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Home My WebLink AboutElim Pre-Reconnaissance Report 1982E:_r 001 c. 2 PRE-RECONNAISSANCE REPORT ELIM HYDROELECTRIC PROJECT Submitted by 00WL ENGINEERS ANCORAGE, ALASKA In Association with TUDOR ENGINEERING COMPANY SAN FRANCISCO, CALIFORNIA DRYDEN & LARUE ANCHORAGE, ALASKA December 1982 for ALASKA POWER AUTHORITY A. INTRODUCTION 1. Background ELIM HYDROELECTRIC PROJECT PRE-RECON REPORT At the request of the Alaska Power Authority a pre-reconnaissance evaluation was made of potential hydroelectric projects in the vicinity of Elim~ Alaska. A team composed of a hydroelectric engineer~ hydrologist and geologist made an on-the-ground reconnaissance of two of the more favorable sites on July 8 and 9~ 1982. A separate geologic reconnaissance report is appended to this report. This additional Elim reconniassance work was recommended to APA in the 11 Reconnaissanace Study for Energy Requirements and Alternatives for Kaltag, Savoonga, White Mountain and Elim 11 , prepared by Holden & Associates, et al. dated June 1981. The results of this work should form the basis for a decision on whether to proceed with a feasibility study. 2. Location The village of Elim is located on the south side of the Seward Peninsula on the shore of Norton Sound. Nome is 95 miles to the west and Anchorage 450 miles to the southeast. The two sites investigated on the ground, Peterson Creek and Quiktalik Creek, are located 5 and 1.5 miles respectively southwest of Eli m, as shown on Plate 1. The powerhouse for eithe.r site would be located near the shore and would be accessable from the sea during the summer or by Iditarod sled trail in winter. B. PROJECT DESCRIPTION 1. Alternatives Studied Two potential hydroelectric sites were selected for field investigation NBISF-313-9528-ER 1 from a group of eight sites screened for power head and stream flow potential. All sites are run-of-the-river with no significant storage at the diversion weir. The sites selected are similar to 11 Plan Two 11 and 11 Plan Four .. as set forth in the report .. Regional Inventory and Reconnaissance Study for Small Hydropower Projects in Northwest Alaska 11 , prepared for the Corps of Engineers by Ott Water Engineers, Inc., May 1981. The basic hydrogeological problem in the Elim area is that drainage basins of two or more square miles with potentially attractive water supplies are invariably characterized by flat stream gradients that would require long, relatively large diameter penstocks to develop significant head and resulting power. In contrast the steep headwaters of these basins, which have a good head potential and are well suited for construc- tion of an economical penstock and power plant, have a marginal water supply. No intermediate situation exists. The Quiktalik and Peterson Creek sites represent, respectively, the best of these two conditions. 2. Peterson Creek Alternative Project This alternative would utilize a 6-foot weir in a 5-foot wide channel to divert water to a 3700-foot long, 14-inch penstock. An impulse turbine would utilize 205 feet of gross head and a maximum flow of 6.7 cfs to develop 68 kilowatts of power. The powerhouse would be located near the mouth of the creek approximately 100 feet from the shore of Norton Sound. A preliminary project plan and profile and typical powerhouse layout are shown on Plate 1. Photographs of the powerhouse and diversion weir sites are shown on Figures 1 to 3. 3. Quiktalik Creek Alternative Project This alternative would utilize a long low (6-foot) diversion dam and/or canal to divert water to a 6,600-foot, 30-inch penstock located on the south side of the broad valley. A tube turbine would utilize 65 feet of gross head and a maximum flow of 18 cfs to develop 69 kilowatts of power. The powerhouse would be located at the base of the bluff approximately 500 feet from the shore of Norton Sound and 1500 feet upstream of the NBISF-313-9528-ER 2 alluvial mouth of the creek. Only 1.5 miles of transmission line would be required to connect the powerhouse to the vi 11 age. Despite the shorter transmission line, the Quiktalik site is judged to be clearly inferior to the Peterson site in overall construction cost. 4. Site Access and Transmission Line Access to the Peterson Creek powerhouse site would be by boat from Elim during the anticipated May through October operating season. The power- house would be located within 100 feet of the beach. Winter access, if needed, would be over the Iditarod Trail. A simple guyed-tower transmission line would follow the coast to fullest extent practical. It would be constructed and inspected from a skiff. A portion of the line may have to be constructed above 150-foot sea cliffs. The Quiktalik site could be accessed by extending a road 1-1/4 miles beyond the Elim airstrip. 