CARLSON CREEK HYDROELECTRIC PROJECT PRELIMINARY FEASIBILITY EVALUATION AEA GRANT #

Transcription

1 CARLSON CREEK HYDROELECTRIC PROJECT PRELIMINARY FEASIBILITY EVALUATION AEA GRANT # ALASKA POWER & TELEPHONE COMPANY DECEMBER, 2011

2 CARLSON CREEK HYDROELECTRIC PROJECT PRELIMINARY FEASIBILITY EVALUATION Table of Contents SECTION 1 INTRODUCTION A. AEA GRANT HISTORY... 1 B. COMMUNITY PROFILES... 1 C. ENERGY PROFILE... 2 D. PROJECT LOCATION AND BASIN DESCRIPTION... 3 E. SITE VISIT... 3 SECTION 2 HYDROLOGY A. STREAM GAGES... 5 B. FLOW DURATION CURVE... 5 SECTION 3 ALTERNATIVE ARRANGEMENTS A. ALTERNATIVE B. ALTERNATIVE C. ALTERNATIVE D. ALTERNATIVE SECTION 4 CONSTRUCTION COSTS AND COST OF POWER A. CONSTRUCTION COST ESTIMATES... 8 B. GENERATION ESTIMATES... 8 C. COST OF POWER... 9 D. SUPPLEMENTAL DIESEL GENERATION... 9 E. RATE IMPACTS... 9 SECTION 5 CONCLUSIONS AND RECOMMENDATIONS A. CONCLUSIONS B. RECOMMENDATIONS... 12

3 SECTION 1 INTRODUCTION A. AEA GRANT HISTORY In 2009, Alaska Power & Telephone Company (AP&T) was awarded a grant of $40,000 by the Alaska Energy Authority (AEA) during Round II of the Renewable Energy Grant Program, based on an application submitted by AP&T in October, The terms of the grant required a 20% matching contribution by AP&T. The approved scope of work for the grant comprised the following Phase I reconnaissance tasks: Installation of two stream gages Site inspection by AP&T engineers Re-evaluation of project capacity and construction cost based on information from the site visit and stream gages. Reconnaissance report to document Phase I activities Request jurisdictional determination from the Federal Energy Regulatory Commission (FERC) AP&T conducted a one-day site visit on September 24, A memorandum summarizing the site visit was prepared, and is summarized in Section 1.C below. The full text of the memorandum is included in Appendix A of this report. Unfavorable conditions were identified during the site visit. In addition, the Governor s veto of Round III funding for the project in 2010 indicated a possible unwillingness to fund a major portion of the project costs, which AP&T knew would be necessary for the project to be of benefit to its ratepayers. Therefore, AP&T elected to not do any significant work on the project in In the spring of 2011, AP&T began preparing the jurisdictional determination request to FERC as required by the scope of services. Based on AP&T s experience, we expected that FERC would rule that they had jurisdiction over the project only if there was a reasonably likelihood that it would affect anadromous fish. Thus, AP&T conducted a preliminary re-evaluation of alternative concepts for the site, and concluded that no alternative would be economically feasible, even with 80% grant funding of the development cost. Because of that conclusion, a jurisdictional determination request was not filed. This current report was developed to document the studies of the alternative considered for the site. It also includes additions in response to AEA comments by on October 25, B. COMMUNITY PROFILES The Carlson Creek Project was conceived as a renewable energy resource to serve the communities of Slana, Mentasta, and Chistochina. According to the DCA Community Information Summaries, these three small communities have the following socioeconomic characteristics: Carlson Creek Hydroelectric Project 1 December, 2011 Preliminary Feasibility Evaluation

