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HomeMy WebLinkAboutBlack Bear Lake Penstock Siphon Study Report 1987J-lARZA ENGINEERING COMPANY CONSULTING ENGINEERS BLACK BEAR LAKE HYDROELECTRIC PROJECT PENSTOCK SIPHON STUDY REPORT 1 50 SOUTH WACKER DRIVE CHICAGO. ILLINOIS 60606-4288 TEL [31 2) 855-7000 CABLE HARZENG CHICAGO TELEX 25-3540 BLACK BEAR LAKE HYDROELECTRIC PROJECT PENSTOCK SIPHON STUDY REPORT 1. SCOPE This report describes a study of a siphon to draw water from Black Bear Lake for the proposed 3.0 MW hydroelectric project. This siphon would be used instead of a dam, which would have raised the lake level to provide storage, and an intake for water withdrawals. The study includes an estimate of the project construction cost with the siphon system. The siphon and upper penstock in this study have been sized for a 3 MW hydro plant, the proposed first stage of a potential 6.0 MW development of the resource. A profile of the proposed upper penstock for the siphon concept is shown on Exhibit 1. The size of the vertical shaft and lower penstock remain as sized in previous feasibility studies for a 6.0 MW project. 2. DESCRIPTION 2.1. The use of a siphon to draw water from a lower water source is practical to a depth up to 25 feet. Theoretically, standard atmospheric pressure (76 em of mercury) could raise water to a height of 33.9 feet at sea level. At the altitude of Black Bear Lake (El. 1687 MLLW datum) atmospheric pressure equals about 31.9 feet of water. However, siphons are consid- ered to be practical for no more than 75% of atmospheric pres- sure. The topography of Black Bear Lake and its outlet permits the use of a siphon to provide the intake of water for a pen- stock to the hydro plant. This penstock, can be routed in ground about 10 feet above the existing lake elevation, thus providing the ability to draw the lake down about 15 feet. An -1- BLA I""J '"' ' ' ~ ,.-~ \ '"'J' intake on the siphon penstock in the lake would be located about 5 feet below this minimum drawdo~1 elevation to provide submer- gence to reduce vortex formation and to protect the intake from damage or clogging by ice. This submergence would also allow a small margin for error in plant operation to prevent a brake in the siphon action in the event that operation of the turbine continues beyond the minimum drawdown elevation. In the design proposed, if the siphon action does break, it would take over an hour to reestablish the siphon. 2.2. The proposed siphon system would consist of the fol- lowing main equipment: two vacuum pumps, electric motor driven, rated 450 cfm at 22 inches of mercury (equals 25 feet of water)7 vacuum tank1 a seal water supply pump1 and unit heaters for a small building enclosing the vacuum pump equipment. Piping would consist of the connections from the penstock to the vacuum t~.nk, from the tank to the vacuum pumps and. for seal water, from the lake to the vacuum pumps& Power for operation of the siphon system equipment would be provided from the powerhouse via an interconnection line as described in the Feasibility Report Updateo 2.3. The proposed siphon system would be designed to start the siphon action at any lake