Preliminary surface investigations indicate the general rock quality in the vicinity to be competent for lake tap construction and tunneling. A concrete plug will be constructed at the downstream end of the lake tap pressure tunnel. A 4-foot diameter pipe will be installed in the plug to convey water from the upper tunnel to the vertical shaft. A valve house will be constructed immediately downstream of the plug, containing two butterfly valves and a vent pipe. One valve will act as the primary intake shut- off valve and the other as an emergency shut-off. Both valves will be motor-operated and connected by power and communication lines to the powerhouse. The powerhouse will be a semi-underground structure constructed at the portal entrance to the lower tunnel. A conventional above-ground structure was considered, but such a structure would be more subject to damage from avalanche. A semi-underground structure will be protected from an avalanche, and will not require extra equipment or make construction more complex since a tunnel portal needs to be constructed regardless of the type of powerhouse. The powerhouse will be essentially an over-excavated tunnel portal. Additional benefits of a semi- underground powerhouse are that it will reduce the amount of concrete required, and heating requirements will be less than in an above-ground structure. The powerhouse will contain a single twin-jet horizontal Pelton turbine. Maximum rated discharge will be 78 cfs and rated net head will be I, 730 feet. The synchronous generator will generate at 13,200 volts and be rated 9,600 kW continuous. Centerline of the turbine shaft will be at El. 150. The general layout of the turbine, generator, and auxiliary equipment is shown on Figure 2-4. An overall site plan of the powerhouse is shown on Figure 2-5. The powerhouse site has been carefully selected to avoid potential impacts to fish using Lower Mahoney Creek. The cascades and waterfalls between the upper and lower lakes end at a deep pool surrounded by bedrock walls at approximate elevation 140 about 8,000 feet upstream of Lower Mahoney Lake. Fish cannot pass this point on Mahoney Creek due to the waterfalls. The water discharged from the proposed turbine will re-enter Mahoney Creek at this pool. March 1994 5 Mahoney lAke Hydroelectric Project FERC No. 11393 "'· "( '11 ~ ::t ~ -< i 0 ~ ~ .... "' o. I o, ~~ ~~ ~~ ~~ ~ 1 ~ z .... a F' iO " p 0 z ~ 1: • r- 8 0~ ~ ~ ~ ~ 8; !! :b. a a~ ------ 1 ) .... ~· / . ,~... . i I \ ... ' '· -.-·- ..... -· IJAI~ PLOITEO: SC'-LE : 1 • 1 ·, \ ' \ \ \ ',_ ·. •\. \ 1. \ ~ \ I \ ... , . . ; ' '···. . .. , · .. > .... ~. \ ... , ... \ . ''. . ···, ' I \ \ '· '-. ·. ' \ \1 \ \\ \ ·.I '\.\ '. ·, '' . \ 0 \ ij '· ' ·, \ \ ' I i '\ •, ·, . \ . '~ ". ' \ '' . i i ·' \ ., ' ' \ \ \ i . '\ ' " t '• \ \ \ '!", ' ... '\\ \ '.\\\ \ •' . . . \ ·, . \ \ \ '· • •• ·,,f.; a \i l \\\\\~ ' \ i \ ' I I I \ ; I I '· ·, / !:1 g \ 111'!1 ·, ' \ \ ' < ; \ i ·, \ ~ \ \ \ \ \ \ \ ) . I I \ \ \ \ • l \ \ i '•. f \ \ J 0, l. ' ,. ' -xREr /S: WI.-TB , . . /' I j ' I I ~·" ' , ,' .' ,· .I I J ,. J T i l ... EL. 510.0 . ' 40'-0" ROCK TRAP ~ 0 I in SHAFT -------r--------------~ ------- SHAFT/TUNNEL SECTION seAL£: ~ * = ''-o" 7'-0" !Ill -::::s 'Jl[J ,_..., ..::::-:- 1111 TYPICAL UNLINED SHAFT SECTION SCALf: !?" = 1'-0" s·-o· 0 I 'i.o TYPICAL LINED SHAFT SECTION (AS REQUIRED) SCALf: »" u 1 ·-o· 10' LONG ROCK BOLT (T'I'l')-~ 'll II II I '-SHOTCR£1E s·-o· ..... ~/· ~,../ ... /·· TYPICAL SUPPORTED TUNNEL SECTION SCALf: »" = 1"-0· 100'-0" ------------ -------------- ~ 8' H.S. TUNNEL ./REOUC!:R // s·-o· •;0 ...... ~ 0 I .... TYPICAL UNSUPPORTED TUNNEL SECTION SCAL[: » -1'-0 CITY OF SAXMAN, ALASKA APPUCA TION FOR UCENSE MAHONEY LAKE HYDROELECTRIC PROJECT FERC PROJECT NO. 11393 SHAFT AND TUNNEL SECTIONS FIGURE 2-3 I!! I -' :E ~ .... ... "' X ... -' .. b: .., "' ' .., 0 ' Q !: a _J n. ;':! " Q ~ ;; ,,) I: " "' cO "' " -· ·' ·.) I: .. ~ :J ~ .:;:; :. I TUNNEL -E- 'o I "' "' s·-o· I I I I I I I I OffiCE AREA TVNNEl ACCESS PLAN SCALF::»~;;, i"-o• PERSONNEl DOOR -~~~,1 \_BURIED 5" YtiDE TAILRACE CHANNEl (ROUTE TO STR£AM) 14'W • 15'H ROLL-UP DOOR 36'-o· s·-o· --------------------',t\ \ \ I _,. ... ~ I /ROLL-UP 0 . ' I L_ ____ -=== I 0 I .... "' PERSONNEL DOOR EQUIPMENT LEGEND G) SURGE EQUIPMENT. CABLE TO SWITCHYARD @ crs @ VOLTAGE RECOI.ATOR/EXCITER 0 NEUTRAL GROUND ® STAllON SERVICE PANEL ® AC PANEL 0 DC PANEL ® DRY TYPE TRANSfORMER (i> BATTERY (§) BATTERY CHARGER (:!!) IAOTOR STARTER @l HYDRAULIC PRESSURE UNIT @ ACCUIAULATOR TANK ~~f\_,~~rr ,.,~ '· J_ I i I l <>-~ j I I II I ! I . ELEVATION -l ', ·,, ~EXCAVATION LINE SCAL(: » • "" 1 ·_ o· ~F;q~q:. ED @ RElAY PANEL @ CONTROL PANEL @ ELECTRIC UNIT H[A TER @ SUI.lP PUI.lPS @ DESK @ nLE @ BOOKCASE @ 1/E.NlllA 110N LOUVER @ OIL/WATER SEPARATOR . 175 l \ "i!. (RUNNER EL 150.0 tLill OTY OF SAXMAN, ALASKA APPUCAnON FOR UCENSE MAHONEY LAKE HYDROELECTRIC PROJECT FERC PROJECT NO. 11393 POWERHOUSE PLAN AND SECTION FIGURE 2-4 I I!! I .... :II ~ ~ I~ .~ I I~ ll I 1! • , • If l ~ II i I I \ '• .... j '.....- ,. ,. ~..) ~~~,s.a..~.~~ .......... _ ......... ,.. I --<.'\' ·. ... \ ., \. .,_ \ / . ... ·--... .:.-·-..... \::-,:::, \:·:,\:;.·:.;:·:·.~---~~.~·--. \l~:~~~r~; __ -_:········•~.::-·.~·~>:'. \'' ·--:::, ' .~ " ·-~ '· ... " ,, ,· ,·"'.~·.,!' / -~;if~ifd~i~~'~j~~"·;:;:~·::~: . ·' -.. . ' / ·' / / .. ~ ' / . . " ... ~ ,..-' # • ; ,t' _,~ .~ , .• / ' I / ' .t : • • •· ~"";, • , • . • • ,'-' .·'., ;••' .. ,/.,/ l I ';) I .' .-1 _.' r'' j / .. :··.·.: .... /< << /( / / /. ~\> :.-.:~/ .... ··,;1 .,.. .-. ,· • •' r f ' ,.. / •.• ; :><~-· . '/ i / /: ... ; .. /~~---.. <~.· /. .. d , .. . /.~">·~/.:,.~. ,/,•' ' ~ / I ' . ........ ~ / ·'' .r' ~ ,.• _., .. ·· , .'"',.~··.,~~ : .. •' I F I I I .· ' ,/ .•' / / . .. i / . / /,'/ .• · .-/..-" ...... / . .·• ,. / .l.• , , / r , .• ·"' ..-· .I . ,£1~~~f~?~c~ c~:: / ~· ,·-~·> '~~~?f(~~:\., ·, ·,.,\ ... -·· ... .· •' ···-"' \?.? ·-,·-~~ ~~-.:·_: .. ;.~; ... ~-... ·":·· •.. ··.:··· .... ,. .... :' ~.>:. ........... ! , :: 1: . ' POWERHOUSE r' . i -· .~· . -. . "~9~~-~· .. ~ ~-:,;...--~~-~~ .. -->-:;..--. ~-~·· ·-----~. •/ · .. __.....-~ . __,...-......--·· ... ~ .. ·~···' -' ... .. ~o .... g VI (]I 0 ~ IJ' 'b 0 ~ 0 . j ~ IJ' .·/ .. ·' . ·<~< ... ·. ~-.. \\ :~ 0 ·.' ". ~ ~ \ ~ IJ' PLAN SCALE: 1"-50'-0" .' STAQNG AREA ., 50 ..J 50 r f[[T kiXL --• I l"""'aa.--- ,--:.0 ·. ···., ! ACCESS ROAD 13.2 KV UNDERGROUND TRANSMISSION LINE <ao ,' / -·· / ! ' . / _.'./ . .. · / 175 •.. · / I ' f / ·· ... · ......... -, ·, ,. ,,-· ~· ,. ~ 125 HOR QTY Of SAXMAN, ALASKA APPUCA 110N FOR UCENSE MAHONEY LAKE H'f'DROELECTRIC PROJECT FERC PRO.E:CT NO. 11J9J POWERHOUSE SITE PLAN FIGURE 2-5 \,. Initial Consultation Document The transmission line route will begin at the powerhouse and follow along the south and east sides of Mahoney Lake, then run northerly to its interconnection point with the 115 kV Swan Lake transmission line near the confluence of the White River with George Inlet. A switchyard will be located 0.8 miles from the powerhouse in a low avalanche hazard area. A power transformer will be located in the switchyard to step up generation voltage from 13.2 kV to the transmission voltage of 115 kV. The transmission line will include 0.8 miles of 13.2 kV underground cable and 4.7 miles of 115 kV overhead construction. The 115 kV transmission line will follow along an existing logging access road recently constructed by the Cape Fox Corporation. The access road and transmission line route are shown on Figure 2-6. Details of the proposed Project are summarized in Table 2-1. A discussion of alternative Project configurations that were considered is included in Appendix A. An alternative transmission line route that connects power output to the KPU system near their existing Beaver Falls Project is feasible from an engineering standpoint, but is more costly. This route could be considered if benefits to KPU exceed the additional cost of this alternative. March 1994 10 Mahoney lAke Hydroelearic Project FERC No. 11393 I!' I ..... :I! ~ ... ~ X ~ .. b: 0 lc'! .... 3 Q. lc'! .. 0 ~ c ~ "' ~ < w a ~ ::> / i .:.; ~ § ;;: r'-.. / I l / J \/ I /) \ \ \\//~ \ ~ REVILLAGIGEDO ISLAND / \ \ / m~~~~)\: UNE "---- 0 " (I' 0 "#) " (1'. ; '$. (' (I' .... REVIu.AGIGEDO ISLAND CTY Of SAXMAN, ALASKA APPUCA110N FOR UC[NSE MAHONEY LAKE HYDROELECTRIC PROJECT FERC PROJECT NO. 11393 NEW ACCESS ROAD AND TRANSMISSION LINE FlGURE 2-6 107659H.DI'II:l Initial Consultation Document TABLE 2-1 MAHONEY LAKE HYDROELECTRIC PROJECT PRINCIPAL PROJECT FEATURES Number of Generating Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Turbine Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pelton Rated Generator Output, MW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. 6 Maximum Rated Turbine Discharge, cfs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Minimum Rated Turbine Discharge, cfs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Turbine Runner Centerline Elevation, fmsl ............................ 150 Average Annual Energy, kWh .............................. 41,740,000 Nonnal Maximum Reservoir Elevation, fmsl .......................... 1959 Normal Minimum Reservoir Elevation, fmsl . . . . . . . . . . . . . . . . . . . . . . . . . . 1890 Gross Head, feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1809 Net Head at Maximum Rated Discharge, feet . . . . . . . . . . . . . . . . . . . . . . . . . 1730 Upper Mahoney Lake Drainage Area, sq. mi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 Surface Area at El. 1959, acres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Active Storage Volume at El. 1959, acre-ft . . . . . . . . . . . . . . . . . . . . . 3,760 Average Annual Natural Outflow, acre-ft ...................... 32,600 Average Annual Natural Outflow, cfs . . . . . . . . . . . . . . . . . . . . . . . . . . 44.4 Diversion Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lake Tap at El. 1880 Upper Pressure Tunnel Type ................................ Partially Unlined Horseshoe Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-foot by 8-foot I...ength, feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1480 Invert Slope, ft/ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0. 002 Velocity at Maximum Turbine Discharge, fps ...................... 1.4 Pressure Shaft Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Partially Lined Rectangular Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-foot by 7-foot Top of Shaft Elevation, fmsl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1850 Bottom of Shaft Elevation, fmsl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480 Velocity at Maximum Turbine Discharge, fps ...................... 2.2 Lower Access Tunnel Type ................................. Partially Lined Horseshoe Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-foot I...ength, feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,350 Invert Slope, ft/ft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.10 March 1994 12 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document TABLE 2-1 MAHONEY LAKE HYDROELECTRIC PROJECT PRINCIPAL PROJECT FEATURES (continued) Lower Access Tunnel ( cont' d) Pipeline Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . Welded Steel on Saddles Pipeline Diameter, inches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Pipeline Length, feet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3350 Velocity in Pipe at Maximum Turbine Discharge, fps . . . . . . . . . . . . . . . . . 14 Powerhouse Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Semi-underground Approximate Dimensions ............... 40-foot by 40-foot by 28-feet high Generator Floor Elevation, fmsl .............................. 147 Tailrace Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Buried Concrete Rectangular Length, feet .......................................... 200 Transmission Line Length of Underground Construction, miles ....................... 0.8 Underground Line Voltage, kV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2 Length of Overhead Construction, miles . . . . . . . . . . . . . . . . . . . . . . . . . 4. 7 Overhead Line Voltage, kV ................................. 115 New Powerhouse Access Road Type . . . . . . . . . . . . . . . . . . . . . . . Single-lane gravel surfacing with turnouts Length, miles ......................................... 1.0 March 1994 13 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document 3.0 OPERATIONAL MODE The proposed Project consists of a "lake tap" on Upper Mahoney Lake at a depth of about 75 feet below the existing natural lake level. The lake tap provides the capability to drawdown any available water in the upper portion of the lake regardless of inflow but without the necessity of constructing a dam. Diverted water would be conveyed through a 1,480-foot long upper tunnel where it would then drop 1,370 feet through the vertical shaft, then flow an additional 3,350 feet in a 32-inch diameter steel pipe to the powerhouse. Total drop in elevation is 1,809 feet. The powerhouse would contain a single Pelton turbine/generator unit capable of generating 9,600 kW of power and 41,740,000 kWh of energy in an average water year. The Project would intertie with the existing Swan Lake transmission line to provide additional energy and capacity to the KPU transmission and distribution system. The proposed Project will provide 9, 600 kW of firm capacity to the KPU system assuming the Upper Lake has some storage available. The Project could operate continuously at full capacity for about 55 days assuming the full pool is drafted and the average inflow of 44 cfs came into the reservoir. Assuming 5 cfs of inflow, and starting with a full pool, the Project could operate continuously at full capacity for about 26 continuous days. Current total generation capacity of all resources available to KPU, including diesel units, is approximately 49,450 kW. The Mahoney Lake Project will operate at a 0.48 plant factor, typical for a storage Project. For comparison, the Swan Lake Project operates at a 0.42 plant factor and the combined KPU-owned hydroelectric projects operate at 0.63 plant factor. A computer-based model was set up to simulate operation of the Project, using average monthly inflows, an area-capacity relationship developed by the U.S. Army Corps of Engineers, and projected seasonal energy demands in the KPU system. Table 3-1 shows projected energy demand in the Ketchikan area based on several different forecasts. If the Project comes on-line in 1999 as planned, it should be possible to utilize all Project energy production in the first year of operation. By the year 2005, if even the conservative forecasts prove accurate, all Project output will be needed in the area. Table 3-2 shows the output from the Mahoney Lake operation model for a typical year after 2005. March 1994 14 Mahoney lAke Hydroelectric Project FERC No. 11393 Table 3-1 p:\hyd\mahoney\tab3-l.v.ic3 CITY OF SAXMAN, ALASKA MAHONEY LAKE HYDROELECTRIC PROJECT Average Annual Energy Generation-Year 2000 Lake Tap Alternative Annual Demand 191196 MWhrs Minimum Pool Elev.: 1890 Storage KPUSummer 44339 MWhrs Pool Starting Elev.: 1959 3760 KPU Winter 103311 MWhrs Turbine Elev.: 150ft Un-met Summer 13020 MWhrs Assumed Head Loss: 80ft Un-met Winter 30526MWhrs Assumed Eff. 0.82 Min. Instream Flow: 2 cfs Inflow Avg .·· Pool ·•· Tl.lrbine Pool Monthly Inflow -MIF Demand Start Flow. Ending Average ·Energy Month (cfs) (ac-Jt) {MWh) Elev (cfs) . Storage EJev Generation Oct Nov Dec Jan Feb Mar Apr Mav June July Aug Sept 69.8 4169 4002 44.8 2547 4152 18.6 1021 4222 30.6 1759 3910 24.4 1255 3645 17.3 941 3773 25.0 1369 3410 61.1 3634 3391 82.4 4784 3125 61.2 3640 3129 44.6 2619 3151 52.7 3017 3629 Endini! Pool Elevation SUMMARY OF GENERATION Un-Met Summer Load Mahoney Summer Generation % Un-Met Summer Load Un-Met Winter Load Mahoney Winter Generation % Un-Met Winter Load 1959 44.8 1959 48.1 1954 47.9 1921 45.1 1901 31.4 1890 15.3 1890 23.0 1890 39.3 1916 36.7 1958 35.1 1959 35.3 1959 42.0 1959 13020 MWhrs 13033 100% 30526 MWhrs 25354 83% 3760 1959 4002 3442 1957 4152 1517 1938 4222 504 1911 3910 0 1896 2460 0 1890 1311 0 1890 1907 1219 1903 3391 3749 1937 3125 3760 1959 3129 3760 1959 3151 3760 1959 3629 Total Generation 38387 Table 3-2 p:\hyd\mahonev\tab3-4.wk3 CAPE FOX CORPORATION MAHONEY LAKE HYDROELECTRIC PROJECT Average Annual Energy Generation-Year 2005 and Beyond Lake Tap Alternative Yearly Demand 198450 MWhrs Minimum Pool Elev.: 1890 Storage KPUSummer 44339 MWhrs Pool Starting Elev.: 1959 3760 KPUWinter 103311 MWhrs Turbine Elev.: 150ft Un-met Summer 15196 MWhrs Assumed Head Loos: 80ft Un-met Winter 35604 MWhrs Assumed Eff. 0.82 Min. lnstream Flow: 2 cfs Inflow Avg Pool Turbine Pool Monthly Inflow · .. -MIF Demand Start Flow . Ending Average Energy Month (cfs) (ac-ft) (MWh) Elev (cfs) Stora~e Elev Generation Oct 69.8 4169 4668 1959 52.3 3760 1959 4668 Nov 44.8 2547 4842 1959 56.3 2957 1952 4842 Dec 18.6 1021 4924 1945 56.4 512 1923 4924 Jan 30.6 1759 4561 1901 36.9 0 1896 3175 Feb 24.4 1255 4251 1890 22.4 0 1890 1749 Mar 17.3 941 4401 1890 15.3 0 1890 1311 Apr 25.0 1369 3977 1890 23.0 0 1890 1907 May_ 61.1 3634 3956 1890 45.9 810 1899 3956 June 82.4 4784 3647 1908 43.0 2948 1927 3647 July 61.2 3640 3652 1945 41.1 3760 1952 3652 Aug 44.6 2619 3677 1959 41.2 3760 1959 3677 Sept 52.7 3017 4235 1959 49.0 3760 1959 4235 Endin~ Pool Elevation 1959 Total Generation 41742 SUMMARY OF GENERATION Un-Met Summer Load Mahoney Summer Generation % Un-Met Summer Load Un-Met Winter Load Mahoney Winter Generation % Un-Met Winter Load 15196 MWhrs 15211 100% 35604 MWhrs 26531 75% Initial Consultation Document 4.0 ENVIRONMENTAL AND REGULATORY ISSUES This section includes a description of the environmental setting, preliminary identification of environmental impacts from the proposed Project, possible agency concerns, and pennitting requirements. The infonnation contained herein should not be considered a complete environmental assessment. ENVIRONMENTAL ISSUES Topoaraphy The Project site is located in southeast Alaska approximately 5 air miles northeast of Ketchikan on Revillagigedo Island. The island is located at the south end of the Alexander Archipelago, which is a belt of mountainous islands off the coastal mainland. The island is roughly oval in shape, about 56 miles long and 42 miles wide. It has an area of 2,352 square miles. The highest peak on the island is 4,560 feet above sea level. In most places, the mountains rise sha:q>ly from the water's edge, although there are a few areas of coastal lowlands along the southern shore of the island. Numerous lakes are distributed over the island, and countless short, swift streams flow down to the ocean. For this Project, water from Upper Mahoney Lake, at approximate El. 1,950 feet MSL, flows down a cascade (Upper Mahoney Creek) to the lower lake (El. 85) and then into George Inlet by way of Mahoney Creek. Climate The Ketchikan area experiences a maritime climate with relatively mild, wet winters, cool summers, and heavy precipitation. According to the 1983 COB DEIS, the average annual precipitation for Ketchikan is approximately 154 inches, including 33 inches of snow. Average monthly temperature ranges from 34 °F in January to 58. 7°F in August. Prevailing winds in the Ketchikan area are from the southeast. The growing season extends from early May to early October. Local climatic patterns are strongly influenced by the mountainous topography of the region (COB, 1983). Water Quality Because of the pristine nature of the Project area, the quality of the water resources are high. Water quality has not been degraded due to limited human activity in the area. There also has been little natural degradation in the streams below the lakes because the lakes act as catchments, reducing the maximum sediment concentrations. Water quality may experience short-term impacts during construction. However, no significant degradation of a long-term nature is expected because the Project will utilize a lake tap on Upper March 1994 17 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document Mahoney Lake and water will flow underground through tunnels and pipe to the powerhouse at the base of the falls above Lower Mahoney Lake. Because the water is not exposed to the atmosphere at any time, problems related to gas supersatu:ration are not expected to occur. Tempo:rary increases in levels of turbidity, suspended solids, and stream siltation may occur as a result of land clearing and other construction-related activities. An Erosion and Sediment Control Plan will be developed as part of the FERC License Application and it will be implemented during construction to control sources of potential sediment. Construction "Best Management P:ractices", including construction scheduling, care of water, erosion and sediment control measures, and re-vegetation plans will avoid or minimize problems associated with land disturbance. Fishery Resources Fish constitute an important recreational and economic resource of the Project area. A variety of fish species are found in the Mahoney Lakes area. Fishery studies were conducted in 1977 and again in 1982 by the U.S. Fish & Wildlife Sexvice (USFWS) (Appendix B). The aquatic system in the lower lake is valuable for fish resources, particularly pink, chum, sockeye, and kokanee salmon. Dolly Varden, cutthroat, :rainbow and steelhead trout use the inlet streams to the lower lake as a spawning ground. Other freshwater species include sculpins and sticklebacks. As stated in the 1978 COE PDEIS, the USFWS reported Upper Mahoney Lake is devoid of fish. G:rayling were stocked in the upper lake in 1966. However, stocking was apparently not successful as biological investigations conducted by the USFWS in 1977 did not indicate their presence (COE, 1978) (see Appendix C, Agency Correspondence). Lower Mahoney Lake provides habitat for resident and anadromous forms of sockeye salmon (COE, 1983; USFS, 1993) (Appendix C). Young anadromous sockeye rear in the lake for a year or more before mig:rating to the sea. Adult sockeye return to spawn along the western shoreline of the lake where there is an apparent upwelling derived at least in part from Upper Mahoney Creek. Sockeye spawning does not occur in Mahoney Creek because of the turbulent flows and unpredictable flow patterns. Aerial counts taken in September 1982 totalled approximately 300 to 500 fish either spawning or returning to spawn. Pink and chum salmon spawn in Mahoney Creek and their fry mig:rate to the sea in the spring, soon after emergence from the stream g:ravel (COE, 1983). The powerhouse will be sited at the base of a large waterfall located at about Bl. 140. At this location, the steep cascades of Upper Mahoney Creek tumble over one last waterfall into a solid rock -lined bow 1 that marks the end of the cascades and the start of a meandering channel that leads about 800 feet downstream to Lower Mahoney Lake. This large waterfall precludes fish mig:ration any further up Upper Mahoney Creek. Flows from the powerhouse will be returned to Upper Mahoney Creek at this point, above Lower Mahoney Lake. This was the ar:rangement preferred by the USFWS as stated in the 1983 COE DEIS. One alternative looked at in the 1970's and 1980's had placed a lake tap 225 feet below the surface of the upper lake, almost at the very bottom. Concerns had been raised previously as to whether or not the water tempe:rature in Lower Mahoney Lake would drop as a result of d:rawing very cold water (4°C) down from Upper Mahoney Lake and adversely impacting salmon redds along the western edge of the lower lake (see Appendix D-Tempe:rature Information). The current proposal has located the lake tap March 1994 18 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document approximately 75 feet below the surface of the upper lake to draw water down to the powerhouse via tunnels and pipe. The depth of water at the intake will vary between 5 and 75 feet throughout a normal operating year, depending on time of year, inflow to the lake, and energy demand. Temperature studies may be necessary to evaluate any impacts on sockeye salmon spawning habitat downstream in the lower lake. Botanical and Wildlife Resources Botanical Southeast Alaska has three general vegetative systems; coastal western hemlock-Sitka spruce forest, bogs or muskeg, and alpine tundra. The western hemlock-Sitka spruce forest system extends from sea level to treeline, which occurs at about 2,500 feet in the Ketchikan area. Most of the forest is mature growth, with some trees more than 200-feet tall, 14 feet in diameter, and more than 800-years old. The forest around the Project area is predominantly a mixed stand of western hemlock and Sitka spruce (COB, 1983). Western red cedar and Alaska cedar are also present in lesser percentages. In addition to these tree species, the forested areas support smaller growths of red alder, cottonwood, mountain hemlock, alpine fir, Pacific fu, and lodgepole pine. Forests have very dense canopy and understory layers blocking out most direct sunlight. Small bush saplings of shade-resistant hemlock and cedar, with blueberry, devilsclub, and other shrubs form a dense understory. Huckleberry, copper bush, Sitka alder, juniper, skunk cabbage, ferns, mosses, and grasses also contribute to this understory. Intermediate plant communities that combine elements of forest and bog grow near the forest edge. Characteristic plants of this vegetative type are shore pine, Alaska cedar, mountain hemlock, rusty menziesia, sedges, mosses, and rooted aquatics. As stated in the 1983 COB DEIS, bogs are the only type of wetland found near the Project area, along the south shore of the lower lake. This area is part of the access road/transmission line route. A wetlands delineation and assessment may be needed as part of the environmental studies to confirm this fmding. The alpine tundra occurs in open terrain above the treeline where barren rocks and rubble are interspersed with low plants including cassiopes, mountain-heath, dwarf blueberry, dwarf willow, avens, alpine azalea, lichens, and mosses. Although Upper Mahoney Lake is below El. 2,500, this type of vegetation is found in the area above the lake due to the rocky, steep terrain. Some vegetation will be lost due to constructing the powerhouse and access road/transmission line route, however, revegetation of disturbed areas will occur as soon as construction activities are completed. Because most of the Project features will be underground, the amount of disturbed area is reduced. Approximately 8 acres will be disturbed as a result of this Project, mostly from clearing forest for the access road/transmission route. Wildlife :Mammals. The Project area is relatively productive for wildlife. Deer, black bear, and wolves are common species. Sitka black-tailed deer are found in varying abundance throughout the Project area and are probably the most important big game animal of the area (COB, 1978). Deer are common on some localized, good quality ranges but are scarce in the remainder of the Project area. Populations have historically fluctuated, with extreme lows being greatest when winter conditions March 1994 19 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document are severe and where wolves are present. During different seasons of the year, deer utilize most habitat types where food is available. Their home range is usually small, but they do make vertical migrations from the beach to alpine areas as a result of snow depths and availability of food. During much of the year, low-growing forbs are the most important plant species used. Summer food is usually not a limiting factor. During severe winters when snow depth is excessive, mortality often occurs because travel becomes difficult and forage is covered. Moose and brown bear are not found on Revillagigedo Island, however, black bears are abundant throughout the timbered and adjacent portions of the Project area and, with the exception of deer, are the most commonly encountered big game animal. The areas in which black bears occur coincide closely with the distribution of forests but seasonal concentrations occur along beaches and tideflat areas in the spring and along salmon creeks in late summer and fall. Black bears prefer semi-open forests rather than dense stands of timber. Semi-open forested areas with understory composed of fruit-bearing shrubs and herbs, lush grasses and succulent forbs are particularly attractive. In the spring, black bears are frequently found in moist lowlands where early growing green vegetation is available. The sedge and grass found in low-lying intertidal areas are particularly important. Black bears spend the summer months in berry-producing areas ranging from sea level to alpine regions. Salmon become an important food item in late August and September at which time spawning is completed, with the exception of some streams with late chum and coho runs, which last into November. Hunting of black bears in the Project area is considered light in intensity (COB, 1983). Wolves occur throughout the Project area with abundance varying greatly between areas and from year to year. Wolf populations on Revillagigedo Island reach greater densities than on the mainland because deer are important wolf prey on islands and are more abundant and vulnerable than mountain goats, the primary mainland wolf prey. Natural controls of wolf populations seem to be related to abundance and availability of prey. The USFS reported that fifteen mountain goats had been transplanted to the alpine area surrounding Upper Mahoney Lake in 1991 (Appendix C). All of the proposed Project features are located below El. 1950 with only two structures and one new access road at elevation 180. Some limited disturbance of goats may occur during Project construction. Once operational, the Project will convey water through underground structures so no migration barriers will exist. Therefore, impacts to goats are anticipated to be minor. Other mammals which may be present in the Project area include lynx, wolverine, red fox, land otter, mink, marten, short-tailed weasel, fisher, beaver, muskrat, and snowshoe hare. Birds. Southeast Alaska supports breeding populations of waterfowl, but the region is used mostly for stopover during spring and fall migrations with some overwintering species. Bays and fjords are important for this purpose. However, waterfowl are not attracted to the Project area because it lacks suitable habitat (COB, 1983). The bald eagle is the most common raptor of southeast Alaska and a few nests have been found north of the Project site (COB, 1983). There are also a few ospreys and a few golden eagles present in the area (COB, 1978). March 1994 20 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document While the region has several large colonies of sea birds, none are located proximate to the Project area. Shorebirds such as killdeers, semi-palmated plovers, sandpipers, and oyster catchers probably occur within the Project area. Other shorebirds are migrant. Rock ptarmigan, willow ptarmigan, and blue grouse are resident game birds. Temporary disturbance of mammal and bird populations will result from construction-related activities and increased hunting pressure on game populations in the lowland areas could occur. Because access roads are not proposed for the upper Project area, no significant upland hunting pressure changes are anticipated. While some alterntion of existing wildlife habitat will occur as a result of the proposed Project, the impacts of this alterntion are not considered to be entirely negative because certain improved habitat conditions may result. These improved conditions may provide greater interspersion of vegetation types and creation of uneven-aged forest stands which improve browse quality for deer and other wildlife species. The 1983 COB DEIS reported the proposed Project at that time would have little or no effect on bald eagles but it is likely an eagle nest survey will need to be conducted. Transmission lines will be designed to protect rnptors from possible electrocution by providing hunting perches and/or by use of approved rnptor-proof designs. Threatened and Endangered Species. According to the 1983 COB DEIS, there were no species listed by either the USFWS or the National Marine Fisheries Service as threatened or endangered in the Project area at that time (Appendix C). This information will be updated prior to fmal design of the Project. Cultural Resources Know ledge of the prehistoric period for southeast Alaska is quite sketchy, although it is known that Tlingit Indians long had fish camps near the present City of Ketchikan and that they had a village at Ketchikan Creek. A petroglyph has been reported near Mahoney Lake in the vicinity of the cove east of the lower lake and an abandoned mine is located near the mouth of Mahoney Creek. As stated in the 1983 COB DEIS, the Project would have no impacts on cultural resources as proposed at that time. An intensive cultural resources survey of the Project area in 1981 did not locate any significant historical or archaeological sites (COB, 1983). There are no known sites eligible for the National Register of Historic Places in the vicinity of the Project. A cultural resource survey may be required for the access road/transmission line route, as this area was not studied in the previous survey. Socioeconomic Ketchikan is the fourth largest city in Alaska. Major industries that effect Ketchikan's local economy include fishing, forestry, mining, government, tourism, and commerce. Most of these industries experience seasonal swings in employment. 1993 unemployment rntes for Ketchikan (city and borough) ranged from a low of 5.9% in August to a high in January of 15.4%. As of September 1993, the population of Ketchikan was 14,000 (Alaska Department of Labor, 1993). March 1994 21 Mahoney Lake Hydroelectric Projea FERC No. 11393 Initial Consultation Document Improved access to previously undisturbed forest lands would increase the potential to utilize the timber and mineral resources of the area, along with providing low cost, renewable energy to the Ketchikan area. Geolo&Y Most of southeast Alaska's present land forms developed from the action of glaciation and volcanism during the Quaternary period, which is the most recent period of geologic time. At the height of this activity, glaciers not only covered nearly all of the land, but also extended miles out over the ocean as a gigantic sheet of ice. Remaining today as evidence of glacial action are the numerous cirques and fjords. Numbers of the fjords formed along faults or joints, mainly as a result of glacial scouring along existing river valleys. The site is crossed by faults and lineaments that are probably indicative of minor shear zones in the bedrock. Slope instability in this area is primarily rock falls and small to moderate size rock slides (Shannon & Wilson, Inc., 1993) (Appendix E). Three belts of metammphic rock and sedimentary rock trend northwest throughout the region. On Revillagigedo Island, metamorphic and sedimentary rocks dip steeply westward, and strike to the northeast. The common rock of the area consists of a metamorphic belt of schist and phyllite intermingled with smaller intrusions of quartz diorite (Shannon & Wilson, 1993). The area is classified as Seismic Zone 3, moderate risk (COB, 1978). Further information about site specific geology is contained in Appendix E. Recreation Fishing, boating, hunting, camping, and picnicking are all very popular among residents and tourists of Ketchikan, which is surrounded by the Tongass National Forest. Sport fishing, largely for salmon and halibut, is very popular. The many miles of shoreline in the area afford opportunities for beachcombing for shells, fish floats, etc. Hunting is a major recreational activity. The Sitka black-tail deer is the most sought after game animal, with bears also attracting hunters. The USFS has constructed and maintains numerous hiking trails with cabins for public use in southeast Alaska. These cabins are usually located on lakes which provide fishing opportunities, however, none exist within the Project area. Sightseeing is also popular since the area has spectacular scenery produced by the mountains, waters, and forests. As stated earlier, Upper Mahoney Lake lacks fish; there are some fish species in the lower lake. The Mahoney Lakes system receives little angling pressure due to the relative remoteness of the site and small populations of fish (COB, 1983). Increased access to forest lands increases the opportunity for dispersed recreation. However, significant changes in recreation patterns of the Ketchikan area are not anticipated due to construction of the Project. March 1994 22 Mahoney LAke Hydroelectric Project FERC No. 11393 Initial Consultation Document Aesthetics Scenic values abound in this largely undeveloped region. Myriad islands, a deeply indented coastline, forests, mountains, glaciers, and the ocean combine to form superb vistas. The study area ranks high in all elements of aesthetic quality including vividness, visual intactness, unity, and visual uniqueness (COB, 1978). The aesthetic quality of the proposed Project area would be affected by reduced streamflow. Most of the flows that form the waterfall at the outlet of the upper lake would be diverted for power generation. Visual impacts caused by the Project features will be minimal since almost all of the Project features will be placed underground. The transmission line will be buried along the proposed access road for 0.8 mile from the powerhouse to a point southeast of Lower Mahoney Lake. The line will continue north along an existing logging access road another 4. 