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Home My WebLink AboutFalse Pass Preliminary Hydrology Report for Unga Man and Waterfall Sep 2015polarconsult alaska, inc. 1503 West 33rd Avenue, Suite 310 Anchorage, Alaska 99503-3638 Phone: (907) 258-2420 FAX: (907) 258-2419 I L E T T E R R E P O R T DATE: September 11, 2015 TO: Bob Christensen, Living Systems Design, LLC FROM: Joel Groves, P.E. SUBJECT: Preliminary Hydrology Estimate for Hydropower Development at Unga Man and Waterfall Creeks near False Pass, AK CC: Unga Man Creek and Waterfall Creek (the "subject creeks') are under consideration for hydropower development to provide electricity to the community of False Pass. Available hydrology data from the U.S. Geological Survey (USGS) was reviewed to provide preliminary estimates of seasonal stream flow at Unga Man and Waterfall Creeks near False Pass, Alaska (Figure 1). Available hydrology data for the region is scarce, and is only suitable for preparing a broad range of estimated seasonal hydrology at the subject creeks. Data from stream gauges installed at the subject creeks in August 2015 will be critical for assessing the feasibility of these resources for hydropower development. Figure 1: Location Map showing Unga Man and Waterfall Creeks 150911-FALSEPASSITYDROLOGYMEMO. DOC POLARCONSULT LETTER REPORT PRELIMINARY ESTIMATE OF HYDROLOGY FOR UNGA MAN CREEK NEAR FALSE PASS, AK 1 Available Regional Hydrology Data Hydrology along the Alaska Peninsula and Aleutian Islands varies significantly with basin location, topography, and orientation, with basins on the Bering Sea side of the peninsula and islands usually being significantly drier than basins facing the Pacific Ocean. Figure 3 is a detail of a USGS map of mean annual precipitation in Alaska, and illustrates the significant difference in precipitation that can occur over short distances in this region. There are four USGS-gauged basins in the general vicinity of False Pass — two in Cold Bay, approximately 40 miles to the northeast, and two in Sand Point, approximately 130 miles to the y east-northeast (Figure 2). Hydrology data also exists for hydropower projects in Atka, Chignik Bay, and Chignik Lagoon (Figure 2), however these sites are significantly farther from False Pass, and are expected to be less predictive of hydrology at the subject creeks. Available USGS stations and data in the general vicinity of False Pass are listed in Table 1. .._:L-1 1 IQf_C C......;— C+,+i—ne nnnr G71cc DMCC DiaCkn Creek Name Stapp Ck Russell Ck Whiskey Bills Ck Humboldt Ck Nearest Community Cold Bay Cold Bay Sand Point Sand Point USGS Gauge ID 15297609 15297610 15297602 15297603 Mean Annual Precipitation (inches, see —50 —50 —70 —70 Figure 3 Location relative to False 40 miles Pass NE 40 miles NE 130 miles ENE 130 miles ENE Basin in East -facing basin in West -facing Northwest facing basin in low-lying mostly low-lying basin in low- mostly low-lying terrain. terrain with terrain. Basin rises lying terrain. Basin rises from tidewater no from tidewater at Basin rises from at northwest to 1,070 ft Basin Description prominent east to alpine along tidewater to 335 summit on ridge along topography western edge of ft. along south-southeast divide. along basin basin with 4,000+ ft northeasterly Significant swampy area divide. peaks. Several divide. in low lands. small lakes present. Gauged Basin Area s mi 1.68 30.9 0.3 5.2 Gauge Elevation 150 7.65 80 55 Record start date 10/16/2000 10/1/1981 8/11/1983 8/10/1983 Record end date 7/16/2015 8/26/2015 3/19/1984 3/19/1984 Record Period rs 14.8 25.1 0.6 0.6 Dail Record Count 52 9,157 221 222 Total Record, Years 0.1 33.9 0.6 0.6 1. No data logger installed, only instantaneous Tlow measurements. Of these four USGS gauges, only Russell Creek near Cold Bay has a continuous record suitable for developing preliminary estimates of long-term stream flow statistics at the subject creeks. The other three USGS gauges have very short or incomplete records that are minimally useful for estimating hydrology statistics at the subject creeks. Whiskey Bills and Humboldt Creeks each have under a year of record, and Stapp Creek only has 52 discrete flow measurements taken over a 15-year period. Annualized normalized stream flows for these four USGS gauges are presented in Figure 4. September 11, 2015 Page 2 of 5 POLARCONSULT LETTER REPORT PRELIMINARY ESTIMATE OF HYDROLOGY FOR UNGA MAN CREEK NEAR FALSE PASS, AK ATKA Figure 3: Mean Annual Precipitation in Project Vicinity CHIGNIK BAY CHIGNIK LAGOON 1 COLD BAY _, t FALSE PASS + 0 t =4. 'i f�uY SAND POINT (Whiskey Bills Creek, Humboldt Creek) i ..c..