level down to the lowest designed drawdown level. The vacuum tank and pumps would be located on the high point of the upper penstock approximately 360 feet downstream from the intake. This point would be about 50 feet downstream of the location of the dam axis shown in the February 1987 Feasibility Report Update. -2- The operating procedure would be as follows: 1. To fill the penstock with water, the turbine inlet valve and by-pass valve at the powerhouse would be closed. An air inlet valve on the vacuum tank would be closed. The intake valve at the vacuum pump would be opened and the pump started to evacuate air from the tank and pen- stock. After the penstock is filled with water, the vacuum pump intake valve would be closed and the turbine inlet or powerhouse by-pass valve opened. With the turbine inlet valve open, the turbine can be started and siphoning action would commence. 2. TO dewater the penstock, the turbine would be shut-down and the by-pass valve opened. The air inlet valve on the vacuum tank would be opened to allow air to enter the penstock and water to drain toward the powerhouse and through the by- pass. The upstream portion of the penstock would drain to the lake. Opening the air inlet valve will break the siphon and will shut-off flow in the penstock which eliminates the need for an intake gate or valve at the entrance of the pen- stock. 2.4. The proposed intake would consist of a cylindrical trashrack formed by vertical steel bars supported by horizontal, bars bent into rings, with a horizontal flat circular plate on top of the cylinder serving as a velocity cap. The cylindrical intake trashrack would be welded to a miter reducing bend of 90 degrees which would be welded to the steel penstock. The intake -3- would be located in Black Bear Lake where the natural water depth is 30 feet. Soundings of the lake show this depth to be about 182 feet from the lake shore near the lake's outlet creek. The discharge required for 3.0 MW of generating capacity is 32 cfs (with net head of approximately 1,300 feet). To obtain an approach velocity of one foot per second the size of the cylin- drical intake would be 3'-6• in diameter and 3 feet high. Sixty 3/8 inch thick vertical bars equally spaced on the circumference of t.he supporting rings would result in openings of 1.824• wide. The height of the intake with miter reducing bend would be 7 feet above the center line of penstock. With a minimum submer- gence of 5 feet the maximum drawdown of the lake would be about 15 feet below the present natural lake elevation. The natural lake is at elevation 1687 and the penstock centerline at the miter bend would be at approximately El. 1660. This would pro- vide a lake drawdown to El. 1672. 