5. Hydrology The preliminary estimates of stream flow presented here for Peterson Creek and Quiktalik Creek are based on recorded stream flows on two streams near Nome, the Snake River and Crater Creek. While these streams are 100 miles west of the project area they are closest known gages with a similar meteorological exposure along the south slope of the Seward Peninsula. The potential project streams drain much smaller basins than the gaged streams and have much lower effective elevations of the basin orographic divide, thus the project basins are less efficient at inducing precipitation and subsequent runoff than the gaged streams. The following Table gives the characteristics of the gaged and project streams: NBISF-313-9528-ER 3 HYDROLOGIC COMPARISON Peterson Quiktalik Snake Crater Stream Creek Creek River Creek USGS Gage No. 15621000 15668200 Drainage Area at Diversion/Gage (sq. mi.) 1.49 7.0 85.7 21.9 Elevation of Orographic Divide (ft.) 1300 1000 2000 3200 Mean Annual Flow (cfs) 2.8* 10.5* 183 55.6 S::Jecific Yield (cfs/sq. mi.) 1. 9* 1.5* 2.0 2.5 M·~asured Flow 7/12/82 at Diversion/Gage 5.9 17.0 172 at Mouth 5.3 25.0 *Adopted values An average annual flow of 2.8 cfs was adopted for the selected Peterson Cr·eek site. The initial estimates of the flow duration curve (Figure 4) and the monthly hydrograph (Figure 5) were based on the 16 years of rE!corded flows from the Snake River near Nome and prorated to Peterson Creek on the basis of the respective mean annual flow (2.8/183). As shown in the monthly flow hydrograph, 90 percent of the annual flow occurs in May through October. This, along with the harsh winter conditions at the remote sites indicates that any hydroplant should be shut down during the winter and the penstock drained. This seasonal operation plan will avoid major icing problems and potentially high operation and NBISF-313-9528-ER 4 maintainance costs while only marginally reducing the total energy production. 6. Power and Energy Production A turbine design flow of 6.7 cfs, equal to 10% on the flow duration curve was selected for reconnaissance evaluation of the Peterson Creek Project. A small skid mounted impulse turbine would be used. This turbine is capable of operating efficiently down to 10 percent of its capacity (C.70 cfs) which corresponds to a 60 percent flow exceedance. In contrast the Quiktalik Creek Project would require a much larger tube type turbine which has a low range limit of about 30 percent of its design capacity. The following table compares the two projects: Power and Energy Development Project Item Peterson Qui kt ali k Design Flow ( cfs) 6.7 18 Gross Head (ft) 205 65 Penstock Diameter (in) 14 30 Length (ft) 3700 6600 Net Head ( ft) 156 54 Efficiency ( %) 77 84 Power (kW) 68 69 Av•:!r age Annual Energy (MWH) 197 195 NBISF-313-9528-ER 5 C. ECONOMIC ANALYSIS Preliminary estimates of costs and benefits associated with the Peter- son Creek Project were assessed to provide an indication of the feasibility of the proposed project. The initial results of this analysis indicate that the Peterson Creek Project is marginally uneconomical. Thru com- pari son of the project features the Qui ktal i k Creek Project was determined to be substantially uneconomical and no further analysis was made. 1. Economic Criteria The Peterson Creek Project was assessed using the criteria and method- ology presented in Section IX of the Old Harbor and other Feasibility Studies recently completed for APA by this firm. These criteria are based on the APA standard criteria for economic analysis. 