Eightmile Lake Storage Restoration Feasibility Study Presented by - - PowerPoint PPT Presentation

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Eightmile Lake Storage Restoration Feasibility Study Presented by - - PowerPoint PPT Presentation

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Eightmile Lake Storage Restoration Feasibility Study Presented by David Rice, P .E. Anchor QEA, LLC April 27, 2017 Eightmile Lake Storage Restoration Feasibility Study 1 Presented by David Rice, P .E. Anchor QEA, LLC Eightmile

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Eightmile Lake Storage Restoration – Feasibility Study

Presented by David Rice, P .E. – Anchor QEA, LLC April 27, 2017

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Existing Dam and Spillway

Historical High Water Surface Elevation ~ 4,671 Feet Current High Water Surface Elevation ~ 4,667 Feet Spillway Notch, Controlled By Stop Logs

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Existing Embankment

Embankment Historical Embankment Crest Embankment Erosion

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Low-Level Outlet Gate

Come Along Gate Stem 30” Slide Gate Debris Rack 30” Pipe Inlet

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Low-Level Outlet Pipe, Near Pipe Inlet

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Low-Level Outlet Pipe, Log-Stave Section

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Low-Level Outlet Pipe, Wood Stave Pipe

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Low-Level Outlet Pipe, Near Pipe Outlet

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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  • Gate Operation

– Requires come along to open and close gate – Rocks/debris make operation challenging

  • Dam Condition and Level Control

– Embankment erosion, reduced water storage – <1,400 acre-feet available without pumping/siphoning

  • Low-Level Outlet Pipe

– Multiple materials, some in poor condition – Pipe collapse has recently reduced capacity

  • Storage releases are critical to IPID late summer

water supply, especially during dry years

Existing Challenges, Deficiencies, Constraints

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Eightmile Lake Drainage Basin

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Eightmile Lake Hydrology

Characteristic Estimated Value Drainage Area 3,822 acres Maximum Annual Watershed Yield 31,001 acre-feet 10% Exceedance Annual Watershed Yield 24,829 acre-feet Mean Annual Watershed Yield 19,686 acre-feet 50% Exceedance Annual Watershed Yield 19,128 acre-feet 90% Exceedance Annual Watershed Yield 15,152 acre-feet Minimum Annual Watershed Yield 11,419 acre-feet

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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  • Reconnaissance Inspection, 1995
  • Initiated review of proposed storage restoration

project with Dam Safety, phone call, February 2017

– Replacement of dam and outlet facilities will require detailed review by Dam Safety…engineering reports, drawings, specifications, inspection plan, O&M Plan

  • Preliminary hydrology and hydraulic calculations

have been completed, per Dam Safety Guidelines

  • Feasibility level design based on conservative design

assumptions (Step 8 design storm)

Consultation with Ecology Dam Safety Office

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Overall Plan

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Elevations

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Eightmile Lake Storage Restoration – Feasibility Study Presented by David Rice, P .E. – Anchor QEA, LLC

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Typical Section – Embankment

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Typical Section – Spillway

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Low-level Outlet

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Anticipated Reservoir Operation

Month Storage Level Stop Logs Low-level Outlet Pipe Operation Isolation Valve Status Control Valve Status January Refill Removed Closed/Filling Open Closed February Refill Removed Closed/Filling Open Closed March Refill/Spill Removed Closed/Filling Open Closed April Refill/Spill Removed Closed/Filling Open Closed May Refill/Spill Removed Closed/Filling Open Closed June Refill Placed Closed Open Closed July Full Placed Release Begins Open Partially Opened August Draw Down Placed Gravity Release Open Partially Opened September Draw Down Placed Gravity/Siphon Release Open Fully Opened October Low Removed Closed Open Closed November Refill Removed Closed/Filling Open Closed December Refill Removed Closed/Filling Open Closed

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Water Surface Area Comparison

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  • Access and mobilization of equipment and materials

– Via helicopter – Overland – On-site materials

  • Seasonal restrictions

– Lake level would need to be drawn down – Impact to lake and irrigation water supply

  • Excavation and earth moving

– Large rock – Deep excavation

  • Minimizing disturbance

Construction Challenges

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  • Refine opinions of cost
  • Complete feasibility study report
  • Review and refine with input from IPID

Ongoing Work

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  • IPID investigation of temporary pipe repair
  • Review feasibility analysis with Dam Safety
  • Develop detailed designs
  • Develop and implement permitting strategy to

secure permits

  • Continue consultation with the U.S. Forest Service
  • Refine construction approach

Next Steps, Following Feasibility Study

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Questions/Discussion