The URL can be used to link to this page

Home My WebLink AboutSilver Lake Hydropower 1992' II June 10, 1992 ----------------~ WHITEWATER ENGINEERING CONSTRUCTOR 1050 LARRABEE AVE . • SUITE 104-707 • BELLINGHAM, WA 98225 PH (206) 733 -3008 • FAX (206) 733-3056 Silver Lake HydroPower Project June 5, 1992 The following pages are brief highlights of several repm1s and studies that different engineering companies have perfmmed on Silver Lake over the past 20 years. Most of the information contained herein are from the reports performed by Stone & Webster and Dowl Engineers (1982-1984). The purpose of this packet is to present to Copper Valley Electric Association, the Mayor of Valdez, and the City Council the basic concept of constmcting a hydroelectric power plant at Silver Lake. This packet shows the location of the Project and the proposed layout of the hydroelectric facilities. The costs that Stone and Webster have presented are on the high side. We feel that the Silver Lake Project could be constructed for a much lower cost, depending on the capacity needs of Copper Valley Electric Association (CVEA). Our preliminaty estimate shows that the energy from Silver Lake could be delivered to CVEA in Valdez for less than 10 cents/kWh. To economically evaluate the Silver Lake Project, we would have to evaluate CVEA's daily load forecast subtracting the energy supplied by Solomon Gulch. This would give us the installed capacity required by CVEA and the annual acre- feet that Silver Lake would need to store behind the proposed dam. The installed capacity dete1mines the penstock(s) diameter and the turbine/generator size. The acre-feet of required storage dete1mines the height of the dam. This infmmation would enable us to design a Project to economically fill CVEA's present and future needs. We look forward to working with Valdez in it's goal of reducing the cost of wholesale power. Sincerely, 1{ . I~. \,-~L_J ThomA. Fischer, P.E. WHITEWATER ENGINEERING CONSTRUCTOR 1050 LARRABEE AVE. • SUITE 104-707 • BELLINGHAM, WA 98225 PH (206) 733-3008 • FAX (206) 733-3056 7.3 SILVE~ LAKE 7.3.1 Technical Analysis and System Descripti~n 7.3.1.1 Locatior. and Description Silver Lake is located about 15 miles southwest of Valdez near Galena Bay on the Valdez Arm of Prince William Sound. The lake is situated in the bottom of a bowl surrounded by mountains on three sides. Streams which feed the lake originate at the Silver Glacier and other small unnamed glaciers. This lake is 3.0 miles in length with a maximum width of 0.7 miles. It's surface area is approximately 978 acres at water surface elevation 306 and the maximum observed depth is approximately 278 ft. The total drainage basin is approximately 24.5 sq mi. Silver Lake discharges into the Duck River through a narrow gorge and falls about 306 ft in about 1 1/2 miles to the lagoon on Galena Bay. Duck River has four sets of falls greater than 10 ft in height with the largest approximately 60 ft in height. Figure 7. 3-1 shows Silver Lake and Duck River topography and profiles. 1.3.1.2 History and Background In 1915 the U.S.G.S. identified Duck River and Silver Lake as the most favorable opportunity for water power development in the Prince William Sound Region. They noted that the geology and topography at the outlet of the lake was suitable for the construction of a dam of a height of 100 ft or more. The Corps of Engineers conducted a brief power assessment of Silver Lake in 1980 but has not conducted any detailed studies of the site. 1.3.1.3 Hydrology On May 13, 1913 a temporary gaging s t.ation was established on the Duck River, abcut 600 ft upstream from the Lagoon. Gage readings were made at intervals of four or five days through December 1913. No other stream flow records are available. Figure 7. 