2. Cost Estimate The cost estimates for the site were based on the information prepared for the feasibility studies for 01 d Harbor, King Cove and Larsen Bay. Quantity estimates were prepared and unit prices derived from the above referenced reports were then applied. These unit prices were judgementally modified as necessary to suit this particular application. This estimate is summarized below: Item Direct Construction Contingencies Contract Cost Engineering and Administration Total Project Cost Power (kW) Cost per kW NBISF-313-9528-ER Cost Estimate 6 Amount $1~626,000 244~000 1~870,000 300,000 $2,170,000 68 $31,900 3. Project Energy Planning The average monthly energy generation that could be realized from the Peterson Creek Project was compared to the monthly direct electrical demands derived from the 11 Reconna i ssance Study of Energy Requirements and Alternatives for Kaltag, Savoonga, White Mountain and Elim 11 , June 1981, and from AVEC approved annual power projections. This determined the amount of hydroelectric energy that could be used to meet the projected demand, and the required amount of supplemental diesel generation that would be necessary if the hydroelectric project is built. A detailed explanation of the methodology used for this energy accounting is included in Chapter VII of the Feasibility Study for Old Harbor Hydroelectric Project. This accounting was performed for 1985, 1990, 2000, and 2034. The results of the accounting are presented below. Energy Demand and Generation Required Direct Direct Demand Diesel Demand Met by Hydro Generation Year ( 1000 kWh) (1000 kWh} ( 1000 kWh} 1985 480 163 317 1990 504 167 337 2000 700 192 508 2034 700 192 508 4. Benefit/Cost Analysis The annual costs associated with the hydroelectric project were esti- mated using the energy values presented above. These costs include the cost of supplemental diesel generation and were developed in a manner consistent with the methodology advanced in Chapter IX of the Old Harbor Study. The costs were discounted to January 1982 at three percent interest. The present worth of the base case is $7,791,500. The present worth of the hydroelectric project, including the supplemental diesel costs, is $8,420,100. The present worth of the cost of the hydroelectric project was considered as a cost. The costs of the base case were consid- ered to be a benefit. This methodo 1 ogy is in accordance with the method- ology requested by APA. A summary of present worths is presented below: NBISF-313-9528-ER 7 Present Worth Summary Present Worth of Benefits Present Worth Base Case Only Present Worth of Costs Present Worth Cost of Hydro Project (Includes Present Worth Cost of Supplemental Diesel) The present worths presented benefit/cost ratio for the project. is as follows: B/C = 7,971,500 = 0.95 8,420,100 $7,971,500 $8,420,100 above were used to determine a The benefit/cost ratio for the project The benefit/cost ratio presented above indicate that the project is not feasible. D. ENVIRONMENTAL OVERVIEW The primary impact of the Peterson Creek Project appears to be disruption of the local wildlife during one season of construction. No fish were observed in Peterson Creek and its comparatively steep gradient and small flow may preclude any material loss of local fisheries. In contrast, salmon were observed in Quiktalik Creek and the substrate is gravel suitable for salmon spawning. NBISF-313-9528-ER 8 E. CONCLUSIONS 1. A 68 kW hydroelectric project capable of producing approximately 200,000 kWh during the six month summer season is potentially developable on Peterson Creek. 2. The preliminary cost estimate of the project designed, contracted and constructed under conventional APA procedures is approximately $2,200,000. 3. The preliminary estimate of project benefit/cost ratio is 0.95. 4. A hydroelectric project is not viable at Elim under conventional development procedures. F. RECOMMENDATIONS 1. APA should reconsider the project under a small engineer- constructor performance contract or demonstration project. The sma 11 size of the project may permit major economies in design and construction costs if it were developed outside of the conventional APA/AVEC institutional framework and bidding procedures. 2. Flow measurements should be made at Peterson Creek during the 1983 May-October season. This may be most economically achieved by installing a 2-foot measuring flume and simple 30-day float recorder. Flows in excess of 15 cfs need not be accurately measured. Reports from local people and the carbonate geology of Peterson Creek suggest that the total season flow may be considerably greater than estimated here. If verified this would materially improve the project•s power benefits. NBISF-313-9528-ER 9 ~-r-----------------------~-----------------------------------------------------------------------·--------------------------------~ ~ \ I I I r -I ! I I J I I ! I I I ! 