7 miles on overhead pole structures to an intertie with the existing Swan Lake transmission line. Land Use The proposed Project would be sited on land owned by the USPS and the Cape Fox Corporation. Project features that would be located on USPS land include the lake tap, and a majority of the shaft and tunnels. A Special Use Permit would be required for this portion of the Project and any proposed development would have to be consistent with the Tongass National Forest Plan. The powerhouse, access road, and transmission line would be sited on land owned by the Cape Fox Corporation. This land was selected by the Cape Fox Corporation under terms of the Alaska Native Claims Settlement Act. REGULATORY ISSUES In addition to the PERC License, other environmental and regulatory permits that may be required for the Project are listed below. Upon PERC approval of the Final License Application and after the public notice has been issued, a package of the following permit applications will be submitted to the Alaska Division of Governmental Coordination (ADGC) and the COB. The ADGC will then distribute the permit applications to the appropriate agency for review. • A Water Rights permit issued by the Alaska Department of Natural Resources. An application for this permit has been submitted. • Under the Clean Water Act, a 401 Water Quality Certification is required from the Alaska Department of Environmental Conservation. A request letter will be sent prior to submittal of the Final License Application and a letter of receipt will be issued by the ADGC. • A Special Use Permit will be required from the USPS for development of the upper portion of the Project. An application has been submitted for a Special Use Permit to study the Project area and a section of road north of the Mahoney Lake outlet creek. March 1994 23 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document • A Section 404 Permit is required from the COB by the Federal Water Pollution Control Act if activities include discharge of dredge or fill materials into waters of the U.S and/or significant wetland disturbance. • Consistency with the Alaska Coastal Management Program is required and the necessary review is conducted by the ADGC. Ketchikan has a local coastal plan and Ketchikan Gateway Borough will issue a certification of consistency with their plan for the Project. • A fish habitat permit will be obtained from the Alaska Department of Fish and Game for instream work. March 1994 24 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document 5.0 STREAMFLOW AND WATER REGIME GENERAL The proposed Project will utilize runoff from a 2.0 square mile drainage area supplying Upper Mahoney Lake. The lake lies within the region of maritime influence of southeastern Alaska as shown on Figure 1-1. The area receives limited sunshine, abundant precipitation, and generally moderate temperatures. The area's rugged terrain causes considerable variations over short distances for both precipitation and local temperatures. A hydrologic analysis was conducted in order to develop streamflow data that could be used for estimating average annual energy generation. Several previous studies of streamflow hydrology have been conducted in the past, and these were reviewed before this analysis was conducted. The methodology and results of the hydrologic analysis performed are described below. A flood frequency analysis for the Project site was also conducted. DERIVATION OF WNG TERM DAILY FLOW DATABASE Daily streamflow data has been recorded at the outlet to Upper Mahoney Lake for water years 1978 to 1989 (USGS Gage #15067900). The gage is considered to be an accurate representation of flow available for diversion. Table 5-1 presents average monthly flows at the gage for the years 1978 to 1989. Based on this 12-year period of record, the average annual outflow from Upper Mahoney Lake is 43 cfs. As explained below, an additional 23 years of streamflow records were developed to provide a long-term hydrologic data base. Based on the 35-year period of actual and synthesized data, the average annual outflow from Upper Mahoney Lake is estimated to be 44.4 cfs as shown on Table 5-1. This compares to previous estimates of 46 cfs (Beck, 1977) and 48 cfs (COE, 1978). In order to obtain an extended period of record of daily flows for the diversion site, flows for years other than the period of record (1978-1989) were synthesized by correlating the gage at the diversion site (#15067900) to gage #15068000, Mahoney Creek near Ketchikan, Alaska. The drainage area of gage #15068000 is 5.7 square miles and includes the 2 square miles contributing to gage #15067900. The period of record for gage #15068000 is 1920-1933, 1947- 1958, and 1977-1981. This gage and the gage at the diversion site have an overlapping period of record for the years 1978 to 1981. First, an attempt was made to correlate the two gages on a monthly basis, producing a separate equation relating flows for each month. However, this resulted in correlation coefficients (r) that varied from 0.98 to 0.01. Six of the 12 monthly coefficients were considered poor. Attempts were also made to correlate the gages on a seasonal basis. This also produced correlation coefficients that were too low to be statistically acceptable. March 1994 25 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document The reason for the poor monthly and seasonal correlations is attributed to the fact that the mean basin elevation for the diversion site is approximately 2,350 feet, while the mean basin elevation for the Mahoney Creek gage is approximately 1,130 feet. The upper basin receives considerably more precipitation than the lower basin and most of the additional precipitation at the upper basin occurs in the form of snow. Finally, the gages were correlated on a yearly basis, resulting in a correlation coefficient of 0.70, which is considered acceptable. Basically, this is a correlation of annual flow volumes between the two gages. A search for a hydrologically similar gaged basin in the vicinity of the diversion site was performed in an attempt to achieve a better correlation. However, a search for a gage with an extended period of record which overlaps the gage near the diversion site revealed no usable gages within a 100 mile radius of the proposed diversion site. Therefore, the gage at Mahoney Creek was used. The relationship between the two gages as established by the linear correlation is Y = 0.41X + 1.8, where X = flow at Mahoney Creek andY = flow at the diversion site. The above equation was applied to the gage at Mahoney Creek for the years 1921-1925, 1927- 1933, and 1948-1958. These are the years of complete records of daily flow at the Mahoney Creek gage. As stated above, since the correlation between the two gages relates only annual volume, monthly adjustment factors were applied to the synthesized daily flow at the upper gage, causing the monthly percentages of the annual average of the synthesized data to match the monthly percentages of the actual gaged data at the diversion site, while maintaining the correlated volume. These 23 years of synthesized daily flows, added to the 12 years of historical flows, provide 35 years of data at the diversion site. Table 5-1 also shows the average monthly flows at the diversion site for the 35-year period of record. Figure 5-1 shows a flow- duration curve for the diversion site for the 35-year period. Actual daily flows for 1978-1989 and simulated flows for the years 1921-1925, 1927-1933, and 1948-1958 are shown in Appendix F. Based on the 15% exceedence value from the flow duration curve, a discharge of 78 cfs was selected for the turbine design hydraulic capacity. This flow was used to size water conveyance facilities and in the energy generation analysis. Month . October November December January February March April May June July August September Average March 1994 TABLES-I UPPER MAHONEY LAKE AVERAGE MONTHLY FLOW ···. A.vg~ MonthlY Flow (efs). / . tm-89· 67.3 43.0 17.3 29.6 23.6 16.5 23.9 58.9 79.4 58.9 42.7 50.8 42.7 26 · · A•l· Monthly Flow (ds) .... · 35 Yr. Record . 69.8 44.8 18.6 30.6 24.4 17.3 25.0 61.1 82.4 61.2 44.6 52.7 44.4 Mahoney LAke Hydroelectric Project FERC No. 11393 120 100 80 ~ ..!! • 60 Q .... ... 40 20 0 0 "" " ~ 20 ~ FIGURE 5-1 UPPER MAHONEY LAKE Flow Duration Curve ~ 40 60 % EXCEEDAICE NOTE: 1. Bmd 01 12 y11n of tclull r.cords an• 23 y11n tf lfllhaizld dala. ---- 80 p:\hydlmahoneylupmahnoy.xls 9/22/93 ~ 100 Initial Consultation Document FLOOD FREQUENCY ANALYSIS Peak annual flows recorded at the Upper Mahoney Lake Outlet (gage# 15067900) for the period of record from 1979 to 1989 were used in computing expected flood frequencies at the diversion site. The computer program, HECWRC, developed by the COB was used to facilitate the analysis. The program computes flood frequencies by fitting the peak annual flows for a period of record to the Log-Pearson Type m distribution in accordance with guidelines established by the USGS Bulletin 17B. Using HECWRC, the magnitude of the expected 1 00-year discharge was computed to be 1, 740 cfs. This flood magnitude can be used later for siting structures to be sure they are above flood-influence zones. Upper Mahoney Lake Capacity In 1983, the COB developed detailed area capacity curves for Upper Mahoney Lake based on soundings of lake depth (see Appendix F, Hydrology Information, Figure A-15). March 1994 28 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document 6.0 PURPA BENEFITS The Applicant will seek benefits under Section 10 of PURP A. The Project will be located at a new diversion as defmed in 18 CFR 292.202. March 1994 29 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document 7.0 LICENSING STUDY PLANS The following paragraphs describe the study plans and associated methodologies that will be used to evaluate the impacts of, and to develop mitigation and/or compensatory measures for developing the Mahoney Lake Hydroelectric Project. Considerable information and existing data already exists regarding the Project and the Project area. As stated earlier, detailed studies were conducted in the late 1970's and early 1980's in consideration of developing a hydroelectric project at that time. The study plans proposed reflect the fact that considerable study work has already been completed. The proposed plans may be modified as a result of comments that are received during the consultation process. To the extent possible, preliminary results of the studies will be distributed to interested parties for their review and comment prior to including the results in the Draft License Application. Ultimately, information that is developed through the studies will be incorporated into Exhibit E of the License Application. WATER QUALITY AND QUANTITY Purpose The purpose of these studies is to determine water quality in both Upper and Lower Mahoney Lakes and to establish baseline information. Data and results of consultations with appropriate agencies and other interested parties will be presented in a Water Use and Quality Report for inclusion in the Exhibit E, Environmental Report, of the Project's License Application. Methods Agencies will be consulted and existing information collected. Additional study tasks will be conducted including literature review, and water quality and quantity measurements. A,&encies to Be Consulted • USFWS • COB • Alaska Department of Natural Resources (ADNR) March 1994 30 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document Existin& Infonnation Water Quality Existing temperature data will be updated (See Appendix D). Sources of existing information may include USFWS, COB, and ADNR. Water Quantity Sources of existing stream flow information are described in Section 5.0 of this document. Study Tasks Literature Review The Applicant will investigate the following sources of information: • USFS • United States Geological Survey • USFWS • COB • ADNR • ADFG Water Quality Water quality at the base of the waterfalls (powerhouse site) and at Lower Mahoney Lake will be measured monthly for one year. Measurements included will be temperature, pH, turbidity, dissolved oxygen, and total suspended solids. Temperature Model Analysis Temperature will be continuously monitored in Upper Mahoney Lake near the proposed intake location with emphasis on placing one temperature probe at the same depth as the proposed intake and one at the lake surface. Such monitoring will be initiated in the summer of 1994 and temperature readings will be logged at two-hour intervals. In addition, temperature profile according to depth from surface to bottom will be measured within deeper portions of Upper Mahoney Lake four times per year (late summer, fall, late winter, late spring) to determine stratification patterns. Stream water temperature will be continuously monitored (two-hour intervals) in Lower Mahoney Creek near the proposed tailrace discharge location. Air temperature will also be measured at this same location and at the same intervals as stream temperature. Temperature within the lake bottom substrate and just above the lake bottom in Lower Mahoney Lake will be continuously monitored at two locations at the west end of the lake at known sockeye salmon spawning areas (probable upwelling areas). The intragravel probes will be buried about 25 em below the lake bottom and the lake water probes will be placed about 10 em above the bottom at the same location as the buried probes. One dual-channel data logging device will be placed onshore and used to record data at each upwelling monitoring site. Temperatures will be logged at two-hour intervals. In addition, temperature profiles according March 1994 31 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document to depth from surface to bottom will be measured within deeper portions of Lower Mahoney Lake four times per year to determine stratification patterns. Water Quantity Stream flow will be measured near the Project intake using a Stevens Type AA or Unidata digital continuous stream gage recorder. On Mahoney Creek, one unit will be installed near the proposed powerhouse location. The exact location of the gage will depend on stream character, terrain, and access. The stream gage will be installed during spring/summer of 1994 and will continue operating for the life of the Project. Results The relationship between Upper Mahoney Lake and creek water temperatures, air temperatures, and Lower Mahoney Lake upwelling water temperatures will be analyzed. This information will be used to help predict post-Project water temperatures within the upwelling areas used by salmon as spawning grounds. The information may also be used to develop mitigation measures to reduce the impacts of water temperature on salmon egg incubation. Information collected will be presented in a draft report and provided to the agencies of record for their comments. After review, any appropriate adjustments to the draft will be incorporated into the fmal report. The format for the report will be in conformance with the requirements for the FERC License Application, Exhibit E (18 CFR 4.41). FISHERIFS AND AQUATIC RESOURCES Purpose Objectives of the fisheries and aquatic studies are to: a) determine existing fisheries resources above, within, and below the diversion reach; b) determine the potential Project impact on fisheries resources; and, c) develop measures to avoid, minimize, and mitigate impacts on fisheries resources. Methods Agencies will be consulted and existing information collected. Additional studies to be conducted include: • Fish population surveys March 1994 32 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document A~:encies to be Consulted • USFWS • NMFS • USFS • COB • ADFG Existin& Information Infonnation for the Mahoney Lake drainage may be available from the USFWS, NMFS, COB, USFS, and the ADFG from previous studies. Some of the existing infonnation is included in Appendix B. Fish Population Surveys Fish abundance and utilization will be surveyed in Mahoney Creek from its mouth in Lower Mahoney Lake upstream to the major waterfall two times per year -June and early September in 1994. Visual observations as well as electroshocking and minnow trapping will be used to detennine the presence, abundance, and habitat utilization of major fish species. Emphasis will be on a detennination of value to rearing juvenile salmonids as well as value to spawning adults. Confmnation of reports that the streambed is sometimes dry will be made. The abundance and location of lake spawning sockeye salmon will be carefully investigated with emphasis on the western end of Lower Mahoney Lake near the outlet of Upper Mahoney Creek. Surveys will be conducted in early to mid-September of 1994 to coincide with the peak of spawning activity. Methods to be utilized will be detennined after further review of existing fish study infonnation and observation of the lake physical characteristics. Methods may include aerial visual surveys, boat-based visual surveys, SCUBA diving, and/or snorkeling. In addition, a minnow trap survey will be conducted in June and September to gain insight into the general use of the lake by rearing fish. Fish abundance and utilization will be surveyed in Lower Mahoney Creek from its mouth upstream to Lower Mahoney Lake two times in 1994, June and early September. Visual observations and minnow trapping will be used to detennine the presence, abundance, and habitat utilization of major fish species. Emphasis will be on a determination of value to adult salmon spawners. Results Infonnation obtained from the temperature modelling and analysis study component will be combined with the results of the fish studies to provide an indication of the kinds of effects that the Project might have on fish productivity. Emphasis will be on the potential effects of any March 1994 33 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document altered temperature regimes on sockeye salmon eggs incubating in lake gravels and on the kinds of mitigation measures that could be employed to alleviate such effects. Information collected will be presented in draft reports and provided to the agencies of record for their comments. After review, any appropriate adjustments to the drafts will be incorporated into fmal reports to be included in the appendix of the FERC License Application. The Fisheries Resource section of the FERC License Application will be prepared incorporating the study results and in accordance with the FERC regulations (18 CFR 4.41). WILDLIFE AND BOTANICAL RESOURCES Purpose The purpose of the wildlife and botanical studies is to describe, map, and quantify the habitats or cover types in the Project area. The potential impact of the Project on these resources will be evaluated and measures to avoid, minimize, or mitigate impacts will be developed. Methods Because many aspects of botanical resources and wildlife habitat are closely related, for the most part, both resources will be studied simultaneously. The studies will include agency consultations, literature reviews, field studies, inte.tpretation of field data, analysis of aerial photographs, and documentation. A&encies to be Consulted: • USFWS • USFS • ADNR • ADFG Preliminary Review In this phase, all existing data on plant and animal species and wildlife habitats in or near the Project area will be reviewed (Appendix B). For the Mahoney Lake Hydroelectric Project this will include lists, survey data, and reports from the ADNR and USFS. Under Section 7 of the Endangered Species Act, a species list request will be submitted to the USFWS. Habitat and cover types maps will be updated using the most current set of aerial photographs and field verified through random sampling and consultation. Field Surveys Two field visits will be conducted to confirm existing Project data. Areas to be surveyed will include the upper lake tap tunnel entrance area, powerhouse site, and the access road/transmission line route. Field studies will confmn presence/absence of common plants and animals, as well as species of concern (i.e., threatened and endangered species). March 1994 34 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document The field survey will consist of: a) qualitative surveys of wildlife habitats and plant communities; b) a general inventory of individual plant and animal species; and c) obtaining general information on topography and historical land use. Special habitats (e.g., wetlands, cliffs, old growth forests, etc.) will be located and examined in a broader area. General wildlife surveys will be conducted for mammals and birds. Ancillary observations will include identification of calls, tracks, scat, and raptor pellet analysis. The Project team will survey the Project area while walking to and from fixed points. Threatened and endangered species which may require additional habitat evaluation could include the bald eagle and marbled murrelet. The appropriate extent of the analysis area for other potential animal species will be determined in consultation with the agencies. If individuals of an animal or plant species of concern are located, the pertinent officials will be informed. Results Results of preliminary review and field surveys will be used to assess the potential effects of the Project on botanical and wildlife resources. Mitigation measures will be developed for species of concern in consultation with appropriate agencies. Information collected will be presented in a draft report and provided to the agencies of record for their comments. After review, any appropriate adjustments to the draft will be incorporated into the fmal report. The format for the report will be in conformance with the requirements for FERC License Applications, Exhibit E (18 CFR 4.41). HISTORIC AND ARCHAEOWGICAL RESOURCES Purpose The pUipose of these studies is to develop information on the nature and distribution of cultural resources within the Project area that have not been previously surveyed (a portion of the access road). This information, together with professional opinions and consultations with affected Native American groups and agencies, will be presented in a written cultural resources report for inclusion in the Exhibit B, Environmental Report, of the Project's License Application. Methods Agencies and Native American groups will be consulted and background research will be conducted. An archaeological/cultural resources field survey will also be performed. Study Tasks Background Research Background research will be conducted on the prehistoric, ethnohistoric, and historic use of lands within and around the Project area. Survey records and cultural resource inventories and registers maintained by the Alaska State Historic Preservation Office (SHPO) will be reviewed. March /994 35 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document Native American and Agency Consultation The Cape Fox Corporation and other interested Native American groups will be consulted to identify potential cultural heritage or traditional religious resources or concerns in the Project area. If the archeological field survey locates prehistoric and/ or ethnohistoric cultural resources, these grouped will be provided infonnation on the resources, which will remain confidential. The SHPO, the National Park Service (NPS), and the USFS will also be consulted during each phase of the cultural resources assessment to ensure compliance with FERC regulations and the requirements of Section 106 of the National Historic Preservation Act, as amended. Archeological Field Survey An archeological field survey of the areas to be disturbed by the proposed site development will be conducted. Maps and aerial photographs will be used in conjunction with infonnation on past land use and previously recorded cultural resources to identify geomorphic features within the Project area. Environmental and geomorphic infonnation will be recorded for areas surveyed. The location, condition, and potential significance of cultural resources identified during the field survey will be recorded on site fonns acceptable to the SHPO and the NPS. Field work will be documented with notes, drawings, and photographs as needed to record field methods and results. Mitigation measures will be recommended if the Project would produce adverse effects on any cultural resources found. Results The results of the cultural resources investigations will be presented in two reports: 1) a cultural resources background report; and 2) a summary Exhibit E document. These reports will be designed to meet FERC regulations set forth in 18 CFR 4.41. Draft copies of each report will be circulated for review, after which comments will be incorporated into the fmal reports. RECREATIONAL RESOURCES Purpose The purpose of the recreational resources study is to identify infonnation regarding existing recreation use, future demand and opportunities, and the potential impacts on recreation resulting from development of the Mahoney Lake Project. This infonnation, together with results of consultations with affected agencies and other interested parties, will be presented in a written Recreation Resources Report for inclusion in the Exhibit E of the Project's License Application. Methods Agencies will be consulted and existing infonnation will be collected. Development of the Recreation Plan will include three phases. Phase I will identify the current recreation types and existing facilities. Phase II will include the evaluation of existing and future recreation demands March 1994 36 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document in the Project area. Phase ill will identify the potential impacts created by the Project on recreation and will evaluate alternatives, recommend mitigation and provide costs, if necessary. Study Tasks Phase I -Evaluation of Existing Recreation Resources Data Collection. The area in which the Project will have an impact will be identified and existing infonnation will be collected. Data to be collected include maps; recreation guides; the USFS Recreation Resource Infonnation System, Recreation Opportunity Spectrum, and the Tongass National Forest Plan; and other sources of recreation infonnation, such as state agencies. Infonnation regarding demographic use will also be gathered. Consultation. Consultations will be held with the agencies who are responsible for recreation planning and management within the Project impact area. Current direction and policies for these agencies will be detennined. Other agencies and native organizations which might track or project recreation use in the area such as local, county, and state administering agencies, will be contacted. Special-interest groups, local residents, and businesses that focus on recreation and tourism will also be consulted. Identify and Map Existing Facilities. From data collected, existing recreation facilities will be mapped for the Project area. Any National Wild and Scenic Rivers systems, National Trail systems, and Wilderness areas within the Project area will be identified. Phase ll -Evaluate Recreation Demand Evaluate Recreation Potential. Existing recreation facilities in tenns of activity type, physical setting, experience required, economic costs, and current demand will be evaluated. Future recreation use within the Project area will be identified and evaluated. &timate Demand. Anticipated recreation demand with and without the proposed Project modifications will be estimated using demographic data. The demand projections will be correlated to regional opportunities for similar recreation. Constraints on development of recreation facilities will be identified. Phase ID -Evaluate Project Impacts on Existing and Future Recreation Project Impacts. Potential environmental, social, and economic impacts created by the Project regarding existing and future recreation in the Project area will be identified. Alternatives will be identified based on data collected, associated impacts, constraints, and demand projections. If appropriate, mitigation measures will be recommended if it is detennined the Project will produce adverse effects. Costs will be estimated for any new facilities and transportation access, plus operation and maintenance costs. Consultation. Agencies, native organizations, and special-interest groups who focus on recreation and tourism will be consulted regarding potential Project impacts. March 1994 37 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document Results The data, maps, and study objectives infonnation will be presented in a draft report and shared with the agencies of record for their comments. After review, any appropriate adjustments to the draft will be incorporated into the fmal report. The fonnat for the reports will be in confonnance with the requirements of FERC License Applications, Exhibit E (18 CFR 4.41). AESTHETIC RESOURCES Purpose The primary purpose of the aesthetics study is to describe measures proposed by the Applicant to make Project facilities blend, to the extent possible with the surrounding environment, and to evaluate aesthetic impacts of proposed changes in stream flow. Inventory and effects assessment activities will be conducted in order to identify and support any proposals for aesthetic treatments of Project facilities. Methods The aesthetics study will evaluate existing visual conditions, assess Project effects, and identify potential mitigation measures. Existing Visual Conditions A summary of existing visual conditions that addresses lx>th Project facilities and the adjacent landscape will be addressed. Existing visual resource data related to the Project area, including the USFS Visual Management System, will be reviewed. Landscape character of the Project area will also be described. Approximate seen areas from selected viewpoints at and near the Project will be identified. Project Effects Assessment The effects of the proposed Project facilities on visual quality will be detennined and presented in the report. This discussion will address the visibility of Project features from the selected viewpoints and will evaluate these views within the local visual context. The primary focus of this assessment will be impacts of reduced water flows over the waterfalls between Upper and Lower Mahoney Lakes and the impact of Project roads and powerhouse construction. Proposed Aesthetic Measures Potential measures that will reduce the visual contrast of Project features with the surrounding environment will be identified and their feasibility will be reviewed. Results The results of the aesthetics study will be presented in the Aesthetic Resources Report of Exhibit E. A draft report will be prepared and distributed to agencies of record for their comments. After their review and comment, a final report incorporating comments will be prepared. The aesthetics report will be fonnatted as required under FERC regulations (18 CFR 4.41). March 1994 38 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document EROSION AND SEDIMENT CONTROL PLAN Purpose The purpose of the erosion and sediment control studies is to evaluate the potential for erosion and sedimentation during proposed Project construction and operation. Based on this evaluation, an Erosion and Sediment Control Plan (ESCP) will be developed to provide guidelines for controlling erosion and sedimentation during Project construction and operation activities. Since most of the Project features are underground, the ESCP will concentrate on access roads and tunnel spoils disposal sites. Methods The ESCP will establish baseline conditions in order to assess potential impacts and allow comparison with conditions during Project construction and operational phases; identify existing environmental hazards which must be taken into account during Project design, construction, and operation; and identify measures which will minimize potential adverse impacts. Aaencies to be Consulted • USFWS • NMFS • USFS • COB • ADNR • ADFG Tasks The following tasks will be performed in order to prepare the ESCP: 1. Existing site conditions will be evaluated including climate, topography, geology, soils, vegetation, surface and groundwater drainage, adjacent waterways, and hazard areas. 2. Erosion/sedimentation potential during construction of Project features and during Project operation will be determined. 3. Estimates will be made on the amount of tunnel spoils and locations for disposal sites will be identified. 4. Timing of construction activities will be identified and evaluated in terms of alleviating erosion potential. 5. Specific locations and techniques for controlling potential erosion and sedimentation during Project construction and operation will be identified, mapped, and detailed drawings and descriptions of such measures will be prepared. March 1994 39 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document 6. Implementation guidelines for general and site specific erosion control measures will be developed. 7. A revegetation plan for disturbed areas will be developed. 8. Procedures for maintenance and monitoring of erosion control measures for plan modifications will be developed. 9. Using existing information from geologic reports, mapping, aerial photos or other sources, a qualitative review of the Mahoney Lake drainage basin will be made which will provide a general characterization of sources and types of sediment inputs into the river. The Universal Soil Loss Equation or another acceptable method may be used to estimate sediment delivery to Lower Mahoney Lake. To the extent feasible, (given the dynamics of the system), the relationship between geomotphic processes, Project operation, and sediment delivery will be characterized and discussed. Results A Draft ESCP will be prepared that details the Project area geology and soils, and characteristics of the Project segments. This report will include maps that illustrate the geologic and geomotphic conditions of the Project area. Upon completion, the report will be circulated to the appropriate agencies for comment and review. Following any necessary revisions, the report will be fmalized and included as an appendix of the License Application. March 1994 40 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document 8.0 BffiLIOGRAPHY CH2M Hill. May 1986. Power SuP,Ply Planning. Institute of Social and Economic Research, University of Alaska, Anchorage. June 1990. Electric Load Forecast for Ketchikan. Metkalata. Petersburg. and Wrangell. Alaska: 1990-2010. Final R~rt. Nuveen, John & Co. Incorporated. June 1992. Bond Prospectus, Municipal Utilities Revenue, Series R, City of Ketchikan, Alaska. R. W. Beck and Associates, Inc. June 1977. AP,Praisal R~rt. Swan Lake, Lake Grace and Mahoney Lake Hydroelectric Projects. R. W. Beck and Associates, Inc. March 1986. AP,Praisal Study 1985 Update. Future Hydropower Resources. Ketchikan, Petersburg, Wrangell and Quartz Hill. U.S. Army Corps of Engineers, Alaska District, Anchorage, Alaska. 1978. Draft Environmental Impact Statement. Proposed Mahoney Lakes Hydropower Project, Ketchikan, Alaska. U.S. Army Corps of Engineers, Alaska District, Anchorage, Alaska. July 1983. Rivers and Harbors in Alaska. Draft Interim Feasibility Report and Environmental Impact Statement. Hydroelectric Power for Sitka, Petersburg/Wrangell, and Ketchikan, Alaska. U.S. Forest Service. June 8, 1993. Comment Letter in regard to Preliminary Permit. March 1994 41 Mahoney Lake Hydroelectric Project FERC No. 11393 Initial Consultation Document 9.0 CONSULTATION DOCUMENT :MAILING LIST U.S. Anny Cmps of Engineers Alaska District Office P.O. Box 898 Anchorage, AK 99506-0898 National Marine Fisheries Service Alaska Region P.O. Box 21668 Juneau, AK 99602-1668 U.S. Fish & Wildlife Service Region 7 1011 E. Tudor Road Anchorage, AK 99503 National Park Service Alaska Region 2825 Gamble Street Anchorage, AK 99503 U.S. Environmental Protection Agency Region X 1200 Sixth Avenue Seattle, WA 98101 U.S. Forest Service Region 10: Alaska Region Box 21628 Juneau, AK 99802-1628 Mr. David Rittenhouse U. S. Forest Service Federal Building Ketchikan, AK 99901 March 1994 42 Mr. Gary Laver U.S. Forest Service Federal Building Ketchikan, AK 99901 Mr. Jack Gustafson Alaska Department of Fish and Game Habitat Division 2030 Sealevel Drive Room 205 Ketchikan, AK 99901 Mr. Frank Rue, Director Alaska Department of Fish and Game Habitat Division P.O. Box 25526 Juneau, AK 99802-5526 Ms. Lorraine Marshall Alaska Office of Management and Budget Division of Governmental Coordination P.O. Box 110030 431 N. Franklin Juneau, AK 99811-0030 Ms. Elena Witkin Alaska Department of Environmental Conservation 410 Willoughby A venue, Suite 105 Juneau, AK 99801 Mr. Tom Stevenson Ketchikan Public Utilities 2930 Tongass Avenue Ketchikan, AK 99901 Mahoney Lake Hydroelectric Project FERC No. 11393 Ms. Bridget Steams Ketchikan Public Library 629 Dock St. Ketchikan, AK 99901 The Honorable Alaire Stanton Mayor, City of Ketchikan 334 Front Street Ketchikan, AK 99901 Mr. Jack Pearson City Manager City of Ketchikan 334 Front Street Ketchikan, AK 99901 Governor Walter Hickel State of Alaska P.O. Box 110001 Juneau, AK 99811-0001 Mr. Dick Emennan Division of Energy Department of Community and Regional Affairs 333 W. Fourth Avenue Suite 220 Anchorage, AK 99501-2341 Mr. Edgar Blatchford Division of Energy Department of Community and Regional Affairs 333 W. Fourth Avenue Suite 220 Anchorage, AK 99501-2341 Mr. Riley Snell Alaska Industrial Development Agency 480 W. Tudor Anchorage, AK 99503 March 1994 43 Initial Consultation Document Ms. Judith Bittner Alaska Department of Natural Resources State Historic Preservation Office P.O. Box 107001 Anchorage, AK 99510-7001 Mr. John Dunker Alaska Department of Natural ResourcesfVVater 400 Willoughby Avenue Juneau, AK 99801-1796 Department of the Interior Office of Environmental Affairs Anchorage Regional Office 1689 C Street, Room 119 Anchorage, AK 99501-5126 Federal Emergency Management Agency Region 10: Bothell Federal Regional Center 130 228th Street, SW Bothell, W A 98021-9796 Mr. Bill Geary Alaska Department of Natural Resources Parks & Outdoor Recreation 400 Willoughby Avenue Juneau, AK 99801-1796 Mr. Arthur Martin Regional Office Federal Energy Regulatory Commission 1120 SW 5th Avenue, Suite 1340 Portland, OR 97204 Ms. Lois CasheD Federal Energy Regulatory Commission 825 N. Capitol St. NE Washington, DC 20426 Area Director Bureau of Indian Affairs P.O. Box 3-8000 Juneau, AK 99802 Mahoney lAke Hydroelectric Project FERC No. 11393 Tongass Conservation Society P.O. Box 3377 Ketchikan, AK 99901 Southeast Alaska Conservation Council 419 Sixth Street, Suite 328 Juneau, AK 99801 Ms. Kate Tessar Alaska Services Group P.O. Box 22754 Juneau, AK 99802 Alaska Environmental Lobby P.O. Box 22151 Juneau, AK 99802 Alaska Public Utilities Commission 1016 W. Sixth Avenue, Suite 400 Anchorage, AK 99501 Mr. Jim Carlton Mayor, Ketchikan Gateway Borough 344 Front Street Ketchikan, AK 99901 Mr. Mike Rody Borough Manager Ketchikan Gateway Borough 344 Front Street Ketchikan, AK 99901 Mr. Steve Segovia Ketchikan District Ranger U.S. Forest Service 3031 Tongass Avenue Ketchikan, AK 99901 Mr. Bob Martin, Director Tlingit -Haida Regional Electrification Authority P.O. Box 210149 Auke Bay, AK 99821 March 1994 44 Initial Consultation Document Ms. Susan Dickinson City Administrator City of Saxman Route 2, Box 1 Ketchikan, AK 99901 Mr. Jack Snyder Senior Project Manager HDR Engineering, Inc. P.O. Box 91201 Bellevue, W A 98009 Mr. Doug Campbell Cape Fox Corporation P.O. Box 8558 Ketchikan, AK 99901 Mr. John Braislin Betts, Patterson & Mines 800 Financial Center 1215 Fourth Avenue Seattle, WA 98161-1000 Mr. Don Clarke Wilkinson, Barker, Knauer & Quinn 1735 New York Ave NW Washington, DC 20006 Mahoney Lake Hydroelectric Project FERC No. 11393 lniliol Consultation Document APPENDIX A ALTERNATIVE PROJECT CONFIGURATION DISCUSSION March 1994 Malwney lAJce Hydroelectric Project FERC No. 11393 Initial Consultation Document APPENDIX A ALTERNATIVE PROJECT CONFIGURATION DISCUSSION WATER CONVEYANCE Two alternative water conveyance configurations, in addition to that proposed for the Project, were evaluated. Those alternatives were: Alternative 1 : Alternative 2: Construct a low-height dam at the outlet to Upper Mahoney Lake to divert flow into a pipeline all the way to the powerhouse. Construct the same low-height dam as in Alternative 1, except convey flow to the powerhouse through a 500-foot long buried pipeline, 1 ,370-foot vertical shaft and 3,300 foot long pipeline placed in an 8-foot wide by 8-foot high horseshoe-shaped tunnel. Average annual energy and construction costs were also developed for these alternative arrangements. Alternative 1 Alternative 1 avoids the use of a tunnel concept completely and instead uses a combination of buried and surface pipeline to move water from Upper Mahoney Lake to Lower Mahoney Lake. A small concrete faced rockfill dam, about 10 feet high would be constructed at the upper lake outlet. A 32-inch pipeline would extend through the dam foundation out into the lake and would serve as the submerged intake. The pipeline would extend downstream from the dam about 500 feet along the creek where it would turn to the right and then drop down the steep rock slope to the proposed powerhouse location. The powerhouse and turbine arrangement are the same as in the proposed alignment, a single 9.6 MW multi-jet pelton turbine, but it would be located in an insulated metal building about 40 ft. by 50 ft. in size. Access roads and transmission facilities would be the same as the selected alternative. This alternative would operate strictly as a run-of-river facility, that is the diverted flow to the turbine would equal inflow to the lake, and the lake level would be generally held constant. A few feet of drawdown might be usable for daily peaking. The positive aspect of run-of-river operation is that there is minimal environmental impact since the lake is at constant levels at all times. After study, this alternative was rejected for two main reasons; 1} the pipeline route is very steep and would have to pass through a rockslide and snow avalanche-susceptible area making construction and maintenance of an above-ground pipeline March 1994 A-1 Mahoney lAke Hydroelectric Project FERC No. 11393 Initial Consultation Document almost impossible; and 2) the operating mode of this Project, run-of-river, was much less beneficial to the local utility in meeting the power and energy needs of the region. Alternative 2 In place of the upper tunnel and lake tap in the proposed Project, consideration was given to constructing a low height dam about 500 feet downstream from Upper Mahoney Lake. In this arrangement Project operation would also be strictly run-of-river. Any dam constructed on the stream will be susceptible to damage by rockslide or avalanche, particularly from the steep right abutment. For this reason, the minimum size structure necessary to divert streamflow into the intake was selected. The dam would consist of a grouted gabion structure with an upstream steel plate impervious barrier. The dam would be about 20 feet high and be designed to withstand overtopping flows. The spillway crest would be located 3 feet above the normal maximum water surface elevation to provide a small amount of flood control storage, about 220 acre-feet. Streamflow would be diverted into a concrete and rock- walled intake structure located in the right abutment. A motor-operated 36-inch butterfly valve would be located in an underground vault on the right bank immediately downstream of the dam. A 32-inch buried steel pipeline would convey diverted streamflow a distance of 450 feet to the vertical shaft. The shaft location would not change with the lake tap or dam alternative. The primary disadvantages of the dam alternative include investment in a structure that has a high risk of partial or total damage at some time during its economic life, and the inability of this arrangement to supply fmn energy due to the lack of storage and run-of-river operation. A higher dam could be constructed to provide storage, but this increases the potential economic loss in the event of a rockslide or avalanche event. By constructing the minimum height dam necessary, the potential economic loss due to replacement costs and lost generation is minimized. Considerable rock excavation would be required to construct the 450-foot pipeline from the dam to the shaft. Construction cost estimates and energy generation estimates for this alternative were prepared and showed that the run-of-river operating mode of this alternative reduced its cost effectiveness considerably. An alternative to the partially concrete lined tunnels and vertical shaft would be to install a 32-inch steel pipeline in the upper tunnel and vertical shaft, placing the pipeline on saddles in the upper tunnel and backfilling the annular space in the vertical shaft with concrete. This is considered an overly conservative approach at this time, adding significantly to the construction cost. Based on preliminary geologic studies, it does not appear warranted to assume the water conveyance system will require containment within a steel pipe for its entire length. Until further studies and field investigations are performed, it was assumed that half the length of the upper tunnel and the shaft would require concrete lining, and the lower tunnel would require a small amount of shotcrete protection. March 1994 A-2 Mahoney lAke Hydroelectric Project FERC No. 11393 JnitiiJl Consultation Document TRANSMISSION LINE ROUTING An alternative to the proposed transmission line route would be to interconnect with KPU's Beaver Falls Project. This route would be about 1.5 miles shorter in total length than the proposed route. However, to construct along this alternative route would be more costly due to more steep and difficult terrain and it would require a new road along the entire route. In addition, reconductoring of the entire line between Beaver Falls and Ketchikan could be necessary to handle the Mahoney Lake output, according to previous studies. The proposed transmission line will be constructed along an existing road on lands owned by the Cape Fox Co1p0ration, and would only require construction of about one mile of new road. March 1994 A-3 Mahoney Lake Hydroelectric Project FERC No. JJ393 APPENDIXB 1982 U.S. FISH AND WILDLIFE SERVICE COORDINATION ACT REPORT United States Department of the Interior IN REPLY REFER TO: FISH AND WILDLIFE SERVICE lOll E. TUDOR RD. ANCHORAGE, ALASKA 99503 (907) 276-3800 Colonel Neil E. Saling District Engineer, Alaska District Corps of Engineers P .0. Box 7002 Anchorage, Alaska 99510 Dear Colonel Saling: Re: Co.ordination Act Report Mahoney Lakes Small Hydropower This letter transmits the attached Coordination Act (CA) Report prepared under the authority of the Fish and Wildlife Coordination Act (48 Stat. 401 as amended: 16 U.S.C., 661 et seq.) for the proposed hydroelectric devalop- ment on 1·1ahoney Lakes at Ketchikan, Alaska. We support the Corps' basic preferred alternative hydropower development plan. However, we recommend that measures to mitigate adverse effects to fish and wildlife resources, as outlined in the attached CA Report, be incorporated into the development plan. The report has been coordinated with Alaska Department of Fish and Game and National t1arine Fisheries Service, however, their convnents were not received in time for incorporation.. We will forward these comments upon receipt. We appreciate the opportunity to comment and advise on matters regarding fish and wildlife resources associated with the proposed hydropower develop- ment plan. Enclosure as stated cc: ADF&G, Juneau, Ketchikan USFS, Sitka FWS, ROES, Juneau, Ketchikan Ft~S, Federal Projects,, WDC tU1FS, Juneau t4AHONEY LAKES PROPOSED St1ALL ·HYDROPOWER DEVELOPHENT COORD 1 NATI ON ACT REP O.RT Prepared By Charles E. Osborn, Fish and Wildlife Biologist Ketchikan Substation Southeast Alaska Ecological Services U.S. Fish and Wildlife Service Juneau, Alaska November 1982 EIS-C-2 I. II. III. IV. TABLE OF CONTENTS Introduction ••• . . . . . . . . . . . . . . . . . Area Description. ... . . . . . . . . . . . . . . . . Page .1 2 Project Description. • • • • ••••• . . . . ·• . . . . . 