2 is a hydrograph prepared by the U.S.G.S. for the period May through December, 1913. This confirms that stream flows are very low in the late winter and early spring, with a m~nimum flow of 30 cfs. Due to the limited availability of stream flow data, regression analysis was employee based en an average annual flo,.; of 200 cfs. This probably understates tte flow available for generation, based on the existing U.S.G.S. c:atc. anc a limited correlation of Duck Riv<~r data ;,.;ith the long historical strea~ flow record at Power Creek. STONE 6: WEBSTER & 7.3.1.3 Geology The bedrock at Silver Lake is mapped as part of the Valdez Group, a slightly metamorphosed sedimentary sequence consisting of graywacke, quartzite, arkose, quartz-schist and some thin beds of slate, shale, conglomerate and mica-schist. Secondary quartz has been emplaced along fractures in these rocks, the quartz ranges from a fraction of an inch to several feet thick. The r•ocks in this area are highly deformed, intensely folded and faulted in the general area of Silver Lake. No detailed geologic map is presently available in the Silver Lake area. The Galena Bay Thrust, a major thrust fault, trends northwest roughly parallel to Silver Lake passing along the northeastern shore of the Lagoon. Other faults have been inferred near Silver Lake from aerial photographs, and trend parallel to Silver Lake, with one extending northwestward from the northwest corner of the lake. 7.3.1.4 Power Operation Due to the lack of flow data at Silver Lake it was necessary to correlate flow data with the gaging station at Power. Creek in order to determine the critical low flow period. As summarized on Table 7. 3-l, this correlation established the spill or depletion from storage as a percentage of the average annual flow. If the percentage is positive, there is spill. If the percentage is negative, there is a depletion from storage. Based upon the critical low flow years from 1962 through 1974 approximately 160,000 acre-ft of storage would be required to maintain an average annual stream flow of 200 cfs. Therefore, to develop the power resource at Silver Lake, the reservoir must be totally regulated, and the amount of storage provided must be able to maintain the annual average stream flow during low flow years. Normal maxim~ operating surface elevation of Silver Lake is 410 ft with an average annual flow of 200 cfs. Based upon the average annual discharge of 237.5 cfs suggested in the t~Reconnaissance Study of Energy Requirements and Alternatives for Cordovat~, a reservoir storage of approximately 200,000 acre-ft is required with a maximum operating surface elevation of 450. 7. 3. 1. 5 Fo·wer The proposed Silver Lake reservoir would be fully regulated. Twc powerhouse locations have been considered: one at tide water and the second located on Duck River at elevation 65. Two dam heights have been investigated to provide required storage to meet critical low flow periods. STONE & VVESSTER ~ a. Case 1 Maximum operating reservoir water surface elevation 410 Powerhouse located at tidewater Average annual discharge 200 cfs Estimated power capacity -5100 kW Estimated firm annual energy -45,000 MW/hrs b. Case la Maximum operating reservoir water surface elevation 410 Powerhouse located on Duck River at elevation 65 Average annual discharge 200 cfs Estimated power capacity -4200 kW Estimated firm annual energy -36,800 MW/hrs c. Case 2 Maximum operating reservoir water surface elevation 450 Powerhouse located at tidewater Average annual discharge 237.5 cfs Estimated power capacity -6400 kW Estimated firm annual energy -56,400 MW/hrs d. Case 2a Maximum operating reservoir water surface elevation 450 Powerhouse located on Duck River at elevation 65 Average annual discharge 237.5 cfs Estimated power capacity -5300 kW Estimated firm annual energy-46,700 MW/hrs . 