` My o . SAND POINT et Inset of Plate 2, USGS Publication WRIR 93.4179. Contours show average annual precipitation in inches. September 11, 2015 Page 3 of 5 POLARCONSULT LETTER REPORT PRELIMINARY ESTIMATE OF HYDROLOGY FOR UNGA MAN CREEK NEAR FALSE PASS, AK Figure 4 shows normalized seasonal streamflow for the four available USGS gauged basins. Figure 4: Normalized Average Seasonal Stream Flow at USGS-Gauged Basins 14 2 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec The hydrology record for Russell Creek shows average flows from June through November are approximately 7 to 11 cubic feet per second (cfs) per square mile, and from December through May are approximately at 3 to 5 cfs per square mile. Hydrology records for Whiskey Bills Creek, Stapp Creek, and Humboldt Creek each show similar average winter flows as Russell Creek, but significantly lower summer flows in the range of 1 to 3 cfs per square mile. Because of the short (single -year) period of record at Whiskey Bills and Humboldt Creeks, there are insufficient data to conclude that these records are characteristic for these creeks. However, the series of discrete flow measurements over 15 years at Stapp Creek is consistent with the low summer flows at Whiskey Bills and Humboldt Creeks, suggesting the limited data at those two stations may be representative of hydrology for those basins. It is hypothesized that the different seasonal hydrology characteristics observed at Russell Creek versus at Whiskey Bills, Stapp, and Humboldt Creeks can be attributed to the fact that the Russell Creek basin has a significant alpine basin divide that can better collect and store rain and snow, sustaining higher flows through the summer season through snowmelt. The other creek basins are generally low-lying basins that lack this high -altitude terrain and resulting storage capacity. Humboldt Creek does have some alpine headwaters within the basin, but the basin may be located in a rain shadow due to its northwest -facing orientation. September 11, 2015 Page 4 of 5 POLARCONSULT LETTER REPORT PRELIMINARY ESTIMATE OF HYDROLOGY FOR UNGA MAN CREEK NEAR FALSE PASS, AK 2. Preliminary Estimate of Hydrology at Subject Creeks Unga Man Creek shares certain basin characteristics with Russell Creek that suggest it may have similar hydrology as Russell Creek. These characteristics include an east -facing basin orientation and alpine terrain along the basin divide. The other three gauged basins are predominately low-lying basins that lack or have limited alpine terrain. Based on the limited available information, it is reasonable for preliminary planning purposes to assume that Unga Man Creek hydrology is similar to Russell Creek hydrology, adjusted for relative basin areas. Collection of actual flow data at Unga Man Creek will be critical for validating this assumption. Waterfall Creek also has an east -facing alpine basin. It may therefore also have similar hydrology as Russell Creek, adjusted for relative basin areas. Collection of actual flow data at Waterfall Creek will be critical for validating this assumption. Table 2 summarizes the drainage basins for the subject creeks and provides preliminary estimates of seasonal flow for each creek. The wide range of the estimate encompasses the range of apparent seasonal hydrology patterns represented in the four gauged basins listed in Table 1. As described above, available data favors the higher -range of the estimates, but there is insufficient available data to rule out the lower range of the estimate at either of the subject creeks. Table 2: Basin Data and Preliminary Hvdrnlnav Fctimatac fnr ciihiart rrcnlre Creek Name Unga Man Creek Waterfall Creek Nearest Community False Pass False Pass Mean Annual Precipitation inches, see Figure 3 -60 -60 Location relative to False Pass 1 `mile S 1.5 rntle NNW , East -facing lowland East -facing alpine basin with glaciated basin on side of alpine divides to mountain. Rises from Basin Description north, west, and tidewater on east to south. Divide 1,000+ ft. on western elevation of 1,000 divide. Some less to 2,800+ ft. steep slopes in alpine areas. Proposed Project Basin Area(square miles note 1 3.14 -0.3 Proposed Diversion Elevation feet above sea level -200 -400 Preliminary Estimated Range of Normalized Mean Flow, June - Nov. cfs per square mile 1 to 10 1 to 10 Preliminary Estimated Range of Normalized Mean Flow, Dec. - May cfs per square mile 1 to 5 1 to 5 Preliminary Estimated Stream Flow, June to November 3 to 30 0.3 to 3 Prelimina Estimated Stream Flow, December to May 3 to 15 0.3 to 1.5 Prelimina Estimate of Annual Average Stream Flow 3 to 25 0.3 to 2.5 03111 U0lQ Dui r INireu 11 ur n nenewaaie rnergy Kesource Assessment for the Communities of Cold Bay, False Pass, and Nelson Lagoon, YourClean Energy, LLC, May 18, 2010. September 11, 2015 Page 5 of 5