11ethods -Genera 1 ... : •• ·~ · •• · .• . ; . . . . . . . . . . . . . 3 3 5 5 A. Terrestr"ial·Study -·nethods •••••• . -· . . . . . .. . . . B. Cover Types • • ~· . . .. . . . . .. . . . . . . . . . Spec·; es Selection • • • • • • • • • • • • • • • • • • • • • 5 Field Sampling; •• ~· • • • • • • • • • • • • • • • • • 6 . . . . . . . . . . . . . •· . . . . . . 10 Results .•• Aquatic Study. . ..... ·• . • • • • • • 17 Cover Typies. . . . . . . ·-. . .. . . . . . . 17 Species Selection •••••••••••••••• Field Sa~pling •••••••••••••••••• • • • • • 17 . . . 10 Results •.•• • • • • • • • • • • • • • 19 Discussion and Reco~endations Literature Cited ••••••• Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 26 TABLES. Table I. Species 1 i:st . . . Table II. Acrea~·es and cond·itions of ter:restrial cover types on ·the target years ' . ' . . . ' ' ,· Table III. HSI and HlJ for each species· in each target year . . Table IV. MHU and HU change during the. 50-year life of the project and during the 275-year· baseline-to-recovery 1 ife of the project · Table V. Fish census in Hahoney Creek, Falls Creek, and South Creek 7/16-J0/31/81 FIGURES Figure 1. Location of the Mahoney Lake System on Revilla Island · Figure 2.1 Symbolistic layout of project Figure 3.1 Map of study area, durect impact area, and cover types at t~ahoney Lake Figure 4. Map of Falls Creek -4/81 Figure 5. Map of Falls Creek -8/81 APPENDICES Appendix A. Determination of photo scale Appendix B. Models used 1 There is some distortion of these maps due to elevation differences at the study site. See Appendix A for explanation. r-rc f" 11 l~ahoney Lake Coordination Report -1- I. Introduction Ma~oney Lakes is one of three Ketchikan area potential hydroelectric power projects. A preliminary feasibility study was done (Retherford et. al., 1976) .in April 1977. The Army Corps of Engineers (COE) requested U.S. Fish and Wildlife Service (FWS)· assess the impact of such .a project on fish and wildlife in the system. A preliminary Coordination Act Report was completed iri Septe~ber· 1977 and concluded that the major losses due to the power project would be of salmon spawning and rearing areas at the base of Falls Creek. Mitigation at that time suggested returning water to the creek near the base of the falls or building a· spawning channel with a controlled flow. In March 1979 a final . . Coordination Act Report was completed which used Habitat Evaluation Procedures (HEP) to document the impacts of the proposed project on fish and wildlife {USFWS, 1979).11 .In that report it was suggested that the COE acquire lands for rehabitation to compensate for losses in wildlife habitat. In t1ay of 1980, the COE requested· that the HEP study at t1ahoney Lakes be reconsidered with particular attention paid to the compensation which would be require~ if the project :were implemented. In addition, the COE requested a detailed map and quantification of use of lower Falls Creek as spawning and rearing areas. This HEP study was designed to answer those questions. 11 The FWS is currently working to bring an aquatic HEP into full operation. The aquatic HEP used in this study does not reflect this effort, but rather is the terrestrial methodology used in an aquatic habitat. t1ahoney lake Coordination Report -2- An interagency team including Charles Osborn, FWS, Richard Guteleber and Harlin LeGare, COE, and Don Cornelius, Alaska Department of Fish and Game (ADF&G), was assembled to review and direct the study. The team met . . during an Apri1 1981 field session to o~tlirie the ~fahoney Lakes study. At this time the species. chosen for evaluation were approved and the levels of HEP for terrestrial and aquat;ic species were decided. Since then, the members have been kept informed of the progress of the study and consulted as necessary in their particular fields of expertise. II. Area Description The t1ahoney Lakes system consists of connected lakes located in the southern portion of Revillagigedo Isl~nd (Fig. 1)~ The upper lake lies approximately 6 miles northeast of Ketchikan at ~n elevation of near 1,950 feet. The upper lake discharge drops approximately 1,900 feet in slightly over 1 mile before entering the lower lake. Discharge from the lower lake travels almost three-tenths mile before entering George Inlet at a point 16 miles by water from Ketchikan. The watershed extends from Mahoney Nountain, an alpine area at 3,335 feet maximum elevation, down throu·gh dense rain forest to sea level. Topographical relief between the upper and lower lakes is extreme and rock cliffs, avalanche chutes, and earth slides are comon. A spectacular falls between the upper lake and lower.lake is .a landmark to the area. EIS-C-6 Manoney LaKe Loora1nat1on Keport -3- III. Project Description The power project {16.5 HW) is designed to take advantage of the nearly 1,900-foot head between the upper and lower lake for generation of hydroelectric power {Fig. 2). The upper watershed would be dammed with a 25-foot dam for increased water storage. The lake would be t~pped at a depth of 225 feet and the discharge would be rerouted through a 36-inch tunnel/penstock to a powerhouse near the lower lake and returned to the natural system in the lower lake. This conduit would be approximately 5,370 feet iry length, of which 4,000 feet would be in a tunnel. The electrical power would be transmitted along the coastline of George Inlet 4 miles to Beaver Falls where it would merge with the existing power network. An optional plan considers the selected plan without the dam and third generating unit in the powerhouse. Access for construction and maintenance of the facilities would begin at a seaplane float terminal located on the saltwater adjacent to the lower lake. An access road 1.4 miles in length would service the lower tunnel portal, powerhouse area and the camp area. Helicopter access is now being considered for construction of the dam, upper tunnel portal and the 34.5 KV transmission line. IV. Methods -General Prior to a detailed analysis of this report, the reader should become familiar with the HEP process through the Ecologica1 Services Manuals (Anon., 1980-1981). However, for the casual reader, a brief sunT.lary of the HEP process follows. EIS-C:-7 Mahoney Lake Coordination Report -4- HEP is a method which can be used to document the quality and quantity of available habitat for selected wildlife species. The procedure provides information for two general types of comparisons: 1) the relative value of different areas at the same point in time; and 2) the relative value of the same area at different points in time. Species which are representative of the area wildlife are selected for HEP evaluation, and models are used to estimate the quality of the habitat for those species. The quality value, an index between 0 and 1, is multiplied by the acres of available habitat to determine habitat units. Habitat units are the basic units of comparison among alternatives and through time. A glossary of HEP terms has been provided to aid the reader in understanding the text. (HEP} was used to evaluate the suitability of the Mahoney Lakes area as habitat for several species and to predict the effect the hydropower project would have on those species. A baseline habitat suitability study was accomplished and future suitability was predicted for 4 target years, both with and without hydroproject development. Two levels of HEP were used: moderate level for terrestrial species and low level for aquatic species. Low level HEP was used for aquatic species because the stream which would be most affected by the power plant is evidently too unstable to support a spawning area. This will ·be discussed in more detail in the aquatic section of the report. The study area was defined as the watershed of the t1ahoney Lakes system plus the transmission line area (Fig. 2). The transmission line area extends from the t·1ahoney Lakes watershed to Beaver Falls and from shoreline to 1.6 miles inland (west). An area was also delineated within the study area which would be more directly impacted by the project. EIS-C-8 f·1ahoney Lake Coordination Report -5- This direct impact area was defined as one-half mile from roads, transmission lines, camp, power plant, and lakes. However, if the distance to the edge of the watershed is less than one-half mile, then it was considered the limit of direct impact. Habitat unit acreages were derived from the direct impact area. Covertypes were delineated from 1974 U.S. Forest Service color aerial photographs with the aid of a stereoscope. These were later verified in the field on foot and using helicopter reconnaissance. The following covertypes were delineated: alpine/snowfields; steep, subalpine coniferous forest; coniferous forest; muskeg; slide; streamside; lacustrine; riverine; and saltwater aquatic (intertidal). Areas of the covertypes were determined using a Keuffel and Esser Co. Compensating Po 1 ar P 1 an imeter, t1ode 1 620000. These areas were converted to acres by determining the sea level scale for the flight line and correcting this scale for the mean elevation above sea level of each photo. Sea level scale and mean elevation of the photos were estimated by comparison of the photos with U.S. Geological Survey topographic map, Ketchikan (B-5), Alaska N5515-W13120/15X20, scale 1:63,360. A detailed account of the photo scale determination is in Appendix A. f! The use of trade names is for descriptive purposes only and does not imply endoresement by the U.S. Fish and Wildlife Service. Mahoney Lake Coordination Report -6- A. Terrestrial Study Covertyp€s Three covertypes were chosen for evaluation of terrestrial species: coniferous forest, muskeg, and intertidal. Slide areas, being devoi~ of vegetation, were not considered important wildlife habitat. Alpine/snowfields and steep subalpine forests were not evaluated for two reasons: 1) impact to these areas by the project would be minimal, and 2) the cost of evaluation would be excessive because the areas are inaccessible by foot and investigation would require helicopter support. Species Selection The species used for HEP evaluation were selected by the guilding technique which is recommended in Ef1S 102 {Anon. 1980-1981). A list of species in the area was made from the tfahoney Lakes Report (Anon. 1979) and is presented in Table I. These species were guilded based on covertype usage for feeding and reproduction, feeding mode, and general niche within a covertype. One species was then selected to represent each cell. Selection was based on hunting or trapping desirability, sensitivity to human influence, niche specificity, and availability of information on species-habitat relationships. The species chosen were black bear, northern bald eagle, blue grouse, Sitka black-tailed deer, and mink. t·1ahoney Lake Coordination Report -7- Field Sampling Ha~itat·evaluation using the models entailed measuring variables (such as percent shrub cover), evaluating plotness variables {such as local topographic variation), and determining spacial relationships between covertypes. Measurable variables were measured in the field using transects and quadrats. Plotless variables were estimated from the aerial photographs and ground truthed ~t the field sample sites.· Spacial relationships between covertypes were done with remote sensing as suggested in the HEP Workbook (USFWS, 1981). A random dot grid was superimposed on the covertype map, and distances from.random points within one covertype to another covertype were measured. · The terrestrial sampling was conducted in spring and late summer of 1981, April 21-24 and August 18, 19, 24, and 26. Clustered, modified random sampling was used in the coniferous forest to reduce travel time between transects and to better represent the variety of habitat conditions which exist in the coniferous forest. The three cluster locations were chosen where the impact of.the power project would be most severe: at the power plant, the camp area, and the transmission corridor. Sample sites were chosen within each area by walking 3 minutes in a randomly selected direction and then establishing a ZO m transect in another randomly selected direction. A total of 10 transects were established in the coniferous forest, four at both the power plant and camp sites, and two at the transmission corridor site. Modified random sampling was used in the muskeg. As in the coniferous forest, sample sites were chosen by walking 3 minutes in a randomly selected direction and then establishing the transect in another randomly selected direction. There were six transects established in the muskeg. ~1ahoney Lake Coordination Report :-8- A number of measurements were made at each transect. The percent cover of shrub species was measured by dividing the linear distance along the transect cover~d by a. shrub by the len~th of the transect, and multiplying by 100: %cover= (x meters/20 meters)(lOO), where x equals the linear distance covered by the shrub. The·percent cover of ground species was estimated occularly withfn a 1 x 1/2 m quadrat frame located at 0, 10, and 20 m along the transect. Tree dominance was measured using the point quarter method at the endpoints of the transects. In addition, the plotless variables were evaluated at each transect site. A detailed description of these methods is contained in Konkel et al. (1980). Plant species were identified according to Viereck and Little (1972). The number of samples necessary was determined for each suitability index (S.I.) at 90% confidence level with 25% relative precision using standard statistical methods (Konkel et al., 1980). Three problems were encountered: 1) there was often a high variance in the S.I.'s because more than one plant species was included in a single S.I.; 2) two different sampling methods (transect and quadrat) were often used because both shrub and ground cover species could be included in some S.I.'s; and 3) a high variance was also encountered because many species have a patchy distribution. In the third instance, increasing the number of test samples increased the variance, thus by the formula in Konkel et al. (1980), more samples were needed for statistical significance. The number of samples determined necessary ranged from 5 to 97 for the different S.I.'s. Because of the questionable validity of applying the sample size test to S.I.'s and the wide range in number of samples determined necessary, a subjective analysis of the mean, median, and mode of the number of samples necessary for each S.I. for each covertype was EIS-C-12 11ahoney Lake Coordination Report -9- used to select sample size. This resulted in selecting 10 transects and 30 quadrats in the coniferous forest and six transects and eighteen quadrats in the muskeg. The intertidal area was evaluated for one S.l.: percent cover of macrophytes. Since the percent cover which indicated a certain index was within broad limits (see Mink model, App. B), an occular estimate of this variable was made at the proposed dock site. All S.I.'s, Life Requisite· values (LR's), Habitat Suitability Indices (HSI's), Habitat Units (HU's), and Average Annual Habitat Units (AAHU's) were calculated according to ESH 102 (USFWS, 1980-81) and the individual models. Five taryet years were chosen for predicting habitat suitability: TVO TV 1, TV 50, TV110, and TV275. Target years 0, 1, and 50 represent the baseline condition, 1 year after the project starts, and the end of the life of the project. HEP mandates that these years be chosen. The 2 additional years were chosen to plot the recovery of the· land when the project ends.. Target year 110, or the end of the project plus 60 years, is representative of canopy closure condition. Target Year 275, or end of the project plus 225 years, should represent conditions after tne forest has returned to the old growth condition. Habitat suitability was predicted for both the with and without project conditions for each target year from the baseline data and from Harris and Farr•s (1974) account of secondary succession. Acreages of.each covertype after project implementation were estimated using information from the f1ahoney Lakes Hydropower Project (Anon., 1978) report. AAHU's were determined for the end of the project life, TY50, as well as for the "recovery life of the project", TV275. This was done because, for some species, major Mahoney Lake Coordination Repo~t -10- impact of the project will not occur until canopy closure; and HU's will continue to be lost until the old growth coniferous forest has recovered. B. Results The total study area includes 5,221 acres and th.e direct impact area includes 2,090 acres (table Il; Fig. 3). The largest percentage of this area is coniferous forest. The study area also includes broad expanses of alpine/snowfields and steep subalpine coniferous forest, much of which is not part of the direct impact area. The other covertypes are a small proportion of the study and direct impact areas. Two types of changes would occur to the habitat as a result of the hydropower project: 1) some area would be temporarily lost as animal habitat, and 2) some would be altered. Altered sections were treated as separate covertypes for HSI determination. The transmission line will cut through approximately 4.9 miles of coniferous forest. According to the Mahoney Lakes Hydropower Project Report (Anon., 1978), the corridor will be 75 feet wide with selective cutting beyond that distance to protect the line from danger trees. The boundary of disturbance was estimated at 100 feet on each side of the alignment (a 200-foot corridor) resulting in a total disturbed area of 119 acres due to the transmission line. Revegetation of the corridor at the project's end should be similar to the recovery of a small logged area, returning to the old growth condition within an estimated 225 years after canopy closure (See blue grouse model; App •. s). As shrubs will remain in the corridor throughout the project life, young conifers should already have become established by the time of project shutdown, and canopy closure may not be long after. Mahoney Lake Coordination Report -11- The road system will also cut through coniferous forest. As proposed, it will be 2 1/3 miles long, 16 feet wide with a 4-foot shoulder, encompassing approximately 7 acres. After usuage is stopped this area should return to the old growth forest. However, it should take longer to revegetate than the transmission line area because the extent of disturbance, such as establishment of the road bed, will have beem much greater. Approximately 14 acres will be covered by the camp, 4 in the muskeg, and 11 in the coniferous forest (difference in area due to rounding). This area will be essentially lost as animal habitat during the life of the project. It is expected that the coniferous forest will return to its original state within the 275-year time period. However, the extent of damage to the muskeg and its recovery route are unknown. The power plant, tailrace, and penstock will cover approximately 8 acres of coniferous forest and eliminate them as wildlife habitat for the duration of the project. It is expected that the construction material of these structures will be long lasting and, therefore, the recovery rate of the coniferous forest in this area is unknown. The dock will cover approximately 0.2 acre of saltwater aquatic, or intertidal, area. This area should rapidly revegetate and return to baseline conditions within a few years of termination of usuage. In addition to direct effects on the habitat, development may result in indirect habitat suitability changes to the other parts of the study area. For example, presence of humans will affect habitat suitability within a half-mile radius of the camp for black bears. Interspersion of covertypes will also change with the development. Mahoney Lake Coordination Report The following information includes species accounts.of model implementation and hydropower project impacts as predicted by HEP. Black Bear -12- The black bear model used was designed by Lana Shea (1981} (App. 8). Two covertypes, muskeg and old growth coniferous forest, were evaluated for the baseline condition. Construction of project features would result in loss of some acreage and create an additional covertype, coniferous forest cut, along the transmission line (Table II). After project closure, regrowth coniferous forest would occupy the areas which had been disturbed. Interspersion and aggregation of life requisites are included in the model, but the model does not aggregate covertypes or bears with and without cubs. To facilitate determining AAHU's, a single HSI was determined for the impact area by averaging the HSI's for the with and without cub conditions within each covertype. These covertype HSI's were thenaggregated to a single number using area weighted averages (ESM 102, Anon, 1980-81). During the life of the project, HU's are lost primarily due to· the presence of human garbage and consequent increased bear-human conflict. This problem is eliminated at project's end when the humans move out. The HSI would return to baseline conditions, but a few HU's would be lost to the acres still covered with project artifacts (Table III). However, at TYllO, canopy closure in the developed areas, includin~ the transmission line and roads, decreases the spring to fall range values {LR 1 and LR 2 ) and again lowers the HSI. By TY225 , baseline conditions should be.essentially restored. Over the 50-year life of the Mahoney Lake Coordination Report -13- project, the AAHU 1 S lost are 84 (Table IV). However, if the forest recovery period is included, the AAHU loss is 53. The longer period results in a net loss of over 14,000 HU•s as compared with over 4,000 HU•s lust during the project•s lifetime. Sitka Black-Tailed Deer The rnodel used to determine habitat suitability for Sitka black-tailed deer is a slight modification of the one developed by Lana Shea 3/6/81 (App. B). On the advice of John Schoen, ADF&G, variable v1, the percent cover of shrubs within x yards, was eliminated. Consequently, the aggregation function for the life requisite spring/summer/fall range, LR 1, was changed. The covertypes old growth coniferous forest and muskeg were evaluated for baseline condition; and old growth coniferous forest, coniferous forest cut for the transmission line, and muskeg were evaluated for the project life, target years TYl and TY50. After project•s termination, regrowth coniferous forest would occupy the coniferous forest sites disturbed by construction (Table II). Snow pack data used was from Beavers Falls (Anon., 1974-1980) for years 1974 to 1980. Winters were classified as high, medium, low or unsuitable or intermediate between two and assigned a SI as specified in v7 of the model (App. B). ln the coniferous forest, these SI•s were then increased by 0.1 or 0.2 to correct for protection afforded by the canopy. Snow pack SI•s in all covertypes were decreased by 0.1 to account for increase in snow pack due to elevation. As directed in the model, aggregation of life requisities were made subjectively. In the coniferous forest, LR 1 was greater than LR 2 (winter range). Winter range was considered t·1ahoney Lake Coord in at ion Report .,.14- limiting, so the HSI was equal to LR 2• In the ~uskeg LR 1 was less than LR 2 • However, since LR 1 is probably not limiting in the ecosystem, LR 2 was chosen as the HSI in the muskeg. The HSI 1 s for the two covertypes wer~ then aggregated using area weighted means. The effects of project development would be felt by the Sitka black-tailed deer population throughout the life of the project and the recovery time of the conifer{)US forest (Table III). The loss in HU's during the life of the project is attribut~ble to a decrease in acreage from the powerhouse, camp., and roads. and changes in HSI at the transmission line corridor. In the transmission line corridor, spring/summer/fa 11 range {LR 1) would improve in quality, but winter range (LR 2 } would decline in quality due to increased snow pack and a decrease in evergreen forbes. During the recovery period, loss in HU's is due primarily to a decrea~e in HSI of the regrowth areas and secondarily to the small loss in acreage (12 acres, Table II). From canopy closure {TYllO} until recovery of old growth forest (TY275), both LR 1 and LR 2 range would be sub-baseline due to lack of appropriate ground cover species. During the life of the project (50 years), 1,782 HU's or 36 AAHU's would be lost; and in the recovery life of the project (275 years) 14,097 HU's or 51 AAHU's would be lost (Table IV). Northern Bald Eagle The northern bald eagle model used (App. 8) is a modification of the one in the Alaska Handbook (Konkel et al., 1980). The coniferous forest type, v2 , was modified to include Alaska yellow cedar and western red cedar, two prominent species in southeastern coastal forests. The Mahoney Lake Coordination Report -15- suitability of the distance of an area from .shore, v6 , was also modified, based on personal communication with Jack Hodges, FWS, and Robards and Hodges (undated). This resulted in three different coniferous forest covertypes: 0-1/8 mile, 1/8-1/4 mile, and greater than 1/4 mile from shore. After project construction~ developed coniferous forest would be added as a covertype. The aggregation function for reproduction was also modified to reflect the importance of distance from . . . shore (App B). ·For each covertype, the HSI value was the lowest LR value; and the.HSI's for the covertypes were aggregated using an area weighted mean. The HSI's which result from the model, 0.34 to 0.44 {Table Ill), make the Mahoney Lakes eagle habitat appear less suitable than it actually is. For example, in TYO the area weighted aggregation function combines 292 acres at HSI 0.8 and 296 acres at HSI 0.08 to give 588 acres which have an average HSI of 0.44. The difference between the 2 HSI's is solely the result of distance from.shoreline, v6: area 0-1/8 mile from shore having a SI of 1.0, and area from 1/8 to 1/4 mile from shore having a SI of 0. 1. Therefore, in reality, there are 292 acres of fairly good habitat and 296 acres of marginal habitat. Although the aggregation of covertypes has no net.effect on HU's, the differences in quality .should be kept in mind when planning mitigation. Effects of the project on northern bald eagles would be primarily due to not having a 1/8 mile leave strip along the shore {Table III). By TY110 regrowth would improve conditions and by TY275, the area should have ·recovered as eagle habitat. The loss would be 62 AAHU, or 3118 HU, during the 50-year project life, and 25 AAHU or 7003 HU during the recovery life of the project {Table IV}. Mahoney Lake Coordination Report -16- Blue Grouse The model used to evaluate habitat suitability for blue grouse is by Maureen Daly (1981) and was followed without modificati~n (App. 8). In the baseline study, conifer.ous forest was evaluated for LR. reproduction, and LR 3, winter food; and muskeg was evaluated for LR 2, late spring/summer/fall food (rearing). After project implementation, coniferous forest that had been converted to roadside and slash was evaluated for LR 1 and LR 2 , not LR 3 •. Aggregation of the life requisites is based on interspersion and is included in the model. Blue grouse habitat would be vastly improved during the life of the project because of the increase in area available for rearing (Table III). From the project's end to TYlOO, the habitat would deteriorate to a level slightly below baseline conditions. By TY275, the blue grouse habitat should return to baseline suitability. The AAHU gained would be 915 (or 45,736 HU) over the 50-year life of the project or 253 {69,631 HU) over the 275-year recovery life of the project {Table IV). tHnk The model for mink in Konkel et al. {1980) was followed without modification. Saltwater aquatic was the only covertype evaluated because: 1) it was assumed that winter habitat (saltwater aquatic) is limiting because of its small area, and 2) the only criterion for summer habitatis area in shoreline which has an SI of 1.0 in the t1ahoney Lakes area. The lowest LR value was chosen as the HSI value for saltwater aquatic, and because only one covertype was evaluated, no further Mahoney Lake .Coordination Report -17- aggregation was necessary. Area in shoreHne was estimated at 3.7 miles long by an estimated average 15 yards wide·, or 21 acres.· The onlY change in habitat from the project would result from a small loss in area due to the docking facility. At project's end, ·the area ·lost should quickly revegetate and·become suitable for mink. Only 1 AAHU would be lost over the 50-or 275~year time period if the project were implemented (Table III & IV).· B. Aquatic Study Cover types The t1ahoney Lakes study area includes two aquatic covertypes, lacustrine and riverine. There are three streams: Falls Creek, South Creek, and t1ahoney Creek; and four 1 akes: Upper and Lower f1ahoney Lakes, and bm lakes which drain into Upper Mahoney Lake (Figs. 2· & 3). Species Selection A number of salmonid species are reported from the ~1ahoney Lakes system. These include: pink, chum, coho, and sockeye salmon, steelhead and searun cutthroat trout, and Dolly Varden char (Anon., 1979). Sockeye salmon was chosen as an evaluation species because of its life history. Sockeye generally spawn in streams which are lake tributaries, or, occasionally, along lake shores. After hatching, the young migrate to the lake were they rear for 1-3 years. The Falls Creek (and South Mahoney Lake Coordination Report -18- Creek)/Lower t1ahoney Lake configuration meets these requirements. Consequently, the removal of Falls Creek could have an ·adverse impact on the sockeye salmon run. Dolly Varden was selected to represent a species which would use Falls Creek for rearing, as fry were trapped there in 1977 by the ADF&G. Removing Falls Creek would. result in the lo~s of this rearing habitat. Field Sampling Fieldwork concentrated on documenting use of the system by salmonids and a HEP study of Falls Creek. Twelve spawning ground counts were conducted between July 16 and October 31, 1981. Only Mahoney Creek r1as surveyed until the salmon began their upstream migration. After the migration began, Fa 11 s Creek and South Creek were surveyed, and t1ahoney Creek was surveyed as time permitted. The HEP study was conducted on the port ion :of Fa 11 s Creek from lower tlahoney Lake to the first permanent blockage to upstream migration of salmon. The study was accomplished in two field trips: April 22 and 23, 1981 and on August 19, 1981. The creek was evaluated in 60-foot sections. Lengths and widths of the creek were measured with a tape measure to the nearest foot. Gravel size, ~epth, and bank conditions were then evaluated for each section. In addition, the percentages of the area suitable for spawning_and rearing were estimated. An area considered suitable for spawning had a cobble bottom with flowing water and was assigned an HSI of 1.0 •. Areas considered suitable for rearing were often pools, had undercut banks and tended to be deeper and slower moving than spawning areas. An area which did not meet the requirements Mahoney Lake Coordination Report -19- for spawning or rearing was assigned an HSI of 0.0. If.any of the variables changed within the 60-foot section, then the section·was subdivided for that variable. During the August ev~luation, the first map was used as ~ ba~eline, and ~hanges in the variables were documented and measured. Results It is approximately 1,500 feet from Lower Mahoney lake to the first permanent blockage of salmon migration at Falls Creek (Fig. 4). During the April mapping and HEP evaluation, there were 1.19 acres of stream, of which 30% (0.36 acre) was suitable for spawning and 12% (0.14 acre) was suitable for rearing. Spawning habitat was concentrated between the lake and the second log jam, approximately 775 feet. However, rearing habitat was fairly evenly distributed between lower and upper sections of the stream. During the August HEP study, there was no surface water from the mouth of Falls Creek to 1,000 feet from the mouth (Fig. 5). However, above that point water was flo\iing and covered 0.26 acre. This dry bed situation was observed on some of the subsequent stream census dates, 8/12, 0/18 and 8/29/81. Even though there were sections of stream where. water was flowing that would be suitable for spawning (19%, 0.05 acre) there was no access to them for the fish and HSI equals 0. A small portion, 2% (.007 acre), of this part of the stream was su;table for rearing. The 1981 salmon run was late, presumably due to dry weather. The fish were observed in small schools just offshore and in the mouth of Hahoney Lake Coordination Report -20- Mahoney Creek from 8/8 to 8/18/81 (Table Vh Pink, sockeye, and chum salmon were running up Hahoney Creek between 8/24 and 9/10/81, with most activity on 9/10/81. No adult fish or carcasses were seen in Falls Creek or South Creek on any of the census dates. However, a few fry (probably Dolly Varden) were observed in the creek 8/12/81, indicating that Falls Creek has some value to stream rearing species. On 14 September 1982, 200-300 adult anadromous sockeyes were observed spawning along the west shore of Lower Hahoney Lake. This was the first confirmation of anadromous sockeyes spawning in the lower lake. The highest number occurred near the mouth of Falls Creek. Several hundred additional sockeyes were observed moving up 1·1ahoney Creek on the same date. Streams flowing into and out of Lower Hahoney Lake are not used by sockeyes for spawning. Velocity chutes and falls in t~ahoney Creek would prevent fry from reaching the lower lake to rear. Falls Creek is not used, and sections of the streambed are often dry. Much of the flow in Falls Creek travels underground through highly permeable alluvial gravels and enters Lo\~er t1ahoney Lake be 1 ow its surface in the form of upwelling. Where suitable gravels are present, areas of upwelling provide critical spawning habitat for sockeyes. The spawning impulse and proper development of eggs is dependent on water temperatures and currents at points of upwelling. A minimum temperature of 6°C is necessary for proper initial development of sockeye eggs. V. Discussion and Recommendations The direct impacts of a Mahoney Lakes power pr.oject would be primarily the loss and alteration of some wildlife habitat. t1ahoney Lake Coordination Report -21- Approximately 30 acres of coniferous forest, muskeg and saltwater aquatic covertypes would be temporarily lost as habitat beginning with the project. construction. An additional 119 acres of coniferous forest would be altered by the project. From the project closure to recovery, 137 acres would be in an altered state and 12 in unknown condition. In the aquatic habitat, the diversion of Falls.Creek would result in a loss of as much as 0.14 acre of rearing habitat and, without mitigation, the loss of the spawning habitat. The loss of the falls would also be an aesthetic loss to the area. There would also be indirect impacts to a much broader area due to human presence. Increased human/b,ear contact, for instance, often results in killing nuisance bears. To minimize this impact we recommend that garbage be carefully stored and disposed of in order to avoid attracting nuisance bears. Even though wolves were not evaluated, it should be noted that they may abandon cubs or den· sites when humans move into their territory {Konkel et al., 1980). During the time from project commencement to coniferous forest recovery, a total of 35,718 AAHU would be lost by black. bear; Sitka black-tailed deer, eagle, and mink. In contrast, 69,631 AAHU would be gained by blue grouse. The. major reason northern bald eagle lost HU's is that the proposed transmission line falls within 1/8 mile of shore. Moving the line back to 1/8 to 1/4 mile from shore slightly reduces the HSI in TY1 and TY50 (as compared with the baseline HSI); and during-TYllO and TY275, the HSI would be equal to baseline conditions. This results in the reduction of AAHU loss from -62 to -12 over 50 years or from -25 to -4 over 275 years. Therefore, it is suggested that a power line further than 1/8 Hahoney Lake Coordination Report -22- mile from shore be considered. Although no eagle nests were found in the 4-mile shoreline from ~1ahoney Lakes to Beaver Falls, the potential for nesting would be greatly reduced if th~.power line were located as presently planned. Another concern regarding bald eagles and other raptors is potential mortality due to electrocution and/or entanglement. We recommend that the powerlines be designed and constructed in such a manner as to avoid this potential problem area. Design criteria should be patterned after those illustrated and discussed in Olendorff et al. (1981). A dam at the outlet of Upper 1·1ahoney Lake would eliminate flows in Falls Creek. This, in turn, would disrupt upwelling processes along the west shore of the lower lake. Sockeyes that spawn in this area would be adversely affected. In the current project proposal, the powerhouse would be located near the west shore of Lower Mahoney Lake. To mitigate the disruption of upwelling processes, taflrace waters should be directed into the braided channels of Falls Creek as far above the lower lake as possible. This would simulate preproject i.ntra-gravel f1ows to points of upwelling along the west shore of Lower Mahoney Lake. Water taken from the bottom of Upper f4ahoney Lake and discharged from the powerhouse into the lower lake would be about 4°C year-round. While temperatures in the lower lake as a whole are not expected to change sig- nificantly, local temperature changes along the west shore of the lake would occur. Negative impacts associated with discharge of colder water to points of upwelling between September and early November include alteration of sockeye spawning behavior and improper initial development of eggs. Mahoney Lake Coordination Report -23- Another consideration is the effect of 4°C water on the total incuba- tion and fry development time frame. If eggs survive the initial shock of colcler water, development would proceed at a slower rate than under. normal conditions during the fall and early winter. However, by mid- winter the 4°C discharges would be slightly warmer than normal, whereby development of eggs may be accelerated. If fry emerge into the lower lake earlier or later than normal, food supplies may be inadequate. To mitigate the impacts of cdlder water on spawning behavior and early development of eggs, three options could be considered: 1) con- struction of a multilevel or floating intake structure in the upper lake; 2) pumping water from the lower lake into the tailrace; and 3) creation of an artificial spawning channel. We understand there are some severe technical constraints associated with item 1 above. We would, therefore, recommend that pump(s) be installed in the lower lake to moderate water temperatures· in the tailrace. Indications are that the pump(s) would only operate during a period in the fall (September and October), and again in late winter (February and March). The exact schedule of pump operation would have to be formulated as a result of a monitoring program. We would, therefore, concurrently recommend that a monitoring study be designed and incorporated into the project plans whereby adverse and or beneficial impacts to sockeye salmon would be evaluated. and a pump operation schedule would be devised. Study participants would include representatives of the COE, FWS, National Marine Fisheries Service {NMFS) and ADF&G. At an agreed upon time the study participants would evaluate the success of the mitigation measure and recommend necessary changes. Mahoney Lake Coordinatio.n Report -24- Reco11111endations To provide mitigation for project associated adverse impacts, the FWS recommends the following: 1. All human garbage should be carefully stored and disposed of. 2. The transmission line location should be located more than 1/8 mile from shore. 