4 Slana Mentasta Chistochina Population Number of housing units Number of occupied housing units Economic basis Recreation, tourism, subsistence Subsistence Subsistence Unemployment rate 25.6% 34.4% 14.3% % below poverty level 48.4% 38.2% 5.3% C. ENERGY PROFILE All three communities are supplied with electric service by AP&T through its Alaska Power Company subsidiary. Until 2009, each community was served by its own diesel powerplant. In late 2009, AP&T completed a transmission line linking the three communities. Since then, generation has been primarily from the Slana powerplant (730 kw in 3 units), which AP&T upgraded in The Mentasta and Chistochina powerplants (395 kw and 220 kw respectively) are relegated to standby service. Generation for the last six years by the three communities is summarized in the following table. All generation is from diesel generators. Generation for 2011 is for January-November. Year Total Generation, kwh Generation Sold, kwh Losses and AP&T use, kwh Average Efficiency, kwh/gal (2) Peak Load, kw ,038, , , /10.41 NA ,094, , , /10.30 NA ,129, , , /10.81 NA ,226,086 1,075, , / ,319,078 1,161, , / (1) 1,285,628 1,119, , / (1) January-November (2) Values are per kwh generation / per kwh sold The generation is typically seasonal, with higher generation in the cold months and lower generation in the warmer months, as illustrated by the graph below. Loads have been growing at a fairly steady rate, averaging about 6% per year for Loads for 2011 appear to be following that same trend. The current retail electricity rate for the Slana-Mentasta-Chistochina system is $0.6887/kWh, which includes the base rate of $0.3391/kWh and a Cost of Power Adjustment rate of $0.3496/kWh. For residential customers, the Power Cost Equilization program reduces the rate for the first 500 kwh/month by $0.5064/kWh. Rates for the Slana- Carlson Creek Hydroelectric Project 2 December, 2011 Preliminary Feasibility Evaluation

5 Generation (1) Mentasta-Chistochina system vary significantly according to the cost of diesel fuel; there has generally been an increasing trend to the rates because of the influence of the fuel costs. 150% 100% 50% 0% Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec (1) Average daily generation as a percent of the average annual daily generation D. PROJECT LOCATION AND BASIN DESCRIPTION The Carlson Creek site is located approximately 6 miles northeast of Slana, at longitude W, latitude N. The creek drains about 9 sq. mi. of land, most of which is part of the Alaska Range. The creek flows into the Slana River, which eventually flows in the Copper River and the Gulf of Alaska. There are two distinct sub-basins. The major portion of the creek drains a 4.5 sq. mi. area, oriented primarily northwest to southeast, with elevations from 2,200 feet to 6,000 feet. There are no significant glaciers, lakes, or ponds in this sub-basin, but there is one rather large and recent landslide that has filled much of the upper valley with debris. There are no roads in the sub-basin, and trails are very limited. The second sub-basin has a more east-west orientation, and includes Carlson Lake, with a surface area of about 103 acres (about 4% of the total sub-basin area of 4.3 sq. mi.). The average elevation of this sub-basin is somewhat lower. There is an ATV trail to the lake, with some primitive recreational development in a park-like area near the lake outlet. Most of the higher elevation area of the drainage basin is owned by the native regional corporation (Ahtna, Inc.), as is much of the area near the confluence of Carlson Creek and the Slana River. There is a private landholding in this lower Ahtna area that spans both Carlson Creek and the Tok Cutoff Highway. The remainder of the drainage area is owned by the State of Alaska (Department of Natural Resources). Vegetation in the Carlson Creek basin is varied, with moderately dense coniferous forest in the lower elevations to treeless tundra at the higher elevations. Climate is typical for interior Alaska, with limited precipitation (about 13 inches average at lower elevations), relatively warm summers and long, cold winters. E. SITE VISIT A site visit was conducted on September 24, 2009 by Larry Coupe (AP&T Senior Civil Engineer) and Dan Burfoot (AP&T Mechanic). ATVs were ridden to the eastern end of Carlson Lake; the middle portion of Carlson Creek was inspected by hiking on game trails. A memorandum discussing the site visit is included in Appendix A of this report. Key information gained from the site visit is as follows: Carlson Creek Hydroelectric Project 3 December, 2011 Preliminary Feasibility Evaluation

6 There is some limited recreational use of Carlson Lake. Significantly more water was flowing in Carlson Creek than was flowing out of Carlson Lake, even though the drainage areas are about the same. A small creek was observed flowing off the hillside from the northeast towards Carlson Lake, but completely disappeared into the ground prior to reaching the lake. No bedrock outcrops were observed anywhere along Carlson Creek; the ground in the valley probably includes a significant depth of alluvium. Based on these observations and the site topography, AP&T has concluded that Carlson Lake is impounded by a moraine deposit, and that a significant portion of the inflow to the lake leaves the lake by percolation through the moraine rather than by surface flow down the outlet channel. Carlson Creek Hydroelectric Project 4 December, 2011 Preliminary Feasibility Evaluation