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MILES STATE OF ALASKA ALASKA POWER AUTHORITY ANa!OfiAGE, ALASKA .ELIM HYDROELECTRIC PROJECT PETERSON CREEK PROJECT DOWL ENGINEERS ANCHORAGE , ALASKA ~~:C~'=" PUTI·l ~ 1.1.1 1.1.1 a:: '-J u.. 0 ::1: 1- ::;) i ~ 1.1.1 1--~ 1.1.1 ~ 1.1.1 ~ 8 ::;) 0 ::1: ::1: r-·~ a:: ~ ~ ~.· 0 /l. ~; Q.. ~ 1.1.1 1.1.1 a:: '-J z ~ a:: 1.1.1 1- 1.1.1 ~ LI.J 1--V') 0::: -!:ij z 0 -V') 0::: LI.J > -c :w:: LI.J LI.J 0::: u z ~ 0::: LI.J 1- LI.J c.. 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 '"fit 1.0 -... ..9 3: 0 ii 0 \ ~ ~ MEANANNUACFLOW-2:8cfs ' \ \ \ ' ~ ' ............_ ' 0 10 20 30 40 50 60 70 80 90 100 PERCENT (0/o) OF TIME FLOW EXCEEDED PETERSON CREEK FLOW DURATION CURVE FIGURE 4 II I 10 9 8 7 6 5 4 2.8 cfs -~---------------AVERAGE ANNUAL FLOW 2 -(f) -.s ~ g LL 0 0 N 0 J F M AM J MONTH PETERSON CREEK AVERAGE MONTHLY FLOWS I i I I I I i ! I I I ------ J A S FIGURE 5 GEOLOGIC RECONNAISSANCE OF THE ELIM AREA Introduction On behalf of the Alaska Power Authority, DOWL Engineers and Tudor Engineering conducted a preliminary reconnaissance level study of potential hydropower sites in the Elim area. Elim is approximately 95 miles east of Nome. Field studies were conducted on July 8, 9, 1982. On the basis of previous work and our own reconnaissance, sites on Quiktalik and Peterson Creeks were selected for study. The geologic reconnaissance work was designed to identify potential fatal flaws in developing these hydropower sites; to provide information necessary for very preliminary design work; and to provide a basis for determining future work necessary if either of these projects went into the detailed feasibility stage. Any comprehensive determination of foundation condi- tions for a diversion structure, penstock, roads, and power- line will require a more detailed feasibility study. Topography Elim is on the south side of the Seward Peninsula bordering Norton Bay which is part of Norton Sound. The area is dominated by gentle slopes between bedrock outcrops that form ridges and hills. The tops of the hills are generally barren with and spruce highest peak Norton Bay. the lower slopes being vegetated with shrubs forests. In the immediate area of Elim the is Mt. Kwinink which rises 2,000 feet from Further to the north, the Darby Mountains reach elevations of over 3, 000 feet.. Valleys, in most cases, are ~ENGINEERS broad and have stream gradients on the order of 50 feet per mile. Geology -Peterson Creek The Peterson Creek Valley is remarkably steeper and narrower than most valleys in the Elim area. Most of the creek flows along a contact between a crystalline limestone and a schistose marble. The limestone is reported to be Devonian in age and the marble is assigned to the Precambrian {Miller et al, 1972). Field evidence including brecciation of the rock, slickensides, and the straightline nature of part of the creek suggest that this valley is excavated along a fault line. Although activity of this fault has not been determined, regional geologic evidence suggests that it is inactive. The proposed diversion site is in colluvial and alluvial materials in the stream bottom at an elevation of approxi- mately 215 feet above sea level. No bedrock abutments are present in the creek bottom although bedrock does crop out on the east valley wall approximately 75 feet away. Thick- ness of the surficial materials has not been determined, however, based on exposed areas, thicknesses are expected to be on the order of 25 feet. If determination of this thick- ness is important to the final design, seismic work or drilling should be undertaken. A powerhouse location near sea level would be located on schistose marble. This marble is strongly foliated and trends N. 45° E. with a dip of 64° W. The marble shows rock clevage along discrete layers which probably average 1/2 -2- ~ENGINEERS inch in thickness. Locally layers of a brown mica schist predominate. In some areas a green talc-chlorite schist tends to form layers up to 3 feet in thickness. The marble should provide excellent foundation material for a powerhouse. Blasting will be required for excavation. Drilling operations are relatively easy in limestone and marble because calcite {CaC03}, the major mineral in these rocks, is relatively soft {Mohs scale 3}. Care should be taken to place the powerhouse out of reach of storm