3. The transmission line be designed and constructed to avoid potential raptor mortality caused by electrocution and/or entan- glement. See Olendorff et al., 1981. 4. Water from the powerhouse tailrace should be returned to the streambed as far above the lower lake as practicable. The use of pumps to accomplish this measure should be investigated. 5. P·ump{s) be installed in the lower lake, capable of supplying a sufficient quantity of water to maintain preproject thermal conditions~ 6. A monitoring program be established concurrent with project development to assess proJect impacts on sockeye salmon and devise a pump operation schedule. This program would provide the data base in determining whether or not additional mitigation and/or alternative mitigation measures are Mahoney Lake Coordination Report -25- necessary. Alternatives which could be considered would include an artificial spawning channel •. The COE, FWS, ADF&G, and N~1FS would be the primary participants in the design and imp 1 ementati on of this study. Mahoney Lake Coordination Report Literature Cited U.S. Fish and Wildlife Service, 1981. Habitat Evaluation Procedures Uorkbook. HEP Group, -26- Western Energy & Land Use Team, U.S. Fish & Wildlife Service. Drake Creekside Building, 2625 Redwing Road, Fort Collins, CO 80526 U.S. Fish and Wildlife Service, 1980-81. Ecological Services Manual Habitat Evaluation Procedures. ES~1 100-104. Division of Ecologica 1 Services, Fish and Wildlife Service, Dept. of the Interior. Anon., 1979. t1ahoney Lakes Hydropower Project. United States Dept. of the Interior, U.S. Fish & Wildlife Service, Anchorage, Alaska. 21 pp. Anon., 1978. t1ahoney Lakes Hydropower Project.· Anon., 1974-80. Climatological Data. Vol. 60-66. U.S. Dept. of Commerce, National Oceanic & Atmospheric Administration. Environmental Data Section. Asheville, D.C. Combs, B. D. 1965. Effect of temperature on the development of salmon eggs. Progressive Fish Cult. 27(3):134-137. Harris, A. 5. & W. A. Farr. 1974. The forest ecosystem of southeast Alaska 7. Forest Ecology and Timber Management. USDA FS General Technical Report PNW-25. Pacific Northwest Forest and Range Experiment Station, U.S. Dept. of Agriculture, Forest Service, P.O. Box 3141, Portland, OR. Konkel, G. W., et a1. Terrestrial Habitat Evaluation Criteria Handbook- Alaska. Div. of Ecological Services, U.S. Fish & Wildlife Service, Anchorage, Alaska. Olendorf, R. R., A. D. Miller, R. N. Lehman. 1981. Suggested Practices for Raptor Protection on Power Lines-The State of the Art in 1981. Raptor Research Foundation. Department of Veterinary Biology, University of Minnesota, St. Paul, Minnesota. Retherford, R. W. Assoc., K. t·1iller, Bentheimer Engineering Co., Inc. 1976. Ketchikan Public Utilities Comprehensive Study. Electric, water and telephone divisions. Robards, R. C. and J. I. Hodges. Undated. Observations from 2,760 bald eagle nests in southeast Alaska. Progress Report 1969-1976. Depart1;~ent of the Interior. U.S. Fish & Wildlife Service, Eagle r.tanagement Studies, Juneau, Alaska. · Viereck, L. A. and E. L. Little. Agriculture Handbook No. 410. Agriculture, Washington, D.C. 1972. Alaska trees and shrubs. Forest Service, U.S. Department of EIS-C-30 Glossary of HEP terms Aggregation function ·-the methematical. function lllhich combines 51 Is to an LR value, LR values to a co.ver type HSI, .or -cpver type HSI to a single HSI Average Annual Habitat Units (AAHJ) -the number of HJ·lost ·or gained over the life of a project on an annual basis as a result of a given action Cover type - a habitat type 111hich can be defined by a set of vegetational or physical parameters; i.e. coniferous forest, cold small lake Habitat Evaluation Procedures (HEP) - a species based method of determining impacts of development to habitat; may be used to compare alternatives, predict impact, and quantify m~tigation necessary · Habitat Suitability Index (HSI) -an index between 0 and 1 111hich represents the quality of a habitat for a given species1 the HSI may be for a single cover type or a number of cover types 111hich meet the needs of a species Habitat Units·(HU)-an abstract value related to the number of 111ildlife individuals a habitat can support; it is determined by the formula HU = HSI x acres Life Requisite (LR) - a need of a species such as food, cover, or reproduction. Life Requisite value (LRi) -_an index bet111een 0 and 1. 111hich represents the capacity of a given habitat to support a life requisite of a species; one or more 51 determines a LRi Suitability Index ( SI) -an index between 0 and 1 111h.ich represents the quality of a cover type variable in relation to a species' needs Target year (TY) - a year in the life of the project for which the habitat is evaluated EIS-C-31 Table I Species List (from Mahoney Lakes Report, March, 1~79) Mammals black bear Sitka black-tailed deer wolf beaver river otter mink martin shrews voles red squirrel weasel Birds northern bald eagles blue grouse ptarmigan ruffed grouse spruce grouse plus a variety of marine winter residents, migrating ducks, shorebirds, and seabirds r ".l? Fish pink salmon chum salmon coho salmon sockeye salmon steelhead trout sea-run cutthroat trout Dolly Varden char Table II. Acreages and condition of terrestrial cover types on the target years Cover type Alpine, snowfields Coniferous forest steep, subalpine Coniferous forest old grolllth transmission line road plant camp regrowth condition unknown Muskeg unaltered camp condition unl4nown Saltwater aquatic unaltered dock Slide Riparian Lacustrine Total 1 not evaluated Acres In St d A u lY rea 1644 .. 867 .2078 ------ . 272 -- 21 - 58 25 256 5221 TYO 668 401 .1651 ---. --- 100 -- 21 - 24 3 222 3090 Acres in Direct Impact Area TYl TYSO TYllO TY2 1 .. - --- ~ ---.. .. ·., ... 1507 "1507 .. 1507 164 119 119 -- 7 7 --·a 8 - - 11 11 ----137 ---. 8 96 96 96 9 4 4 ----4 20.8 20.8 -- 0.2 0.2 21 2~ 1 ---- 1 ---- EIS-C-33 Table I II. HSI ·and HJ for each species in each target year Target year Spec~es 0 1 50 110 275 Black bear HSI 0.83 0.76 0.83 0. 79 0.83 HJ 1453 1309. 1425 1381 1444 Sitka black- tailed deer HSI 0.62 o. 6~ 0. 61. 0.57 0.62 HJ 1086 1055 1055 995 1079 N. bald eagle HSI 0.44 0.34 0.34 0.41 0.44 HJ 259 196 .196 241 259 Blue grouse HSI 0.48 1.0 1.0 0.47 0.44 HJ 840 . 1729 1729 818 835 Mink HSI D. 93 0.93 0.93 0.93 0.93 HJ 20 19 19 20 20 Table IV. AAI-I.J and HJ change during the (50 year) life of the project and during the baseline-to-recovery (275 year) life of the projec AAHU AAHU Species TYO ~ TYSO Total #.HU's TYO -TY275 Total II HJ's Black bear .. 84 ·4188 -53 14343 Sitka black-tailed deer -36 1782 -51 14097 Northern bald eagle ;.,62 3118 -25 7003 Blue grouse +915 45736 . +253 69631 Mink -1 50 . , -.... 275 EIS-C-35 Table V. Fish Census in Mahoney Creek, Falls Creek, and South Creek 7/16-10/31/81 Number of each species Date · Mahoney· Creek Falls Creek South Creek 7/16/81 0 7/22/81 0 7/28/81 0 .. . k 8/8/81 100 ~ g~~ so eye 8/12/81 0 0 0 8/18/81 ? - · 111ater too milky 0 0 but fish seen jumping 8/24/81 2f p~R~eye 8/29/81 f9 ib~eye 0 0 9/10/81 f~ ~gckeye 0 0 1 p~H~s 9/24/81 0 0 10/14/81 0 0 10/31/81 0 0 Project Map 1-~ L & II;£ 5 • 5 11 '15 Sule il lilts F ICIIE 1 r"Tf' ------- .--.. "' ,. __ ,_ .......... -.-· ....... I \ \. \ \ ' \ ' --,_.,; " \ ..... ... , -- --' ' ........ .... ' ' ' \ ' I I ' ' I I ' Direct impact / area boundar}// \, / / / -~ / / . / / / EI S-C-38 \ \ \ \ \ It' Tunnel '\ \ \ \ \ / Power line/· ~-~ / / Dock shone)( Creet. ., ' ' ..... -- .. E:!S-C-39 G:J D ~ L...-J D . . ·s· .... .... . · ... Lake Alpine/sno111fiel Steep,subalpint eoni f-erou'! fort Coniferous fon Muskeq Slide Streamside Dir~ct impact l. d-8 •-40 r-40 d-5 a-5!l r-~0 t;~ravel- 1-6" riffle 1-1" vool d-ZO s-;o r-10 J I I I grav1l· Hj - I I I ' \ \ \ \ ' .. \ yt a-;!! ;md'~ \ shruL "l ' , __ ., ..._/ l-t I I I I I •1-lo n-20 r-25 1-11 l s-40 1 J,-.-115 ·-10 lnq•. :tllrl l t tHt ~. EIS-C-40 hr'l'' bo~;).lpr !ISUhSlt·-.t" i. I I I I I . \ I ttm•k-luv \IPO\\ fllli lllPt.l 1'UDHJI tx., dN ul-I h:u;.;-loill h~"'locl<< I I ·1-l p ~-1" r-" ~-)11 I r-F1 I I I I I •t-lS I I 5 .n \ r-1~ ;. t ho>~ldrr rt,t>fll t & ur~~.~.,.l ~~" · I I I d-7" j ..__C:,Il ; ,Jj ' lflhl t,.. ........ J \ huHl !l"t I I I l ,t,.\.:I"P H!bi<-•, \\" 9-"li~ ~lf·~ pnjt.l r-1" 'U·t•t t!i 1 1 ________ ..,; i, I I I I ' ' I I I L , .... ,:. I ' \ \ j J 1 I I I I I \ d-6 s-20 r-20 I I 1 \ l \ \ I t I I I <I-ll!~ !;-0 ! \) r...,n I . l ' t ' ' . \ ~ / . ~;/ l \ l l I J I I I l 1- J:. ~ J: c t t. \ r r I \ J J / EI s-C-41 r-0 . d-7 s-5 r-0 d-9 s-5 r-0 d-2ll s-50 r-0 cl-6 s-50 ·r-·5 \ \ \ 1 \ I I I ' l ' ' I I I . f \ \ .J I \ . I I I J Fig. 4 and Fig. 5 Key: water boundary ----gravel boun.dary l II I I ' ... ...Jw ...J ..J undercut bank log jam .12-61 size of rock in section of stream (inches) p-22 pool -depth (inches) d-5 depth of stream -inches s-15 %of section suitable for spawning r-10 % of section suitable for rearing Seale: 1 " = 60 ' EIS-C-42 ....... " \ \ \. \ \ • I \ 5 / / / s \ . -·------...:.,-------- ---·, .... ,.,· .-·-· ...... / / ;' / 1 EIS 7C.,.43 ........... , ~-, -.--.. ; ., ..... -, .. ~ ~. ..... ~~ . .v----~t.-1 ..... _ ..... , .... .._ .... 1~ ... ,:-~ ... ---~~~~ ...... ....,._ .. ~..........-.------.-.-- Key -App.A -Fig. 1 1 Coniferous forest 2 Muskeg 3 Slide 4 Steep, subalpine forest 5 Alpine, snowfields 6 Streamside 7 Intertidal (saltwater aquatic) 8 Lacustrine photo boundaries .-.-. boundary of direct 'impact area SHANNON &WILSON. INC. TABLE OF CONTENTS 1.0 MAHONEY LAKE TRIP REPORT 1 1.1 General ........................................... 1 1.2 Goology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1. 3 Intake/Diversion Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1. 4 Penstock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.5 Powerhou.se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. 6 Acce,ss Roads • • . . . • . • • • . • . • • • • • • • • . • • • • • . • • . . • . . • . • • 4 2.0 GEOTECHNICAL PRE-FEASIBILITY OF PROPOSED TUNNEL ALIGNMENT 5 2.1 Scope of Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Description of the Proposed Layout . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.1 Intake Shaft Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.2 Outlet Portal Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.3 Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Excavation, Initial Support, and Final Lining . . . . . . . . . . . . . . . . . . . . 6 2.3.1 Excavation and Support at the Outlet Portal . . . . . . . . . . . . . . . . 7 2.3.2 Tunnel Excavation and Initial Support . . . . . . . . . . . . . . . . . . . . 7 2.3.3 Final Lining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3.4 Intake Shaft Excavation and Support . . . . . . . . . . . . . . . . . . . . . 8 2.4 Design Level Explorations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2. 4 .1 Geotechnical Mapping and Trenching . . . . . . . . . . . . . . . . . . . . . 9 2.4.2 Borings and Seismic Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Table .1&... TABLE 1 Estimated Construction Quantities and Costs i W-6527..01 TABLE OF CONTENTS (cont.) Figure No. I Site Plan 2 Tunnel Profile SHANNON &WILSON. INC. LIST OF FIGURES APPENDIX IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL ENGINEERING REPORT 11 SHANNON &WILSON. INC. MAHONEY LAKE HYDROPOWER PROJECT TRIP REPORT AND GEOTECHNICAL PRE-FEASffiiLITY OF THE PROPOSED TUNNEL ALIGNMENT 1.0 MAHONEY LAKE TRIP REPORT 1.1 General The purpose of this trip report is to describe observations, conclusions and preliminary recom- mendations regarding the geotechnical aspects of a proposed hydroelectric facility at Mahoney I...ake, located approximately 7 miles northeast of Ketchikan, Alaska. The project involves the diversion of water at or near the outlet of Upper Mahoney I...ake in the vicinity of elevation 1850 feet, and conveyance to a powerhouse along Mahoney Creek, upstream from its entry into Mahoney Lake, as shown on Figure 1. The elevation of Mahoney Lake is 130 feet and the elevation of the proposed powerhouse site is 160 feet. Prior to this site visit, Mr. Jack Snyder of HDR used U.S. Geological Survey (1:63,369) and U.S. Army Corps of Engineers (COE) (1:4,800) topographic maps to prepare a preliminary project layout. He was aided by previous studies that had been performed by R.W. Beck of Seattle and the COE. The purpose of this site visit was evaluate the feasibility of a hydroelectric project at the site, based on field observations. Shannon & Wilson's scope of work included the review of reports and letters by R.W. Beck and the COE that were obtained by HDR; review of published geologic literature; and a site visit on June 21 and 22, 1993. Accompanying Bill Laprade of Shannon & Wt.lson on June 21 were Jack Snyder and Don Thompson of HDR; Doug Campbell, Eric Mench and Bud Johnson of Cape Fox Corporation; and Jan Risla of Ketchikan Public Utilities. On June 22, Shannon & Wilson and HDR personnel visited the site alone. There is no road access to the site. Access was gained by helicopter, provided by Temsco of Ketchikan. 1.2 Geology Geologic conditions in the project area are dominated by bedrock formations. The most widespread rock in the area is a schist or phyllite. Where this Paleozoic to Mesozoic formation has not been affected by igneous intrusions, it is relatively weak and much slope instability is common. However, heat from a large Tertiary intrusion of gabbro baked these rocks in an aureole around the perimeter of the intrusion. The heat transformed the schist/phyllite to a much harder, more competent rock. The unconfined strength of the rock increased by perhaps as much as 2 to 10 times. The very large gabbro intrusion is closest to the project area just west of the west end of Upper Mahoney Lake, and it extends westward to the city of Ketchikan. Within the project area are smaller intrusions of quartz diorite, based on reports by others and the 1 W-6527-01 SHANNON &WILSON. INC. observation of quartz diorite cobbles in the creek. The number, size and location of these small intrusions are unknown. The area is known to have been glaciated; however, no glacial deposits were observed during this site visit. Holocene deposits are colluvium, alluvium and muskeg. Colluvium included talus, avalanche deposits and landslide deposits. Alluvium included active stream deposits and alluvial fans. Muskeg is fragmented remains of decayed vegetable matter accumulating in bogs; it can range from nearly all vegetation (peat) to organic silt with peat (muck). The site is crossed by faults and lineaments that are probably indicative of minor shear zones in the bedrock. Two of the faults recognized by the COE may cross the alignment of the penstock/tunnel. Other parallel lineaments are also shown on the Site Plan, Figure 1. Many of the avalanche chutes in the area are in the lineaments, some of which are not recognizable on the topographic maps. It should be noted that the topographic maps by the U.S. Geological Survey and the COE are not detailed enough to represent the actual topography of the site. In my opinion, the ground is much more rugged and broken than indicated on these published maps. Slope instability in this area is primarily rock fall and small to moderate size rock slides. These incidents appear to occur even where bedding is apparently favorable, the instability being the result of bedrock joints. Because of the hard and blocky nature of the schist/phyllite, the rock blocks are generally rectangular. Where recent debris avalanche deposits were observed, large woody debris comprised a large portion of the deposit. 1.3 Inta:ke/Diversion Site Diversion sites were evaluated over a distance of about 2,300 feet starting at the outlet (north end) of Upper Mahoney Lake. The sites were (1) at the mouth of the outlet, (2) about 450 feet downstream of the outlet, and (3) about 2,300 feet downstream of the outlet. In general, the bedrock at the sites dipped steeply (36 to 58 degrees) to the west and bedrock was exposed on the right bank at each of the three sites. The left side of the valley was heavily laden with talus that was shed from high cliffs to the west. The site at the mouth and the site farthest down- stream appear to have significant volumes of talus on their left abutments; however, the site about 450 feet downstream from the mouth contained bedrock on the left abutment. Access to the site about 450 feet downstream from the mouth would require minimal amount of rock excavation for road and penstock access compared to the site at the mouth of the outlet. While access to the site 2,300 feet downstream would be favorable, a higher dam would be needed for an entrance to a drop shaft or penstock and a subsidiary dike would be required across a low saddle to the east. In my opinion, the site that is 450 feet downstream of the mouth of the lake (see Figure 1) is preferred from a geotechnical standpoint. 2 W-6527-01 SHANNON & WILSON. INC. One hazard that cannot be mitigated at any of the diversion sites is rockfall. The bedrock cliff to the west of the creek did not appear to be affected by large scale or deep-seated rock slides; however, there appeared to be continual rock falls and small rock slides. Such rockfall or slides could damage the diversion dam and the intake structure. Rock deflection berms have been constructed in alpine areas; however, such a structure would not be effective against a large volume of rock debris. We understand that a rock fill dam with a concrete facing, similar to that at the nearby Beaver Falls Hydroelectric Project, is anticipated. We concur that the ubiquitous schist/phyllite rock blocks would be suitable for such a structure. The hard schist/phyllite bedrock on both abut- ments would be suitable for embedment of the concrete cutoff and wing walls. Because of a bedrock swale that is present to the west of the west bedrock abutment, it may be necessary to fill in that area to create a buttressing effect for that abutment. 1.4 Penstock There are two distinct topographic sections on which the penstock would be located. The upper portion is relatively flat gradient from the preferred intake site to about 1,500 feet downstream. Because the wide bowl just downstream of the intake site is subject to flooding, channel migration, loose alluvial soils and avalanche deposits, it will be necessary to keep the penstock on the higher ground to the south and east of the bowl. This route would be in bedrock (schist/phyllite). Where the penstock crosses two avalanche chutes, the pipe would have to be encased in concrete and buried in rock. The second portion of the penstock is the very steep slope that has an average inclination of 45 degrees between about elevations 1 ,900 and 400 feet. There is a gently sloping bowl between elevations 400 and 300 feet, where a major tributary (avalanche chute) crosses the proposed alignment. The ground surface then steepens to about 30 degrees on the hillside just above the proposed powerhouse site. Based on the contours on the two published maps, the construction of a penstock would have been feasible; however, as discussed above, the actual ground topography bears little resemblance to the contour maps. In reality, the ground is a series of cliffs and swales. The cliffs are vertical to overhanging and 50 to 200 feet high; the swales are incisions that appear to be avalanche chutes. In the large bowl area between elevations 400 and 300 feet, much of the bowl appeared to be filled with slide or avalanche debris. The only route around this bowl would require a southward tum of the penstock that would require sidehill construction. In my opinion, this is inhospitable terrain for the laying of a surface penstock. It was agreed among all interested participants that a tunnel was the only viable means for water conveyance. In order to match the preferred intake site, a gradient would be required that is too steep for tunnel mucking equipment. Therefore, a combination of tunnel and raise-bore was considered. Gerry Millar of Shannon &. Wilson is preparing a pre-feasibility report for the 3 W-6527-01 SHANNON &WILSON. INC. geotechnical aspects of the tunnel. A relatively level saddle in the topography about 1 ,SOO feet downstream of the intake site would require minimal site grading to create a level working area for the raise bore and the installation of the vertical penstock section. l.S Powerhouse From the inlet of Mahoney Creek to Mahoney Lake, our field party walked approximately 1 ,200 feet upstream across an alluvial fan, at which point the creek became incised in a bedrock channel, as indicated on Figure 1. Hard schist/phyllite, similar to that at the right abutment of the intake/diversion site, outcropped on both side of the creek and in the channel bed. The dip of the bedding was at approximately right angles to that at the intake/diversion site; that is 60 to 80 degrees to the north. As discussed in the COE report, this divergence of bedding dip requires a fault in between the two sites. In my opinion, this site is suitable for construction of a powerhouse. It should be built into the bedrock hillside. The excavation would have to be blasted and the south side, in particular, would require temporary support by rock bolts to prevent bedding plane rock slides during construction. The ridge of rock in which the power- house would be situated would be out of the path of the avalanches that appeared to have endangered the powerhouse site as shown on the COE project. 1.6 Access Roads We understand that road access will not be attempted to the intake/diversion site. By inspection of topography and the geologic conditions, such a road would be cost-prohibitive for the proposed hydropower project. We understand that a new road would be required from the White River delta to the proposed powerhouse site, a distance of about S miles. Reconnaissance of this alignment was limited to observations from the helicopter, except for the 1,200 feet from the west end of Mahoney Lake to the powerhouse site. Between the White River delta and the outlet of Mahoney Lake the road would traverse gently to moderately sloping terrain; n<f. signs of slope instability were observed from the helicopter. The ridge containing Mahoney Lake on the east side appeared to be composed of bedrock . Along the south side of Mahoney Lake, a delta has been built into the lake and two d_~tributaries run across the fan. In between the creeks, muskeg was widespread. In the area between the inlet to Mahoney Lake and the powerhouse site, there was abundant evidence of an actively migrating channel and periodic inundation. A road located in this area would have to be constructed on an embankment to reduce the chances of destruction during an avulsion or from an avalanche. Nevertheless, periodic maintenance and reconstruction may be required during the life of the project. 4 W-6527-Ql SHANNON b WILSON. INC. 2.0 GEQIECHNJCAL PRE-FEASIBILITY OF PROPOSED roNNEL ALIGNMENT 2.1 Scope of Work The present scope of work consists of the evaluation of preliminary engineering geology and geotechnical information at the intake shaft, outlet ponal, and along the tunnel and shaft align- ment. Included in this information are the preliminary selection of shaft location, support and lining types and excavation procedures for the tunnel and shaft, and the preparation of prelimi- nary engineering estimates of quantities and costs for the tunnel and shaft construction. Preliminary engineering geology information is presented in section 1.2 of this report and in Appendix B of the Corps of Engineers report dated 1978. The principal objectives of the investigation are to establish the foundation conditions and the nature of the ground along the tunnel route and shaft, and identify any major geotechnical problems that could adversely affect project costs or schedules. Furthermore, the report makes detailed recommendations on the type and location of subsurface explorations (borings, seismic surveys, etc.) required for further project design. No borings were contemplated during the present study because of the cost of access to the principal sites. Once the overall feasibility of the project is established, the considerable cost of access and subsurface exploration can be justified. 2.2 Description of the Pro.posed Layout The objectives of the proposed layout are to deliver water under a head of approximately 1, 700 feet and to produce electricity at a new powerhouse near Mahoney Lake. The intake area will require an approximately 10-to 15-foot-high dam just north of Upper Mahoney Lake and an intake structure 1,800 feet downstream of the dam on the right bank of the river, as shown on Figure 1. The water will drop down a 32-inch-diameter pipe placed in a 48-inch-diameter shaft from elevation 1,850 to elevation 200 feet, and then along a pipe placed in an 8-foot-wide by 8-foot-high horseshoe-shaped tunnel to elevation 160 feet. The tunnel is aligned approximately east-west, and will be 2,700 feet long. Cover over the tunnel varies from 10 feet at the outlet portal to 1,650 feet at the junction with the drop shaft. 2.2.1 Intake Shaft Area The intake portal (elevation 1, 850 feet) will be located on the right side of Upper Mahoney Creek approximately 1,800 feet downstream of the damsite. Bedrock is slightly weathered, schistose to slabby greenstone (phyllite to schist) that will require minimal preparation as part of the intake shaft construction. Only limited construction will be performed at this site, likely only the concrete pad for drilling of the pilot hole for the raise bore since the rest of the tunnel and shaft will be excavated from the outlet portal. Access to the area is difficult and construction 5 W-6527-01 SHANNON bWILSON.INC. activity will have to be supported by helicopter. The intake shaft will be 4 feet in diameter and constructed in one pass with a Robbins or Atlas COPCO type raise borer. 2.2.2 Outlet Portal Area The outlet portal will be located at elevation 160 feet on a shallow slope (1.511 to 111). The portal face will require remedial support, likely in the form of shotcrete and rock bolts, and possibly a concrete portal extension if the slope above the portal produces runoff and rockfall. An access road will have to be constructed to the outlet portal area from the vicinity of the White River delta. The 32-inch-diameter steel surface penstock will transmit the water through the tunnel to the powerhouse. Support for the penstock will be required along the entire length of the tunnel. 2.2.3 Tunnel The 2, 700-foot-long access tunnel will have an excavated dimension 8 feet width and 4-foot radius above springline. The alignment is tangent on an approximate azimuth of E-W and the slope of the tunnel is constant at 1.48 percent between the base of the shaft (elevation 200 feet) and the outlet portal (elevation 160 feet). Tunnel ground conditions are expected to be very good for drill-and-blast excavation. Bedrock consists of regionally metamorphosed phyllite and schist further altered by contact metamorphism around a large quartz diorite intrusion, with some veins and dikes of quartz diorite. Short sections of blocky ground related to faults, possibly with localized high water inflows ( > 500 gpm), are also anticipated. Cover is greater than 200 feet along almost the entire length of the tunnel, and reaches a maximum of 1,650 feet at the shaft. The overall good quality of rock mass will allow for long sections of the tunnel to be left unlined, with only light support required for safety reasons. 2.3 Excavation. Initial SYJWOrt. and Final Uning This section presents the expected tunneling conditions along the proposed route, including initial ground support and final lining for the drill-and-blast (D+ B) method of excavation. Estimated construction quantities and costs are presented in Table 1. Anticipated geologic conditions are presented in Section 1.2, and on the cross-section in Figure 2. The latter also depicts the expected ground conditions and required support methods as bar graphs. This information is preliminary, and requires further investigation by borings and seismic surveys to be performed during a future design effort. The tunnel excavation setup will likely consist of the following: .. A six person crew using jacklegs for the drilling of blast holes and rock bolt holes. 6 W-6527-01 SHANNON &WILSON. INC. • A small rubber-tired front-end loader to muck the tunnel. • A dry-mix pot to place shotcrete. • Compressors at the portal for ventilation fan and air for the jacklegs at the face. • Electric plant at the portal for lighting in the tunnel. • Shared field office and support facilities with the powerhouse construction crew. • Raise bore equipment. Mucking of the shaft excavation will be with the same equip- ment as used in the tunnel construction. 2.3.1 Excavation and Sypport at the Outlet Porta! Talus and colluvium will be removed and the portal established where there is a minimum of 10 feet of rock cover over the crown of the tunnel. The face will be squared-off and the brow above the crown stabilized with rock bolts and shotcrete for stability and safety measures. An extended portal structure consisting of multiplate and concrete may be required to protect the work activities from rockfall and runoff above the portal. Excavation in from the portal will be full-face in rounds of 5 feet length, becoming gradually longer as the effects of weathering decrease and ground cover and rock mass quality increase. Areas of low rock cover and weathered blocky ground will require heavy initial support consisting of rock bolts and 10 em of shotcrete, and locally steel sets and shotcrete. Again, initial support requirements will decrease as weathering effects decrease and ground cover becomes higher. The outlet portal area is logged as Ground Type 3 on Drawing 2. 2.3.2 Tunnel Excavation and Initial Sumx>rt In from the outlet portal where the rock is to some degree weathered and de-stressed leading to a loosened, blocky condition (support category 3), the greenstone is classified as slabby to slightly blocky tunneling ground along most of the tunnel. Weathering ceases to be a consider- ation where ground cover is greater than about 200 feet, and joints become fairly tight at about the same depth. Very localized blocky fault zones will occur, however these do not present significant problems for excavation except where they coincide with high water intlows. The latter condition (blocky ground and high seepage rates) probably only occur beneath large permanent streams or in large fault zones fed by streams. Some stress slabbing in the sidewalls may occur in areas of high cover ( > 1,000 feet) where steep joints parallel to the bore also occur, requiring additional rock bolt support. Rock mass characteristics for the tunnel have been divided into three categories: 1) massive, unweathered rock mass with minor seepage at the face ( < 100 gpm) 7 W-6527-01 SHANNON &WILSON. INC. 2) heavily jointed rock mass or highly weathered ground, and/or significant seepage at the face (100 to 500 gpm) 3) wide shear or fracture zones or highly weathered ground, and/or high seepage inflows at the face ( > 500 gpm) Whenever required, the initial support requirements follow a similar categorization: 1) no initial support to local rock bolts placed in the crown and sidewalls to stabilize localized blocks or slabs of loose rock 2) rock bolts placed on a pattern supplemented with several centimeters of reinforced shotcrete in small blocky fault zones or weathered zones at the portals 3) steel sets encased in shotcrete at the portal or in large blocky fault zones, shear zones, or at the portal, especially those with high seepage inflows Rock bolts will be 5 feet in length, untensioned and anchored full-length with epoxy resin. At the portal face, longer bolts may be required as spiling. Shotcrete will be fiber-reinforced and placed in layers of 2 inches to the desired final thickness. Steel sets will be equivalent to W4-13 horseshoe ribs and will likely be required only in blocky fault zones with high seepage where shotcrete will not stick, or for a short section of the portal. 2.3.3 Final Linin~ Since the tunnel is required only as temporary access for the shaft excavation and for placement and inspection of the steel penstock, it need only be lined for ground support that is meant to stop progressive loosening and collapse of the rock mass. The final lining will therefore consist of the same elements as the initial supports, with greater thicknesses of shotcrete and closer spacing of rock bolts. No additional steel sets will be required for final lining. 2.3.4 Intake Shaft Excavation and Sup_port The shaft excavation (4-foot-diameter) will consist of the boring of a pilot hole from a concrete reaction pad at elevation 1850 down to the end of the tunnel at elevation 200, and lifting a raise borer to the reaction pad. Muck produced by the raise bore excavation will drop to the tunnel level, and be removed by small loader. No initial support will likely be required for the shaft. Final lining will consist of the embedment concrete or grout placed around the annulus of the pressure pipe centered in the shaft. 8 W-6527-01 SHANNON & WILSON. INC. 2.4 Desir,n Level Explorations 2.4.1 Geotechnical Malmin& and Irenchin& Once the layout is set, site-specific mapping (microgeology) of the portal and shaft areas should be performed at a scale of l-inch = 200 feet. Some trenching to expose bedrock may be required as part of this effort. Detailed mapping of features considered to be important rock mass defects such as fault zones, should also be performed. 2.4.2 Borin&s and Seismic Surveys A program of borings and surface reformation surveying should be performed once the results of the geotechnical mapping locates the important project sites (outlet portal, powerhouse, etc.) and larger scale rock mass defects (fault zones, etc.) that impact the project. SHANNON & WILSON, INC. Vice President William T. Laprade, C.E.G. Associate WTL:GM/lkd 7-22·931W6527-0l.RJ'TIW6527·lkd/lkd 9 W-6527..01 SHANNON & WILSON. INC. TABLE 1 ESTIMATED CONSTRUCTION OUAN'I'l'l'IES AND COSTS . Item .Fstimated Unit Cost Plan Cost ····· Construction ······· ... ··Quantity Excavation Tunnel 8 ft + 8 ft 2,700 LF 6,400 cy $150/cy $ 900,000 Tunnel Support Shotcrete 100 cy @ $600/cy $ 60,000 Rock bolts, #7, 5 ft long 5,000 LF@ $20/LF 100,000 Steel Sets, 4W13 100 units @ 300/unit 30,000 Excavationnnitial Support Shaft 4 ft diameter 1,700 LF $1,000/LF $1,700,000 Mob/demob LS $300,000 s 400.QQQ $3,190,000 7-I6-93fi'ABLE.lfW6S27-Ikdllkd W-6527-01 APPENDIX C AGENCY CORRESPONDENCE UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE 1011 E. TUDOR RD. IN REPL V HEf F:R TO· S~ ANCHORAGE, ALASKA 99503 1907) 276·3800 H 1 1 Colonel Lee R. Nunn District Engineer Alaska .District, Corps of Engineers P.O. Box 7002 Anchorage, Alaska 99510 Dear Colonel Nunn: 3 0 MAY 1980 This responds to your May 19, 1980, request for a list of threatened or endangered species which may occur in the following project areas: Location Village of Hekoryuk on Nunivak Island Village of Scammon Bay Cordova Interim Chichagof Island Mahoney Lakes near Ketchikan Activit:y Two breakwaters and revetment Small hydroelectric prnject Southcentral Railbelt hydro- electric project Small hydropower project at Tenakee Springs Southeast hydroelectric project Based on the best information currently available to us, no listed or proposed threatened or endangered species for which the Fish and Wildlife Service (F\~S) has responsibility are known to occur in any of the five project locations listed above. You may~ therefore, conclude that these projects will have no affect on those species and that preparation of a biological assessment or further consultation with the FWS pursuant to Section 7 of the Endangered Species Act is not required. Protection of threatened or endangered marine mammals is the responsibility of the National Marine Fisheries Service (NMFS). Whereas some of your proposed projects are in or adjacent to marine waters, you may wish to contact NMFS to determine potential effects of the projects on those species. New information indicating the presence of currently listed threatened or endangered species administered by the FWS or the listing of new species which might be affected by the proposed project will require re- initiation of the consultation process. --- Thank you for your concern for endangered wildlife. As always, personnel of our Endangered Species office are ava:iliiible. to answ.er your questions. ·o;;;:;d&#L; Area Director EIS-A-2 ( Dif}l•.c\RTitlEl\'T OF N.ATURAL RESOURCES ·DIViSION OF PARKS May 20, 1980 Re: 1130-2-1 Harlan E. Moors Chief, Engineering Division Alaska District, Corps of Engineers P. 0. Box 7002 · Anchorage, Alaska 99510 Subject: Mahoney Lake Hydroelectric Project Dear Mr. Moors: . JAYS. HAMMOND, GOVERNOR Chip Dennetl~in, Director 619 Warehouse Dr., Suite 210 Anchorage, Alaska 99501 274-4676 We have reviewed the subject proposal and. would like to offer the follmdng connnents: STATE HISTORIC PRESERVATION OFFICER The proposed hydroelectric ·project may impact significant cultural resources. AHRS site KET-017 is located .within or very near the proposed project. No systematic cultural resources survey is known to have been conducted in the at.