7 SECTION 2 HYDROLOGY A. STREAM GAGES When the scope of work for the AEA grant application was being developed, AP&T anticipated that the project would include a diversion from Carlson Creek to Carlson Lake and a siphon intake at Carlson Lake into a penstock leading to a powerhouse near the Tok Cutoff Highway; Carlson Lake would be used to store excess summer flows for use in the winter. Therefore, in the scope of work for the AEA grant, AP&T proposed to install two stream gages to begin measurement of the flows in Carlson Creek and the Carlson Lake outlet. As a result of the site visit, AP&T became concerned that the project as described above would not be feasible due to the high cost of grouting the moraine impounding Carlson Lake. The storage potential of Carlson Lake was what made the site attractive, since it might allow the site to provide a renewable energy source that meets the year-around needs of the Slana-Mentasta- Chistochina system. AP&T therefore elected to forego the gage installation while it decided whether to look any further at Carlson Creek as a generation resource. As a result of that additional evaluation, AP&T concluded that no alternative would be economically feasible, even with 80% grant funding of the development cost. Because of that conclusion, stream gages were not installed. B. FLOW DURATION CURVE Because there are no gage records for Carlson Creek, AP&T has evaluated the generation potential using a regional flow duration curve that was developed by AP&T during its studies of the Yerrick Creek site. This regional flow duration curve is based on flow duration curves for various USGS gages in the area, for various size drainage basins and record lengths. The flow duration curve judged to be most appropriate for Carlson Creek is shown in the table below: Preliminary Flow Duration Curve % Time Exceeded Flow, cfs/mi This regional flow duration curve results in an estimated average annual flow of 0.77 cfs/mi 2 Carlson Creek Hydroelectric Project 5 December, 2011 Preliminary Feasibility Evaluation

8 SECTION 3 ALTERNATIVE ARRANGEMENTS As noted in Section 1, AP&T conducted a preliminary evaluation of alternative arrangements for the project to determine if any looked attractive enough to warrant further study. A key factor in this evaluation was the desire to find an arrangement that would not trigger FERC jurisdiction by potentially causing an impact to the anadromous fish in the Slana River. Another key factor was the desire to avoid impacts to the private landholding surrounding Carlson Creek near the Tok Cutoff Highway. AP&T looked at four different alternatives, as shown on the attached four figures and described below. For the first alternative, there are two options presented for location of the powerhouse, depending on whether to completely avoid a private landholding or not. Similarly, there are three optional powerhouse locations for the second alternative, but only one option for each of the third and fourth alternatives. A. ALTERNATIVE 1 Alternative 1 is the project arrangement that was contemplated in the grant application (see Figure 1). It includes the following features (Option A): A diversion structure on North Fork Carlson Creek A 18 x 6,900 long pipeline to from the diversion structure to Carlson Lake A siphon intake at Carlson Lake A 24 x8700 long pipeline/penstock from Carlson Lake to the powerhouse A powerhouse adjacent to Carlson Creek and just above the private landholding. A 2300 long transmission line to interconnect to our Slana-Mentasta-Chistochina intertie. Access roads along the penstock and pipeline. With Option B, the powerhouse would be located downstream at the Tok Cutoff highway, which would increase the pipeline/penstock length by 1700 feet, eliminate the transmission line, and increase the head by about 70 feet. Note that this puts the powerhouse and part of the penstock on private land; it was considered only to show the benefit of the additional head. FERC would probably rule that they would not have jurisdiction with this alternative. However, AP&T has some technical reservations, as follows: The lake may not be usable for storage without expensive grouting, as explained previously in Section 2. If the project releases directly into the Carlson Creek channel, wintertime operation could be problematic because of ice build-up in the channel, which could back water up into the powerhouse and/or create a hazardous situation for the downstream property owner and highway bridge. A lot would depend on how stable the flows are. Load-following operation in the winter might not be possible. Carlson Creek Hydroelectric Project 6 December, 2011 Preliminary Feasibility Evaluation

