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Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) damage to infrastructure, changes in hydroelectric production, and increased flooding of residential and commercial areas. Flooding is already a problem on a 5- to 10- year basis. The Eyak Lake watershed also has an active restoration program in place that can provide ideas and examples for land managers in other areas. The Copper River Watershed Project (CRWP), a local nonprofit group, has led a watershed restoration planning team with representatives from the Alaska Department of Fish and Game (ADFG), the Native Village of Eyak, the City of Cordova, the USDA Forest Service, the Prince William Sound Science Center, and other agencies, organizations, and individuals. Some of the completed activities and proposed projects will be discussed in the section on recommendations. Watershed Values • Large sockeye and coho salmon runs, average annual index counts 19,000 and 10,000, respectively (Botz et al. 2009). Extensive rearing areas in a shallow lake. Spawning habitat along the shore and in tributaries. No current population concerns exist. • Salmon populations support commercial, sport, and subsistence fisheries. Other salmonids provide sport fishing. • Residential and light industrial areas around lake and on floodplain downstream from the lake. This floodplain currently experiences flooding every 5 to 10 years. • Hydroelectric power generation on Power Creek. • Floatplanes use lake, small wheeled planes land on airstrip along lake. • Backup water supply for city of 2,000 people, three salmon processors/canneries. • Wildlife viewing – bears, waterfowl, and fish. Ecological Triggers and Thresholds for these Values • Water temperatures: 12-15 °C is optimal. 25 °C is lethal for salmonids. • A minimum of 5 cfs is needed in the Power Creek area bypassed by the hydroelectric diversion. The plant can utilize up to 320 cfs. (Mean creek flow 50-500 cfs.) • Flooding occurs when lake rises approximately 5-6 ft. • Floods at an unknown velocity may mobilize spawning gravels, destroy eggs. Data Available, Data Needs • Power Creek (main tributary) gauge data 1948-1995. Currently, the required 5 cfs flow is maintained mechanically and is monitored by the electric company. The total flow above that level is not monitored. • The Prince William Sound Science Center and CRWP have done some monitoring of water quality in Eyak Lake for the past few years. Eventually they will have more consistent data for temperature, dissolved oxygen, and other parameters. There is only limited water quality data for Power Creek. • Historic precipitation and air temperature data are available from gauges at the Cordova airport and a station in town. These are not in the Eyak watershed but are geographically close. • Need to correlate precipitation, cfs in Power Creek, with flood events in lake and Eyak River. No lake height data available, but a gauge has been installed on a downstream bridge this past year. • Preliminary groundwater temperatures for one winter taken by Gordon Reeves and Steven Wondzell, USDA PNW Research Station. • SNAP program conducted by the UAF has predictions for temperatures, precipitation, and freeze/thaw dates at a 2km scale. This was calculated with PRISM and five climate models. On- 278 Assessing the Vulnerability of Watersheds to Climate Change
Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10) line maps and bar graphs are available for Alaska communities. Raw data are available for use with GIS. • Total salmon spawning area not known. Sensitivity The sensitivity of the Eyak Lake watershed is due mainly to natural conditions –steep slopes, shallow lake, and high precipitation. Human activities, such as road building and other development, have been relatively minimal but there are stressors that might affect watershed’s ability to respond to the predicted increases in temperature and precipitation. • The mean high elevation of the watershed makes the watershed less sensitive to the effects of higher temperatures on the glaciers and snowpack. However, the current storm patterns from the relatively warm ocean already cause frequent rain-on-snow events. These are likely to increase and occur at higher elevations. • The relatively high percentage of area covered by glaciers and icefields makes the watershed more sensitive to the effects of melting glaciers: increased flows and erosion of glacial moraine. • Stream temperatures could rise with predicted changes in air temperatures but should be well within the suitable range for salmonids. Power Creek temperatures were no more than 10 °C at a downstream location (Sea-Run Fisheries 2006) and should rise no more than the predicted 2 to 3 °C air increase. All streams are relatively steep and short, so there is little opportunity for streams to warm. • Water temperatures for most of Eyak Lake are dominated by stream and groundwater flows. Summer surface temperatures are generally less than 13.5 °C and data at two sites suggest there is a thermocline at about 1 m (Crawford 2010). • Parts of Eyak Lake could be sensitive to higher water temperatures. The west arm of the lake has less circulation, is less than 3 m deep, and currently has recorded surface temperatures of 15 °C (the top end of the optimal range for salmonids). • Watershed is naturally flashy due to 19.7% being unvegetated, 23.1% having steep slopes (>70%), along with thin soils, high precipitation, and long duration of storm events. • Flooding already occurs in residential areas along Eyak River and Eyak Lake. Floods have occurred in 1983, 1985, 1986, 1995, 2004, and 2006. • Hydroelectric power generation is sensitive to flows in Power Creek, which are at a minimum in winter when precipitation is bound as ice and snow. Higher precipitation, warmer temperatures, and rising snowline could increase winter power generation. • Salmon spawning in the lake and smaller tributaries not sensitive to redd displacement by floods. Those fish spawning in the main channel of Power Creek may be susceptible to substrate mobilization. • The risk of avalanches could increase as warmer temperatures create more frequent wet, heavy snowpacks. There are a high percentage of avalanche-prone slopes of 58 -173%. There have been three fatal incidents in past 15 years. • Landslides. High precipitation, long steep slopes characteristic of glacial U-shaped valleys, thin soils, underlying bedrock, and glacial till increase propensity for landslides. Stressors Stressors from residential development include hydrocarbon input to the lake from the streets and snow dumping, nutrient input from fertilizer and leach fields, minor sediment input from unpaved roads, and runoff from two subdivisions. Low levels of hydrocarbons have been detected in water samples, but the overall effects of oil and the other stressors have not been quantified. 279 Assessing the Vulnerability of Watersheds to Climate Change
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AUTHORS AND CONTRIBUTORS Authors* M
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ASSESSSING THE VULNERABILITY OF WAT
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staff; the task group included repr
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Figure 2. Conceptual model for asse
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Figure 3. Density of springs and sm
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Using Historic Data One finding con
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NF (Region 8) relied on information
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level of uncertainty. Though there
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climate (Casola et al. 2005). Only
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sensitivity. Most were derived from
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The sensitivity evaluation typicall
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in exposure. The result of combinin
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highest priority for management act
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to information affected the assessm
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with and rely on in many resource d
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Pilot National Forest Reports Conte
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Assessment of Watershed Vulnerabili
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Gallatin National Forest Watershed
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Helena National Forest Watershed Vu
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Sawtooth National Forest Watershed
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Umatilla National Forest Watershed
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