2.5. In the Feasibility Report Update of February 1987, the water conduit system for the 6.0 MW alternative consisted of the following: a) An upper steel penstock of 48 inch diameter and about 325 feet long, b) A vertical concrete lined shaft of 48 inch diameter about 1237 feet deep, and c) A lower steel penstock of 30 inch diameter about 2,800 feet long. The computed total head loss for this system is 106.84 feet for 64 cfs and 33.24 feet for 32 cfs. Replacing the dam (as shown in the feasibility report update) with a siphon will increase -4- the upper penstock length by 310 feet~ The increase in length consists of 128 feet from the dam axis location to the lake bank and 182 feet from bank into lake at penstock intake. It is proposed that the upper penstock for the 3.0 MW siphon alterna- tive be sized to have approximately the same total head loss as the 6.0 MW alternative (at maximum plant discharge) but without changing the shaft and lower penstock diameters" On this basis the diameter of the nearest standard size pipe for the upper pensi:ock would be 20 incheso The head loss in t.he 20 inch O.Do upper penstock~ 48 inch I.D. shaft and 30 inch O.Do lower pen- stock for 32 cfs flow is estimated to be about 76 feeto At minimum lake Elo 1672 the net head for the plant would be 1335 feet. For future expansion of the plant to 6.0 MW, the upper penstock would be replaced by a larger pipe, but the shaft and lower penstock would not require change. 2.6. Approximately 182 feet of pipe would be placed under- water at the upstream end of the upper penstock. It is proposed that this pipe be protected by dumping rock fill underwater to a one foot thickness over the top of the pipe. A layer of rip-rap would be placed over the rockfill. This protection would pre- vent damage to the pipe by ice with lake drawdown and possible erosion of pipe foundation by wave action in the vicinity of the pipe. During project operation, the lake bed adjacent to the pipe and its protective material should be inspected when the lake is drawn down and rockfill/rip-rap placed 'if necessary. In the event of failure of the power supply or control lines from the powerhouse to the siphon equipment, an emergency portable generator could be flown by helicopter to the siphon site. 2.7. The total internal volume of the water conduit sys- tem, as proposed, equals 30,607 cubic feet. With the 450 CFM -5- vacuum pump capacity proposedf the time required to evacuate all air in the conduit is 68 minutes. 2.8. Black Bear Lake has not been surveyed below its water surface; therefore, its water volume below the surface is not known exactly. An estimate of its volume can be made by extra- polating the reservoir area/volume curves. Extrapolation from natural snrface at Elo 1687 to El. 1672 gives a volume of 2650 ac.re~·feet. Since there is so1ue uncertainty about the under wateL topography, it is recommended that a usable storage of 2000 acre-ft be assumed for the 15 feet of drawdown. Based on reservoir operation studies performed for the 3.0 MW B.W.EL. 1695 alternative (2000 acre-feet of storage) the estimated 3.0 MW siphon intake alternative average annual energy generation would be about 18,000 MWh. 2.9. The environmental impacts of this alternative include the following: a) Shores not previously or naturally exposed will be exposed. b) Fish habit will be reduced when the lake is drawn down during winter. There may also be a drawdown during late summer in dry years. c) Lake outflows, by way of the creek, will be eliminated during drawdown. d) The distance from the Forest Service cabin to the lake shore will increase