~a. 'Therefore, under provis:l.ons of 36 CFR~OO, a preconstruction cultural resources sunrey is rP.commended. ~~ Sincerely, ~. rup Dennerlein Director CD/cw EIS-A-3 " DEI•.tUt1'ltiEl\~ OF NATUitAL ltESOUitCES February 2, 1979 Re: 1130-2-1 J. K . Soper, Chief [nqineering Division DIVISION OF PARKS Alaska District, Corps of Engineers P.O. Box 7002 . Ar;chorage, Alaska 99510 Dear Mr. Soper: 0 9 J ... J • ·"':7. JAYS. HAMMOND, GOVERNOR 619 Warehouse Dr., Suite 210 Anchorage, Alaska 99501 This letter is in response to your request of January 29th for our views on the Mahoney Lakes and Lake Grace projects and their involvement with archaeologicul or historic properties (your reference NPAEN-PL-EN). Our comments nenerally parallel those of Dr. Gerald Clark in his letter to your office which you had enClosed. We feel that the Mahoney Lakes area of the camp ilnd access road and the saltwater access area should be archaeologically survcyf!d prior to any finalization of plans. The power line as Dr. Clark noted appe<Jrs to be a low potential area; however, we would like to see the document<Jtion of the possible or probable impacts on the lnines indicated in your routing sheet. In the Lake Grace area the power line as Dr. Clark arFdn mentioned is a low probability area; however, the access area and camp drcil near salt water is very high in potential and we again concur .by feeling that an archaeological survey should be done in that area. If you have any further questions, please contact us. Sincerely, 1/JL,~ WJiliam s. llanable Statt Historic Preservation Officer D!{ :pg cc: Dr. Gerald Clark, Regional Archaeologist U.s. D. A. Forest Service P.O. Box 1628 Juneuu, Alaska 99802 EIS-A-4 .,. FEDERAL ENERGY REGULATORY COMMISSION · REGIONAL OFFICE . 555 Battery Street, Room 415 · San Francisco, California 94111 Colonel George R. Robertson District Engineer Alaska District; Corps of Engineers P. 0. Box 7002 Anchorage, Alaska 99510 Dear Colonel Robertson: March 1, 1978. In response to your letter of January 30, 1978 {NPAEN-PR-R), we are supplying updated power values for the· proposed Lake Grace .and Upper Mahoney hydroelectric projects near Ketchikan, Alaska. The at-market values are based on the estimated costs of power from alternative diesel-engine driven generatin~ plants at Ketchikan and Metlakatla. The Ketchikan Public Utility (KPU) alternative plant con- sists of a 6,450 kW unit with a heat rate of 9,300 Btu/kWh, capital cost of $330 per kilowatt, service life of 35 years, and fuel oil cost of 42¢/gallon. An interest rate of B.O% was used for KPU financing. The Metlakatla Power & Light (MPL) alternative plant consists of a 1,500 kW unit with a heat rate of 10,500 Btu/kWh, capital cost of $370 per kilowatt, service life of 35 years, and fuel oil cost of 44¢/gallon. REA financing at 5.0% interest rate was used for MPL The values given on the following tables are applicable to both the Lake Grace and Upper Mahoney projects at the appropriate power markets. They are based on January 1, 1978 price levels. As requested, the power values are given for power utilization at Ketchikan only, and for a combined Ketchikan and Metlakatla market. Very truly yours, --& ~-S<~~::.i Eug~~eblett Acting Regional Engineer Attachment cc: North Pacific Div. Corps of Engineers ETS-A-5 Table 1 Value of Hydroelectric Power at Ketchikan Market Municipal Financing .(@ 8.01 interest) . Capacity Energy 49.50 $/kW-yr . 32.60 mills/kWh Federal Financing (~ 6·5/81 interest) Capacity Energy · 41.38 $/kW-yr. 32.60 m111 s/kWh Table 2 Value of Hydroelectric Power at Combined Ketchikan and Metlakatla Markets Composite Financing (Municipal @ 8.0% and REA @ 5% interest) Capacity 1/ Energy 2/- 47.61 $/kW-yr. 33.82 mills/kWh Federal Financing (@ 6-5/8% interest) Capacity Jj Energy 2/ 42.93 $/kW-yr. 33.82 mills/kWh y 75Z KPU pZant capacit;y value + 251 MPL pzan-t capacit;y value •. Y 80% KPU pZant energy val-ue + 20% MPL pZa:n.t energy value. EIS-A-6 r l::>P. _ R_(c~-/J1d ..... ) T'~-E'-' United States Department of the Interior FISH AND WILDLIFE SERVICE ALASKA AREA OFFICE 8130 STREET ANCHORAGE, ALAS~A 9950-1 2 S J/\N. lq 71 tolonel George R. Robertson District Engineer · Alaska Di'strict, Corps of Engineers P. 0. Box 7002 Anchorage, Alaska 99510 Attention: Environmental Section Dear Colonel Robertson: Re: . NPAEN-Pn-R This planning aid report follows our iAitial assessment of fish and wildlife impacts which may result from the proposed Upper Mahoney Lake hydroelectric project near Ketchikan. Subsequent to our initial response of June 6, 1977, the ice finally cleared on the upper lake allowing biological investigations there. The result of that field trip resolved our concern for the fate of 1966 introductions of grayling into the upper lake. We found no evidence of survival. {Our letter of June 6, 1977, indicated the grayling introduction occurred in the 1950's but was in ertor). The adequate flow of water through suitable spawning gravel in the transfer of water from the upper lake to the lower lake remains our primary concern. Since the initial assessment, other conceptual alternatives concerning the disposal of the tailrace waters have developed. This report summarizes and initially assesses these alternatives. Also, this report includes a summary of the physical and biological data concerning the Mahoney Lakes systems which are now available in our files. The conceptual alternatives for use of the. tailrace waters as we see them are: ( 1 ) (2) As was originally proposed, the tailrace waters to be channeled directly into the lower lake. As we originally recommended, the tailrace waters to be returned · to the stream near the base of the falls with a minimum flow pattern guaranteed. (The minimum flow required at any given time would Save Energy and You Serve America! ElS-A-7 2. depend on the specific activity, such as spawning, incubation, rearing, etc., taking place at that time and would .vary through the year. This will be referred to as the minimum flow pattern). (3) Same as #2 without minimum flow pattern guarantees. (4) A mitigating alternative which would direct a controlled flow through a spawning channel, then into the original stream channel. (5) Same as #4 except the discharge would be directed into the lower lake. The use of alternative #1 would effectively eliminate all spawning and rearing within the stream. Thus, greater than 50 percent of salmonid production in the drainage would be curtailed. This alternative appears to be the least acceptable. Alternative #2 should be an acceptable choice provided the magnitude of minimum flow could be determined and maintained. Further study of the tninimum flow pattern required would be necessary. Alternative #3 would likely curtail .production in some years while not affecting it in other years. The overall impact would ultimately result in a degraded system. This alternative is also among the least desirable. Alternatives #4 and #5, with a controlled flow spawning channel would offer an apparently desirable mitigating feature, provided there was a guaranteed minimum flow pattern incorporated in the artificial channel. Alternative #4 would be highly desirable during times of high flow when sufficient water would be available to utilize the natural stream spawning areas in addition to the spawning channel. On the other hand, during low flow times there may be insufficient water in the natural streambed to allow fish passage to the controlled spawning channel. Alternative #5 would make spawning gravel available regardless of the flovJ conditions. Also, as a result of a greater hydraulic head this alternative potentially offers the largest stable production area. Alternative #5, therefore, appears to be the most desirable--it.s greatest drawback being one of esthetics. Physical Profile -fisheries oriented Drainage size Lake surface area Upper Mahoney Lake 2 .2 ml 57.5 ac. (115.2 ac. by Retherford) EIS-A-8 Lower Mahoney Lake 5.7 mi 2 (includes upper lake) 160 ac. ·-- Lake depth Lake volume Surface flow Spawning gravel Water temperature Biological Profile Plankton Aquatic vegetation Invertebrates Fish Native Introduced ~~r Mahoney Lake 265 ft. (B0.8 m.) 5000 acre-feet (Est.) •A• Inlet -15 cfs 8/4/77 •a• Inlet -40 cfs 8/4/77 Insignificant W/77 Air 24°S Surface -9.ooc Thermocline 0 4/5 m-7.2/6.6 C Some diatoms & others 1977 Secchi disc -30 m 1977 No data available 1977 -abundant {including chironomids, stoneflys, diptera, caddis, mayflies and leeches} None obse·rved Grr1yling -1966 (without apparent success) EIS-A-9 3. Lower Mahoney Lake 220ft. (67.1 m.} 20,400 acre-feet Outlet records show a range from 2 cfs to 171 cfs and an average of approx. 40 cfs • . 540m 2 from base of fa~ls to lower lake. 1060 m total. 4/21/77 Surface -4.7oc 6 m -4.ooc 4.oo C to bottom No data available - however, appears more productive than upper lake. Sparse -AOF&G 1952/70 Present -AOF&G 1952/70 "Insects & larvae, snails and pea clams 11 All salmon except kings; kokanee, rainbow, steel- head, dolly varden, cut- throat, cottids and stickleback. Eastern brook 1931-32 (without apparent success) ·An introduction of kokanee was also apparently made. 1977 Observations Upper Mahoney Lake No fish observed *Note: Historically, many people subsistence fished for sockeye salmon. The system has since been closed to all subsistence fishing. Other vertebrates l~aterbi rds, bear, deer and furbearers. 4. Lower Mahoney Lake Abundant kokanee and dolly varden in lake. Sockeye*, pink, and .chum salmon observed in spawning condition in streams. Dolly varden fry observed in all .areas. Eagles, ducks and other water- birds, grouse, bear, deer and furbearers. We a~preciate the opportunity to provide planning aid comments and data. Please keep us advised as to project status and let us know if we can be of further assistance. Sincerely you~';u,;.Gm £1M) tor(/ (}L EIS-A-10 -· r L. UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE P.O. Box 1628, Juneau, Alaska 99802 Mr. George R. Robertson District Engineer Corps of Engirieer~ P. Ow B6x 7002 . Anchorage, Alaska 99510 Dear Mr. Robertson~ .2360 b-.:; :_; ., i:}{{ The following is in reference t6 NPAEN-PR-R, letter of November 18, requesting preliminary historical/archeological report for three potential hydroelectric sites near Ketchikan, Alaska. a. Lake Grace: No historic/archeological sites are presently known in this vicinity; however, the vicinity of the dock and work cainp have a high potential in view of the salmon runs in Grace Creek and the estuarine nature of the mouth of the creek. The inland areas of the tl·ansmission line to Carroll Inlet have low potential. -. b. Swan Lake: No historic/archeological sites are presently known 1n the near vicinity of the lake, powerhouse~ and transmission line to the point of crossing Carroll Inlet. Potential for historic/archeological ;naterials in these areas is judged to be low. The transmission line from Niyelius Pt. -Shelter Cove -Watd Cove will be in the vicinity of a petroglyph reported in Shelter Cove and a large historic site identified by Sealaska Corporation in Leask .Cove .. The potential for archeological sites along the inland portions of the transmission line is low. c. Mahoney Lake: There is a petroglyph reported in the vicinity of the cove east of Mahoney Lake, and anabandoned mine near the creek mouth. Potential in this area may be considered high. The first half of the transmissiot, route to Beaver has a medium to low ·potential; the second half has a low potential.· Dt. Robert Ackerman, Department of Anthropology, ~lashington State University, Pullman, Washington, has conducted a partial archeological survey of the Swan Lake Hydroelectric Project for R. W. Beck and ~s:.a:iates. When this survey is completed, we will be in a position tn provide firmer data concerning historic/archeological materials for that portion of the study area. 6200-11 (1169) E IS-A-11 • 2 I hope the above information is of help.. Please do not hesitate. to call if your require further assistance. Sincerely~ rl I n . . 'l . . 'Jp A~·O(Y f..!. ( J ,'1 t GERALD H. CLARK Regional Archeologist EIS-A-12 United States [)epartmcnt of the Interior FISH ANIJ WILDLIFE SERVICE Al,ASKA AREA OFFICE 8130 STREET ANCHORAGE, ALASKA 99501 . Co 1 one 1 George R. Rober.tson District Engineer . Alaska District, Corps of Engineers P. 0. Box ?002 Anchorage, Alaska 99510 Dear Colonel Robertson: Re: . NPAEN-PR-R t JUti 1977 This responds to Mr. D. G. Hendrickson's letter of April 27, 1977, which requested field data and our initial assessment of fish and wildlife impacts which may result from the proposed Upper Mahoney Lake hydroelectr.ic project near Ketchikan, Alaska. The time constraint of:your draft EIS schedule precluded investigations of the fish and wildlife resources in the Upper Mahoney Lake portion of the system because of ice and snow cover. We have rescheduled field investigations in the upper lake for early June, 1977, and will modify our comments should the results of that investigation so ~ictate. Due to the ·lack of sufficient quantitative data on the salmon runs in the system, we will conduct follow-upspawning ground surveys during August through October, 1977. Again, should the results so justify, this initial assessment shall be modified. The project area is used by a variety of fish and wildlife species. The aquatic system is of significant value to fish resources, particularly pink, chum, coho, and sockeye salmon; and Dolly Varden, cutthroat, rainbow, and steelhead trout which use the inlet streams to the lower lake as a spawning ground •. Grayling were stocked in the upper lake in the 1950's and would depend on its inlet streams for spawning. Other freshwuter fish species include sculpins and sticklebacks. The estuarine system provides life requirements for numerous organisms including both resident species and those which depend on the estuaries at some stage in their life history. Among the estuarine fish resources areall species of Pacific salmon, the searun varieties of trout, Save Energy and You Serve A me rica! EIS-A-13 Pacific herring, several species of rockfish, several species of flatfish, and cod. Shellfish resources include several species of clams and mussels, several spee.ies of shrinlp, and Oungeness and other crab species. · · · .Hi.ldlife resources that are closely associatedwith this estuarine system include waterfowl, seabirds, shorebirds,-and seals. Bald eagles, deer, black bear, grouse~ beaver and other furbearers usP substantial portions of the ecosystem. 2. Based on the data availableat this time, the maintenance of spawning and rei'lring habitat for salmon and trout in the stream flowing between Upper Hahoney Lake and LO\'!er. Mahoney Lake is our primary concern relative to the proposed project. The water discharged from the powerhouse should be returned to the natural stream above the spawning habitat, preferably near the base of the falls. Any overflow from the upper lake should be allowed to follow the existing natural route. ft. minimum water flow in the natural stream channel during the spawning and incubation periods of July through March must be maintained. The magnitude of the minimum flow required will be determined after further study. The concept applied, however, is that on a given stream with all else remaining constant, the production of that stream will decrease directly as spawning gravel becomes exposed. The proposed access road will cross inlets to the lower lake. Where this occurs the crossings sh~uld be constructed so as to effectively prevent siltation and disturbance of spawning grounds. The four miles of proposed transmission line along George Inlet to Beaver Falls will be traversing an area likely to contain eagle nesting trees. The specific route should be so designed to effectively avoid nest tree disturbance. The results of the Upper Mahoney Lake investigation will determine the status of the grayling stocked there. The presence of grayling may require further restrictive conwnents on the proposed project. L·ie appreciate the opportunity to provide comments at this early stage of project planning and to alert you to our primary concerns relative to this project. S ·ncerely;.s 'pJ ~-~~ ector~ EIS-A-14 APPENDIX EIS-B CORRESPONDENCE FROM FINAL SCOPING ACTIVITIES (1982) DEPARTMEIYr OF lVAnJ'RAL RESOIJRCES DIVI$10N "'PAliK$ April 27, 1982 File #: 1130-2-1 Harlan E. Moore Chief, Engineering Division Corps of Engineers, Alaska District P .0. Box 7002 · Anchorage, AK 99510 Dear Mr. Moore: 7(-- JAYS. HAMMOND, GOVERNOR · 116 WAREHOUSE DR., SUITE 210 ANCHORAGE, ALASKA 99501 PHONE: 214-4676 We have reviewed the "Cultural Resources Assessment for Mahoney Lakes Hydropower Project" {Re: NPAEN-PL-EN) prepared by Julie Steele of your office. In light of Ms. Steele's survey results we concur with the finding of no probable impact to significant cultural resources by presently proposed construction. However, should cultural resources be located during the course of construction, we request that the project engineer halt all work which may disturb such. resources and contact our office immediately. As always, thank you for your concern for Alaska's cultural resources. l Di1l1plane Historic Preservation Offi SLK/jdg MEMORANDUM l L--·-, ·state of AlaskapL -e r'J TO Dave Haas DATE · State-Federal Assistance Coordinator Division of Policy Development FILE.NO: and Planning Juneau TELEPHONE NO: ..DC FROM: Don Corne 1 ius suBJECT Area Habitat Biologist Department of Fish an·d Game Ketchikan Y:,.'l- . . April 14. 1982 AK 820325-02 225-5195 11ahoney Lake Hydropov1er Feasibi1ity Study The Department ofFish and Game has revie·wed informat·ion supplied by the U.S. Army Corps.of Engjneers. regardtng Mahoney lakes Hydropovler Feasibi- lity Studies. We have the following comments regarding this proposed project: 1. The potential effects of this project on red salmon which s~awn above lower Mahoney Lake must be investigated. As proposed, the penstock tailrace route would vi.rtually dry up the probable Sj)a\·m- ing beds of this salmon population by removing water from the s t;~eam between Upper and Lower f4ahoney Lakes. 2. Several opportunities for mitigation to protect or enhance fisheries r.~ay exist: A. A realignment of the penstock to intersect the lower portion of the channel of the stream between Upper and Lower Mahoney Lakes may prevent dewatering of this channel. Additional spawning channels could also be created below the tailrace. B. During construction of this project a fish passage structure could be constructed at the Falls between Lower Mahoney Lake and George Inlet. This would facilitate fish movement past this marginally passable obstacle and potentially improve escapements. C. The potential for fertilizing Mahoney Lake in conjunction with the aforementioned mitigation measures could be evaluated. 3. The proposed facilities should be designed to alleviate problems associated with air entrainment in t.he penstock which could potenti- ally kill fish with "gas bubble., disease. Project design should include methods to remove gases including nitrogen and oxygen which may supersaturate the water di scha·rged from the ta i1 race. EIS-B-2 02·00 l A{ Rev.! 0/79 I - 2 - April 14, 1982 4. The need for this facility in the. Ketchikan area should be evaluated. The SNan lake Hydroelectric Project will soon be on line .and Grace Lake .located in the Swan lake vicinity ·has been mentioned as a possible hydroelectric. power source whi.c~ may be constructed after Swan Lake. Do other alternatives exist? . Thank you for the opportunity to revfew this proposed project. We look fon-.rard to \vorking ·wah the'Cor.ps dur:ing completion ·of this EIS. cc: R. Reed -ADF&G -Juneau H. Moore -COE -Anchorage C. Osborne ~ USFWS -Ketchikary EIS-B-3 U. S. E N V I R 0 N M E NT A l P R 0 T E C T I 0 N A G E N C Y R£PlY TO M/S 443 ATIN Of, I APR 1$~ Colonel Lee R. Nunn District Engineer REGION X 1200 SIXTH AVENUE SEATTLE, WASHINGTON 98101 Alaska District, Corps of Engineers P. 0. Box 7002 Anchorage, Alaska 99510 SUBJECT: Mahoney Lakes Hydropower Project, Ketchikan EIS Scoping Suggestions Dear Colonel Nunn: Thank you for inviting the Environmental Protection Agency to participate in the scoping process for the Draft Environmental Impact Statement on the Mahoney Lakes Hydropower Project. One impact to be examined is the project's potential effects on water quality. Parameters of particular concern during project operation include \'later tempera- ture and dissolved oxygen, nitrogen, suspended sediment, and metal concentra- tions. Existing water quality conditions at all depths of Upper Hahoney Lake should be measured, and the impacts of discharging the deeper waters of the upper lake into Lower Mahoney Lake should be analyzed. Dra\vdown of the upper lake and the result·ing exposure of unvegetated slopes could affect the upper lake's turbidity and suspended sediment concentrations and should be reflected in the analysis. It may be worthwhile to consider the results of various intake levels on both lakes• water quality. Consideration should also be given to the project's impacts on water quality in the river between the two lakes, highlighting stream temperatures, flows, suspended sediment loads, and the potential for nitrogen supersaturation problems. The evaluations should indicate seasonal impacts, possible miti- gation measures, and whether the operation of the project will cause or contribute to any violations of applicable water quality standards. The water quality impact of construction and maintenance of the access road, transmission line, and penstock and the disposal of tailings from construction of the tunnel should also be discussed. r~itigation measures and alternatives should reflect soil conditions and slopes, and preventive erosion control measures. Attention should also be given to minimizing the \'later, air, and noise impacts from the construction camp. temporary _generating facility, and obtaining and process construction material such as sand, gravel and rock. EIS-8-4 2 We appreciate the opportunity.to participate in this .scoping process. · Dick Thiel, my Environmental Evaluation Branch Chief, may be contacted for more. information. He can ·be reached at (206) 442-1728 or (FTS) 399-1728. ' ~ h ·Gary . O'Neal, Director ·. ·.· / t dL Env i ronrnenta 1 Servkes Di vi.' ion cc: Ron Kreizenbeck, AOO, ·Juneau EIS-B-s· UNITED STATES DEPARTMENT OF AGRICULTURE ~. Harlan E. Moore Tongas'S0 VaYio'n'a~1 cForest Federal Building Ketchikan, Alaska 99901 907-225-31 01 u. s. Anny Engineer District, Alaska ATTN: Chief, Environmental Section P. 0.· Box 7002 Anchorage, Alaska 99510 L Dear Mr. Moore: 1950 March 31 , 1982 Thank you for your f~arch 22 letter c;oncerning the proposed Mahoney lake hydropower project feasibility study and environmental impact statement. The Forest Service was a cooperating agency in preparation of the Swan lake hydropower project and is currently participating in this capacity in preparation of the Black .Bear lake project. This is in line with the Council on Environmental Quality Regulations 40 CFR Part 1501.6. To be responsive to these regulations and assure that National Forest management is appropriately coordinated during the preparation of the environmental statement, I request that the Forest Service be designated as a cooperating agency for the Mahoney lake hydropower project environmental impact statement. Sincerely, ~~:;_ c?. 4~;.. ~MES A. CALVIN Acting Forest Supervisor 62011-11 (1/611) EIS-B-6 I March 31, 1982 Colonel lee R. Nunn District Ergineer UNI!ED STATE~ DEPARTMENT OF COMMERCE NattonaJ Oceanac and Atmosphert;: Administration National Marine Fishe!"ies .Ser.;iae P. 0. Bo~ 1668 . . Juneau., Alaska 99802 Alaska District, Corps of Engineers P.O. Box 7002 Anchorage, Alaska 99510 Dear co·lonel Nunn: This letter is in response to your Section 7 request for information regarding threatened or endangered species under the National Marine Fisheries Service's responsibility that may be present.in the vicinity of the Mahoney lake system near Ketchikan, Alaska Endangered Species National Marine Fisheries Service bears responsibility for eight species of endangered whales which occur in Alaskan waters; they are: Blue Sei Fin Black Right Bowhead . Sperm Gray Humpback Balaenoptera musculus Balaenoptera borealis Balaenoptera ph¥salus Balaena glacial1s .Balaena mysticetus Physeter macrocephalus Eschrichtius robustus Megaptera novaeangliae Humpback whales are probably the only endangered whale that w4y occur near the project area. About 1,000 humpback whales (of a total world population of 6,000) inhabit th~ North Pacific. During the summer feeding season, they range widely from the subarctic boundary (ca. 40° N lat.) north into the Bering Sea. The greatest population densities are reached in certain inshore waters, where the animals appear to be largely resident during the summer and autumn. It is estimated that between 100-260 humpback whales inhabit southeast Alaska. Alaskan humpbacks spend the winter around the Hawaiian Islands and along the west coast · of central Mexico. The main foods of humpback whales .in southeastern Alaska are euphausiaceans (Euphausia pacifica), herring (Clupea harengus), and capelin (Mallotus villosus}, (Jurasz and Jurasz 1979). Gray whales are endemic to the north Pacific. The eastern Pacific population now numbers about 16,000 animals, whereas the western Pacific population is apparently on the verge of extinction. The eastern population spends the summer in the northern Bering and Chukchi seas, and migrates along the coast to winter grounds on the west coast of Baja California, where the calves are born. 2 ' Twice each year virtually the entire eastern Pacific population of gray whales passes along the outer coast ... mostly within 5 km of the beach. The northward migration of animals, by southeast Alaska, without calves ·takes place from March to early May, with a peak in early April; cows with calves migrate later.· The southward migration takes place during November and December. Gray whales do not feed while migrating along the California coast, but possible surface-feeding be:1avior has been reported during spring migration at Cape St. Elias (Cunningham and Stanford 1979). On the summer grounds gray whales feed primarily on benthic gammaridean amphipods. The fin, sei, blue, and sperm whales generally move in and out of the offshore areas seasonally. · The right whale n1ay be resident in the Gulf of Alaska year round and may enter coastal waters frequently. · The bowhead whale has not been reported in the Gulf of Alaska. It is our conclusion that the proposed project is not an action that "may affect" endangered or threatened species or their habitat for purposes of regulations implementing Section 7 of the Endangered Species Act of 1973, and thus does not require formal consultation under Section 7. Our agency has not conducted studies on the fish resources inhabiting the Mahoney Lakes system. However, it is our ~nderstanding that the upper lakes are barren of fish life. Lower Mahoney Lake and its associated stream system provides habitat for several fish species,· i.e., pink salmon, sockeye salmon, chum salmon, coho salmon, steelhead trout, sea-run cutthroat trout and Dolly Varden char. Juvenile sockeye salmon rear in the lake while juvenile coho salmon, steelhead trout, cutthroat trout~ and Dolly Varden char inhabit the lake and stream system. Pink and chum salmon spawn in the stream and their fry migrate, in the spring, to the sea soon after emergence from the stream gravel. Our concern is that construction and operation of a hydropower project on the Mahoney Lake system be compatible with the present fish resources and their habitat requirements. We will offer our comments and recommendations on the proposed project when we review the draft environmental impact statement. We hope this information will be useful in the planning process. Sincerely, EIS-B-8 REFERENCES Cunningham, W., and S. Sandford. 1979 .. Observations of migrating gray whales (Eschrichtius ro~u~tu~) at Cape St~ E1ias~ Alaska~ Un~ublished manuscript (to be submitted.to Fishery·Bulletin). Jurasz~ C.M., and V.P. Jurasz. 1979. ·Feeding modes of the humpback whale. Sci. Rep~ Whales Res. Inst. 31:69-84 EIS-B-9 United States Department of the Interior IN REPLY REFER TO: FISH AND WILDLIFE SERVICE 1011 E. TUDOR RD .. SE ANCHORAGE, ALASKA 99503 (907) 276-3800 Colonel Lee R. Nunn District Engineer Attention: Mr. William D. Lloyd Alaska Distd.ct, Corps· of Engineers P. 0. Box 7002 Anchorage, Alaska 99510 Dear Colonel Nunn: Re: NPAEN-PL-EN 1 6 MAR 1982 This responds to your ~arch 9, 1982 request for a determination of the presence of proposed or listed threatened or endangered species in the vicinity of a proposed hydropower project at Mahoney Lakes near Ketchikan, Alaska. Based on the best information currently available to u5, no such species occur ]nor near the proposed project area. Hence, a biological assessment is not required. The discovery of threatened or endangered species in the proposed project area or the designation of new species as threatened or endangered may require a reassess8ent of this finding. Thank you for your interest in endangered species. If we can be of further assistance, please contact us. Director cc: ES EIS-B-10 United States Department of Agriculture Forest Service Alas'ka R~gion P.O. Box 21628 .... - - --- - - - - ----'J ..,· MS. Lois D. Cashell Secretary Federal Energy Regulatory Commission 825 North Capitol Street, NE Washington, DC 20426 Dear MS. Cashell: Juneau, AX 99802-1628 Reply to: 2770 Date: JUN 0 8 1993 We have reviewed the March 12 Notice of Application, filed by the City of Saxman, for a preliminary permit for the upper Mahoney Lake Hydro Power Project No. 11393·000 located northeast of Ketchikan, Alaska. The Federal lands within the project boundary have been selected by Cape Fox Village Corporation, but have not yet been conveyed. Therefore, the lands are still National Forest System lands. • This proposed project will impact lands and resources within the Tongass National Forest. It is probable that impacts will occur to the following resources: 1. Cultural resources. An inventory will need to be completed before any ground disturbing activities are conducted. There are two reported cultural sites within the project area. 2. Fish habitat. Lower Mahoney Lake provides habitat for resident and anadromous fish. There are reports that sockeye salmon spawn along the shoreline of Lower Mahoney Lake. The impacts of the hydro project on fish populations should be addressed. 3. Scenic values. The project area has high scenic values. The Alpine region is free of human modifications at this time. The proposed dam, penstock, powerhouse, road, and transmission lines will alter the visual integrity of the area. 4. Mountain goats. Fifteen goa1:s were transplanted into the alpine area surrounding upper Mahoney Lakes in 1991. The direct, indirect, and cu.mulati ve effects of the proposed project on the animals needs to be addressed. s. Birds. As in other projects of this type, the possibility of birds colliding with transmission lines will need to be addressed. Cering for the Land and Serving People FS-0200-28b(3/92l Ms. Lois D. cashell 2 6. Access. Road construction to the project across Cape Fox Corporation lands would provide_opportunities to access timber on National Forest System lands, and would also provide opportunities for hiking, camping, skiing, and snowmobiling in the alpine area near Ketchikan. The related effects of new roads and changes in access will need to be addressed. It is evident, however, that additional data must be gathered before we can quantify these impacts and their effects upon National Forest Management objectives. Accordingly, the Forest Service'has no objection to the issuance of a preliminary permit subject to the following special condition: Prior to undertaking, any entry or work on National Forest System lands pursuant to a preliminary permit, the Permittee shall prepare and file with the Forest Service a plan of studies to be conducted under the permit; and, the Permittee shall secure a Forest Service special-use authorization and, if appropriate, enter into a Memorandum of Understanding (MOO) with the Forest Service. The Permittee shall file with the Commission, within 90 days of the issuance of this preliminary permit, copies of the special-use permit and, if appropriate, the MOO. The special-use authorization would include Forest Service requirements for fire prevention and control, prevention of damage to Federal property, natural resources, and any requirements for repair or rehabilitation of damage resulting from study activities. The MOt1 between the Forest Service and the Permittee, if prepared, would document the needs for studies and arrangements for consultation and cooperation not included in the special-use permit. Sincerely, &~~ ~ Regional Forester cc: Ketchikan WO Lands Mr. Doug Campbell APPENDIXD TEMPERATUREINFO~TION United States Department of the Interior IN REPLY REFER TO: FISH AND WILDLIFE SERVICE P. 0. Box 1287 · Juneau; Alaska 99802 Colonel Lee R. Nunn District Engineer Alaska District, Corps of Engineers P. 0. Box 7002 Anchorage, Alaska 99510 Attention: Environmental Section Dear Colonel Nunn: December 21, 1981 Re: NPAEN-PR-R This planning aid letter is to re-evaluate some ·of our recor:mendations and to transmit new information relative to the Mahoney Lakes hydropower project near Ketchikan. We have been involved with this project to sooe . degree since 1977 and produced planning aid reports and finally a Coordination Act report containing some recommendations ..._.hich were ultimately challenged. In the early stages of the project we judged the most significant adverse effect to be expected from the project ..._.ould be the loss of the stream bet\17een Upper Hahoney Lake (storage reservoir) and Lower Nahoney Lake. The suitable spawning gravel contained in this stream co~prised about one-half of the total spawning gravel in both tributaries to Lower Mahoney Lake. Since the Mahoney Lakes system supports a run of sockeye salmon, we keyed in on this potential loss as the most significant adverse effect expected from the project. Ultimately in the CA report we recommended serious consideration of measures, including an artificial spawning channel, to mitigate this expected loss. These early evaluations assumed use of the stream in question by adult sockeye salmon since adults were .observed in the stream leading to Lower Mahoney.Lake from saltwater. The assumptions were based on accepted life cycle knowledge for the species. Observations made this past fall significantly modify these early assumptions and will be reported later in this letter. Also challenged in the CA report were problems relating to use of the Habitat Evaluation Procedures (HEP) format. During the drafting of the CA report, the decision was made to use the HEP format which was just being developed. Unfortunately, misconceptions of the use of HEP prevailed among the authors. Also, the data base, which had not· been collected with HEP in mind, was used without the benefit of the appropriate sample design. The overall result was a rightfully criticized presentation of the procedure. EI S-B-11 2. At the outset, HEP \Jas considered to be a highly involved standardized procedure in which the major product would be the identification of a quantity of other lands necessary for mitigation. As HEP evolved it became clear that HEP can be used to accomplish any one or more of the follmJing: 1. Quantify lands necessary for mitigation (as before) 2. Evaluate alternatives 3. Predict recovery Also, it has become evident that the procedure.can range from an expensive large scale elaborate procedure (when the project merits it) to a rather informal minimum expense project for a specialized purpose; and, there are many projects which are not suitable for the application of REP. The suitability of the Mahoney Lakes project for the application of HEP is questionable and it may not have been initiated under our present state of knowledge. However, we do see some value in the salvage of these efforts. Testing models and streamlining the HEP process for southeast Alaska could be an important part of this project. The southeast Alaska ecosystem is relatively homogenous and information acquired here could be applied on more suitable projects. In the normal life cycle for sockeye salmon the adults swim upstream into a watershed system containing a lake. The adults then usually spawn in the gravels of tributary streams to the lake. Occasionally, when forced to, the adults are known to spawn in the gravels downstream from the lake and/or along the lakeshore in the gravels of the alluvial deltas formed by the tributaries. The young fry, after hatching, migrate to the lake and rear a year or more before migrating to sea. When the young fish hatch downstream from the lake they must be able to navigate upstream to reach the lake. This is likely not possible in the Mahoney Lakes system. Between July 16 and November 1, 1981, ten stream censuses were conducted. Adult sockeye salmon were again observed to be present in the stream from tidewater to the lower lake but not in either tributary stream to the lake. Also, the stream between Upper Mahoney Lake and Lower Mahoney Lake was observed to exhibit extreme variance in surface flow both from date to date and from the base of the falls to the lake. Also, the rocks, gravel and other characteristics of the stream exhibited evidence of violent flo\J patterns. These observations and the lack of observed s~e.•min?, unstrea:rt from the lake serve to stron3l~ sug~est that the adult socke~e are not S!'aHnin:-unstream from the lake. Since it is extremely i1~rrobable that the youn~ fis~ can Di~rate upstream to'the lake, we strongly suspect that the adult fish are spawning in the lake along the face of the tributary deltas at unobservable depths. If the above is correct then the primary concern would be to insure that the tailrace waters re-enter the stream sufficiently to percolate through the gravels of the delta. As we view it, that stipulation should be easy EIS-B-12 ... -.. ·.-· .. 