9 B. ALTERNATIVE 2 Alternative 2 would be a simple run-of-river development of North Fork Carlson Creek (see Figure 2). As with Alternative 1, there are A and B options depending on the powerhouse location with respect to the private landholding. The diversion site is moved further up the North Fork than with Alternative 1 to gain about 50 feet of additional head. There is a large landslide in the valley upstream of the diversion that appears to be relatively recent. That could be beneficial in that it might moderate stream flows somewhat, which would enhance run-of-river operation. However, the slide is likely to contribute substantial bedload during floods, which could be problematic for the diversion structure. The third option (Option 2C) is to locate the powerhouse at the edge of a pond system near the Slana River to gain about 170 of additional head (compared to 2A). It would require 1400 of additional penstock, but 500 less road. The transmission line would only be a couple of hundred feet long. This option could be worthwhile because it could be developed entirely on state land, and would facilitate winter operation by allowing discharge below a stable ice cover. However, there is a possibility that FERC would rule that they have jurisdiction because the pond system drains directly into the Slana River, which is a cataloged salmon stream. C. ALTERNATIVE 3 Alternative 3 is similar to 2C, but includes a diversion out of Carlson Lake to possibly enhance winter operation (see Figure 3). Both the Carlson Lake and North Fork Carlson Creek diversions would be routed to a forebay at an existing pond, which would probably need to be deepened substantially. From the forebay, the penstock would be routed to the pond system near the Slana River as with Option 2C. However, because of the lower elevation, the penstock could not be located to avoid Ahtna land. Note that this option does not overcome the leaky lake and FERC jurisdiction issues discussed above. D. ALTERNATIVE 4 The final alternative is meant to address the leaky lake issue by developing a reservoir in a basin to the north of the Carlson Creek drainage (see Figure 4). Google Earth images and the USGS topography suggest there might be a reasonable dam site at about the 2500 feet elevation, and there are a couple of lakes to the north that perhaps could be incorporated into the reservoir. The USGS topography is not detailed enough to allow development of a storage curve; the minimum required dam height is estimated to be 80 feet. Inflow to the reservoir would be from Carlson Lake (on a run-of-river basis), North Fork Carlson Creek, and an unnamed creek to the north of the reservoir. The main powerhouse would be located on the same pond system along the Slana River as with Alternatives 2C and 3. Depending on where the North Fork is diverted, there could be enough head to justify a second powerhouse on that diversion. Carlson Creek Hydroelectric Project 7 December, 2011 Preliminary Feasibility Evaluation

10 SECTION 4 CONSTRUCTION COSTS AND COST OF POWER AP&T has made a preliminary cost estimate for each of these alternatives and options in order to allow a reasonable comparison. AP&T has also estimated generation amounts based on the regional flow duration curve described previously, and has calculated a preliminary cost of power for each. Obviously, these are very preliminary values, but are considered to be in the ballpark. A. CONSTRUCTION COST ESTIMATES An estimated construction was developed for each alternative and option based on unit prices for the major components, as follows: Access roads: o Easy construction - $50/ft o Moderate construction - $100/ft o Difficult construction - $200/ft Diversion Structures - $500,000 Embankment dams - $25/cy Pipeline/penstock: o 12 diameter HDPE - $160/ft o 18 diameter HDPE - $200/ft o 24 diameter HDPE - $350/ft Power plants o Structure - $200,000 o Generating equipment - $1000/kW o Miscellaneous equipment - $500/kW Transmission lines - $200,000/mi Contingencies 35% Indirect costs 12% Construction quantities for the alternatives and options were derived by measured lengths from digitized USGS topographic mapping. The construction cost estimates are summarized in the following Table 2. B. GENERATION ESTIMATES The installed capacity for each of the alternatives and options was calculated based on the following assumptions: Flows are proportional to the drainage area, and are defined by the regional flow duration curve described previously; drainage areas were measured from digitized USGS topographic mapping. Hydraulic capacity set at the 10% exceedence level (1.75 cfs/mi 2 ). Carlson Creek Hydroelectric Project 8 December, 2011 Preliminary Feasibility Evaluation