waters. A road connecting the powerhouse and the diversion structure would be on the colluvial and alluvial materals in the creek bottom. Near the powerhouse some bedrock may be encounter- ed. Slope stability appears adequate although further investigations should be made once a specific road/penstock route has been identified. Permafrost is expected to be prevalent in this area, except immediately next to the stream and the bay. A more detailed geotechnical investiga- tion is necessary to determine actual conditions along the penstock, access road and powerline routes and to provide adequate design data to address this condition. Springs are common in the Peterson Creek valley. This fre- quency may relate to the presence of a fault and associated breccia. Typically fault zones contain impermeable materials which form a barrier to the flow of ground water and cause it to surface. While the Peterson Creek basin is small {2 square miles}, flow in the creek may be augmented by recharge from other basins. Limestones and marbles typi- cally have water flowing in solution cavities and it may be that the fault breccia has sufficient resistance to impede deep ground-water flow and allow it to surface. -3- ~ENGINEERS Sand and gravel for construction purposes are not available at this site. Sufficient material is probably present at the mouth of Quiktalik Creek, approximately 3 miles away. Quiktalik Creek The site investigated for possible diversion is in a broad valley filled with colluvial and alluvial materials. No bedrock abutments are present. The underlying bedrock is probably a recrystallized Devonian limestone. Springs are common in this area and may also be related to faulting. Faults have been mapped in this area (Miller, et al, 1972) although evidence for them was not gathered during this reconnaissance study. A possible powerhouse site would be located on alluvial sands and gravels that appeared to be permafrost-free. A connecting road/penstock could be built in the valley bottom, however there would be local drainage problems because of the low gradient to the valley (approximately 50 feet/mile). Slope stability should not be a problem. Sand and gravel for construction purposes are probably available from the mouth of this creek. Further testing would be necessary to define the extent and quality of this resource. Gravel deposits also exist at Moses Point and along the Moses Point -Elim road. Seismic Risk Seismic risk in this area is low. As shown in Figure 1 peak bedrock acceleration over a 50-year plant life is expected to be within 5 to 10% g. These g values have a probability -4- ~ENGINEERS of exceedence of 10%. Standard Uniform Building Code con- struction procedures should provide an acceptable level of seismic hazard protection. The Elim area is sufficiently far away from major earthquake zones on both sides of the Pacific such that Tsunami are not a major hazard in this area. Transmission Line Corridor Between Peterson Creek and Elim, two options should be investigated for powerline siting. Option A would be to run the line along the beach and tie the poles into the bed- rock. Option B would run along the Iditarod trail. If Option A were selected, poles could be bolted to the bedrock which is present for approximately 3.5 miles of the 4.5 mile distance. Beach sands and gravels are present the remainder of the way. This option would have two major advantages: (1) avoidance of permafrost (2) easy construc- tion since access could be from the water. Option B would involve a line higher up on the slope. Power poles would be set in colluvial and alluvial materials that are in the permafrost zone. Some poles (probably less than 10%) would have to be set in bedrock. An alignment along the Iditarod trail would allow for winter maintenance of the line. Summer maintenance could be via all-terrain vehicle, if a road was too expensive to construct. Geotechnically either option may be acceptable. However, if it is consistent with design requirements Option A probably would be more economical to construct. -5- ~ENGINEERS The powerhouse at Quiktalik Creek would be less than 1. 5 miles from Elim. Either a beach route or a route along the Idi tarod trail would be sui table should this site be de- veloped. -6- ~ENGINEERS UJ a: :::;) CJ L&. c: 0 ·--al ... <D -<D () () < ...111:: () 0 a: ...111:: as G) a.. ~ Cl) a: 0 ::E Cl) -UJ Cl) CD a: ..Jw 3: w O! O<' z w