final Sedimentation Report - City and Borough of Sitka

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3500 3000 2500 2000 1500 Distance along creek (ft) 1000 500 1957 Topo/2007 LiDAR Estimated Existing Delta Existing Spill Existing Max Drawdown Estimated Expansion Delta Expansion Spill Expansion Max Drawdown Figure 23. Estimated Existing and Expansion Brad Creek Delta. 500 450 400 350 300 250 0 Sheldon Creek Sheldon Creek has a drainage area of approximately 4 square miles. The existing delta deposits are quite thin and spread across the broad valley floor (Figure 24). Figure 24. Photo of Existing Sheldon Creek Delta. Blue Lake Reservoir Sedimentation Report 28 Blue Lake Project Expansion Watershed GeoDynamics December 2009 FERC No. 2230 Elevation (ft)
A longitudinal profile of Sheldon Creek was plotted from the 1957/2007 topographic data (Figure 25). No data on the Sheldon Creek delta are available; an estimated existing delta surface was plotted based on photographs. The Expansion delta will be formed in a confined, higher gradient section of Sheldon Creek and will likely have similar characteristics to the current Becky Creek delta in the canyon reach. The Expansion delta in Sheldon Creek will be mobile; the substrate will be re-worked as the lake level fluctuates. The stream length of spawning habitat available at the interface of Sheldon Creek will be less than is available in the existing project. 3000 2500 2000 1500 Distance along creek (ft) 1000 500 1957 Topo/2007 LiDAR Estimated Existing Delta Existing Spill Existing Max Drawdown Estimated Expansion Delta Expansion Spill Expansion Max Drawdown Figure 25. Estimated Existing and Expansion Sheldon Creek Delta. SUMMARY The City and Borough of Sitka Electric Department is evaluating raising the dam at the Blue Lake Hydroelectric Project as much as 83 feet above the current dam height to provide additional generation capacity. Operation of the Blue Lake Project under proposed Expansion conditions would inundate approximately 1.9 miles of the current Blue Lake Creek bed upstream of the existing Blue Lake and change the location of reservoir sedimentation and delta development. Rainbow trout use the current Blue Lake Creek delta for spawning and incubation. The objectives of this Reservoir Sedimentation Study are to determine the extent and estimated Blue Lake Reservoir Sedimentation Report 29 Blue Lake Project Expansion Watershed GeoDynamics FERC No. 2230 December 2009 0 500 450 400 350 300 250 Elevation (ft)
Page 1: FINAL RESERVOIR SEDIMENTATION STUDY
Page 4 and 5: Figure 11. Cross Sectional Profiles
Page 6 and 7: Brad Creek Figure 1. Proposed Expan
Page 8 and 9: 2. Evaluate probable future fish ha
Page 10 and 11: The mapping units were transferred
Page 12 and 13: in June flows were greater than 541
Page 14 and 15: Peak flows in Blue Lake Creek were
Page 16 and 17: In lakes and reservoirs with fluctu
Page 18 and 19: 2. The operations model provides a
Page 20 and 21: Elevation (ft) Elevation (ft) 370 3
Page 22 and 23: Under expansion operation condition
Page 24 and 25: Relative Elevation (ft) Relative El
Page 26 and 27: 100% 90% 80% 70% 60% 50% 40% 30% 20
Page 28 and 29: Table 5. Estimated Spawning Use, Me
Page 30 and 31: 3500 3000 2500 2000 1500 Distance a
Page 34 and 35: volume of sediment deposition and e
Page 36 and 37: Comment Number Comment Summary Resp
Page 38 and 39: Blue Lake Creek Delta Sediment Samp
Page 40 and 41: pan 3,876 14.36 mm 0.0471 ft Blue L
Page 42 and 43: December 2009 Blue Lake Creek Reser
Page 44: Blue Lake Creek Delta Sediment Samp

final Sedimentation Report - City and Borough of Sitka

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