11 Pipeline/penstock head losses calculated by Manning s equation with n= Generating equipment combined efficiency of 80%. The average annual energy for each of the alternatives and options was calculated based on the following assumptions: 90% of the available streamflow is diverted from creeks for generation (10% spill). 50% of the Carlson Lake inflow is diverted for generation (to account for leakage). Pipeline/penstock head losses calculated by Manning s equation with n= Generating equipment combined efficiency of 80%. 20% of the potential generation for run-of-river alternatives is unusable due to mismatch of loads and generation. The calculated installed capacity and average annual generation values are shown in Tables 2. C. COST OF POWER The first year cost of power was calculated for each of the alternatives and options for three levels of grant funding: 0%, $4,000,000, and 80%. Other assumptions for the calculation were as follows: 8.0% interest rate for debt service. 30 year term for debt service. $75,000 incremental O&M cost for run-of-river alternatives $100,000 incremental O&M for storage alternatives The calculated production costs for the alternatives are shown in Table 2. For comparison, the current production cost of diesel generation for the Slana-Mentasta-Chistochina system is about $0.32/kWh (assuming a fuel cost of $4.00/gallon and an efficiency of 12.5 kwh/gallon. D. SUPPLEMENTAL DIESEL GENERATION By comparing the current annual energy requirements shown in Section 1 to the estimated generation by the alternatives, it can be concluded that only Alternative 4 has the potential to generate more than the current energy requirements. All other alternatives would require substantial amounts of supplemental diesel generation, varying from about 100,000 kwh per year to 600,000 kwh per year. As noted in Section 1, loads have been increasing at a rate of about 6% per year; if that trend continues then the amount of supplemental diesel generation would also increase, and even Alternative 4 would require supplemental diesel generation by the time it was built. E. RATE IMPACTS Rate impacts associated with the various alternatives and grant funding levels are also shown in Table 2. As can be seen, only Alternatives 1B, 2A, 2B, 2C, and 3 with 80% grant funding show any beneficial rate impacts. Even with those alternatives, the benefits are quite small compared to the overall retail electricity rate of almost $0.69/kWh. Note that this is based on comparison to current conditions. If diesel fuel costs continue to rise as expected, then the benefits of a Carlson Creek development would also increase. However, it is AP&T s opinion that a more detailed evaluation of the Carlson Creek site to consider the long-term economics would indicate a marginally-economical project at best. It is also AP&T s opinion that there are other Carlson Creek Hydroelectric Project 9 December, 2011 Preliminary Feasibility Evaluation

12 renewable energy options available for the Slana-Mentasta-Chistochina system that are more promising. In particular, AP&T believes that a transmission line interconnecting the Slana- Mentasta-Chistochina system to the Tok system in combination with renewable energy development in the Tok area would be superior to a Carlson Creek development. Carlson Creek Hydroelectric Project 10 December, 2011 Preliminary Feasibility Evaluation

13 Project Feature Table 2 Construction Cost Summary Alternative 1 Alternative 2 Alternative Option A Option B Option A Option B Option C 3 Alternative 4 Access roads $1,555,000 $1,555,000 $1,275,000 $1,300,000 $1,400,000 $2,110,000 $1,875,000 Diversion structures $1,000,000 $1,000,000 $500,000 $500,000 $500,000 $1,500,000 $1,500,000 Storage dam $0 $0 $0 $0 $0 $0 $6,000,000 Pipelines/penstocks $4,425,000 $4,915,000 $2,160,000 $2,360,000 $2,440,000 $5,475,000 $5,165,000 Power plant $494,000 $562,000 $560,000 $609,000 $686,000 $635,000 $979,000 Transmission line $87,000 $0 $87,000 $0 $8,000 $8,000 $265,000 Subtotal $7,561,000 $8,032,000 $4,582,000 $4,769,000 $5,034,000 $9,728,000 $15,784,000 Contingencies $2,646,000 $2,811,000 $1,604,000 $1,669,000 $1,762,000 $3,405,000 $5,524,000 Indirect costs $907,000 $964,000 $550,000 $572,000 $604,000 $1,167,000 $1,894,000 Total construction cost $11,114,000 $11,807,000 $6,736,000 $7,010,000 $7,400,000 $14,300,000 $23,202,000 Installed capacity (kw) Usable generation (MWh) 860 1, ,000 1,260 1,590 Capacity cost ($/kw) 0% grant funding $4,000,000 grant funding 80% grant funding Energy cost ($/kwh) 0% grant funding $4,000,000 grant funding 80% grant funding Rate impact ($/kwh) 0% grant funding $4,000,000 grant funding 80% grant funding 55,600 35,600 11, ,200 32,500 9, ,100 11,400 5, ,700 11,000 5, ,900 10,500 4, ,300 35,500 9, ,500 49,300 11, Carlson Creek Hydroelectric Project 8 December, 2011 Preliminary Feasibility Evaluation