7.3.3 Siting, Conceptual Design and Capital Costs 1.3.3.1 General The hydroelectric development proposed for Silver Lake is based a 120 ft high concrete darn located at the lake mouth. Water would be transported by a 6000 f~ penstock 7 to 8 ft in diameter to a powerhouse and would then be returned ~o the Cuck River. The dam would have a concrete gravity non-overflow section, with intake diversion works incorporated into the dam proper. A spillway would be located in the southwest abutment. It has been assumed that the foundations at the proposed dam site are suitable for the proposed dam and that there is a suitable aggregate source on-site for required construction materials. 'lhe powerhouse would contain two or three horizontal Francis units of ~.0 ~o 5.0 MW capacity each, depending on final demand requiremea.t. STONE & VVEBSTER ~ I I T•.w scf:s:::es ::ave been studied, ca~aci '::.~;. Ccnceptua l site plan providec in Figures 7.3-3 through one with 9 and one witr. 15 anc designs for the 15 M'.-i 7-3-5. :·:·,.; installed :-acili ty are The power!"louse for each scheme is located at elevation 65 c.::out 3000 ft upstream of the river mouth at low mean tide. This location is advantageous because the water would be returned to the channe~ upstream of the stretch identified by the Alaska Department of Fish and nildlife as a major spawning grounc. Should powerhouse generation be ~~terrupted a by-pass ~auld divert penstock water into the Duck River. A potential design problem affects the siting of the powert:::..:se since a major thrust fault crosses the Duck River at the Lagoon. This must be studied in detail before its impact on the proposed develc;:>:nent can be assessed. 7.3.4 ~aintenance and Ooerations Silver L.ake hydroelectric equipment would consist of a hc:-izontal axis Francis Turbine, governor, generator, transformers, breakers and auxiliary support devices. Standard equipment would be used to allc....-for easier parts replacement and maintenance. Operations would be remote controlled, but will require cc.ily in-plant inspection of control and equipment settings, daily equipmen~ lubrication, and other minor work tasks. Assumed annual maintenance and operations costs of $120, OOC c.re based on one full time employee living at the project site and all o:~er personnel "on-call" from one of the surrounding communities. This est:..::iate compares favorably with existing hydroelectric installations of sim:..::..ar installed capacity and automation. The prc;::csed plant design provides for continuous a vailabi ::_::_ ty. Outages would be strictly related to the availability of the trar,smission line between Silver Lake and Cordova. Diesel generators would be c.vailable as a back-up ;:JOwer source in Cordova should power from Silver :...ake not be available. 7.3.5 ":cncmic Analysis The capi:al costs for Silver Lake were developed based on :· .. ;o installed capaciL .. es, one of 9 MW and the second of 15 MW. Thes-::: costs are $39,186,COO and $50,200,000, respectively and incluce :: 30 percent continge~2y for indeterminants. Operation and maintena~ce costs are estimat-:::~ tc be $120,000 per year, and diesel generator tack-~p would have a capita::.. ccst of $3,400,000. Present ~~r:~ life cycle cost for the 9 MW installa~ion is ~~~.200,000 and r or the _ :: ~< •· installation is $6 6 , 0 0 0 , 0 0 0. STONE 8: WEBSTER ~ TABLE 7.3-2 COST ESTIMATE SILVER LAKE Costs ($1000) Installed