during winter and some late summer periods. -6- 3. COST ESTIMATE Based on the cost estimate for the 3.0 MW H.W.EL. 1695 Stage I alternative presented in the Feasibility Report Update, the construction cost of the project has been estimated for the 3.0 MW generating plant with the siphon system. This estimated cost is for the complete power generating plant but without any transmission lines from its substation. The estimated transmis- sion line costs for several options of serving load demand cen- ters are shown in Table III-1 0 on page III-2'7 of the February 1987 Feasibility Report Update. The elimination of the dam and its replacement by a siphon system, reduces the work required in the vicinity of Black Bear Lake which reduces mobilization and logistics costs. Contractor's indirect costs have been revised for these changes. The changes in quantities for construction consist of elimination of all dam work, revision of upper pen- stock steel, excavation, backfill and bedding, underwater place- ment of pipe and its protection. Quantities for the vertical shaft, lower penstock, powerhouse, access roads and substation are unchanged. Costs have been estimated for the siphon system equipment and a small building to protect this equipment. A summary of the estimated construction cost is shown in the table below. A detailed estimate is shown on Exhibit 2. -7- Item No. SUMMARY OF COST ESTIMATE January 1986 Price Level Description Estimated Cost 330 331 332 333 334 335 33(~ Land & Land Rights $ 73,000 630,000 7,499,000 641,000 584,000 57,000 560,000 196,000 1,100,000 353 Powerstation & Improvements Reservoir, Dams & Waterways Turbine & Generator Accessory Electrical Equipment Miscellaneous Mechanical Equipment Access Road Substation Equipment & Structures Mobilization & Logistics Subtotal Direct Cost Contingency Allowances Civil 15% Equip. 10% Total Direct Cost Engineering & Administration 17.5% Total Estimated Construction Cost -8- 11,340,000 1,480,000 150,000 12,970,000 2,270,000 $15,240,000 DATE MAR 06 1987 HARZA ENGINEERING COMPANY I3MWSF1284C1 FEASIBILITY ESTIMATE (LFC/RAM D) PROJECT 3.0 MW. HWL EL 1687. SIPHON INTAKE ITEM DESCRIPTION QUANTITY UHIT UNIT PRICE TOTAL PRICE ------------------------------------------------------------ 330. LAND & LAND RIGHTS 1 LS 73088.00 73#080 SUBTOTAL.PAGE 73.000 SUBTOTAL -A/C 330. LAHD & LAND RIGHTS 73.000 ~ ~ ~~ ' ' ,, ~~ ~ ., """ ,:·\ DATE MAR 06 1987 HAR2A EHGIHEERIHG COMPAHY I3MWSF1284Cl FEASIBILITY ESTIMATE <LFC/RAM D) PROJECT 3.0 MW. HWL EL 1687, SIPHOH IHTAKE ITEM DESCRIPTION QUANTITY ·UHIT 330.5 MOBILIZATIOH & LOGISTICS 1 LS UHIT PRICE lt0000B~a0 ------------------------------------------ SUBTOTAL.PAGE 2 SUBTOTAL -A/C 330. S MOB ILI2ATIOH & LOG lSTICS TOTAL PRICE 1.1aa.aaa t.taa.aaa t,taa,aaa ~ ~t ' "-l'1.:_ ~~ ~ n ,., DATE MAR B6 1987 HARZA ENGINEERING COMPANY 13MWSF12B4C1 FEASIBILITY ESTIMATE <LFC/RAM D) PROJECT 3.B MW, HWL EL 1687, SIPHON INTAKE UNIT TOTAL ITEM DESCRIPTION QUANTITY UNIT PRICE PRICE ---------------------------------------------------- 331. POWERSTATION & IMPROVEMENTS 331.1 POWERHOUSE 331.11 DIVERSION & CARE OF WATER 1 LS 35BBB .• BB 35,BBB ' ~ 331. 12 CLEARING. HEAVY 3 AC 1B5e!B.BB :·. 