3. to meet. We \vill be submitting a modified CA report with re-evaluated recommendations. Additional information requested by your engineering section follow: Water temperature profile in Upper Mahoney Lake on August 3, Depth Temp. Depth "Tem2. DeEth Temp. De:eth Surface 9.0 8 6.0 16 4.8 32 1 8.5 9 5.8 17 4.8 40 2 7.7 10 5.6 18 4.6 50 3 7.4 11 5.4 19 4.5 4 7.2 12 5.2 20 4.5 5 6.6 13 5.0 21 4.5 6 6.4 14 4.9 30 4.2 7 6.2 15 4.9 31 4.2 Depth measured in meters; temperature in degrees centigrade. Date Water temperature on surface of u22er lake near outlet Tem2erature °C April 24, 1978 0.2 May 8, 1978 0.5 March 21, 1979 0.1 July 25, 1979 10.0 February 16, 1981 0 May 17, 1981 0 August 29, 1981 11.5 1977 Temp. 4.2 4.1 4.0 Water temperature in lower lake on the f~ce of the delta (the area suspected to be used for spawning). December 9, 1981 EIS-B-13 4. On December 9, 1981, a recording thermograph was installed on the face of the delta in approximately 15 feet of w•ter and will be recovered five months later. The re.sultant information should help define the. temperature regime in this area. Incubation time varies wit'h water temperature from around 140 days at about 4°C to arounrl 50 days at about 15°C for sockeye eggs. The ecological implication of a modified incubation time (an expected result of a change in water temperature) is fry being released into the lake at a different stage of seasonal lake plankton development. The overall impact to the fishery resource could vary from positive to negative depending on a multitude of factors including the degree of change. We feel it is beyond the scope of our resourc~s to study this sufficiently to predict it and that the relati\•e :-otential imoact on the fishery resource in this project does not ,,•arrant it. \o:e hope the information in this letter proves useful. Sincerely yours, _;;yl/~ t. ~ Field Supervisor EIS-B-14 APPENDIXE GEOTECHNICAL INFORMATION SHANNON & WILSON GEOTECHNICAL INFORMATION #*1¥ 1 '" ti Mahoney Lake Hydropower Project Trip Report and Geotechnical Pre-Feasibility of the Proposed Tunnel Alignment July 1993 HDR Engineering, Inc. 500-108th Avenue N.E., Suite 1200 Bellevue, Washington 98004-5538 Ell I .. SHANNON &WILSON. INC. GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS 400 N. 34th St. • Suite 1 00 P.O. Box 300303 Seattle, Washington 98103 206•632•8020 • t .. !;"' I I I . , Lake W. Elev. 1950 Ft. NOTE COE map provided by Cape Fox Corp. 0 400 BOO b3 E3 I I Scale in Feet LEGEND • ,. Avalanche Shute Contour Interval = 40 Feet Lower Mahoney Lake W. Elev. 88 Ft. HDR,Inc. Mahoney lake Hydropower Project Ketchikan, Alaska SITE PLAN July 1993 W-6527-Q1 SHANNON & WILSON, INC. I FIG 1 Geollclrical.-.:1 E.nvionrneiUI c:cr.llara • . ~: Gi Q) iii t:: 0 D.. 2000 1800 1400 u.. 1200 .& 600 A/ ••• ,o· ? I ? ) •/ ' Phy!IHe and ~~~J:. / .. ...:· ? > /' 400 Shaft { .o Foliation Chamber ? CD @ CD @ Intrusive CD 0 ,0, @ 0 b=3 ESTIMATED SUPPORT CATEGORIES G) None to spot rock bolts 0 Pattern rock bolts and shotcrete @ Steel sets and shotcrete ? Support Categories Rock Mass Categories 400 E3 I Scale in Feet Phyllite/Schist and Quartz Diorite {?) CD CD BOO I HOR,Inc. 0 ,0, 0 0 Mahoney Lake Hydropower Project Ketchikan, Alaska TUNNEL PROFILE July 1993 SHANNON & WILSON, INC. Glolechricalll'ld EnviiOnmenlal Conslilants W-6527-01 FIG. 2 SHANNON &WILSON. INC. APPENDIX IMPORTANT INFORMATION ABOUT YOUR GEOtECHNICAL ENGINEERING REPORT W-6527-01 ~Ill SHANNON & WILSON, INC. Geotechnical and Environmental Consultants AJtacbment to Report Paae 1 of 2 Dated: July 22. 1993 To: HDR Engineerini{ I Inc I Bellevue. WA Important Information About Your Geotechnical Engineering/ Subsurface Waste Management (Remediation) Report GEOTECBNICAL SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND PERSONS. Cousulting geotechnical engineers prepare reports to meet the specific ueods of specific individuals. A report prepared for a civil eapeer may not be adequate for a CODStnletion contractor or even another civil eopoer. Unless indicated otherwise, your c:onsultant prepared your report expressly for you and expressly for purposes you indicated. No oae other than you lbould apply this report for its inteaded purpose without first conferrin& with the c:onsultant. No party lhould apply this report for any purpose other than that ori&inally contemplated without first conferrin& with the potcclmical eo&incer/geoecieotist. AN ENGINEERING REPORT IS BASED ON PROJECT-SPECIFIC FACTORS. A potechnical engineering/subsurface waste management (remediation) report is based on a subsurface exploration plan designed to c:onsider a unique set of project-specific factors. Dependin& on the project, these may include: the general D&ture of the structure and property involved; its size and configuration; its historical use and practice; the location of the structure on the site and its orientation; other improvements such as access roads, parking lots, and underground utilities; and the additional risk created by acope- of-aervice limitations imposed by the client. To help avoid costly problems, have the CODSUltin& eogineer(s)/scieotist(s) evaluate how any factors which change subsequent to the date of the report, may affect the recommendations. Unless your CODSUlting aeotechnical/ civil engineer and/or scientist indicates otherv.ise, your report should not be used: 1) when the nature of the proposed project is changed (for example, if an office building will be erected instead of a parking aarage, or if a refrigerated warehouse will be built instead of an unrefrigerated one, or chemicals are discovered on or near the site); 2) when the size, elevation, or c:onfiJUration of the proposed project is altered; 3) when the location or orientation of the proposed project is modified; 4) when there is a change of ownership; or S) for application to an adjacent site. Geotechnical/civil engineers and/or scientists cannot a.cc:ept responsibility for problems which may occur if they are not consulted after factors which were considered in the development of the report have changed. SUBSURFACE CONDITIONS CAN CHANGE. Subsurface conditions may be affected as a result of natural c:hanaes or human in1lueoce. Because a acotechnical/waste management engineering report is based on conditions which existed at the time of subsurface exploration, construction decisions should not be based on an engineering report whose adequacy may have been affected by time. Ask the geotechnical/waste management c:onsultant to advise if additional tests are desirable before construction starts. For example, groundwater conditions commonly vary seasonally. Construction operations at or adja.ceot to the site and natural events such as floods. earthquakes, or groundwater fluctuations may also a1fect subsurface conditions and, thus, the continuing adequacy of a geotechnical/waste manaaement report. lbe geotechnical/civil eopeer and/or scientist should be kept apprised of any such events. and should be COD.Sulted to determine if additional tests are Dec:essary. MOST GEOTECHNICAL RECOMMENDATIONS ARE PROn:ssiONAL .JUDGMENTS. Site exploration ~nd testing identifies actual surface IDd subsurface conditions only at those points where samples are taken. lbe data were extrapolated by your consultant who thea applied judgment to render an opinion about overall subsurface conditions. The actual iDterface between materials may be far more padual or abrupt than your report indicates. Actual conditions in areas not sampled may diff'er from those predicted in your report. While nothing can be done to prevent IUCb situations, you 1nd your c:onsultant can work together to help minimize their impact. Retaining your consultant to observe lllbsurfac:e construction operations can be particu- larly beneficial in this respect. A REPORT'S CONCLUSIONS ARE PRELIMINARY. The conclusions contained in your geotechnical engineer~s report are preliminary because they must be based on ihe assumption that conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Because actual Page 2 of2 IUbsutface conditions can be discemed only during earthwork. you should retain your geotechnical eapeer to observe actual conditions and to finalize conclusions. Only the geotechnical eagineer who prepared the report is fully familiar with the bac:qround information Deeded to determine whether or not the report's recommeodations based on those conclusions are valid and whether or not the contractor is abiding by applicable recommendations. lbe aeotechnical eapeer who developed your report cannot assume responsibility or liability for the adequacy of the report's recommendations if another party is retained to observe construction. THE GEOTECHNICAL ENGINEERING/SUBSURFACE WASTE MANAGEMENT (REMEDIATION) REPORT IS SUBJECT TO MISINTERPRETATION. Costly problems em occur whea other design professionals develop their plans based on misinterpretation of a geotechnical eapeering/subsurface management (remediation) report. To help avoid these problems, the aeotechnical/civil eapeer and/or scientist lhould be retained to work with other projoct design professionals to explain relevant aeoteclmical, aeoloJical, hydrogeoloaical and waste management &dings and to review the adequacy of their plans and specifications !elative to these ~. BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE ENGJNEERING/W ASI'E MANAGEMENT REPORT. Final boring logs developed by the geotechnical/civil eapeer and/or scieatist are based upon interpretation of field logs (assembled by site personnel), field test results, and laboratory and/or office evaluation of field samples and data. Only fiDa1 boring logs and data are customarily included in gc;otechnical eapeering/waste management reports. These final logs should not, under any circumstances, be redrawn for inclusion in architectural or other design drawings, because drafters may commit errors or omissions in the transfer process. To minimize the likelihood of boring log or monitoring well misinterpretation, contractors should be Jiven ready access to the complete geotechnical eaaineering/waste management report prepared or authorized for their use. If access is provided only to the report prepared for you, you should advise contractors of the report's limitations, assuming that a contractor was not one of the specific persons for whom the report was prepared and that developing construction cost estimates was not one of the specific purposes for which it was prepared. While a CODtractor may gain important knowledge from a report prepared for another party, the contractor should discuss the report with your consultant and perform the additional or alternative work believed necessary to obtain the data specifically appropriate for constructioD cost estimating purposes. Some clients hold the mistakeD impression that simply disclaiming responsibility for tbe accuracy of subsurface information always insulates them from attendant liability. Providing the best available information to contractors helps prevent costly construction problems and the adversarial attitudes which aggravate them to a disproportionate scale. READ RESPONSIBILITY CLAUSES CLOSELY. Because geotechnical enaineering/subsurface waste management (remediation) is based extensively on judgmeat and opinion, it is far less uact than other design disciplines. This situation has resulted in wholly unwarranted claims being lodged against seotechnicalf waste manaaement consultants. To help preveat this problem, seotechnical/civil enaiiJeers and/or scientists have developed a number of clauses for use in their contracts, reports and other documents. These responsibility clauses are not exculpatory clauses designed to transfer the enaineer's or scientist's liabilities to other parties; rather, they are definitive clauses which identify where the eapeer's or scieatist's responsibilities bep and end. Their use helps aU parties involved recognize their individual responsibilities and take appropriate action. Some of these definitive clauses are likely to 1ppear in your report, and you are eacouraged to read them closely. Your mpeer/scientist will be pleased to give full and frank answers to your questions. 1/93 The preceding paragraphs are based on information provided by the ASFE/Association of Enpeering Firms Practicing in the Geosciences, Silver Spring, Maryland U.S. ARMY CORPS OF ENGINEERS GEOTEC~CALINFORMATION FROM 1983 DRAFf INTERIM FEASIBILITY REPORT AND ENVIRONMENTAL IMPACT STATEI\fENT J GENEP.AL GEOLOGY REGIONAL GEOLOGY . SITE GEOLOGY SEISMICITY PREVIOUS INVESTIGATIONS FOUNDATION CONDITIONS Damsite Lake Tap Penstock Tunnel Porta 1 Surface Penstock Powerhouse MATERIAL SOURCES Powerhouse Stream Damsite Quarry Disposal Sites CONCLUSION APPENDIX B FOUNDATIONS AND MATERIALS Table of Contents Figures Page B-1 B-1 B-5 B-8 B-13 B-13 B-13 B-14 B-15 B-16 B-16 ·B-16 B-17 B-17 B-17 B-18 B-18 B-1 Earthquake Epicenter Map B-2 B-2 Regional Geology B-4 B-3 Site Geology B-6 B-4 Stereographic Plot of Primary Joint Attitudes B-7 B-5 Geologic Section Through Tunnel and Penstock B-10 Alignment B-6 Modified Merca11i Intensity Scale B-12 Table B-1 Maximum Peak Bedrock Accelerations at the Mahoney Lakes Appendices APPENDIX B-1 Tests on Gravel from the Powerhouse Stream APPENDIX B-2 Tests.on Damsite Quarry Stone B-11 GENERAL GEOLOGY APPENDIX B FOUNDATIONS AND.MATERIALS Southeastern Alaska is part of the circum-Pacific "ring of fire," a belt of seismic ~nd volcanic activity. The region, which includes Mahoney Lake, has been tectonically active since early in the Paleozoic era and has a complex geologic and structural history. It is divided into nine distinct geotectonic terranes~ or groups of formations. Each terrane is bounded by faults and each has a unique stratigraphic sequence. The terranes reflect an extensive history of large scale tectonic transport, continental accretion, crustal subduction, metamorphism, magmatic intrusion, and local disposition of volcanic and sedimentry rocks. Faulting has played a major role in the structural development of south- eastern Alaska. Large scale faulting, particularly right lateral strike- slip movement, has been common. Active faults and major lineaments are shown on the earthquake epicenter map, Figure B-1. The trends of many of southeastern Alaska's inlets, waterways, straight valleys, and coastlines reflect episodes of major faulting. The two most prominent fault systems · of southeastern Alaska are the Denali and the Fairweather-Queen Charlotte Islands faults. The Denali fault system is a great arcuate series of faults extending more than 1,000 miles subparallel to the Gulf of Alaska far to the north of the site. The Fairweather-Queen Charlotte Islands fault system extends southeastward from Yakutat Bay to the Queen Charlotte Islands, a total distance of about 650 miles. A few large and many moderate and small earthquakes have been generated by the Fairweather-Queen Charlotte Islands fault system. Most of the small scale landforms of southeastern Alaska are the result of glaciation during the Pleistocene epoch. Continental glaciers attained great thicknesses, as much as 3,000 feet, and rounded the peaks of many mountains in the region. Possibly, ice depths were as much as 5,000 feet in eastern Revillagigedo Island. Many glaciated areas later experienced uplift resulting from the gradual disappearance of the overlying ice. At present, Glacier Bay, to the north, is experiencing one of the fastest rates of uplift in the world, 1.5 inches per year. No glaciers are on Revillagigedo Island, although snowf1elds may persist at higher elevations and in shaded valleys. The present relief, classic U-shaped valleys, cirques, aretes, and hanging valleys, is a result of later alpine glaciation following the Pleistocene continental glaciation. KEGIONAL GEOLOGY The region is in the Cretaceous Wrangell-Revillagigedo metamorphic belt that trends northwest across Revillagigedo Island. The degree of met~norphism increa$es from west to east. The eastern contact with the coast range batholith is indistinct and consists of a broad belt of gneisses and Jurassic or lower Cretaceous intrusive diorites. 0 SS 0 t ' ' .. ' <; .. 0 ... ~0 0 0 tot Mtl£5 ~---..... --... .. •• " tOO K tlOMl:ff: AS 137" 0 0 0 0 • 0 ·--/ !8l ~~ ~ 1 ~ ~ tlc· \ Ec;, T R A N C E \ 0 /SLAI'ID 133'" "-"· +!.... . -4 0 • •• HIGH ANGLE FAULT THRUST FAULT ilotted where concealed; queried where uncertain -----LINEAMENT • MAGNITUDE ~ 8 ... MAGNITUDE > 7 and <8 • MAGNITUDE > 6 and <7 • MAGNITUDE > Sand <6 0 --MAGNITUDE <5 or not determined Note: tncludH kno*n or Inferred events froM 1199 to pruent ~ References :!..:~ '"':;;;• tJftd o\twra .. ~~~ 'tJfel'd~kJ:t"lken r.~-rt:nJ.. 1 ott.~. s_~jj~~i'-~!tJ.! tt=l, tf'l; t .. tt •• "· w •• 9'1' of the Kete~'dk..., Ar• -- hUi NaXA t-.rt~ ... fit• for Eptcent•r• to • RacUvt of 101 kM fro.t K.t.:;hUun. 1110: Pacif\<: Cmschtnc• Centn hrthqUIIk• (pk::ant•r File, 1U1 • IJ71, SJdn-v, 8. C,, C•nad•· EARTHQUAKE EPICENTER MAP B-1 The region within about 12 miles of the project site contains three tectono-stratigraphic terranes that generally trend northwesterly. The terranes from southwest to northeast are the Annette subterrane and the Gravina-Nutzotin Belt, which·are described briefly, and the Taku terrane, which is pertinent to the project area. On the regional geology map, Figure B-2, the Annette subterrane occupies the extreme southwest corner of the map. This subterrane consists of a heteroganeous assemblage of Devonian age and older intrusive, extrusive, clastic, and carbonate rocks. The assemblage records episodes of volcanism, magmatic intrusion, and sedimentation that began early in the Paleozoic era. The subterrane has been complexly deformed and metamorphosed. The Gravina-Nutzotin Belt consists of upper Jurassic to 1ower Cretaceous volcanics, sediments, and dioritic to ultramafic plutons. This assemblage has been identified as the remnants of a collapsed upper Mesozoic volcanic arc. Regionally, it is metamorphosed to greenschist facies and is folded into southwest converging, locally refolded isoclines with axial surfaces dipping moderately northeastward. The Taku terrane, within which the project area is located, consists of upper Paleozoic and lower Mesozoic volcanic and sedimentary rocks. The terrane is intruded by upper Cretaceous dikes, sills and stocks of granodiorite, a batholith of Cretaceous quartz diorite, and other plutons ranging in age from Late Jurassic to Miocene. The terrane is characterized by metamorphism increasing northeastward from greenschist to amphibolite facies of upper Cretaceous age and older. Locally, there is contact metamorphism near the edges of plutons up to the hornblended- hornfels facies. Structures include northeast dipping thrust faults cut by younger high angle faults. The stratified rocks are complexly folded into southwest overturned to recumbant folds and locally refolded isoclines. The northeast boundary of this terrane is near Behm Canal, where it is in contact with elongate stocks of quartz diorite emplaced along a Mesozoic shear zone tnat is the contact between the Taku terrane and the adjacent Tracy Arm terrane. Surficial deposits include drift, elevated marine deposits, alluvium, fan- delta deposits, beach deposits, talus, and landslide debris. Faults and lineaments are common throughout the area and many topographic features reflect these structural elements. Some of the lineaments are associated with jointing and foliation planes that have been emphasized by glacial scour. Four major structures in the region are the Fairweather-Queen Charlotte Islands fault system, the Chatham Strait fault system, the Clarence Strait lineament, which may reflect faulting along all or part of its length, and the Coast Range linement, at least part of which is the result of faulting. Clarence Strait and Chatham Strait faults may be continuations of the Denali fault system of Southcentral Alaska and are, as such, associated with the North Pacific subduction zone. Recent investigations indicate as much as 120 miles of total right lateral movement. This is based on offsets of major features on opposite sides of the faults. B-3 -a .. QTw T~T"'IIII4 >lq l<pq ..... t<,j, IUv .............. ......,_ .. ........ ",.' £ ... ,~...,. <••• .. t.f:-1'1 , .... ,u ...... •-•u•c TA"' ...,. ,,,. • .., Hh>l' MtJ\~ Mz:Pr.d ~tPtt MtP..,. ... ,...: .. -'"'II 'olU(I-""' ,_ ... , ... ,.,t """' Ptv Q., or, T""! T""'d K.q Kpq K.on KJ1 KJv TRv TR•v M,Pn M.P.d MtAt• M•A:" p,~ Ptv -+-+ :'"~:' .. , .. toi'KlH.., .... Cif ..... ~.,, 44U-&tt-\ -'*HI'\MIIIV't>"t""" ........ ~_,, ........ 10; ....... , .... ,*Go!: .. .~ .. ·-~-........ ~, , . ....__. .,. • ..._,un.....-, ~~=-~~==.. -::.::. ....... -.~ .. -.-..--·· ,...,..,.,,<•.oo"'"•«-••-... n••e·--• .,.,., ........... aot•tlt-C•flllil!l- l!t-.,..h•-1 .. U'fll6olC<lilt( -.t•t 1(•--• ..,._, 1=: .:=:=:;=:::,:=-.= :::..... L_..,....,_ •. , . .,.,,_., ...... ... ---· .. ·· .............. , ................ 'II'Oo.tl .. M: ~ ............. , ....... , ... , ..... h<ION ....... f .... t~ ..... ··~· ·-·""""""'"--· ~~=::.:::·:.: =·:..:..=~* ::-::..::..':!!\~.:r ~Uiili( flOUt---.,.- tttflt ........ ,,. .. "' ._ .. *--_, ·-· ....____ .... ...,."""""' .......... ..._ -........... __ .......,. __ _ -·--·-..._ .. ___ _ e ...... ..,....._.._ ........ :.:-.. ·:.::-:o.~-;-.::.-r.t ._ ..... REGIONAL GEOLOGY .......... ....._ .. , .... IIOUYIIIAH -LICT--·· Major faulting is common throughout the area and many topographic features have been controlled by the presence of great fractures and intersecting fracture systems. The locations of many erosion features, such as stream valleys and fjords with the;.r abrupt changes of direction, are·due primarily to such p 1 anes of wea_kness. SITE GEOI OG Y As shown on the site geology map, Figure B-3, the project site is underlain by two major rock units. The bulk of the site, to the west and north of Mahoney Lake, consists of steeply dipping sediments (MzPzs), which have undergone greenschist to hornblende-hornfels grade metamorphism. The proposed sites for the lake tap, the tunnel, and the dam are all within the metasediments (metamorphosed sedimentary rocks), which have been classified as sericite schist on the basis of thin-section analysis! The second major unit is a large intrusive body (stock) of quartz-diorite. The body is located on the south and west sides of Mahoney Lake. The lower portions of the surface penstock and the powerhouse site are underlain by quartz-diorite bedrock. The metasediments are part of the Wrangell-Revillagigedo metamorphic belt that trends northwestward across Revillagigedo Island. The bedding planes strike mainly north-northwestward and dip steeply westward. Thicknesses of the individual beds, where measured, range from 1 to 18 inches and perhaps more elsewhere. Figure B-4 presents stereographic plots of joint attitudes that were measured during field reconnaissance. Jointing occurs at various attitudes but the dominant set is parallel with the bedding planes .. Secondary joints often strike northeastward and dip southeastward. The rock is generally hard, unweathered, and strong but tends to part along preferred cleavages. Iron staining due to weathering of large pyrite crystals within the rock can be observed at outcrops. The metasediments are intruded by granitic dikes and veins that are somewhat more frequent toward the east. The granitic rocks at the site are related to the northwest trending Admiralty-Revillagigedo intrusive belt. The belt contains bodies of granodiorite porphyries, quartz diorites, and diorites. Where exposed at outcrops, the rocks are hard and fresh. Petrographic analyses of bedrock samples confirm the classification of the intrusive body as quartz diorite. Because of its limited exposure at the site, preferred jointing or foliation in the rock has not been identified at this time. In general, bedrock is exposed or covered by thin, discontinuous surficial deposits throughout the higher elevations near Upper Mahoney Lake. The lower areas surrounding Mahoney Lake have both alluvium and talus that reach substantial thicknesses. · Surficial deposits observed during the reconnaissance fall into three categories: 1) talus, 2) alluvium, and 3) avalanche deposits. The distribution of these deposits is shown on the site geology map, Figure B-3. B-5 --z- I I l . ! t i ! ~ ~ I Talus generally consists of angular, hard, and virtually unweathered boulders of metasedimentary rock ranging from several inches to masses up to 20 feet. Typically, talus is found at the base of steep slopes or cliffs. Talus also includes scree, or loose material, lying on slopes without adjacent cliffs. · . . Alluvi.um consists·primarily of subrounded to angular fragments of metasedimentary and intrusive rock. It is found in the stre.am draining Upper Mahoney lake, other small streams, and in small fans where streams enter Mahoney lake. The alluvium is a mixture of silt, sand, and gravel. Several avalanche chutes are apparent in the Mahoney Lakes basin, as shown on Figure B~3. These elongated areas are marked by a disti~ct lack of trees and by slopes covered with coarse, clastic rock fragments. Several faults and lineaments pass through the project site. Initial observation indicates that the stream flowing from the upper lake is fault controlled. Numerous north-south striking faults and fractures of various magnitudes pass through the east ridge. Two major features stand out because of their surface expressions. One fault, Skyline fault, has a much longer surface expression than other faults and crosses the projected tunnel alinement some l,OOO.feet from Upper Mahoney Lake. One seismic survey line crossed the lineament but rock of varying seismic velocity was not detected. The fault surface is exposed approximately 800 feet north of the alinement and has a strike of N25E and a ·dip of 85° NW. Tr1e other fault, Portal fault, crosses the tunnel west of the.portal and has the widest and deepest surface expression. It is through the trench of this fault that snow avalances. Its strike is N30E and its dip is 60° SE. The tunnel would pass under the trench to prevent avalanche· damage to the penstock. There is no indication of recent movement along these faults and no seismic events are recorded anywhere for. the area. The amount and direction of offset on the faults are indeterminate. The geologic section through the tunnel and penstock alinement, Figure B-5, shows the projection of the faults onto the plane of the section. SEISMICITY Southeastern Alaska is tectonically and seismically active. The boundary between the Pacific and North American crustal plates occurs along the southeastern Alaska coastline and movement of.one plate relative to the other is responsible for coastal mountain building and seismicity. Major faults cross the r·egion in general {y northwest-southeast directions. Most are strike-slip faults with high dip angles. but th~ust faults have also been recognized. Literature and data sources (Pacific Geoscience Center, 1980, and National Oceanic Atmospheric Administration, 1980) indicate no earthquake epicenters within 40 miles of the site since 1899. There have been two earthquakes of magnitude 5.0 or less within 50 miles, eight more .of magnitude· less than 5.0 within 100 miles, and one of ~t least magnitude 8.0 within 150 miles of the site. Earthquake epicenters in the region are shown on the earthquake epicenter map of Figure B-1. Most of the earthquakes appear to be · B-8 associated with the Fairweather-Queen Charlotte Islands fault system, which Hes approximately 140 miles southwest of the project area. The Fairweather fault extends from a point near Prince of Wales Island northwestward to Yakutat Bay. The 1 argest recorded earthquake generated along the Fairweather .fault had a magnitude of 8.6. · The Fairweather ·fault j s ·160 miles from the Mahoney Lakes. The Queen Charlotte Islands fault extends southeastward from near the southeastern end of the Fairweather fault to the Queen Charlotte Islands, The largest earthquake generated along this fault had a magnitude of 8.1.. This fault is 110 miles southwest of the Mahoney Lakes. The Chatham Strait fault is apparently either truncated by the Fairweather fault or is an offshoot of it. Historic earthquakes magnitude 5.0 have been generated by movement on it, but judging length, it is capable of producing earthquakes of magnitude 8.0. Chatham Strait fault is 125 miles northwest of the Mahoney Lakes. of by its The Revillagigedo Island ~urrently is considered to be in Seismic Zone 3. In Zone 3, earthquakes of magnitude 6.0 and greater can be expected. Its proximity to large fault systems increases the earthquake probability, but the low level of recent activity shows the area ·to be relatively inactive. There are many 11neaments in the region, although based on microearthquake data, none is the locus of recorded earthquakes. The intensity of shaking at the site would be a function of the amount of energy released by an earthquake, the distance to the epicenter, and the geology of the site, particularly the extent and thickness of unconsolidated deposits. The largest earthquakes that could be expected on the active faults in the region and corresponding bedrock accelerations at the Mahoney Lakes area are presented in Table B-1. The most intense shaking would be generated by the maximum probable earthquake on the Queen Charlotte Islands fault. Peak acceleration at the site due to that event is estimated to be less than 5.percent of gravity; this roughly corresponds to a maximum intensity of about V or VI on the Modified Mercalli Scale given in Figure B-6. B-9 N. s Contoured lower hemisphere stereographic plot of the poles of 35 primary joint attitudes measured within the metasediments. A Kalsbeek counting net was used to develop the data. Contoured at: 5-10% . ~ .. . . .. .. . STEREOGRAP~IC PLOT OF : ... -.. ·_,··::· .. :,· .. . . ' . .. ..... 10-15% PRIMARY JOINT ATTITUDES • ..,... AIID ""...._ • ALAMA .. ,..,C':IIIIIII 4111111 I • IOUTMAST tfY'DitOCLIECTRIC POWaR I.TI .. ........ FIGURE B-4 l llilt:IJ;.,..n. . << -.... ............. ~..)' .... 0 DISTANCE (FEET) / FouH. Apparent dip ~ Alluvium. Smsom depoaite l2.i.J of sand, lilt, and Qrovel. Quartz Diorite. 1 projec:ted from nearby / exposures. ~Colluvium. Talus and ~ slope debris (scree). schitl. Apparent dip projected from surface exposures" REF'ERENCE: TopofrOPhJ !ol<tft from mop 111 A. W" &••~ and A .. <>eiotu, eortaln facilil1 location lntorn>atlcn tram Corps ol Entin,.,. '""'· No, I>ACW&!Il Geologic contact, approximate; queried where uncertain. GEOLOGIC SECTION THROUGH TUNNEL & PENSTOCK ALIGNMENT FIGURE B-5 ..... --................ __ -·----0 , I ..... ..... Table B-1 Maximum Peak Bedrock Accelerations at the Mahoney Lakes Maximum Historical Maximum Credible Distance Maximum Credible length Earthquake Earthquakef to Site Bedrock Accelerationl/ Fault (miles) Magnitude l/ Magnitude I {miles) (% of gravity) Fairweather (offshore segment) 300 8.6 8.6 160 5 Queen Charlotte Island 350 a. 1 8.6 110 5 Chatham Strait 200 5.0 8.25 125 5 11 Magnitude refers to the Richter Scale. 2/ Magnitude credible earthquakes are based on correlation of earthquake magnitude and length of fault rupture in Greensfelder, Roger w., 1974, Maximum Credible Rock Acceleration from Earthquakes in California, Map Sheet 23, California Division of Mines and Geology. 3/ From Schnabel· and Seed, July 1972, Acceleration in Rock for Earthquakes in the Western United States, Report No. EERC 72-2, Earthquake Engineering Research Center, College of Engineering, University of California, Berkeley, California. ' MODIFIED -MERCALLI rNTENSITY SCALE OF 1931 I Not felt by people, except under especially favorable circumstances. However, dizziness or miusea may be experienced. Sometimes birds and animals are uneasy or disturbed. Trees. structures, hquids, bodies of water may sway gently. and doors may swing very slowly. 11 Felt indoors by a few p«)ple, especially on upper noon of multi·story buildinp. and by aensitive or .nervous penons. As in Grade I. birds and animals are disturbed. and trees, structures, liquids and bodies of water may sway .. H;,mgmg objccls swmg, especially· if they are delicately suspended. Ill Felt indoors by aeveral p«)ple, IIAially u a rapid vibration that may not be recoanized u an earthquake at-first. VibratiOn is similar te that of alight, or l;ptJy loaded trucks., or heivy trucks some distance away. Duration may be estimated in 10111e cues. Movements may be appreciable on upper levels of tall structures: Standing motor cars may rock sbghily. IV Felt indoors by many, outdoors by few. Awakens a few individuals, particularly light sleepers, but frightens no one e,.;cept those 'pprehensive from previous experience. Vibration like that due to pusing of heavy, or heavily loaded trucks. Sensation like a heavy body striking building, .or the falling of heavy objects· inside. Dishes. windows and doors rattle; gLassWare and crockery clink and dash. WaHs and house frames creak, especially if intensity ism the upper range of this grade. Hanging objects often swing. Liquids in open vessels are disturbed slightly. Stationary automobiles rock notJcea'ble. V Felt indoors by practically everyone, outdoors by inost people. Direction can often be estimated by those outdoors. Awakens many, or most sleepers. Frightens a few people, with slight excitement; 10me persons run outdoors. Buildings tremble throughout. Dishes and glauware break to some extent. Wrndows crack m some ca..es. but not gencr· ally. Vases and small or unstable objects overturn in many instances, and a few fall. Hanging objects and doors 'wmg generally or considerable. Pictures knock against walls, -or swmg out of place. Doors and shutters open or close abruptly. Pendulum docks stop. or run fast or slow. Small objects move, and furnisi1ings may shift to a slight e,.;tcnt. Small amounts of liquids spill from well-filled open containers. Trees and bushes shal-e slightly. VI Felt by everyone, indoors and outdoors. Awakens all sleepers. Frightens many people: general excitement, and some persons wnou~oors. · Persons move unsteadily. Trees and bushes shake slightly to moderately. Liquids are set rn strong motion. Small bclh in churches and schools ring. Poorly built buildings may be damaged. Plaster falls in small amounts Other pla~tcr cracks somewhat. Many dishes and glasses, and a f.:w wmdows. break. Kmck-knacks. books and pictures fall. Furmturc overturns in many imtanccs. Heavy furnishings move. VII Frightens everyone. General alarm, and everyone runs outdoors. People find ·It d1fficult to stand. Persons driving car> notice shakmg. Trees and bushes shake modtntely to strong!; Waves form on ponds, lakes and streams. Water is muddtcd. Gravel or sand stream banks cavr in. Large ··hurch beU' ring. Suspended obJeCts ljUiver. Damage •~ negligible in buildings of good design and constrcctJon; slight to modcr~tc in well-built ordinary buildings: considerable in poorl; built or badly designed buildmg' ado!:>~ house,, old w~lh (espccJ· ally where Laid up without mortar), spires, etc. PLaster and some stuco.:Q fall. Many windows and ~omc furnnurc break Loosened brickwork and tiles shake down. Weak chimneys break. at the rooflmt. Cornices fall from tower~ and high buildings. Bricks and ston~' are dislodged. Heavy furniture overturns. Concrete irrigation ditchc' arc con~ideral:>i) damaged. VIII General fright, and alarm approaches panic. Persons dnving ear~ are disturbed. Trees shake strongly. and bra.nches and trunks break off (especially palm tree,). Sand and mud erupts in small amounts. Flow or springs and wells is temporarily and sometimes permanently chanJ!Cd. Dry wells renew flow. Temperatures of sprmg and well waters varies. Damage slight in brick structures built ~sp\:nally to withstand earthquakes; considerable m ordmary substantial buildings, with some partia: colLapse; hca,·y .m 'omc wooden houses, with some tumbhng down. Panel walls break away m frame stru•·tures. Decayed pilinJ!s break off Wall-f.tll Solid stone walls ~rack and brt:ak seriously. Wet grounds and steep slopes crack to some extent. Chmmey,_L-olumns. monuments and fa,·tory stacks and towers twist and fall. Very heavy furniture moves conspicuously or overturn,_ I X Panic is general. Ground crack' •·onspKuously !)a mage i< considerable m masonry strueturcs built espeo.:Jally to withstand carrhljuai<c'. great in other masonry buildmgs ··some collapse m large part. Some wood frame houses built especially to withstand earthquakes arc thrown out of plumb. other~ arc shtfted wholly off foundations. Reservoirs arc senously damag~d and underground p1pcs sometimes break. X Panic is general. Ground. especially when loose and wet. cracks up to width' of several mchcs; ftssurc' up to a yard in w1dth run parallel to canal and stream banks. Landslidmg is considerable from river banks and steep roasts. Sand and mud <hiih houzon· tally on beaches and flat land. Water level changes m wells. Water is thrown on bank' oi •·anab. lakes. nvcrs. et .. Dam<. dikes, embankments are ~riously damaged. Well-built wooden structures and bridJ!Cs ar: severely damaged. and some collapse. Dangerou~ cracks develop in ex.ccllcnt brick. wall~. Most masonry and frame structure~. and thcu foundataom. are destroyed. Railroad rails bend slightly. Pipe lines buried in earth tear apart or arc crushed cnti,.,.isc. Open cracks and broad wavy folds open in cemen! pavements and asphalt road surfaces. · . XI Panic U. seneral. Disturbances in ground arc many and widespread, varying with the ground material. Broad fissures. earth slump,. and land slips develop in soft, wet ground. Water charged with sand and mud is ejected in lllfgc amounts. Sea wave~ of stgm· ficant magnitude may develop.Oamagc 1s severe to wood frame structures, especially ncar shock centers, great tod.tms. d1kcs and embarkments, even at long distances. Few if any masonry structure~ remain standing. Supporting t>icr' or pillars of large, well·built bridges are wrecked. Wooden bndges that "give" arc less affected. Railroad rail< bend greatly and some thrust endwise. Pipe hnes buried in earth are put completely out of service. XII Panic is seneral. MODIFIED o-.. mage is total, and pra•·tically all works_ of construction are dam;r.ged greatly or destroyed. Disturbance' m the ground are great and vaned. and numerous shearmg cracks develop. Landslides, rock. falls. and slumps in river banks are nurncr· ous and e~tensive. Large rock masses are wrecched loose and torn off. fault slips develop in firm rock.. and honzontal and vertical offset displ.a_cemcnu are notable. Water channels, both surface anC: underground. arc diUurbcd and modtfted greatly .. Lakes ~~~e dammed. new waterfaUs are produced, rivers are deflected, etc. Surface waves are seen on ground sur· faces. Lines of Sight and level are distorted. Objects are thrown upward into the air. B-6 Ill ._ ... ___ __ :acCllilla ....,..., *_,...,.. """ ..... ,"', .. __ MERCALLI INTENSITY SCALE --- PREVIOUS.INVESTIGATiONS Numerous reports on potential hydropower sites.fo~ ketchikan and the surrounding southeastern· Alaska area were .initi-ated :as far ba·ck as 1947. The first report specifically conc.erned with the Mahoney lakes was by R.W. Beck and A~sociates entitled Swan Lake, Lake Grace, and Mahoney Lake . Hydroelectric Proaects, June 1977. A contract·with Harding-Laws.on . Associat·~s for aeologic Reconnaissance for Mahoney Lake Hydroelectric Project, Ketchikan, Alaska was completed .in March 1981 and.provided an assessment of geologic condi.tions at· the project area. Additional field invest·igations by Alaska District Corps of Engineers geologists provided more specific data c·oncerni ng va·rious project features. FOUNDATION CONDITIONS Dams ite The tlamsite would ·be located near the outlet of Upper Mahoney Lake. This valley is V-shaped with relatively steep sides and virtually no flat area in the streambed •. Bare rock is exposed on the east side of the vall~y. The west side of the valley is blanketed with talus deposits that consist of angular rock fragments ranging from coarse sand to cobbles. In the streambed, there are occasional large boulders up to several feet in diameter. Based on a seismic refraction survey,· the talus is generally about 20 feet thick at the left abutment and probably varies slightly from place to place. The talus is probably extremely permeable and would not provide a stable and .finn foundation for the dam. Bedrock at the site is a jointed metasedimentary rock of quartz sericite schist composition. Due to the scouring action of the glacial ice, most weathered rock has been removed. It is possible that very litt.le bedrock would need to be removed for the binwall structure foundation. However, it has been assumed that 2 feet of rock would be removed for the foundation structure. The two existing talus slopes on the left abutment would be removed to construct the dam foundation and for fill of the binwall structure. The two talus slopes contain an estimated 10,000 cubic yards of rock, more than enough to fill the binwall. On the left abutment, the bedding planes dip into the ridge, producing an over-steepening effect of the s 1 ope. Freeze-thaw action in the rock .; s probably the most dominant weathering element that causes the rocks to slab off. Bedding and principal joints strike N30E and dip steeply to the west, or roughly parallel to the east side of the valley. Secondary jointing is prominent and due to multiple direction stress relief. Joints that are s 1 ight ly open at the surface could be paths for seepage to sever a 1 feet below the surface. Most potential seepage would be eliminated by keying the dam into the foundation from abutment to abutment, a maximum of 5 feet into bedrock. At the damsite, three prominent secondary joint se~ attitudes were noted on each side of the river. The dips of the individual joints in the joint sets and the relationship of one joint to another are similar on each side B-13 of the river. One joint set has-been (Otated approximately 30° compared to the other set. The river downstream of the dainsite h.as a 200-to 300-foot, 90° offset. The offset occurs where the Skyline fault intersects the river that drains Upper Mahoney Lake. A waterfall is.