Capacity l. MOBILIZATION AND SITE PREPARATION WORK 2. LAND AND DAMAGES 3. DAM, INTAKE AND SPILLWAY 4. PENSTOCK 5. POWERPLANT 6. BUILDING, GROUNDS AND UTILITIES 7. TOTAL DIRECT COSTS 8. ENGINEERING AND DESIGN (10%) g. CONSTRUCTION MANAGEMENT (10%) 10. SUBTOTAL ll. CONTINGENCY ( 30%) 12. TOTAL PROJECT COSTS 13. INTEREST DURING CONSTRUCTION 14. TOTAL COST 9 MW 15 M\.oJ 1,100.0 1,100.0 -0--0- 5,254.0 5,539.9 13,540.0 18,080.0 3,879-3 5,799.9 250.0 250.0 24,014.3 30,769.8 2,401.4 3,077.0 2,401.4 3,077.0 28,817.1 36,923.8 8,645.1 ll' 077 .l 37,462.2 48,000.9 1,723.3 2,207.9 39,185.5 50,208.8 STONE & WEBSTER & Year Pink Chum 1960 64,128 15 ,-sao 1961 41,250 23,228 1962 61,600 28,240 1963 36,490 9,680 1964 38,520 21,500 1965 7,160 6,892 1966 91,240 9,560 1967 52,560 6,680 1968 23,000 16,910 1969 33,980 13,650 1970 77,210 3,900 1971 92,800 2,840 1972 ~,090 12,300 1973 ~650 29,960 1974 ,540 28,360 1975 24,330 2,380 1976 123,920 7,300 1977 69,500 10,980 1978 43,800 24,460 1979~ 31,740 2,310 1980 ~ 60,180 2,710 1981 42,100 3,920 Source: ADF&G files FIGURE E DUCK RIVER ESTIMATED SPAWNING ESCAPEMENT 1- UJ w u.. 0 z 0 u w (l'j ~ UJ ~ IX: <( :r: u (l'j 0 soor-----~----------------------~------------------------------~ 700 600 500 10 20 30 9 19 29 9 19 29 8 18 28 7 17 27 7 17 27 6 16 26 6 16 26 0~~--~~--._----~--~~--~----~~~~--~~~._----~r-~~--~----~~~~ MONTH Sourae: U.8.G.8 •• 1U13 temporary gaging station FIGURE C DUCK RIVER HYDRO GRAPH (MAY-DEC, 1913) ~~ \1: j<:. ::. ·-r ... t .,..... ,., ........ , •"···· ...... . .. '-. ' ~ •·· cj: : ~ ~ I\' .. -' ' .. \ ... ., t~ ... r \; .... .,~. \ . 'r.r.;. ... ,. ( '\' ' ;H,_. ' ' : :. ' :) •.. " '::';'>;. , . , . .I ~-'L--·~• ;o~: .. £1· T.-/ ·~··"A.'--'h!" .. ~·H · . ~/t:.-/ , .:-.. -~! ~~ /:· .. : . ~-/ ~7'~1? ...!-;1 '~ \ I i§ )kSi,.. _ __;_,J~> POOT \'\ • \' ,.....> :±--. !t r .') ~·x:JJ(fl VALDI<E 'IE TRANSMISSION CABLE ~ L.)!_;~~..4--~ ' ' .. ;~ ~.,.,, __ .. ~1o .. ~ .. ~ + .. .. ·~: JO I -~4 ' -.-•I" '+ f P 0 R T - " I.. VALDEZ -. J. -l :._:.llL ~- VALDEZ riT ' ,'·~· ,=-.;~~--= :,i'~ ~-..... ! .:.:.:: •. ::~ ··.,~j?· :\~: . :I ·'~'~;.·~ ~~) . v-1~. . '-: . . • _.. ,. .., J ·q,:__s -: . ~~~~.... . .'' : -~ ~_-::,_;; .~. .. ... ·~· }·: ~":~ ' (' . f • j.~ r-c-:" _, ·' ~ , \ 1 .. ·' .L <.;;;."~ .. v:,, •.:d iS .,_ 'io;,:'"-~~~---,---f .•· ~- .. T. . -. -~: ·~. ..·.~ , ~ it. .. . q~ ., ... ,.·.•, ... ~ ' . j v~'y_>~~:~,~ .. !~~~·.··,,.!,. I_,· .,_}·1 . .,·:.iL I SCALE : I I • ' CDrlaiM-.. KI)Rl'f -·---=~.:.::r:.:=:=- .J' SILVER LAKE OVERALL PROJECT BOUNDARY FIGURE 1 15 500 2000 6000 SCALE iN FEET FIGURE 2 OVERLAND PROJECT BOUNDARIES AND PP 138 BOUNDARY 16 0 0 i ~ ~ ..., $ 0 ~ 0 ~ 0 " <0 1-w w LL 0 z 0 ~ -w ..J <( ~ 0 0 0 N 0 0 0 ..... 0 f6 FIGURE 3 PROJECT FACILITIES 17 I FIGURE 0 I CONCEPTUAL SITE PLAN I ... .... .... -I ,.. ,.., V£R LAX~--..... "' "' -"' ... U'l "" 1 " .., l "' I'ROFILE ,_ FIGURE 8 SILVER LAKE AND DUCK RIVER TOP.OGRAPHY AND PROFILES I y GAGING STATION w/· TEMP/PRESS. e TEMf'ITEMP RECORDING SYSTEM z 0 0 PROPOSED DAM SITE\ 300 276 250 225 200 175 150 125 100 " c ~------------+----------------------------+--------------450 ..J ~--~--------------------------~----------------------------~------------~0 1 2 MILES FEET A,B,C,D and E are major falls FIGURE F GAGING STATIONS AND DATA RECORDING SYSTEMS (1982) Qc -Quaternary coluvium Qca- Qp - Kv - -Rur 4 ~g location -Joi~~ transect location , 11 200' SILVER LAKE DAMSITE GEOLOGIC MAP SILVER LAKE I G U R E PLACE NAMES FIGURE 1 --4) 4) .... - A 375 20L 0 20 Scale in feet EXPLANATION Kv Late Cretaceous Valdez Group -M.etaQraywacke ......... Metashale Drillhole No.3 '--Approximate Apparent Dip of Bedding Geologic Cross Section A-A -Silver Lake Figure 14-