31.500 331. 13 EXCAVATION. TALUS 175B·CY 10.5B 18.375 331. 14 FILL 750 CY 8.80 6,.600 331. 15 SUBSTRUCTURE CONCRETE 345 •CY 53B.BB .. 182,.850 331. 161 SUPERSTRUCTURE CONCRETE 65 CY 79B.BB 51.350 331.162 ~ MASONRY 47B SF 2B.50 9,.635 ~ 331. 163 ~k INSULATED METAL PANELS 37BB SF 7.05 26.085 ~~ --------------------------------------------------~~ Ul SUBTOTAL. PAGE 3 361.395 DATE MAR 06 1987 HARZA ENGINEERING COMPANY · I3MWSF1284C1 FEASIBILITY ESTIMATE (LFC/RAM D) PROJECT 3.0 MW. HWL EL 1687. SIPHON INTAKE ITEM DESCRIPTION QUANTITY UNIT 331. 164 ARCHITECTURAL TREATMENT 1 LS 331. 165 STRUCTURAL STEEL 58a0e:Ls 331. 166 INSULATED METAL ROOF 3900 SF 331. 167 HVAC & PLUMBING 1 LS 331. 168 MISCELLANEOUS METALS 2080 LB 331.2 STATION YARD 331.21 FILL 25B CY 331.22 CRUSHED ROCK SURFACING 60·cy 331.23 CHAIN LINK FENCE & GATE 160 LF 331.24 CONCRETE FOUNDATION PADS 28 CY UNIT PRICE 55500.00 2.75 6.45 251380.08 2.75 8.88 25.00 : 32.50 548.00 TOTAL PRICE 55.5B0 137.500 25. 155 25.800 5,500 2.200 1.5013 5,200 10.800 ------------------------------------------------------- SUBTOTAL. PAGE 4 268,355 SUBTOTAL-A/C 331. POWERSTATION & IMPROVEMENTS 629,750 .~, ~ ~~ ~~ ' ~~ DATE MAR 06 1987 HARZA ENGINEERING COMPANY I3MWSF1284Cl FEASIBILITY ESTIMATE <LFC/RAM Dl PROJECT 3.0 MW. HWL.EL 1687, SIPHON INTAKE ITEM DESCRIPTION QUANTITY UNIT 332. RESERVOIRS, DAMS, & WATERWAYS 332.3 WATERWAYS 332.31 IIHAKE 332.311 CONCRETE -STRUCT. <BUILDING EQUIPMENT & FOUNDATIONS) 7 CY 332.312 TRASHRACK & BEND 930 ·LBS 332.313 BUILDING 240·SF 332.314 VACUUM PUMPS. CONTROLS. TRANSFORMER. AND MISC. EQUIPMENT 1 LS 332.315 POWER SUPPLY & CONTROL LINES 1 LS 332.32 PENSTOCK 332.321 UPPER PENSTOCK 332.3211 EXCAVATION 332.32111 EXCAVATION. OVERBURDEN 360 CY UNIT PRICE 875.00 3.70 55.50 1000130.00 735130.00 13.00 --------------------------------------------- SUBTOTAL.PAGE 5 TOTAL PRICE 6.,125 3,441 13.320 100.000 73.500 4.680 201.066 ~ ,, ~\ ~ ·~ ' IJ~ \ ' \"K ~f\l DATE MAR 06 1987 HARZA ENGINEERING COMPANY · 13MWSF1284C1 FEASIBILITY ESTIMATE CLFC/RAM D) PROJECT 3.0 MW. HWL EL 1687. SIPHON INTAKE ITEM DESCRIPTION QUANTITY UNIT UNIT PRICE --------------------------------------------------- 332.32112 EXCAVATION. ROCK 400 CY 57.50 332.3212 BACKFILL 690 CY 16.50 332.3213 BEDDING 35·CY 45.50 332.3214 CONCRETE THRUST BLOCKS & SADDLES 6 CY 1150.00 332.3215 GRAVEL FILL <FOR PENSTOCK SUBMERGED PORTION) 300:cy 42.50 332.3216 RIPRAP (FOR PENSTOCK SUBMERGED PORTION) 200:cy 62.00 332.322 LOWER PENSTOCK 332.3221 EXCAVATION 332.32211 EXCAVATION. TALUS 3900 CY 19.00 TOTAL PRICE 23,000 11.385 1.593 6.900 12.750 12 .. 400 74. 100 ----------------------------------------------------- SUBTOTAL. PAGE 6 142,128 .I) !"' ~ ~\ S:.. . ' ()\~ ~' ~I\ ~ DATE MAR 06 1987 HARZA ENGINEERING COMPANY I3MWSF1284C1 FEASIBILITY ESTIMATE <LFC/RAM D) PROJECT 3.0 MW. HWL.EL 1687. SIPHON INTAKE ]TEM DESCRIPTION QUANTITY UNIT UNIT PRICE TOTAL PRICE ----------------------------------------------------------- 332.32212 EXCAVATION. ROCK 332.3222 BACKFILL 4100 CY 8.80 36.080 332.3223 BEDDING 1800 CY 25.00 45,000 332.3224 CONCRETE THRUST BLOCKS & SADDLES 15 CY 985.00 ' 14.775 332.323 PENSTOCK SHAFT 332.3231 EXCAVATION 1240:LF 1350.00 1,674.000 332.3232 CONCRETE LINING 730 CY 1150.00 839.500 332.324 TUNNEL EXCAVATION & SUPPORT 1660 LF 20130.00 3,320.000 .. 