·near the-offset in. the river .in a stretch of the river that has a uniform g_radient •. The joint set rotation; the. river offset,'-an~ wate'rfall suggest pivitol rotation of the geclogic units· ·at .tne damsite. on one side of the river . compared to the other. The individual jo.ints in the joint sets dip steeply .and ~ppear open at the ·surface. The steep dips and probable rotation suggest that the joints may be open at.depth. Another prominent joint attitude that is present only ·at the ·damsite strikes east~west and dips 70° south. This jointing was open at the surface·and would probably also be open at depth. Aerial photography and slickensided primary joint surfaces suggest a fault/shear zone trending N30E and di~ping west. This is the attitude of the primary bedding plane jointing. The rotation of the geologic units on one side of the river compared to the other also indicates faulting. This possible fault and the Skyline fault intersect near the waterfall and river offset. · · The metasedimentary bedrock is hard and excavations would require blasting. Unretained temporary cut slopes as steep as vertical would be stable except where they would undermine slabs of rock on the right abutment. . Cuts steeper than the existing slope could lead to block-glide failure of rock parallel to the existing slope. Once the dam were . constructed, the rock spalling would cause minimal damage; however~ some treatment of the abutment for safety during construction would be required. Other Corps projects with similar conditions were protected by using wire mesh and sufficient rock bolts to hold the mesh in place.· Talus and alluvium at the site and further downstream are sources of rock fill for the dam. Fine grained material for an impervious core is not available at the site. Riprap for shore protection could be developed by selecting larger sizes from the talus and alluvium. Talus and alluvium at the dam site and nearby areas is not suitable for use as concrete aggregate. Lake Tap The lake entry could be located about midway along the east ·shore of.the upper lake in good rock between two northeast trending fault5 that are several hundred feet apart. The rock through which the entry would be drilled is thinly bedded, fine grained, hard and brittle ~hyllite. Bedding strikes north-south and dips 54° to the west. Secondary pyritizaton has permeated much of the country rock. Bedrock is exposed nearly continuously on the slope above the lake and, based on previous investigations, is also exposed on the slope below the lake surface. The rock is jointed and the joints may be somewhat open to a depth of several feet beneath the ground surface. No adverse joints or fractures could be found in the rock above the lake and in the vicinity of the tap site, but slabs of loose rock, within several feet of the surface above the tap, could break off the slope without some sort of permanent support to stabilize potentially loose blocks. The site of the lake tap is not critical; any location within several hundred feet of that shown on the site geology map would be satisfactory. B-14 The multipipe scheme has been studied to the e~·tent that .it. appears feasible. The Alaska District queried contractol"s and Waterways. Experiment Station personn·el abou~ the feasibility and desir<ability of .such a ·scheme. Danger from slab rocks sliding down and closing·off the· intake area is · virtually nonexistent with this scheme and the fractures·:.near the. lake ·become less important. By using several pipes.to penetrate.into the lake, loose slabs·of rock. would be stabilized.by the pipes passtng·through the slab. Studies and explorat·ions of the tap ar.ea will be made·to assess the rock for the· tap •.. During construction, as the .tunnel approaches the lake· tap site, careful.drilling ahead to the lake would be done from the tunnel to locate fractures and to determine the lake bottom slope· for final design of the rock trap and iQtake angle. Fractures ·an·d ·joints .passing through. . the valve· chamber of the multipipe scheme are of more concern than those near the. lake, but possibly, the g~outing used·to·seal the. pipes would be sufficient for~he.fractures near the lake. · Penstock Tunnel Based on surface exposures, the tunnel would be entirely·within.metasedi- mentry rocks. The rock is hard, strong, and jointed with spacing varying from a few inches to a few feet; however, the joints are likely· to be fairly tight at depth. Some overbreak should be anticipated in the tunnel and may partially depend on the excavation method. Occasional granitic dikes and sills have been mapped in the area, but do not appear to intersect the tunnel. Numerous small veins of silica can be found throughout the rock •. The tunnel alinement intersects two faults at high angles as shown on Figure B-5. The faults are·less than one foot wide at surface exposures and could be paths for concentrated seepage, but the rock in general probably contains little ground water. The headwall of the lower basin has been oversteepened by glacial plucking. Special mountain climbing equipment and skills would be required to investigate the rock over that portion of the tunnel. The tunnel is the most convenient means of access to the tap area beneath the lake. A 17° slope is proposed foi the penstock tunnel to ensure adequate cover over the tunnel at the avalanche chute of. the Portal fault. Reduction of the tunnel slope would also require b~idging the avalanche chute with sufficient height to allow snow to cascade through the trench beneath the penstock bridge. The tunnel was discussed with a contractor to get a better understanding of the difficulties of driving a tunnel at such· a steep angle. The contractor felt that the steepness of a tunnel was a matter of selecting proper equipment and planning and therefore posed no particular problem. A 10-foot-diameter tunnel.would afford room for all phases of work. For a multipipe scheme, the tunnel length would be roughly 4,000 feet long. The manifold chamber would be located· some 70 feet from the lake. In this scheme there would be no pressure tunnel. The kinds of support anticipated for the tunnel are rock bolts, mine ties, and limited amounts of shotcrete. Concrete is not expected to be used as a primary tu~nel support material, but would be used in the manifold chamber for support of the manifold pipes and other equipment. Concrete could also be used at the portal for a tunnel closure structure. B-15 Portal The steep slope· of the tunnel would plac~ the outlet portal location at elevation 396 at the base of a prominent cliff, where the metasedimentary rock is less jointed than elsewhere. On the face of the cliff there is no overburden or weak rock that would require s~ecial support. figure B-3 shows the four secondary joint.s attitudes.at the portal site. The east-w.est striking joint with a vertical d·ip ·is the only joint that is probably open at depth that would result in wedge failure. West of the portal site·is the Portal fault, which is a pronounced lineament on aerial photographj. ·The fault strikes N30E and dips 60° to the southeast, with a sharp and narrow fault zone less that 200 feet wide. Fractured and broken rock should be exp.ected between the surface and a 300- to 500-foot depth. Future exploration should determine the proximity of the Portal fault to the portal opening. As projected on Figure B-5, it passes within 300 feet of the portal at tunnel depth. Surface Penstock The penstock would be constructed on the surface between the tunnel outlet portal and the powerhouse. The .area is underlain by talus and avalanche debris, which contains rocks up to 20 feet in diameter. The talus has a thickness of about 25 feet near the portal and 10 feet at the base of the slope near the powerhouse site with some bedrock exposure along the penstock route. The talus is composed of loose fragments of rock that may have large voids between individual fragments, and thus would not provide suitable foundation support. Considering the size range of the talus, it would be extremely difficult to excavate with conventional equipment unless large blocks of rock were first broken by blasting. The bedrock beneath the talus would provide suitable foundation support for the penstock. Powerhouse The powerhouse site is accessible by a brushed survey trail that begins where the upper creek enters lower Mahoney Lake and trends southwest for 500 feet. The powerhouse site is adjacent to an intermittent tributary stream channel and is 5 to 10 feet above flood stage for the stream · channel. The alternate powerhouse site can be reached by walking approximately 1,500 feet upriver from lower Mahoney Lake. This site is adjacent to the river and in the flood way. Local geology at the powerhouse and alternate powerhouse sites consists of blocky unsorted alluvial and colluvial deposits primarily composed of avalanche talus debris. The debris overlies granitic and metasedimentary basement bedrock. A seismic refraction survey indicates the talus deposits range in thickness from zero at the contact with bedrock to 75 feet at the lake shore. The seismic refraction survey at the alternate powerhouse site indicated 22 feet of overburden. The unsorted talus-avalanche debris ranges from gravel to 20-foot boulders. Boulders and blocky talus form 50 to 75 percent of the unconsolidated deposits. B-lfi By building the powerhou~e inta·the toe of the. hill; stability problems could be· avoided.·. Some talus may need to· be removed, but ·the underlying ·bedrock. should be suitable for the· foundation .•. Tl'le granfte. rock consists . of slightly metaf!Jorphosed ·schistose grandiorite. The metasedimenta·ry rock consists of carbonaceo.us quartz sericite schist. The-schist was derived ·t~rough low to medium grade contact metamorphism of geosyniclinal sediments. The gr-anodiorite intruQ.es, ov~rlies, and postdates the schist beneath the powerhouse site •. Contact relationships between the schist and granodiorite are concealed and inferred.from surficial deposit distl'"ibution. ·Primary bedding within the schist strikes northeast-southwest and dips steeply to the west.· ·The jointing follows relict bedding. No aerial lineaments due to faulting:were observed nea.rthe .sites. -. . ' .. The all.uvial deposits: at the alternat'e site may· be unst-able in. the event of an earthquake. The dynami·c response of the foundation materials should be .studied in more detail,· so that the alternative site can be considered further. · · · · MATERIAL SOURC,ES Exploration for coristruction materials, particularly for concrete aggre~ates, has bee~ a part bf all investigations for the Mahoney Lake hydroelectric project to date. Although only moderate. quantities are required, the accessible sources ~re difficult to find.and those that are available will require careful processing to produce suitable material. Two sources were ·sampled and are considered to be the most feasible. Powerhouse Stream A fairly extensive deposit of sand and gravel exists in the alluvial deposits of the creek draining into lower Mahoney Lake. Laboratory tests and microscopic (petrographic) examination of the material show it to be acceptable for concrete aggregate, road surfaces, etc, if properly processed. See Appendix B-1 for these data. Access to the site would be via road. Damsite Quarry An extensive talus deposit is located immediately adjacent to the left abutment of the-proposed structure. laboratory tests and microscopic . (petrographic) examination of this material show it to be. acceptable for concrete aggregate, roc~fi 11, or riprap of limited sizes. See Appendix B-2 for these data. Extensive processing of this material would be required for concrete aggregates. Access to this source would be via helicopter. In general, it appears that the bulk of any or all rockfill and riprap could be produced from the damsite quarry source. Material for any roadways or pad areas could be obtained from the powerhouse stream site. B-17 There are no local sources of cement or pozzolan,-sc that all such materials would have to be imported from the continental United States. _Further studies will include,-but not be Jimited ~o, mix-designs, · _ processiblility studies, temperature studies, freeze/thaw tests, and exact quantity surveys of any source selected. Disposal Sites Sufficient sites would be available for disposal of tunnel wastes. Areas close to the tunnel portal would be suitable if environmental constraints were met. · · CONCLUSION . In conclusion, the f)roject· appears feasible based on the information available. The engin~ering characteristics of"the bedrock should be assessed and additional explorations will be required. Future investigations should include driliing of two holes -at the damsite and drilling of one hole each at the portal, powerhouse. Skyline fault, and lake tap. Foundation investigations, which are often hampered by difficult access and by erratic weather conditions, should be initiated early in the design memorandum phase. B-J8 APP£NDIX B-1 -FOUNDATIONS·AND MATERIALS Tests on Gravel from the Powerhouse Stream Nl'DEt.-GS-L ( 82-C-118) 1 9 Jan 82 MAHONEY LAKE HYDRO neport of Teats on Gravel From The Power House Stream, Alaska l. ~cope: On 9 Nov 81, 1290 lbs of pit run natural gravel composed of tw~nty sack samples were submitted to NPD Lab for bulk gradation, concrete aggregate quality tests, and processing studies. Analysis of the bulk gradation indicated the following: (1) 1 1/2" MSA could be produced, .(2) the natur~l aggre@ate contained a signlficent quanity (20J) of flat particle~, (3) rescreening of the 3-l 1/2 and 1 l/2-3/4 inch sizes to meet gradation specifications was only minimally successful primarily due to the flat particle pieces, and (4) roctmill sand would be required. Aggregate. quality tests were made on tn~ natural material. fbllcwing completion of the bulk gradation and aggregate quality tests a processing scheme was devised to produce 1 1/211 MSA blended crushed and natural aggregate. Due to the relatively small size of the sample, the laboratory processing study may not be representative of full scale processing efforts. Uetailed results are as follows: NPDEN-GS-L (82-C-118) SUBJECT: Mahoney Lake Hydro 2. Bulk Gradation: 6"-3" 3"-ll:i" a. Weight, lbs 216 365 b. Percent, % 16.8 29.8 c. Gradation-Percent Passing 5-inch 100 4_-inch 3-inch 0 100 2 1/2-inch 82 2-inch 48 l l/2-inch 12 l-inch 1 3/4-inch 0 1/2-inch 3/8-inch No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 F.M. 3. Aggregate Quality Tests (Natural Gravel) Specific Gravity, BSSD Absorption, % Los Angeles Abrasion % loss·@ 100 rev % loss @ 500 rev Sow1dncss of Coarse Aggregate by Accelerated Freezing and '!}law log _____ -----------·--· X loss by weight @ 300 eye les ~-lat_ fl_!l~-El~W_e_~ __ Part ic.!_~ '1.. Flat by weight % Elongated by weight "(,,Lll, :? 3"-1~" 2.69 0.7 Nominal 1~"-3/4" 209 16.2 100 98 50 10 1 1 1.1 . 2.2 20.0 1.0 2T~-o 5.2 22.5 19 Jan 82 Size 3/4"-No. 252 19.5 100 97 59 35 2 2.1 14.0 0.0 14.0 4 -Fines Total 228 1290 17.7 100.0 100 83 78 68 57 46 38 29 100 25 98 18 77 14 55 10 32 6 14 2 7 1 3. l 7 2.7 NPIJEN-CS-L (82-C-118) 19 Jan H2 SUBJECT: Mi.lhoney Lake Hydro 4. frocessing: Nominal Size a. Bulk f.radation Lbs Percent * Stockpile • Plus 3" 3"-1~11 . 216. 17.7 316** 25.9 209* 17.1 l52* .20.6 ** 69 lbs of 3"-1!2" mat:er~al .sampled for .petrographic examination. b. Pr imarv Crushing: 1) Crusher: · 18x24 inch jaw at 2 15/16 inch setting 2) · F-eed: los 216 316 3) Pcoduc;t: · Lbs Percent. c. Secondary Crushing: .83 15.6 351 66.0 68 12.8 23 4.3 1) Crusher: 18x24 inch jaw at 1 15/16 inch set:t ing 2) fe~d: lbs 83 351 3) · Product: i.bs Percent * Stockpile 119 lbs. d. Ternary Crushin_£! 250 119* 57.7 27.5 1) Crusher: 18 inch Gyratory at 3/ 4" MSA setting 2) Feed: lbs Primary Secondary 3) Product: Lbs Percent * Stockpile 165 lbs. e. Rodmill Sand: 250 68 64 21.4 1) Rodmill: 18 inch 0 x 42 inch Drum 2) 'Feed: lbs Primary Secondary Ternary J) Product: Lbs :..) Loss: lbl:i Perct.'nt ,:.: :-.[, . .:1-.j·ilo..· ltJU th,.; 64 47 10.9 185* 61.9 -23 47 20 Fines 228* UL 7 7 1.3 17 3. 9 50 16.7 7 1 7 50 160* h8 29.8 1221 100.0 532 100.0 434 433 100.0 318 299 100.0 228 160 NPDEN-GS-L (82-c-118) 19 Jan 82 SUBJECT: Mahoney Lake.Hydro f. Product: 1) Lbs Natural 209 252 228 689 Crushed '119 185 160 464 Total 328 437 388 1153 2) Percent Crushed, each nominal size 36.3 42.3 41.2 40.2 Each. nominal' s.ize 28.4 37.9 33.7 100.0 3) Total Processing Loss, Percent 5.6 g. Gradation: Combined Crushed and Natural Gravel Nomfnal Size 1~"-3/4" 3/4"-No. 4 Sand % % % Alt. No.1 Size Pass Specs Pass Specs Pass Specs 2-inch 100 100 1~-inch 94 90-100 l-inch 44 20-45 100 100 3/4-inch 10 0-10 98 90-100 1/2-inch 1 62 3/8-inch 1 0-5 34 20-45 100 100 No. 4 3 0-5 98 95-100 No. 8 82 80-95 No. 16 62 55-75 No. 30 39 30-60 No. 50 19 12-30 No. 100 8 2-10 F. t-1. 2.92 2.40-3.10 NPDL 1794 •t.lli.l .II: :: :. J .' I l' loj It ,, .! \ . . \ l I\ ,. .'I I I t: Nu. ' . ''. I •' ;j I 'I. [ h: L. 'I : ·, lj I I . ' . ! ·;; :f ~~ 1 '· . '! j Paul D. Hecht t~l)l·:h Ul\111:.1\ th•, :. Jtf·l1 .1 (.) ' !. 1 n ·, ·! r: i · · :: j j ! '. J: ; . :' If ; _* ' L(•l'{lf~{. H•!: :' , :. · • I :: i H'111 J /'i'. I· I i I ; ·::·I :I ~ .ii t ·;,.:~~-~!."~!.! . : ~~ . \. ' , ~~~nr:w.ry. l'he aggretate was cmupuscd of generally hard sound material. The principle rock .ypeo: was a fine grained quartz-muscovite schist which was foliated. _This produced an t6gregate which was genenally flut to elongate in shape with 9% of the coarse aggregate .ccting the CRD 3 to 1 ratio of a flat particle. Much of the material showed secondary •ineralization with numerous vdns of pyrite present in both the schist and the quartzite. lVc..•rage pi.!rCI.!nt composi tiuu of the coarse aggregate was 91 schist and 9 quartzite. Percent .and c.omposithm was 61 sdd::;t, l) quartzite, 16 quartz, 4 muscovite!, 2 hornblende, 2 pyrite magnetite and 1 gamct. Percent b:z: Sieve Size 4>ck 1:. Hincrals 1 1/2" 3/4" 1/2" No.4 No.8 No.16 No. 30 No.50 No.100 !!n Schist 96 93 89 85 84 82 80 65 39 18 l,luartzite 4 7 11 15 16 16 15 13 10 7 (.!ua rt z 2 5 17 29 42 Hus~ovite 3 9 14 l!o m b 1 en de 1 5 6 Pyrite 1 4 5 ~1.1gncti t.: 1 3 ( ..• rnct ] 5 I I ~ I I ' ' t ' I 1 I ., j : i ! I ! ' t I .. i : '. I ' I ' .. .!" .. ' ! t I I i 1 : I ' ' . . ·--r-or· ~ .---,--.. 1 i r· : ' 1 -- ! .! 1 i i ·-. I --. . I i -i .-i ' ~----· _..:._ __ _.....,._ __ -.. _--..---'--__,-·~-~~-----------------.. --'~ 1 ' : : : "J:-0.0 ! . : z --· --··---+--·-·-... "'---•-• • -. . ·-. .. ' . .. .. -w ., ' ' I : u I I . ' I I a: ; i --w ~--·----~ ---------~ ---·-----·-. f ·-· ---. . ·--·---· -I ---·-~ . ~ -~ 0.. ~· ,. !f>.O ! \.? -l--~-,:__..:;._ _ _: _____ ,_ _-,. ___ ,. _ .. ·--·-· l . --------. -----·-·------------z ' . l < ' I v --·-.... -1--·--.. ----... -----. . +-·-·· ---.. ~-. -+ --------------------.... ... t!;O·O ~ I I / ' z. . --·----.....,....-.. -.... -. ----~ --·--~--t---~t-··· .. ___ ,__ ---------. W _... .J w~ -I I ~4 I ' ~-+-~ . ---:--------.--------·-· ---. _,_ . ~ ·-_., _____ : I ! ; . I 0 i ,_ .. -.. . -... . . . . . . .. - I .. I . -t).Q_,. ~0 100 ISO 2,iO 1'>0 300 3o5 AGE. DAYS NC'TI::: E.tch lUfVIIt rerrc~~nt~ a"erag<' of ba•5 SPEC• MEN PROJECT' SYMBOL COMBINATION S£'! N(• 1794 • Righ Alkali Ce1llent MAHONEY LAKE HYDRO DISTRICT Alaska . ·-- 179.4 • Low. Alkali ~~~nt AGGREGATE Pit natural sand from . -··-~· --run ------·----~-··-----.. Pot'er Bouse Stream, Alaska. . -------· --... " . ··---·-------- Hl.MAHI\!> HIGH· ALKALI CFMI NT 1.0! -....Na_.O ·Whitehall Cemen Co., Whitehall. PA LriW· ALKALI ClM!:;NT 0. 48'~ N.:>:O l Blend 0~ Oregon, Idaho, and Lehigh Tvoe T & IT Cements Pi.:otred J.H. w;o NO. Ch...-kcJ 82-C-118 r t ' ' --JAMES K. HINDS ----lOot.-..,., R'•pon) Chirf. ((l..,.cr'!'"~f! t:!l•.tf"'(.r Nf"'~ FORM~65 REACTIVITY OF AGGREGATES WITH ALKAliES IN PORTLAND CEMENT JULY -49 _. (MORTAR BAR METHOD) METHOD CRD c. -_123 CORPS OF' ENGINEERS NORTH PACIFIC DIVISION TESTING LAB Or<ATORY .... r-~----T-~-----r----~~-----.-.~r-----~4-------~------~~- tO.Ofr---~··~----~;,1-~~--~----~r-~--~----~-4------~~ z .. .. .. . .. .. I w u cr .:.J a .. ~>.Ott-~~--~~~~·~·~----~~--w-----t-------~------~--------~ ~ z ·l -u ; .. .. _..;....--;---• .? i;o. o·~-~-t-;it=::::::-:w"T--~-+---+-----+----f...__---. __ t---i •J ~ A ''W" .. / ./ L ----+--• ---~ ... .J - ~------~--------~----~---4-----..... ---r------------------+---------+1--4 -o.J-· _· __ ..:._ ___ ..~.-______ ---____ · t_ .. ---··--·-----"~--j_ !>.1~) I L p • 'I '• o "•·' ~ ' . ~. d'. I I I I 1794 r----MA_I_It_>N_E~~--~·-A_KI_~ ~ I_Y_u __ R_o _________ ___.j ,,,~;1HIII· Alaska· i ~----+---+----------,------ • High Alka I i Ct!ment ------------------------4 ~GGRE~ATf Pit run ·natural sand from~ Powerhouse ·Stream, Alaska. ~-------L-----~----------------------~~--------~---------------------kL~.:.··'"''' tt"·"· .. •-'-'\1• .,,~~,~~1 01 ·.·, .. Whitehall Ce~~nt Co. , Whi.teha ll, PA ,. --------------.. ---------·---- ' .V ·>•'-·"''' I .·ltl.• 0.48 •· ~ Blend of Ore~un, ldaho •. and Lt:high ~'.:::: • Ty~-+ .§_l ~~~-:C-11 ti '----· I I ==----=.:~~~~~~ K. HI:\ OS J ~===..========r===============================~J:==~======~~ ' • Low Alkali Cement 1.794 l,t .. l" TI\ITY Of J\GGRfGAlLS Wlll.t .\lt<-1'.111 •, ltl i'•d~lli-UII t:l :~11-:.1 J' ·l!l.h'HTJ\H tS.\H Mi ft,.11•) ~.II l!t,H• 'lxl.• ' ,·•~ '"·Cl~P:.; -.')F 1t'.4.,tt·atU!oi Ldt-\Hti~/~ ''~·.~_:_'~~·.'~·~• ~~IH:~.~-:-.h _:::~:_: .. : __ ---------~--- ... -. . APPENDIX B-2 FOUNDATIONS AND MATERIALS Tests.on Damsite Quarry Stone NPDE~.;.GS-L ( 82-C-1-18) 2 5 February 1982 MAHONEY LAkE HYDRO .Report· of Tests on Damsite Quarry Stene 1. · ~QODe: . On Q9 N9v 81, · ,078 lbs. at pit run quarry stone composed of twenty sack samples.were submitted to NPDLab for bulk gradation, rock mechanic tes~s, processfng studies, and aggregate quality tests. The sample was generally flat and slab shaped with a heavily'foliated structure. Numerous pieces also contained visable fracture planes. 2. A bulk gradation was made of the entire·· sample. Analysis of the bulk gradation indicated that 3" MSA CO\lld be p·roduced and that ·.rodmill sand would be required. Following completion of the bulk gradation, approximately 173 lbs of the larger pieces of stone were removed for rock mechanic tests. A processing scheme was devised to produce 3" MSA. Due to the flat angular structure of the rock, recycling of the crusher product was required ·to ·produce the 1 l/2"-3/4 11 size.. Due to the relatively small size of the sample, the laboratory processing study may not be representativeof full scale processing efforts. Detailed results are as shown in Table I. 3. .Tne larger size stones for the rock mechanics tests w.ere cast in concrete prior to coring. Cores were drilled both normal and perpendicular to the plane of foliation. NX cores were drilled where possible; however, due to the small size of the stone most tests were made on 1 1/4" diameter specimens. Recovery of cores drilled·parellel and perpendicular to the foliation plane averaged 86 percent and 38 percent, respectively. Tests included splitting, tensile and compressive strength, modulus of elasticity and Poissons ratio. Where possible, four to five specimens were scheduled for each test. Detailed results are showp in Table II. · 02 Mar 82 MAHONEY LAKE HYDRO DAMSITE .. TABLE I .&ep<;~rt of Processing Studies and Aggregate Quality Test& on Quarry Stone L Bulk Cradat ion: a. lOeight, lbs b. · Percent. % .c. ·. Cradat ion-Percent t>assing 9-inch 6-inch ·s-inch 4-inch 3-inch l!rinch 2-inch 1l,i-inch l-inch 2. Processing: a. Prtmarv Crushing 9"-3" ""'8'4'7 78.6 100 91 47 30 0 Nominal Size 3"-1 1/2" 231 21.4 100 29 ll 5. 3 Total 1078 100.0 100 93 58 45 21 6 2 1 1 ·o) Crusher: 18x24-inch jaw at 2 15/16-inch setting ( 2) reed : 8~8 lbs P.i t Run 9" MSA (3) Product (a) lbs (b) Percent St<>ckpile: 250 lbs b. Scc()ndarv Crushing (l) Crusher: 18x24-inch jaw ( 2) Feed: lbs (3) Product* (a) lbs {b) . Percent • Doe to flat particle shape the recycled through the jaw crusher.· **.Stockpile: 180 lbs c. T<•rnan· Crushing Plus 3" 265 29.7 Nominal Size 3"-!l.i"· 11,"-3/.t." 3/4"-No. 4 ~ 108 45 50.7 12.1 5~1 at 1 15/16-inch setting 265 202 2 155 209** ·. 74 0.4 33.2 41..8 15.8 plus 1~-inch material from the initial Results are for the two passes. (I) Crusher: 18-inch Gy;;otory at 3/4" HSA setting (2) Feed: lbs (a) Primary 108 (b) Secondary 2 ISS 29 (J) Product: (a) · lbs 78 16{>* (b) Percent 26.5 56.5 * St.:lckpile: 166 lbs d. R<•dmi 1l Sand (l) iti>dm ill: 18-inch ~x42-inch Drum (2) Feed: lbs (a) Primary . 45 <b} &e::onda::y 7!. (c) ·Ternary 78 (3) Product: (a) · lbs (b) Percent (4) l..)SS: (a) lbs (b) Percent Fines !oral 2'1 ~ 2.4 100.0 467 27 467 5.8 100.0 crushin;z was 29!. 5.0 29~ 17.0 100.0 21 27 50 295 203 203 100.0 JOD.O 92 31.2 NPDEN-GS-L (82-c-118) SUBJECT: Mahoney Lake Hydro 02 Mar 82 Nominal Size Plus 3" ~ 1~"-3/4" 3/4"-No. 4 !:.!!!!!. 12!!.1 e. Product (l) lbs (2) Percent (3) Total Processing Loss, Percent 250 31.3 180 22.5 166 20.8 3. Aggregate Tests-Processed guarry Stone: Nominal Size •• Gradation 3"-15" 1~"-3/4" 3/4"-No. 4 % % % Size Pass Specs 4-inch TOO 100 3-ind. 98 90-100 2~-inch 68 2-inch 37 20-55 100 100 1~-inch 8 0-10 90 90-100 l-inch 2 o-s 28 20-45 100 100 3/4-inch 6 o-10 97 90-100 1/2-inch 2 62 3/8-inch 1 O-S 33 20-45 No. 4 4 o-s No. 8 No. 16 No. 30 No. so No. 100 F.M. b. Specific Gravity, BSSD 2.74 2.74 2.73 c. Absorption, % o.s 0.7 1.0 d. Los Angeles Abrasion % loss ~ 100 rev. 3.6 % loss @ 500 rev. 16.1 e. Flat & Elongated Particles % Flat by weight 33.0 9.0 7.0 % Elongated by weight 2.0 1.0 0.0 Total 35.0 10.0 7.0 f. Soundness of Coarse Aggregate by Accelerated Freeze-Thaw % loss by weight @ 300 cycles 0.4 (2) 203 25.4 Sand 799 100.0 10.3 % Alt. ~.:) 1 100 100 96 95-100 81 80-95 62 55-75 41 30-60 20 12-30 7 2-10 2.93 2.40-3.10 2.73 1.1 NPDDI-GS-L (82-t-118) 25 Feb 82 MAHONEY. LAKE HYDRO DAMSITE TABLE II Summar.y of Tests an Cores Drilled from Damsite"Quarry Scone Tests !l Cores Drilled Normal to Cleaverage Plane ! Splitting Strength,· T~nsile Compressive Modulus of Poisson's Core (BraZilian) Strength, Strength~ Elas!~·c ity, Ratio No. EBi ESi ;ESi Ex10 2s1 lJ A-1 1895* 4_7 ,810* . 9.19 0.161 . A-2 37]5* 25,900 . 7.83 0.162 A-3 580 A-':4 3860 ; 8-1 2345 26 '700 7.43 0.163 . B-2 ·1625 19,61.0 B-·3 ·1050 1155 F-1 480 i:;-1 2610 · G-2 2745 J-1 285 61,500 8.79 0. t44 .J-2 65 K-1 2255 K-2 .3225 ':" Q-1 360 Average 2625 490 :v .310 8.31 0.158 High 4895 1155 61,500 9.19 0.163 Low 480 65 19,640 7.43 0.144 Std. Dev. 1290 415 17,640 0.82 0.009 C-1 1905 '}_/ C-2 28,960 11.44 . 0.204 C-3 35,330 12.82 0.297 C-4 11 ,050 D-1 1745 D-2 1120 12,4£.0 10.22 0. 326 D-3 1210 980 E-1 3955* 1475 E-2 3305* 1620 E-3 35,170 10.38 0.189 H-1 610 o-1 24'63 S-1 1.::95 S-2 1430 Average 2125 1285 24,590 11.22 0.254 High 3955 1745 35,330 12.82 0.326 Low 1120 610 11,050 10.22 0.189 Std. Dev. 1135 475 12,010 1.20 0.068 NPDEN-CS-L (82-c-118) 25 Feb 82 TABLE II MAHONEY LAKE HYDRo-Summary of Tests on· cores Drilled from Damsite Quarry Stone NOTES: . l/ Laboratoq· Te$t Methods: * a •. RTH 113-:80, "Standard ·Method of Test for Determining the Splitting Streng,th of R.ock 11 (Brazilian Method) . b.. RTH. .112.-80,. 'n:l:re~t Tensile· Strength of Intact Rock Core Specim.ansu · (ASTM D2936:.,;i8) . c. d. RTH.ili-80,. "U~confined Compressive Strength of Intact Rock Core Specimans" · (AS'nf ~2936-78) · · . RT11.201-80, :,'Elastic Moduli of Rock Core Specimans in Uniaxial Compression.. (ASTM D3148-79) All tests on nominal 1~-inch diameter cor.es except as noted. Failure occurred through epoxy at end of. core speciman, test result not included in computation of average and standard deviation. Test made on nominal 1 3/4-inch diameter core. (2) NPDEN-CS-L (82-c-118) 02 M:ar 82 HAAONEY LAKE .HYDRO DAHSITE . TABLE' I Report. of' Processing Studies and Aggregate·Quality Tests on Quarry Stone 1.-Bulk Gradation: Nominal Size 9"-3" 3"-1 1/2" . a. Weigl-.t. lbs '847 . 231 b. Perce.nt, % 78.6 21.4 . c. Gradation-Percent Passing· ··9;..tnch 100 ·6-:'inch 91 '5~1nch 47 :.-inch 30 3-ioch. . . 0 100 2~-tnch. 29 2-inch 11 · V4-inch· 5 . l-inch. 3 2:. Processing: .a. Pd~:rry ·crushing (1) Crusher: 18x24-inch jaw at 2 15/1.6-inch setting {2) Feed: 898 lbs Pit Run .9" MSA l'<:l"!!linal Plus 3" 3"-1 1/'· Tntal 1078 100.0 100 93 58 45 21 6 2 1 1 Size 3/4"-No, 4 Fines (3) Product (a) · lbs 265 452* )!i"-3/1.." 108 __ 4_5 __ '""2'1' (b) Percent * Stockpile: 250 lbs b. Secondarv Crushin] 29.7 50.7 12.1 (1) Crusher: 18x24-inch jaw at 1 15/16-inch-setting 5.1 2.4 Total 891 100.0 (2) Feed:· lbs 265 202 467 Oj Product* (a) lbs 2 ISS 209** 74 27 46/ (b) Percent 0.4 3:l.2 44.8 15.8 5.8 100.0 * Due to flat particle ·shape the plus P;z-inch m;ttcrial frC'tm the in.itial crushin:! was recyc1ed:through the jaw crusher. Results _are for the ·two passes. ** Stockpile: 180 lbs. (1) ·Crusher: 18-inch Gyratory at 3/J.." HSA setting (2) Feed: · lbs . (a). Pri111ary 108 (b) Secondary 2 155 29 29!. (3) Product: (a) lbs 78 :66* 50 29C. (.b) Percent .26.5 56.5 17.0 100.0 * St.•ckpile: 166 tbs d. Rodmill·Sand (1) Rodmill: 18-'inch l&x42-inch Drum (2) Feed: lbs (a) Primary 4S 21 (b) Se1=ondary 74 27 (c) Ternary 78 .so 29S · (3) Product: (a) lbs 203 203 (b) Percer.t 100.0 100.0 (4) Loss: (a) lbs 92 (b) Percent )1.2 NPDL~-GS-L (R2-C-118) SUR..IF.CT: Mahoney Lake Hydro 02 Mar 8:.! Nomimil Size Plus 3" 3"-l~" 1\s"-3/l." 3/t.''-~o. l. .Fines Total e. !:!~ (1) lbs (:.!) Percent (3) Total Processing Loss, Percent 3. A~~regate Tests-Processed quarry Stone: 250 31.3 180 22.5 166 20.8 . Nominal Size .,..-,IT"""""----:l'"'"!l'""" .... -""3""14""" 3/4 .. -';i. 0. l. a. Gradation 3"-IJi" % Size Pas!i ·specs I.-inch 100 100 3-incl. 98 90-100 2 1~-inch 68 2-inch 37 20-55 1'~-inch 8 0-10 l-inch 2 0-5 3/.<-inch 1/2-inch 3/8-inch No. 4 No. 8 No. 16 No. 30 t;u. 50 No. 100 F.l'i. b. Specific Gravity, BSSD 2.74 c. Absorption, % 0.5 d. kos Anseles Abrasion ~~ loss ~ 100 rev. ,. loss @ 500 rev. J. e. Flat & Elonc.ated Particles f. -f flat by weight '· Elongated by weight Total Soundness of Coarse A~~rP~~te bv Accelerated Frer.:zc-Tha\0 --;.-fos7 .;.;bc::y..;..w_c_ig....,·h-t--,-C•--=3-=-oo· ,·yc l cs 33.0 2.0 35.0 0.4 (2) % % 100 100 90 90-100 28 20-45 100 6 G-10 97 2 62 1 o-s 33 .4 2.74 0.7 3.6 16.1 9.0 1.0 10.0 100 90-100 20-45 o-s 2. 73 1.0 7.0 0.0 7.0 203 2 5. 4 799 l 00.0 10.3 Sand ~ A 1 t. :;.:l l : 100 96 81 62 41 20 7 2.93 100 95-100 80-95 55-75 30-60 12-30 l 2-10 1 2.40-3.10 2.73 1.1 .. NPDEN..CS-L (8~..:.C~l18) OZ Mar 8-2 . MAHONEY. LAKE HYDRO DAHSITE TABLE II Summary of Tests on Cores Prilled from Damsite Quarry Stone· ' ·~ : Tests !I 2 Cores Drilled Normal t~ Cleav.J!.&~ Plane .· Spl~tting . : Stt:ength~ .. TenSile Compressive Modulus of Poisson's Core . (Br,.ztl~an). Strength, Strength~ . Elas!.~city, Ratio No. .... J!Si .. J!ai. J!Si Ex10 J!si .. A-:1·· · 4S~~-47,810* 9.19 0.161 A-2· · 377~· 25,900 7.83 0.162 A.;3 .. ~580 A-4 3860· 8-'-1 .2345 26,700 7.43 0.163 B-2 1625 19,640 J-'3 . 1050 1155 'F-1 480 G-1 2610 G-2 2745 J-1 285 61,500 8.79 0.'144 J-2 65 X-1 2255' K-2 3225 Q-1 360 Average 2625 490 36.310 8.31 0.158 ·.High 4895 1155 61,500 9.19 0.163 Law 480 65 19,640 7.43 0.144 Std. Dev. 1290 415 17,640 0.82 0.009 Cores .Drilled Parallel to Cleavage Plane** C-1 1905 '}_/ c-~ 28,960 11.44 0.204 C-3 35,330 12.82 0.297 C-4 11,050 D-1 1745 1>-2 1120 . 12,460 10.22 0. 326 D-3 1110 980 E-1 3955* 1475 £-2 3305• 1620 £-3 35,170 10.38 0~189 H-1 610 o-1 . 2465 S-1 D95 - S-2 1430 Average 2125 1285 24,590 11.22 0.254 High . 3955 1745 35.330 12.82 0. 326 Lev 1120 610 11,050. 10.22 0.189 ·Std. Dev. 1135 475 12,010 1.20 0.068 DEPARTMENT OF THE ARMY wRo L•b· No. _s,...2"-'/3111.i0~f..._J ---- MISSOURI RIVER OIVIS10N, CORPS OF ENGINEERS DIVISION LABORATORY 16 FEB 1982 ~AHA, NEBRASKA 68102 Sybject: __ ~P~e~t=r~o~g~r~a~p~h~i~c~E~x~am~i~n=a~t~i~on~· ~o~f~Q=u=a~r~£Y~S~t~o~n~e~--------------~------------- .Report Series No. 8 · Project: Mahoney Lake Hydro Intended use: Concrete Aggregate Source of Material: Mahoney Lake Hydro Damsite QuarE¥, Alaska Submitted by: Director, North Pacific Division Laboratory Date Samp1ed: , Date Received:~1~4~J~an~~8~2~--------------- He t hod of ln t ·or Spec Hi cation: _...;C;.;;RD.;;;;..-...:C;.....;;l;.;;2;.;,7.;....-...:6..;.7 _______________ ~------ R e. f e r e n c e 5 : --.!.N:.::o:.:r...:t:.:.;h:...' ..:.P.::a:.::c.;!:i.:.f.:.i.:::.c-'D:::..:..i V.:..J.:.:. s~J.:.:. o~n:.:....:L::::a::b::.:o:::.:r~a::..;t:::.:o:::.:r .... y~R~e::.::g~u::.::e::.::s:.:t:;.....:.;N::.::o;.:.--=:E:.:8:.:5:.:8.:2.:.9.:.5.:.0...:4_d;:;.a=t c;:;.;d=------ 12 November 1981 and NPDL W/0 82-C-118. SAMPLE IDENTIF1CATION · MRD Lab No. 82/30H. Sample of quarry stone for use as concr&te aggregate taken from Mahoney Lake Hydro Quarry, Alaska. TEST RESULTS 1. Petorgraphic examination of the quarry stone reveals it to be a dark gray, fine-grained quartzo-feldspathic gneiss probably derived from a sandstone. The rock has a fairly well developed foliated structure in which quartz grains and lenses tend to have augen shapes. The feldspar, mostly orthoclase, is abundant in the rock and is generally finely crystalline. It is closely associa~ed with tremolite having a lineated trend. A small amount of chlorite is also present. Finely crystalline magnetite occurs in the lines of schistosity. A considerable amount of pyrite is distributed throughout the r·ock as small crystal masses. The rock is fresh and hard, and appears to be durable. However because of oxidation of pyrite, the outer surfaces.are ~tained with brown iron oxide, especially along joint surfaces. The pyrite upon alteration to iron oxide may have a detrimental effect on concrete by producing stained surfaces and possibly cause sulfate expansion. Particle s~pe may be a problem with this rock due to the closely spaced joint system. Director, MRD Laboratory :~ ~g'l•• I l 5 EDITIOfl OF FEB 67 IS 08SOL£TE. tcb NPDEN-GS-L (82-C~ll8) 02 ~ar 82 TABLE II MAHONEY LAKE HYDRO-Summary of Tests on Cores ·Drilled from Dam~ite Quarry Stone NOTES: 11 Laboratory .. Te!:jt ·Methods:· a. : .RTH .113-80, ''Standard Method of Test for Determining the Splitting ~~re~gth 9f. 'Rock~' (~t~zilian Methoa) ,., . . . . . . - ·b. :RT:H. ni-80~ .)'I:)it;e~t .·Tensile .·strength of Intact Rock Core Specimans" . (ASTM .D2.936,-78) · . . . . . . ~ . -· -: . . . . . . c. · RTH.lll~So·, .''.'Unc:onfined Compressive Strength of Intact Rock Core Spe~inums" (ASTH D2936-78) · d~ RTII. 201'.:,.80, "Elastic Moduli of Rock. Core Specimans in Uniaxial Co~pression" (ASTHD3148-79) 11 All tests on n~i~al· 1~-inch diameter cores except as noted. 3/ Failureoccurred through epoxy at end of core speciman, test result not incl~ded in.computation of average and standard deviation. * Test made on nominal 1 3/4-inch diameter core. ** Kevis~d 02 March 1982. (:!) tp.o z w u Q: w 0. ilfLO 0 z ~ :I u +o.o l- l9 z w J -0.0 . .. ~ /~ ,..- I~ l \ I I I f - .. - .a ~ .~ - I ! AGE. DAr.:. I I 1828 ' . • •• !1 ': • l l828A I I I ! • C.:::JME:!INATION High Alkali Cement Low Alkali Cement I I l lkl'.lhh"·~----~--------------------------- 1 t c;F' MAHONEY LAKE HYDRO I ! 111 c.,-,-::,-,--A-l"".;sk:a·-----------------11 Laboratory manufactured sand from Damsit Quarry stone, Damsite Quarry, Alaska. t ! - - APPENDIXF HYDROLOGY INFORMATION HDR ENGINEERING HYDROLOGY INFORMATION AVERAGE DAILY FLOWS 1921 I 7S 71 53 39 29 22 17 14 92 106 53 39 79 .S. 3S 23 17 13 12 IS 51 43 C!O 58 58 58 58 58 58 58 58 2171:!111753%71$1110 918 7 7 7 6 6 6 6 72525252$252525252$2525 3 16 I I 13 14 13 13 II 9 7 6 6 6 7 6 6 6 6 $ $ $ $ $ $ $ 6 39 43 25 II :II 4 62 59 50 rT eo 21 17 14 IS 17 %1 26 20 16 13 11917667111010917667 $ II 24 21 16 14 42 61 $2 91 56 :16 23 17 13 II 16 16 us 16 16 16 16 149 149 149 149 149 149 6 6$ 39 24 24 17 17 13 9 9 • 7 6 6 $ $ 4 4 4 ' 3 ' • 3 4 4 4 9 1 6 8 ro 7 II II 10 10 9 I 7 7 7 8 12 38 33 20 U 13 12 12 13 17 23 22 17 14 14 13 12 II 10 9 I II 13 14 U 1$ 21 %1 21 17 IS II 22 26 31 53 Q 10 13 10 113 3S 49 9$ .. 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211 46 46 9t 143 99 • 3S 46 rT 37 46 68 46 41 3S 33 3S 76 1113 106 1113 9 12S 142 143 101 ... 71 10 80 • 17 74 114 104 ... 10 5852$$64107271686$10766$5115032 10 $9 113 58 C!O 113 113 67 67 67 67 72 69 61 .s. 48 «<rt37:163S37373S36«146505048393S II 29 3$ 42 «< 32 211 34 36 31 31 :n 2S 26 23 22 22 21 20 20 19 I& 34 53 37 24 21 20 19 16 16 64 12 63 48 3S 43 34 28 24 46 77 64 45 31 23 18 IS 13 u 29 30 47 13$ 148 4%7 261 139 91 49 34 $9 74 1923 47 29 21 I$ 21 142 1615 88 $1 33 22 17 13 10 9 7 1 6 • 23 ... 215 18$ !116 13$ 162 63 36 93 ., 34 2 34 24 52 41 141 " 46 36 24 19 19 " 113 59 13 77 53 .... 42 10 208 93 80 129 Ill 17S 171 61 41 53 3 'Z7 II 9 7 6 $ 4 4 3 3 3 3 3 3 3 2 2 3 72161:5061311112 9 7 6 s j 4 7 6 s 710 ti0101623232120::D21 19 16 12 Ill 9 9 I 7 7 7 6 7 6 6 6 6 5 7 6 7 9 10 IS 19 11 14 12 9 I I 16 19 21 II 16 14 16 19 30 3S 45 37 142 248 122 6 53 61 23 21 16 IS 13 11 II 9 I 7 7 6 I 7 6 34 $2 30 25 2S 31 29 3$ .fO 53 43 32 %7 24 7 22 21 19 II 16 IS 12 II II 10 II 'Z7 5I 92 192 I. 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4 $ 13 II ~ n n 11 .., " :!II ~ 22 21 :13 3 21 H c I 52 60 49 31 4$ ~ 83 163 91 47 » 21 J4 44 60 $2 31 211 21 :13 19 :II 21 29 47 4$ 44 S4 91 86 11 9 64 49 '' 61 63 ss 51 41 46 o 46 57 134 1116 1n 124 62 rt 52 J9 71 64 '18 92 74 47 33 33 :rt :rt 10 41 :!II 32 31 29 26 2$ 26 2IJ 33 39 41 4$ 41 39 :18 42 33 3D 34 21 26 24 ll) 17 16 16 19 19 17 17 II 18 18 l5 47 26 19 U 13 12 II 10 10 12 14 13 12 II 10 9 16 36 22 I$ II 10 10 9 9 8 1 7 12 6 1 226 9S 33 II 16 13 10 I 7 6 S 5 4 4 4 :II 4S 99 100 :Ill 211 17 II 10 9 21 «< 22 1M above tloiG QTe lhe avemge d.aily jlow6 for lhe given MGUr Yfi4T· 1M WIOflllu QTe Nmlbend illlhe /M left colwrut (ltlllii41'Y u 1, Febf111Jry l.r 2, etc.) and lhe jfowt1 for «M::t day Mlilltilllhat IIUHith wrap around ro lhe follo!Wig line. 6 U.S. ARMY CORPS OF ENGINEERS HYDROLOGY INFORMATION FROM 1983 DRAFT INTERIM FEASIBILITY REPORT AND ENVIRONMENTAL IMPACT STATEMENT APPENDIX A HYDROUXlY Table of Content~ . GENERAL Basin Description Streamflows CLIMATE Temperature Prec i pit at·; on Snow Wind Storms Ice and Frost Snows 1 ides STREAMFLOW RECORDS Extension of Streamflow Record Sedimentation and Water Quality Evapotranspiration FLOOD CHARACTERISTICS Snowmelt Floods Rain Floods Past Floods Probable Maximum Flood Area Capacity Low Flow Frequency Tables A-1 Monthly Streamflow Distribution A-2 Stream Gaging Stations as Percent A-3 Mahoney Creek Correlation with Fish Creek A-4 Average Monthly Precipitation and Runoff, Mahoney Lakes Basin of Annual A-5 Percent·age of Tot a 1 Month 1 y Runoff At tri butab 1 e to Upper and Lower Basins A-n Evaporation Losses A-7 Maximum Instantaneous Recorded Discharges A-8 Annual Maximum Instantaneous Recorded Discharges at Mahoney Creek A-9 Mahoney Creek Flood Frequency A-ll Rainfall Distribution of the Probable Maximum Storm . Page A-1 A-1 A-4 A-4 A-4 A-5 A-8 A-10 A-10 A-10 A-11 A-11 A-11 A-17 A-17 A-19 A-19 A-19 A-19 A-21 A-25 A-25 A-4 A-12 A-15 A-16 A-17 A-19 A-20 A-21 A-22 A-24 Figures A-1 Ketchikan Area. A-2 A-2 Percentage of basin area below an elevation A-3 A-3 Climatologic a 1 data for the. City of Ketchikan A-6 and the Beaver Falls power plant . A-4 Precipit~tion vs. elevation relationship between A-7 . Juneau {sea leve 1) and Mt. .Juneau { 3, 400 feet)' with Mahoney basin•s elevations superimposed A-5 Drainage area elevation vs~ unit ru~off A-9 . . A-13 A-6 Gaged aAd synthesized streamflow .at Mahoney Creek A-7 Corre 1 at iori analysis -·-M~honey Creek vs. Fish Creek A-14 A-8 Monthly Distribution of annua 1 flow from Upper Mahoney and.Mahoney Lakes A-18 A-9 Peak discharge .frequency at Mahoney Creek A-22 A-10 Su~nary hydrograph of. the Mahoney Lakes basin A-23 A-ll Probable maximum flood hydrograph for the Upper. A-26 . f4ahoney basin A-12 Inflow and outflow hydrographs for the standard A-27 ·project flood A-13 Relationship of peak discharge and pool surcharge A-28 to spillway width for a normal maximum pool elevation of 1,980 feet A-14 Storage vs. discharge· for weirs on Upper. Mahoney Lake A-29 A-15 Area capacity curve for Upper Mahoney Lake reservoir A-30 A-16 Upper Mahoney Lake A-31 A-17 Low flow frequency curve for the Mahoney Lakes basin A-32 A-ii GENERAL Basin Description APPENDIX A HYDROLOGY lhe project area lies within the region of ma~itime· influence of south~astern Alaska and is in the path of. most cy'c·lonic storms that cross the Gulf of Alaska. Consequently, the.