14 SECTION 4 CONCLUSIONS AND RECOMMENDATIONS A. CONCLUSIONS AP&T concludes the following as a result of this reconnaissance-level study of the Carlson Creek site: 1. There are significant challenges with development of Carlson Lake as a storage site for a hydroelectric development. In particular, there is evidence that Carlson Lake is impounded by a moraine which is relatively porous. In addition, there is some limited recreational use of the lake outlet area that could be problematic. 2. A run-of-river development of Carlson Creek appears to be the option that would have the most economical cost of power. However, it would be very seasonal and would require supplemental diesel generation during all of the year except during the early summer. 3. There appears to be potential for developing a reservoir in an area north of Carlson Creek (Alternative 4). However, AP&T has not visited that site and therefore the costs and benefits calculated for it are more speculative than for the other alternatives. It does provide the greatest amount of power. 4. It is unknown whether any of the alternatives could generate during the winter months, either because of a lack of inflow (run-of-river options) or ice buildup below the powerhouse (all options). Discharge into a pond system adjacent to the Slana River might mitigate this latter concern, but that could also trigger FERC jurisdiction. 5. The cost of power from all of the alternatives considered in this study would be significantly higher than the cost of diesel generation unless almost all of the construction cost is funded by grants. It is unclear whether the State would be willing to provide grant funding to the level that would make a Carlson Creek development economical. B. RECOMMENDATIONS As a result of this study, it is AP&T s opinion that the Carlson Creek site does not exhibit a sufficient degree of feasibility to warrant any further study. AP&T believes that there are other options for supplying renewable energy to the Slana-Mentasta-Chistochina system that are more promising. Carlson Creek Hydroelectric Project 12 December, 2011 Preliminary Feasibility Evaluation

15 CARLSON CREEK PROJECT

16 CARLSON CREEK PROJECT

17 CARLSON CREEK PROJECT

18 CARLSON CREEK PROJECT

19 APPENDIX A Site Visit Memorandum

20 Alaska Power & Telephone Company ENGINEERING DEPARTMENT 193 Otto Street, P.O. Box 3222 Port Townsend, WA FAX (360) Telephone: (360) Ext Ext address: MEMO TO: FROM: Bob Grimm Eric Hannan Vern Neitzer Larry Coupe DATE: September 30, 2009 No. of PAGES: 5 RE: Carlson Creek MESSAGE: On September 24, 2009, I visited the Carlson Creek site near Slana with Dan Burfoot from the Tok Office. We first rode ATVs from a trailhead just south of the Carlson Creek bridge over the Tok Cutoff highway to the outlet of Carlson Lake. The trail is in good condition, and the lake is easily accessible. Following the inspection of the lake outlet area, we rode back towards the trailhead and headed upstream on Carlson Creek. We were only able to follow an old trail for a few hundred feet before having to dismount and follow foot and game trails upstream. We first went to an area about 75 feet in elevation above the lake level, which would be a possible site for a diversion over to Carlson Lake. We then went several hundred feet further upstream to see if we could reach the toe of a large landslide that is apparent in Google Earth images. We were able to view the slide toe from a distance, but judged it too distant to be worth the continued hike. We then proceeded downstream to the ATVs, rode to the trailhead, loaded up, viewed the creek from the highway crossing, and returned to Tok. The total trip was from about 8:30 AM to 2:30 PM. 1