332.325 PENSTOCK STEEL 332.3251 UPPER SITE POWER CONDUIT 33500 L8 3.05 102.175 --------------------------------------------------------------- SUBTOTAL,PAGE 7 6.031. 530 ~\~ ~ "-l~ ~~ ~f\, DATE MAR 86 19B7 HARZA ENG.INEERUIG COMPANY I3MWSF1284Cl FEASIBILITY ESTIMATE CLFC/RAM DJ PROJECT 3.8 MW. HWL EL 1687. SIPHON INTAKE ITEM DESCRIPTION QUANTITY ;UNIT UNIT PRICE TOTAL PRICE ----------------------------------------------------------- 332.3253 LOWER SITE POWER CONDUIT 3628EI8 .. LB 3.85 1,1El4,1EI8 332.326 TAILRACE & STREAM CHANNEL IMPROVEMENT 332.3261 EXCAVATION. TALUS 1988 CY 1a.sa 19,950 ------------------------------------------------ SUBTOTAL,PAGE 8 1.124.asa SUBTOTAL -I:VC 332. RESERVOIR. DAMS, & WATERWAYS . 7,49B,774 ~~ l))~ ,, ' ~f\) •:""' '"'I DATE MAR 06 1987 HARZA ENGINEERING COMPANY I3MWSF1284Cl FEASIBILITY ESTIMATE (LFC/RAM D> PROJECT 3.8 MW. HWL EL 1687~ SIPHON INTAKE ITEM DESCRIPTION QUANTITY UNIT 333. TURBINE & GENERATOf.! 333.1 TURBINE c. GOVERNOR 333.2 GENERATOR SUBTOTAL;PAGE 9 1 EA 1 EA SUBTOTAL -0/C 333. TURBINE & GENERATOR UNIT PRICE 399000.00 253808.08 TOTAL PRICE 399~000 253,888 641 .. 000 641~088 .; ~~ ·~ ~~ ' \ '\.a- '" l" ~£\) ...() ll) co DATE MAR 06 1987 HARZA ENGINEERING COMPANY · I3MWSF1284Cl FEASIBILITY ESTIMATE CLFC/RAM D) PROJECT 3.0 MW~ HWL EL 1687, SIPHON INTAKE ITEM DESCRIPTION QUANTITY :uNIT 334. ACCESSORY ELECTRICAL EQUIPMENT 334. I ACCESS. ELEC. EQPT. 334.2 SUPERV'SRY CONTROLS 334.3 COMMUNICATIONS I. LS LS 'LS UNIT PRICE .39B00E1.0EI 125000. EIEI · 690El0.BB TOTAL PRICE 390,EIEIEI 125,EIEI0 69.800 ---------------------------------------------------------- SUBTOTAL,PAGE lEI 584,EIEIB SUBTOTAL-A/C 334. ACCESSORYELECTRICAL EQUIPMENT 584,BBB ~ ~\~ ~~ ~" \ ~~ ( ' DATE MAR 06 1987 HARZA EHGINEERIHG COMPANY · I3MWSF1284Cl FEASIBILITY ESTIMATE <LFC/RAM D> PROJECT 3.0 MW. HWL EL 1687, SIPHON INTAKE ITEM DESCRIPTION QUANTITY:UNIT 335. MISCELLANEOUS MECHANICAL EQUIPMENT 335. 1 POWERHOUSE CRANE 335.2 MISC. EQPT. 1 LS 1 LS ----------------------------------------· SUBTOTAL.PAGE 11 UHIT PRICE 48008.013 955B.BB SUBTOTAL -A/C 335. MISCELLANEOUS MECHANICAL EQUIP~ TOTAL PRICE 48.888 9,558 57.558 57.558 ~ ~~ ·~ ~~ ~f\) ·;') DRTE MAR 06 1987 HARZA ENGINEERING COMPANY I3MWSF1284Cl FEASIBILITY ESTIMATE CLFC/RAM D) PROJECT 3.0 MW, HWL EL 1687. SIPHON INTAKE ITEM DESCRIPTION QUANTITY:UNIT 336. ACCESS ROAD 1 LS SUBTOTRL,PAGE 12 SUBTOTAL -R/C 336. ACCESS ROAD UNIT PRICE 560000. 013 . TOTAL PRICE 5613.000 560,000 560.0013 N ' . ~\~ ' ~ ~' ~~~ ~f\) DATE MAR 86 19B7 HARZA ENGINEERING COMPANV I3MWSFI2B4CI FEASIBILITY ESTIMATE <LFC/RAM D) PROJECT 3.8 MW. HWL EL 1697. SIPHON INTAKE ITEM DESCRIPTION QUANTITV:UNIT UNIT PRICE TOTAL PRICE --------------------------------------------------------------- 353. SUBSTATION EQUIPt'ENT 8. STRUCTURES 353.1 TRANSFORtERS 353.2 SWITCHES, BREAKERS, 8. MISCELLANEOUS SUBTOTAL.PAGC 13 1 EA 68580.08 . 68 .. 588 1 LS 135888.88 . 135 .. 888 195.588 SUBTOTAL -0/C 353. SUBSTATION EQUIP. & STRUCTURES 195.588 GRAHD TOTALS 11.339.,574 . ~~ ' ~ ~ ~' '\ ~f, ~~ 0 ..0 ("()