·ar:ea receives· little sunshine, generally moderate temperatures,. p.nd abundant precipitation. ·The rugged· terrain exerts a fundamental influence upon local temperatures and the distribution of preci~itati~n, creating considerable variations in both weather elements within ~elatively short distan~es. 'The are~ is subject to frequent. winter storms of varied precipitation intensifies, with rare occurrences of. ha i 1· an(! thunderstorm.s.. The Mahoney Lakes project area is shown on th~ location ~ap of Fig~re:A-1. · · · The Mahoney Lakes d~ainage basin is located appro~imately 6 air miles northeast of :Ketchikan and 5 miles north of the Beaver Falls powerhouse on George Inlet. The Upper Mahoney basin varies in elevation from 1,950 to 3,350 feet above mean sea level (MSL) with an average elevation of 2,350 feet above MSL (Figure A-2). The Upper Mahoney basin is the watershed area above the-outlet of the upper lak~. This watershed is 2.1 squire mil~s. The Upper t-1ahoney Creek basin is the ·watershed be 1 ow the out 1 et of the upper lak€, but above·the inlet to the lower lake. Runoff.from this 0.5-square-mile watershed enters the creek channel and delta directly and th~n flows into Mahoney Lake. Average Upper Mahoney Creek basin elevation is 1,350 feet above MSL. (In ~orne publi~ations Upper Mahoney Creek ·may be referred to as Falls.Creek.) The Mahoney Lake drainage basin, above the lower creek inlet, is 3.1 square miles. Th~ entire Mahoney Lak~s drainage basin is 5.7 square miles with an average elevation of 1,130 feet above MSL. The nearest climatological station with the most similar meteorological conditions to those of the project area is located at the Beaver Falls (Figure A-1) power plant east of Ketchikan. Much is known about the Beaver Falls basin, so that this basin is often used in comparison with the lesser known Mahoney Lakes basin. The Beaver Falls basin shares a common divide with Mahoney basin and appears to contain similar topography, geologic features, and exposure. However, the higher elevation of the Upper Mahoney basin would indicate that the climate in.that area would. have higher total precipitation, less temperature extr~mes, and higher total snowfall than th~ B~av~r Falls basin. Nopermanent snowpack exists in the drainage areas, although considerable snow is received during the winter months. Although the climatic data from Beaver Falls are fairly representative of sea level conditions near the project area, lower temperatures and qreater precipitation amounts will occur over the higher Upper Mahoney basin. I KETCHIKAN AREA A CLIMATOlOGICAL STATION FIGURE 0 5 RIVERS AND HARBORS IN AU.S«A A-1 e GAGING STATION SOUTHEAST HYDROELECTRIC POWEll! IHTERI .. SCALE lN MILES 10 20 . 30 40 50 60 70 80 90 100 Percentage of basin area below elevation Figure A-2. Percentage of basin area below an elevation Streamfl ows Runoff characteristics of streams in southeastern Alaska.are.representative of the maritime influence. This influence greatly increases the runoff per square mile and al.so changes ·the timing o.f .high 'floOd flows from those experienced in central or interior Alaska. W,hile flood peaks occur in May· and June due to snowmelt runoff, the.yearly maximum peaks ·generally center around October. Normally~. about 75 perc~nt of the annua 1 runoff occurs during the 7-montt: period f.r.om May through NQvember. ·Within the study basins there is very.·:little.soil ·ove'r the underly'irig.rock; hence, the· fac i 1 it·ies for ground water stor-age are. exceedingly limited and the major components of runoff are mainly··surface· flow <:oupled with some subsurface or interflow. Therefore,.shortdry sp-ells.have the effect of generating extremely low streamflow. Streamflow distributions for the period of record at five stream ga~ing stations in the area are given below. ==== Tab1eA-1 Monthly Streamflow D~stribution as Percent of Annual Grace Fish Beaver Mahoney Cr.eek . Creek Falls Creek Month (%) {%) (%) (%) Oct 14.1 14.2 13.6' 13.9 Nov 10.4 ll. 4 11.6 10.5 Dec 7.7 7.9 1.9 6.7 Jan 6.2 6.7 5.5 4.9 F-=b 4.7 5.4 4.9 4.0 Mar 4.7 4.9 4.6 3.6 Apr 6.5 6.8 5.9 5.2 t~ay 12.2 10.4 12.0 11.0 Jun 10.9 10.0 11.4 12 .. 3 Jul 7.9 7.1 8. 1 10.4 Aug 7.2 6.8 6.0 8.5 Sep 7.5 8.4 8.5 9.0 Total 100.0 ' 100.0 100.0 100.0 *=="'=--=-:-:~ CLIMATE Temperature Temperature records are not available for the Upper Mahoney basin or the Mahoney Lake basin; however, records maintained at Beaver Falls may be considered representative of those encountered at the lower elevations of the Mahoney Lake basin. Temperature variations, both daily and seasonal, are usually confined to relatively narrow limits as a result of the dominant maritime influences. Although var.iations between maximum and minimum temperatures may.vary as much as 40°F during clear periods, the differences between norma 1 daily maximum and norma 1 daily minimum A-4 temperatures range from as little as goF in December to around l6°F in June. Seasonal variations range from a monthly normal temperature of 35°F in January to 58°f in July for th~ Mahoney l,.ak~ basin. · Extremes of record CQVer a range· from the maximum 88°F' in June to the minimum Of l°F in . January. Extreme maximum readings above 80°F have occurred in May through August •. Low temperature extremes of around 0°F have occurred in both January and December. During. periods ·of calm ·or 1 ight winds, local temperature variations· are frequeotly·very·prooounced. Variations in local radi-atii.Jn and air drainage produ.ce wide differences in temperatures, particularly between u~l~nd o~ sloping areas and the flat, low terrain, which is greatly affected .by a.i.r drainage from high elevations. Precipitation :Records of·attua1 precipitation measurements at the proposed site are non- existent. The.S.7-square-mile drainage basin above the discharge gage located ·.on Mahoney Creek produces an average annual flow of 104 cubic feet per second {cfs). Not considering infiltration, evapotranspiration~ or interception, this average annual runoff equates to an average annual precipitation over.the entire basin of at least 248 inches. Rainfall ·records for B~aver.Falls indicate an average annual precipitation of 149 inches for the period of record. The Beaver Falls gage is located in the same area, but near sea level. Tne high elevation of the Mahoney Lakes basin and orographic effects have a marked influence on the precipitation in that local area. Also, because the 248 inches per year represents an avera.ge cohdition, it is apparent that the Upper Mahoney basin receives considerably greater amounts of precipitation. for instance, if the lower Mahoney basin is assumed to receive the 149 inches characteristic of Beaver Falls, the 2. l~square-mile area of the Upper Mahoney basin would have to receiye precipitation amounts in excess of 450 inches per year. Obviously this is a gross approximation; however, the implications are valid. June through August marks the period of lightest precipitation, with monthly averages at the Beaver Falls station ranging from about 2 to 11 inches. After August, monthly amounts increase until a peak of 32 inches is reached in October. Monthly averages then tend to decline from November to July. The heaviest storm precipitation amounts in the southern coastal areas are the result of fall and winter storms. A summary of clim~tological data from Beaver Falls is given in Figure A-3. "Mountain versus Sea Level Rainfall Measurements During Storms at Juneau, Alaska," by Murphy and Schamach, (1965 Western Snow Conference) a precipitation variation with elevation study, specifically shows the elevation precipitation relationship between Juneau (sea level) and Mt. Juneau (3,400 feet) (Figur€ A-4). Although this study was in the Juneau area, the relationship is believed to approximate the relationship between the Beaver Falls precipitation gage and precipitation in the Upper Mahoney basin. Figure A-4 indicates that a basin with an average elevation of 2,350 feet (Upper Mahoney) would have 2.3 times the precipitation experienced at sea level (Beaver Falls) and a basin with an average elevation of 1,350 feet {Upper Mahoney Creek) would have 1.75 times that of Be!!ver Falls. Based on· this factor and the ~verage annual precipitation of 149.3 inches at Beaver Falls, it would be apparent that 343 inches of average annual precipitation A-5 CLIMATOLOMICAL nATA MEAN MONTHLY PRECIPITATION INCHES STATION JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV OEC ANNUAL Beaver Falls 13.63 12.56 10.71 8.29 7.52 6.17 5.98 9.93 15.88 23.77 16.77 16.15 147.4 Ketchikan 15.06 12.74 12. 15 12.88 8.62 7.20 8.48 11.27 15·.29 24.77 17.63 16.18 162.3 MEAN MONTHLY T H1 PERATURE -F : Beaver Falls 32.5 35. 1 37.8 41.9 50.6 57.0 59.4 59.2 54.2.·. 41.0 37 .. 8 33 ·. 7 45.4 Ketchikan 35.1 36.2 38.7 43.6 50.1 55.2 58.2 58.9 54.6 47.3 40.9 36.7 46.3 J:>o I "' SUMMARY OF CLIMATOLOGICAL RECORDS Average Ground Tem[!erature {Degrees F. ) Annual Average Eleva-Years Prec1pi-Annual tion of Maxi-Mini-Mean Mean Mean tation · Snowfall STATION (Feet) Record mum mum ·Janu~ July Annual (Inches} (Inches} --·- Beaver Fa 11 s 35 24 88 1 35.0 58.4 45.4 147.4 . 97.3 Ketchikan 90 64 96 -8 35. 1 58.2 46.3 162.3 32.9 Figure A-3. Climatological data for the City of Ketchikan and the Beaver Falls power plant 4.0 -3.0 ..., QJ QJ '+- 0 0 0 ....... -c 0 ...... 4..> ~ 2.0 .QJ r- LLJ f -1---1 . , -L I' "T--H-It-. v. ::r-~ .JJ :fl:-1--i-t Aver.Jge Elevation Upper I ' • Mahoney Basin ' -i - -l - -r I I ; I I I I I. 1.0 ~~-· ' · Average Elevation Lower Mahoney Basfn ' I , ..!.....L.l ~ 0 , '.I ,. 1 1.5 2.0 2.5 3.0 3.5 4~0 Ratio of 24-hour precipitation at sea level to precipitation at higher elevations Figure A-4. Precipitation vs. elevation relationship between Juneau (sea level) and Mt. Juneau (3,400 feet) with Mahoney basin's elevations· superimposed 1'. 7 fa 11 on the Upper Mahoney basin and 261 inches on the Upper Mahoney Creek basin. In compiling the elevation runoff relationship {Figure A-5), gaged streams in two different locations {southern and east side of Revillagigedo Island) were analyzed to determine unit runoff as a function of basin mean elevation. As shown, the bas1n on the·east side of .Revillagigedo Island {Lake Grace) had less unit runoff per square.mile than the basins near Upper Mahoney on the southern tip of the. island. If a line through the average elevations of the gaged basins: on the southern tip of Revillagigedo Island is extended beyond the three known points out to·the average elevation of Upper Mahoney. {2,350 feet·), an average unit runoff of 16,300 acre-feet per square·mile per year {48 cfs/year or 310 inches/year) is apparent. The difference of 33 inches between the average runoff and average precipiation could be att~ibuted t6 evapotranspiration. Conservatively, then, it .can .be assumed that while the Upper Mahoney basin represents an area only 36 percent of the entire Mahoney lakes basin, 43.8 percent of the averageannual runoff com.es from the upper basin. This results in an average annual runoff of 48 cfs for the upper basin. Applying the same procedures to the Upper Mahoney Creek basin, an average unit runoff of 11,450 acre-feet per square mile per year (8 cfs/year or 215 inches/year) is derived. An analysis of 3 years of comparable streamflow data (October 1977 - September 1980) for the Mahoney Lakes basins indicates that original assumptions concerning the precipitation/flow relationship between the two are essentially correct. The observed m.ean annual discharge for the short period of record at the Upper Mahoney Lake outlet is 40 .cfs (estimated at 48 cfs when no data were available) and, at the lower lake for the same neri8d, 83 cfs. Although the observed di~charges are lower than estimated, the upper basin contributes 43 percent of the discharge for the entire basin as predicted. ·The lower flows can be attributed to the fact that for 2 of the 3 years of record, the annual precipitation recorded at Beaver Falls was 23 inches lower than the 23-year average of 149 inches/year. For the other year it exceeded the average by only 14 inches. Snow Snowfall reco1·ds are not available in the immediate vicinity of the study area; however, snowfall characteristics for the area can be described through a study of the Beaver Falls records. A trace of snow falls as early as October at Beaver Falls, although the first snowfall usually occurs in the latter part of October. On the average~ there is very little accumulation on the ground at low levels until the last of November, although at higher levels and particularly on mountain tops, a cover is usually established in early October. Snow accumulation usually reaches its greatest depth during the first of March. November, December, January, and February have the heaviest snowfall, although individual storms may produce heavy falls as late as the first half of May. Snow cover is usually gone before the middle of May, except at higher elevations. During some winters, when temperatures are above normal, there is a great deal of thawing, which causes slush tnat later freezes. There are occasional intervals of rain that freeze into glare ice on contact with the ground or structures. A-8 ;!> I 1.0 3,SOCr-----------------~--~------------~----------------------------~----~ Legend C) Beaver Falls Creek A Ketchikan Creek * Mahoney Creek • Falls Creek -3,000 .jo) cu ClJ 'f.. -c 0 ,,_. .4-) "' > ClJ ...-cu "' cu s.. "' cu 0'1 "' c .,_. "' s.. "<;:J c "' ~ "0 ClJ .4-) .c tJ) .... cu :z 2,500 2,000 1,500 1,000 500 D Grace Creek * · E1la Creek 0 Manzanata Creek e Fish Creek I . -Weighted mean elevation for. Upper Mahoney Creek bas in . ·. · ·· · ·· -.. , --. Unit runoff= 11,450_acre feet/mt 2/yr . :.::.i .. ; ~-F :. · . ' ... ' ·. . . I.' -l ! . -.- • I • ' • • • · · ~ r t · 1 East Side Revillagigedo Island-~===-~:~=:.::.~: ____ _ I.----~--'-· ----... ; ·'---····---·-t-----i-t-'-·~.--'----~..__,.,.. •• ---. l---... Southern Tip ReVillagigedo Island . ,, ·-+~ ... . +"L I ' ---·· ·~--~ ;:·; . . -. J..-~c;_, . . --. ~ -. --: ~ :· 1 • · 1 •• =+.t.~ .. , · Heighted mean elevation ·--·-· • • · ·' 1 above Upper Mahoney Lake --~·.-.:. --:·.T~:·:-.. ..:. -·-::. 1 Unit runoff = 16,300 acre feet/mi2/yr ····~-~:~.~:=;~1-~~~;--~••':_:-~~~~-O<A.·~-~-·~~ --~~-~~-:.~~ ~~·~ ~.~-·~.~~--. ••:•• ~--· -~~.~~:::-:--=--~=~-., ~- ' . .. --. -. -• • . 1-: .. • ·'-' -. .. L •. : . ' -~ . . ----,------·-·-. 0 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 15,000 Unit runoff, acre feet/mi2/yr · 16,000' 17,000 Figure A-5. Drainage area elevation vs. unit runoff · Wind Wind records are available from the National Weather Servi~e Station at Ketchikan. Observations· indicate that the highest w.inds occur from September through March. In the Ketchikan area, the. high winds (greater than 50 knots) ordinarily blow from the southeast up Tongass Narrows. These winds are caused by the shorev.rard movement of maritime air. Speeds of 50 to 60 knots are possible, but extreme gusts are rare. Surface winds in the southeastern regions of Alaska vary greatly in direction and force. because of the varyiflg exposures and the highly irregular configuration of the coasts and mountains.· The winds tend to follow the contours of the terrain and, thus, adjacent areas.can have average winds of opposite di;·ection. High velocity winds probably occur in the area· being studied. Abnve 2,000 feet MSL, high speed wind flows may occur from almost any direction, but the greatest prevalence se-ems to be from a southeasterly qoacrant. Direct observations of peak winds near 2,000 feet above MSL were maae in the Juneau area during construction of the Snettisham project, where wind speeds in excess of 200 mph were observed. Additional calculations would be required to determine maximum wind velocity and direction r~lative to the location of a transmission system serving a selected hydropower site. However, for preliminary design, winds in excess of 100 mph should be considered. Storms Because of the dominating maritime influence, thunder and hail storms rarely occur in the study area; however, the area is subject to heavy autumn and winter storms. These storms are cyclonic in nature and are generated by the stmipermanent, Aleutian low pressure system. This cyclogenesis takes place as a result of the cold flow of southeasterly air from Asia, which generates a wave or series of waves on the polar front. These storms move eastward fro111 their point of origin into the Gulf of Alaska, where they cause high winds and low ceilings for 2 to 3 days. Storms of this nature usually c~use copious amounts of precipitation on the coastal mountain ranges. i.ce and Frost Icing Icing is rarely significant in the first few hundred feet of elevation; ~ccumulations of over a few tenths of an inch are considered rare. From 1.000 feet above MSL and upward, both the incidence and accumulation of ice increase rapidly. A 6-to 8-inch accumulation of ice on the windward side of objects probably occurs above 3,000 feet MSL. Moreover, the frequency of accumulations of an inch or more of ice probably increases to as much as t~ice a week during some intervals from late fall to early spring. F.·ost Frost penetration in the Ketchikan area wi 11 vary significantly from one site to another, dependent on such things as the nature of the soil, its water content, recent geology, and proximity to continental and maritime A-10 influence~. In ~eneral, there is little-evid~nce of frost penet~ation of · over 1 foot in the first 200 feet above:M$L. The Environmental .Atlas of Alaska indicates no· permafrost near sea· level in Southeast Alaska •. Snowslides In the higher elevations of the study area, po.rt ions of the terrain .are devoid uf snow cover for only short periods throughout the year. It has been·estimated that ·snow depths, as a result of:drlfting~ in excess of 20 feet may be reached ~t higher elevations. Snows of lhese magnitudes accumu- late on the precipitous. slopes of the drainage-basin· and at high elevations above the transmi ss·ion lirie route until ·enou·gh weight is accumulated to overcome ·the ·she.ar: friction in the snow. At th·is time" ·the.snow begins to move .. causing ari: avalanche~ . These avalanches occur with great regularity at specific. p-laces: in the local area and are apt to occur at any susceptible location. -The sriowsl ide~ denude the land of trees and loose surface materi)l a~d are capable_of de~troying any structure not able to resist their tremendous force •. Winds created by displaced air move with blast velocity and·a~e iapable of destroying buildings because of the rapid change in differential. pressures. with .respect to the inside and outside of a structure. ·special care was taken in prospective routing of the transmission line and placement of project features to avoid the avalanche threat. STREAMFLOW RECORDS Several potential hydropower sites in southeastern Alaska have attracted the interest of private and government development agencies since the early years of this century. This interest is specifically reflected in the rather high density of strea~ gaging stations in the ~icinity of Ketchikan and a ~ubstantial period of record for several of these stations. The U.S. Geological Survey (USGS) has published data for many of these stations and now actively monitors many other stations in the area. One or.more of these stations has been in operation each year since 1916. The period of record and the drainage area for Upper Mahoney and Mahoney Creeks are presented in Table A~2. Extension of Streamflow Record Stream discharge records are available throughout 1915 to date on one or .. mor.e of the six gaged streams shown in Table A-2. An annual histogram over the period of e~tended record for the entire Mahoney basin is provided in Figure A-6. A-ll table A-2 Stream Gagin~ Siations Ora·inage Area· Station (sg. ~iles) Grace Creek near Kztcbikan· 30.2. Manzanita Creek near Ketchikan 33.9 · Ella Creek near Ketch.ikan 19.7 Fish Creek near Ketchikan . 32.1 Mahoney Lake Outlet near Ketchikan 5.7 Upper Mahoney Lake Outlet 2.1 near Ketchikan Period of Record Oct. 1927 -Sep 1937 Aug l963.-1969 Oct 1927 -Oct 1937 Aug 1947 -1967 Oct 1927 -Sep 1938 Oct 1947 -Sep 1958 Jun 1915 -Oct 1935 Oct 1938 -Present Oct 1920 -Sep 1933 Oct 1947 -Sep 1958 Oct 1977 -Present Oct 1977 -Present Existing USGS streamflow records from the Fish Creek gaging station using linear regression correlation techniques were compared to determine the optimum equations for calculation of missing records for the Mahoney Creek gage near Ketchikan. Linear regression equations were prepared for Mahoney Creek on a monthly basis. Individual monthly streamflows were extended. using streamflow data for the corresponding stream with recorded data that had the highest correlation coefficient. Records from the Fish Creek gaging station, because of the long period of record and accurate monthly correlation, were utilized to extend the record at the Mahoney Creek gaging station. The specific monthly equations are presented in Table k-3 and are also shown in Figure A-7. A-12 ...¥. (]) "' .CIJ = s.. u >. (]) c 0 ..c II) :E +:I II) ~ 0 ..- 4- E II) CIJ s.. ~ +:I Ill 'U CIJ N .,... Ill .v ..c +:I c s... >. II) Ill CIJ >-'U ... c ., b II) ~ 'U (]) 01 "' ~ II) ;; C!l c t' ~ a '; 1.0 ~ "' .s I l c:( :;; CIJ • .., ~ !:: s.. ~ :::5 .. j 01 " !!!. "' -l i. ....... .,. • ~ ~ "' 'I " I .,. ~ ~ § ~ § li ri 0 ... (+ee,J.-a..t:.>~} .J..J.OUnJ A-13 Figure A-7. Correlation analysis --Mahoney Creek vs. Fish Creek Table A-3 Mahoney Creek Corre 1 at ion w·i·t·h ·F1 sh Creek Correlation · Mahonel Creek, Fish ·Creek (c;fs) Coefficient October Mahoney· creek flows·= 1-17 Fi~h Creek flows +4.01 0.83 November Mahoney Creek flows = 1&30 Fish Creek flows -0.73 0.90 December· Mahoney .Creek flows = 1.46 Fish Creek flows -3.43. 0.98 January Mahoney Creek flows ·= 1~33 Fish Creek flows -1.25 0.96 February · Mahol'}ey Creek f 1 ows = 1.29 Fish Creek flows . -1.10 0.96 March . Mahoney Creek flows =·1.30 Fish Creek flows -1.46 a. 91 Apri 1 Mahoney Creek .f 1 ows = 1.23 Fish CreeK flows -0.85 0.90 May Mahoney Creek flows = 1.20 Fish Creek flows +2.94 0.90 June Mahoney .creek flows = 1;14 Fish Creek flows +10.06 0.81 July Mahoney Creek flows = 1~47 Fish Creek flows -6.52 0.88 August Mahoney Creek flows = 1. 51 Fish Creek flows +4.85 0.91 September M~honey Creek flows = 1.28 Fish Creek flows +2.25 0.93 Because of 2 years.rif missing records at Fish Creek~ additional correlations with Ella Creek were necessary to complete the extended record. Since these correlations·.are of only minor significance, they are not included here. The elevation of the Upper Mahoney basin (average 2,350 feet) contributes to the abnormally high amount of precipitation that falls over the basin as well as the seasonal or monthly variance in runoff di~t~ibution. As shown in Table A-4, the winter precipitation generally exceeds the sunvner · precipitation. However, the winter precipitation in the Upper Mahoney basin is mostly snow, which accumulates durini the winter and melts from late spring through summer, contributing greatly to the high summer discharge reflected in the Mahoney Creek gaqing station records. A-15 Table A-4 ·Average Monthly Precipitation and Runoff, Mahoney ·Lakes Basin January February March April ··May June July August September October · November . December Annual Mahoney Creek.· Period of .Record Avg. Precip. (inches /month) 14.4 12.5 . 11.2 . 12.8 ·26. 5 . . 30. 2. 26.0 ·19. 8 22.8 34.4 28.7 20.5 259.8 Mahoney Lakes Basin Monthly Runoff (%) 6'. 7% . 4. 2 3.8 5.3 9.7 11.7 10.0 9.0 8.2 13.6 9.9 7.9 1oo.m, Seasonal runoff from the Upper Mahoney basin behaves considerably different than that which represents tne composite basin. This is primarily due to the orographic effects on precipitation and the seasonal difference in snowpack accumulation between the upper and lower basins. Therefore. while the lower basin tends to shed precipitation in relation to influx, the upper basin will accumulate winter precipitation~ which is then released into the lower basins as ablation occurs. Thus, the percentage of flow recorded at the lower Mahoney gage, which also represents the Upper Mahoney hasin contribution is variable throughout the year. In an effort to obtain realistic monthly distribution and average annual runoff from the Upper Mahoney nasin, records from the highest gaging station in Southeast Alaska, Long Lake (1,000 feet MSL), were compared to records from nearby Speel River, which is a sea level gage. Upper Mahoney and Long Lake are both located in areas of maritime influence and have hi~h, similar average basin elevations (2,350 feet for Upper Mahoney and 2,700.feet for Long Lake). Although Long Lake has glacial input, from November through April the monthly distribution of inflow may be similar to what could be expected from the snow covered, southerly Upper Mahoney basin. The monthly distribution in Table A-4 was applied to the appropriate month over the period of extended record from the Mahoney Creek gaging station. (For example, Upper Mahoney's February contribution over the period of extended record is estimated to be 22 percent of the flow at the lower· gage.) When the Long Lake monthly percentage flow distribution is compared with Speel River, monthly flow distributions for the Mahoney basins, as shown in Tdble A-5 and Figure A-8, resulted. A-16 Table A-5 . Percentage .of Total MonthJY.Runoff A~t·ributab·le to Upper .and Lower· Basins October November December January .February March . Apri 1 . May June July August September Average Annual From Upper Mahoney (%) 46% 30 . 28 25 . 22 24 30 40 55 65 60 55 43.8% 1 I Inc 1 udes Upper Mah:oney Creek basin. From· Lower Mahoney 1/ (%} - 54% 70 72 ·75 78 . 76 70 60 45 35 40 45 56.2% The effect of this-adjustment would be to gen~rally reduce the winter flows and increase suinrner flows in relation-to the distribution indicative of the m~asureo flow of the total basin. Sedimentation and Water Quality Although sediment and water quality data for the Mahoney Lakes basin .are not available, the drainage area characteristics of all the_potential sites indicate a very -low rate of sediment production. The upper area i-s predominately covered by muskeg and no glaciers or permanent. ice fields are in the area. Based upon the limited sediment data available for the area, the rate of sediment production for the drainage area is estimated to be about a. 1 acre- feet per square mile ~er year, or less. ·This cbrresponds to an annual sediment inflow to the Upper Mahoney reservoir of only 0.21 acre-feet per year, which is a negligible amount. ·There are_nci change·s to· sediment yield as an effect of possible future lan-d use. The area proposed-for the Mahoney Lakes project is void of any marketable timber. In view of· the low sedimen- tation rate and projected location of the power intake works· and dam, there are no anticipated sediment problems associated with Mahoney Lakes project features. Evapotranspiration The normal hign relative humidity, high percentage of overc.ast days, scarcity of trees in the upper basin, and relatively cool climate preclude anJ appreciable percentage of water loss from evapotranspiration. Estimates A-17 15 14 13 12 11 10 3: 0 ,.... 9 \!-. ,.... its :::l 8 c c 1'0 +-1 7 C. (I) u s.. € (I) 0.. 5 if JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Figure A-8. Monthly distribution of annual flow from Upper Mahoney and Mahoney Lakes A-18 of flow were bas·ed on records from existing or historical.gaging stations near the project areas. These records reflect any.past e·vaporation, and for these teasons, no corrections were made in the runoff ·analyses for evaporation.· The difference of 29 inches between the esti.mated average precipitation at Upper Mahoney and average rlinoff.from Upper Mahoney could be attributable to evapotranspiration. As·~hown in.Table A-6, ·~verage evaporation losses totaling 15.6 inchE;s were observed at the Juneau airport from May tl\rough September~ ·Th~s may be somewhat. indicative of evaporation losses that may occur in the project area. · June 3.31 3.65 ·July 3.85 ·Table A-6 Evaporation Losses l/ (inches} · August September · 3.37 1.40 _y Juneau airport, 1968-1978. FLOOD CHARACTERISTICS Snowmelt Floods Tot a 1 15.6 Tne vroposed project site has flood peaks in the early sum~er that are pr~dominate1y from snowmelt runoff. The magnitude of the spring·flood peaks is oependent upon three conditions: (l) the amount of accumulated snow, (2) the temperature sequence during spring melt, and {3) the amount of precipitation. A large snowpack over the basin will give a large volume of ru~off during the spring and summer; but, if the temperatures increase gradually, causing slower snowmelt, the flood peak will be just slightly abovE: normal. However, if the early spring is co 1 der than norma 1 and the temperatures rise rapidly for a prolonged period, the flood peak will probably be extremely high with the duration of flooding dependent upon the tot a 1 snowpack. Rain Floods Rain floods produce the highest flows, which usually occur in the fall between late August and October. The flood peaks .are quite sharp due to the fast runoff caused by the steepness of the terrain and. the low infiltration losses into tne underlying rock. Past Floods The maximum instantaneous recorded discharges from six gaging stations in the area are provided in Table A-7. A-19 Tab1e·A-7 Maximum Instantanepus. Recorded Discharges Watershed.Size Station Discharge Ccfs) (mi2) cfs/mi2 Date Grace Creek near 3,990 Ketchikan . 30.2 132.1 4 Sep 1966 Manzanita Creek 5,820 33.9 171.7 14 Oct 1961 near Ketchikan E 11 a· Creek near· l,-720. l9 ~·7 87.3 7 Dec 1930 Ketchikan Fish Creek near 5,400' 32.1 168.2 15 Oct 1961 Ketchikan Mahoney Creek 2,530 5.7 443.9 2 Feb 1954 near Ketchikan The annual maximum instantaneous recorded dishcarges over the period of record at the Mahoney Cre~k qaging station are provided in Table A-8 . . Tab 1e A-8 Annual Maximum Instantaneous Recorded Discharges at Mahoney Creek Annua 1 Peak Water Year Oischar9e (cfs) Date 1923 1,850 31 Aug 1923 lq28 762 12 Oct 1927 1929 1.460 21 Aug 1929 1930 1,920 8 Nov 1929 1931 2,400 2 Oct i930 1932 1,250 13 Oct 1931 1933 1,090 20 Sep 1933 1948 1,210 31 ·AUg 1948 1949 1,260 21 Sep 1949 1950 1,640 5 Sep 1950 1951 970 11 Jun 1951 1952 866 7 Oct 1951 1953 842 20 Oct 1952 19~4 2,530 2 Feb 1954 1955 1 ,640 6 Aug 1955 lq56 1,530 20 Oct 1955 1957 838 ·25 Dec 1956 1958 1,350 11 Apr 1958 A-20 ·Peak discharge frequency a·t the Mahoney Creek gage is shown. in Figure A-9. Because of the.sma.ll potential for heavy monetary loss .if flooding would occur, it is anticipated that a flood frequency of 10 Year·s .can· be used for design pr6tection during the construction period. The upper basin, using the September..contribution of 55. percent, would ·produce a peak flow of approximately 1,200 cfs~ ·A suiTITlary hydtograph of the Mahoney Lakes ·basin, which provides minimum,· maximum, and mean daily flows as well as maximum instantc.neou~ flow, is provided on Figu~e A-10. Probable Maximum Flood · Table A-9 · ·Mahoney Creek Flood frequency . . . " .. Return . . Interval (yea·rs) 2 5 10 20. 5.0 100 Flood ·. Magnitude · (cfs) 1,304 1,785 2,125 2,450 2,938 3, 311 The U.S. Weather Bureau Technical Paper No. 47 gives general values of the 24-hour probable maximum precipitation (PMP) for the Upper Mahoney basin as approximately 24 inches. Applying these data to the upper basin necessitates special ·consideration in view of the method used in calculating the PMP and the problems created by the limited high elevation observational data for Alaska. The location of the Upper Mahoney basin, lying in line wit~ the prevailing southeasterly storm patterns and coupled with the high e]evation of the basin, contributes to the high PMP used in thisstudy. The PMP used in deriving the maximum probable flood was obtained from the Hydrometeoro1ogical Branch, National Weather Service. The hourly distribution of accumulative and incremental rainfall and accumulative and incremental runoff is provided in Table ~A-10. A-21 VI \I- ):> u ' N c N .... ~ 0 ..... 1..1.. 6000 5000 4000 3000 2000 1000 900 800 700 600 500 400 300 200 Exceedence frequency per hundred years 98 95 90 80 70 60 50 20 10 5 2 1 0.1 0.01 ~---~----··j ___ j_:.l_l_j ___ l __ __l_j ____ L__ I . t'~ --- ··-,-1. Frequency Analysis is based on 18 years± _1 ____ L ____ -:.:-~: _ --of record (1923,1928-1933 and 1948-1958). '--~ . · -'--!~~- --2. Frequency Curve was computed using the Log --· ~ _____ _ ~--Pearson Type III Method... . .. _· ~--------+-......._.. • ' •· ' • : ' • • : • I ' ' ~ j : • ; -.' ' ' • • ~-:·----·"---:----~----~,;__ • ---+•4 ••• ------• ·----7 ----• -; -----------··· Figure A-9. Peak discharge frequency at !~a honey Creek -V' 11-u -cv C"' s.. ta ..c u VI .... Cl ........ . ...... Period of R~ord: 10/1/22 -11/31/27, 1/1/28 -11/31/47, 1/1/48-2/28/58 Ordinate values between 1200 and 2400 have been deleted. However, respective flows hive been shown in parenthesis. ....... , .. .... ....... JULY .IUL1' ••"1'•11··· Month Figure A-10. Summary hydrograph of the. Mahoney lakes basin .......... occr.w••• 0. l ·Table A.:l 0 · : . . Rainfall·IJi.stribution of the Probable Maximum· Storm Accumu 1 at·i ve .. · Inc rem€-nta 1 . Accumulative Incrementa 1 · Time Rai nfa 11 Rainfan · · .. Runoff Runoff (hrs) (inches). · ( indu~s) {inches) {inches) . 1 0.6 . 0.6 O.D 0.0 . 2 L3 . o. 7 ·. o. 2. . o. 2 3 2. 1 0.8. 1..0 . 0.8 ·4 3.0 0.9 1.9 0.9 5 3.9 0.~ 2~8 0.9 6 5. 0 1.1 3.9 Ll 7 6 •. ). l. 1 5.0 1.1 8 7.9 1.4 6.8 1. 8 9 9.'3 4.0 .8.2 1.4 10 13. 3 . 2. 5 12.2 4.0 11 .·15. 8 . 1.2 . 14.7 2.5 12 17.0 0.9 15.9 1.2 13 17.9 0.6 . 16.8 0.9 14 18.5 0.5 17.4 0.6 15 l 9. 0 0.5 17.9 0.5 16 19. 5 0.5 18.4 0.5 1 7 20.0 0.4 18.9 0.5 18 20.4 0.7 19.3 0.4 19 21.1 0.7 20.0 0.7 20 21.8 0.7 20.7 0.7 21 22.5 0.6 21.3 0.6 . 22 23. l 0.6 . 21.9 0.6 23 23. 7. 0.4 22.5· 0.6 24 24. 1 22.9 0.4 It was determined from Figure A-4 that 1~2 inches of precipitation would be lost through infiltration during the 24-hour probable maximum ·Storm. Following this intilt~ation loss, it was assumed that the soil would be saturated and, therefore, precipitation and direct runoff ~auld be equal. The c~nputing of hydrographs for ungaged basins is dependent on an estimate of the time of concentration (Tc --time of travel from the most distant point in the basin to the point rif interest of the ba~in). Time of concentration, base time, time to peak, and unit peak discharge for the Upper Mahoney basin are provided below. L = H = s = Tc = 2.2 mi = 11,616 feet {channel length) 1,400 ft (diff. el. headwater to site} H = 1400 ft = 0.1205 I 11616 ft L0.77 = 0.0013 (11.616)0.77 = 0.397 hr. 50.385 {0. 1205)0.385 A-24 A = 2.1 mi2 Q = 1.00 in. D = 0.5 hr. Base Time: Tb = 2.67 .Tp = 2.67 x 0.49 = 1.30 hr. Time to Peak:. Tp = ·¥ + 0~6 Tc· = ¥ + 0.6 x 0.397 · 0.49 hr.· Peak Discharge: Qp = 4¥4AQ = . 484 X 2.1 p 0.49 = · 2074 cfs. The 24-hour PMP was applied to the unit hydrograph, which results in a probable maximum flood of approximately 5,000 cfs (Figure A-11) •. Because the dam is designed to be overtopped, a standard project flood (SPF) of 2,500 cfswas used in lieu of the·probable maximum flood. As shown in Figure A-12, the SPF was routed th~ough the reservior using assumed weir lengths of 100, 150,. and 200.feet with peak outflows of 1,915, 2,075, and 2,100 cfs, respectively. As shown on the discharge-surcharge curve (Figure A-13), the ?urcharge resulting from the SPF at the spillway with weir lengths of 100, 150, and 200 f~et would be 3.25, 2.70, and 2.50 feet, respectively. The storage versus discharge curves for·weir lengths of 50, 100, 150, and 200 feet are shown in Figure A-14. This storage is held temporarily becat.Jse it is all above the wier crest. The outflow hydrographs for the SPF, with a wier controlled lake outlet., show r1ow storage is temporarily held (Figure A-12). Area Capacity The capacity curve of the Upper Mahoney Lake reservoir is shown in Figure A-15. The curve shows that the total storage capacity of the lake is roughly 8,300 acre-feet at the normal outlet invert of 1,954 feet. If the existing lake surface were raised by 25 feet tQ 1,979 feet MSL and a lake tap were installed at elevation 1,730, a net storage capacity of 9,100 acre-feet would be provided. A contour map of Upper Mahoney Lake is shown in Figure A-16. Low Flow Frequency As shown on the low flow frequency curve for the Mahoney Lakes basin (Figure A-17), an average annual flow of 76 cfs would have an occurrence interval of 500 years. The lowest average annual flow recorded over the 23-year period of record is 88.2 cfs, which, when applied to the low flow frequency curve, would have an occurrence interval of approximately 10 · years. A-25 ........ In If-. 5000 4000 ~ 3000 2000 1000 500 0 I) 1 2 3 4 5 6 7 ·r·----~---· ···· 1 · w • • ' •-l.u! -: . .., > • •• PROBABLE MAXIMUM FLOOD 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hr) Figure A-11. Probable maximum flood hydrograph for the Upper Mahoney basin 2500 2000 II) """ 0 ..... """ 1500 """ > 0 . I ~ N -~ 1000 500 ·--.. ------------------------· --------------------------·--'--. 0 1 Inflow and Outflow Hydrographs for the Standard Project Flood .. i I ' I ' ·• -~ ·-· ~--··--·~---.. -~-·-· ! ' . ·; i i ----;--.. ~ -~-·· --:-:---·r~ ·· · '· · ---·-,._: ·-··Joflow foii~ici.' ~ Ft~ .tiel r ifi(l!o;r j50 Ff. Melr ouifJ;; ioo rt. \iitr· -· .. ~---i . . ' ., 'I !. -' -.ot;,--o;t,!lj;,""h1arog;:;pi;l r.,;· ~ilitlii- '-<. ~ 100'. 15('' ~ ·~d 200'. !' .i ; , .. .'; . ----______________________ __, 2 3 4 5 6 7 8 9 10 11 12 14 15 115 17 18 Time (ht) Figure A-12. Inflow and outflow hydrographs for the standard project flood 0 1.5. 200 150 100 50 Surcharge (feet) I . I I 3.0 4.5 0 ~--------------------~~------------------------~ 1800 2000 2200 2400 Peak discharge (cfs) Figure A-13. Relationship of peak discharge and pool surcharge to spill- way width for a normal maximum pool elevation of 1.980 feet A-28 "' ! 0 0 tJ') N j ~ 0 0 0 N " - ; ~~~-,~~~~~"~"--""~-L4-4-~~~~~~~-4~--------~- -i--Jr-+ ___ _.___._.._..;.__._,-l----. --. ~t---~~~~~~~~~-~~4--·~·~·~,~·~!--~--4-4---~~---- J_ ; . ~ ... ---4 ,, .i .. ·-_,.,._.; .... I ' I 0 0 tJ') ...... ( SJ.::>) 0 0 0 ...... 3SCIVH3SIO A-29 d 0 \0 0 0 0 ..:::r ...... 0 0 0 0 ...... 0 0 0 co 0 0 0 \0 0 0 0 ..:::r -c LL.. V) - 0 + ~~~ ~ (.!) ex: c::: 0 ..... V) ¢ -I ex: Q) s- :::1 0'1 .,... LL.. )> I w <.."') Figure A-15. Area Cnpacity curve for Upper Mahoney Lake reservoir . N~ / ·, .,. __:..:::.-----honey Lake Upper· Ma ·mate Scale Approx•. 1" : 400' . z~~,-.iiiiiiiiii~40· o· 4~-o' . Mahoney Lake Figure A-16. Upper J"- 1 w ,"-J Ill 1+-u - Exceedence frequency per hundred years 99 98 95 90 80 70 60 50 10 1 0.1 0.01 700 ~~~~--~~~--~~--~~~--~~~------~--~~--~~~--~ 600h~~~==~~~~ld.~l~~~~~ 300 40 20 30 INTERVAL IN YEARS 20 Figure A-17. Low flow frequency curve for the Mahoney Lakes basin