21 Prior to the site inspection, I had looked at USGS topographic maps and Google Earth images, and had measured drainages areas and potential head. Based on that information, I had conceived of a project arrangement that included a diversion from Carlson Creek to Carlson Lake and a penstock from Carlson Lake to a powerhouse near the Tok Cutoff highway. Carlson Lake would be used for storing excess flow in the summer for use in the winter. The following are my first impressions of the potential for hydro development at the site, particularly with regard to this perceived concept. CARLSON LAKE Carlson Lake has a drainage area of about 4.3 square miles and a surface area of about 103 acres. Depth is unknown, but judging from the steepness of the shorelines it may be relatively deep. The large surface area would allow for a significant amount of storage with a modest drawdown. The lake outlet area is relatively level, with a park-like setting. It is obviously used occasionally for recreation. Dan indicated there used to be a cabin on the lake that was a permanent residence, accessible by a trail around the shoreline. Dan is not sure if the resident is still alive and/or if the cabin is still being used. The lake level is currently controlled by a beaver dam about 5 feet high at the northeast end of the lake. Only a small amount of flow was observed in the outlet stream below the beaver dam (<1 cfs). There is a small creek running towards the lake from the northwest. As it approaches the lake, it percolates into the ground. During our inspection, the flow never reached the lake, but during high flow periods it would. The fact that this stream disappears into the ground indicates a pretty high porosity for the material damming the outlet end of the lake. My supposition is that the material is unconsolidated glacial drift, possibly a lateral or terminal moraine. This is rather problematic for using the lake in a hydro development, as it is likely that a considerable portion of the lake inflow leaves the lake as subsurface flow. We would need to install some sort of a cutoff (such as a grout curtain) if we want to use the natural or diverted lake inflow for generation. Bedrock is probably quite deep, so a grout curtain could be quite expensive. If we want to consider use of the lake further, we should plan on some seismic refraction studies of the lake outlet, and possibly a test boring and pumping tests. CARLSON CREEK Carlson Creek appears to be a typical high-gradient stream, with a drainage area of about 4.5 square miles at the diversion site. The streambed is primarily gravel and cobbles. The floodplain is perhaps 100 feet wide near the lower end, but tends to narrow and become somewhat steeper as you move upstream. Much of the floodplain is overgrown with brush and small trees, leaving only a primary channel about feet wide. During our visit (a recession flow period) the stream was about 8 feet wide and less than a foot deep, with an estimated flow of perhaps 4-5 cfs. No bedrock was apparent anywhere in the stream channel or on the banks. The stream appears to be cutting though glacial till and/or debris flows. Any intake structure will need to consider both the seepage potential of the substrate and the likelihood of substantial bedload during high flows. A smaller version of whatever we use at Yerrick Creek might be appropriate. 2

22 When I first looked at this site on Google Earth a couple of years ago, the image quality was poor. When I looked at it this year, newer photography was available with much higher resolution, and a large landslide is clearly visible in the basin above the likely diversion site. It is so large that I would have noticed it in the earlier photography, which leads me to believe the slide is quite recent (maybe triggered by the 7.9M 2004 earthquake on the nearby Denali fault?). The slide debris will probably continue to move downstream during high flows. The north side of the creek would provide the best access to the diversion area, and would be the preferred route for the penstock if the flow is not diverted over to the lake. If the flow is diverted to the lake, there appears to be a reasonable sidehill route; the sidehill slopes to not appear to be too steep, although we did not make a thorough inspection of the area. POWERHOUSE SITE The gradient of Carlson Creek appears to be significantly less near the highway than at the diversion area. Carlson Creek eventually flows into the Slana River about 3,000 feet below the highway. There is a native allotment encompassing the highway and Carlson Creek; depending on the cooperativeness of the allotment owners, it may be necessary to locate the powerhouse above the allotment, which would provide a gross head of about 300 feet. However, that location would only work with a project that does not operate in the winter, since a winter discharge could create an ice dam above the allotment that would not be acceptable. If we want to operate in the winter, we should probably plan on running the penstock all the way to the Slana River and discharge there to prevent ice formation; that would provide a gross head of about 450 feet. FLOW MEASUREMENT If we choose to install a stream gage on Carlson Creek, my recommendation would be as follows: Locate the gage in the lower portion of the creek where it is more accessible; there appeared to be a reasonable site where the ATV trail first crosses the creek. This is well below the diversion site, but the channel is probably more stable further down. When flow measurements are made to develop the stage-discharge curve for the gage, on the same day measure flow at the diversion site and at one or two more locations between the diversion and the gage. This would allow us to determine how the flow varies along the creek during high, medium, and low flows so the flows at the diversion site could be derived to the gage flows. Measurement of flow in the outlet stream of the lake near Carlson Creek might also be valuable if that channel can be found. 3

23 Carlson Lake looking south from near outlet (outlet to left of photo) Carlson Creek near diversion; flow estimated at 4-5 cfs 4

24 Carlson Creek above diversion; landslide debris visible in the distance 5