Cornforth Consultants
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    • Earth and Rockfill Dams >
      • Barney Reservoir
      • Frog Lake Reservoir
      • Iron Gate Dam Raise
      • McGuire Dam Raise
      • Bonneville Cofferdam
      • Bull Run No. 2 Seismic Stability Analysis
    • Levees and Canals >
      • Libby Dike Rehab.
      • St. Johns Dike Stabilization
      • Cowlitz River Levees
      • Swift Canal Failure
    • Earthquake Engineering >
      • Barney Dam Seismic Analysis
      • Fern Hill WTP Liquefacation Study
      • Bull Run No. 2 Seismic Stability Analysis
      • Mt. Tabor Seismic Stability Analysis
      • Port Westward Power Plant Seismic Design
    • Rock Slopes and Tunnels >
      • Libby Rockfall Mitigation
      • Sandy River Pipeline Tunnels
      • Ketchikan Third Avenue Extension
      • Sain Creek Water Supply Tunnel
      • Montana Rockfall Hazard Rating System
    • Foundations >
      • Port Westward Power Plant
      • Cascade Locks Casino
      • Air National Guard Hangar
      • Biglow Canyon Windfarm
      • Oakridge Water System Improvements
    • Concrete Dams and Locks >
      • John Day Lock & Dam
      • Marmot Dam Removal
      • The Dalles Dam
      • Willamette Falls Dam
      • Bonneville Dam
    • Transportation >
      • OTIA Cracked Bridge Geotechnical Baselines
      • Newburg Dundee Bypass Design DEIS
      • I-84 Sandy River Bridge Investigation
      • Tanana River Bridge Foundation, Tok, Alaska
      • Montana RHRS Implementation
      • Ketchikan Third Avenue Extension
    • Ports and Airports >
      • Navy CVN Drydock
      • Depoe Bay Seawall Distress
      • Willamette Falls Flow Control Structure
      • Air National Guard Hangar
    • Water and Wastewater >
      • Fern Hill Water Treatment Plant
      • Tualatin Valley North Transmission Line
      • Evaluation of 28 Water Storage Facilities
      • City of Sandy Water Treatment Plant
      • Mt. Tabor Reservoir No. 5 Cap Study
      • Oakridge Water System Improvements
  • Key Staff
    • Mike Meyer
    • Gerry Heslin
    • Brent Black
    • Ben George
    • Chris Carpenter
    • Charlie Hammond
    • Darren Beckstrand
    • George Machan
    • Tom Westover
    • Wade Osborne
    • Adam Koslofsky
    • Andy Kost
    • Aine Mines
    • Logan Allender
    • Anna Casady
    • Noah Kimmes
    • Aleyna Link
    • Justin McCarley
    • Michael Bunn
    • Larry Pierson
    • Andy Vessely
    • John Sager
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Frog Lake Dam Reconstruction​

Three Lynx, Oregon
Frog Lake Dam was built in 1953 to provide additional storage capacity for the Oak Grove Hydroelectric Project near Estacada, Oregon. The reservoir allows Portland General Electric to cycle water levels to produce electricity at peak times of usage. However, the reservoir leaked excessively and prevented the full use of off-peak storage. Sinkholes would form in the reservoir floor and redevelop shortly after remedial backfilling. PGE retained Cornforth Consultants, Inc. (CCI) to evaluate the cause of the sinkholes and develop repair options. Geologic reconnaissance by CCI revealed that the reservoir was built on a massive, 3-square mile ancient landslide. The sinkholes were developing as landslide movements stretched and cracked the reservoir. Leakage from the reservoir raised groundwater levels within the slide mass, exacerbating the ground movement.

​Portland General Electric considered abandoning the facility. CCI recommended an alternative plan of constructing a new central embankment dam to create a smaller reservoir that would reduce embankment loads and avoid the area of major sinkhole formation. Following reservoir reconstruction, groundwater and slope stability conditions dramatically improved. The facility now allows PGE to cycle reservoir levels to meet peak power demand. The increased revenues generated by cycling allowed PGE to recoup the cost of reconstruction in just three years.
Large Rockfall Blocking Access Road to Ross Dam
Frog Lake Central Dam Reconstruction

Services Provided:

  • Site Reconnaissance
  • Geologic Hazards
  • Field Explorations
  • Laboratory Testing
  • Embankment Design
  • Dam Modifications
  • Instrumentation
  • Home
  • Services
    • Earth & Rockfill Dams
    • Reservoirs, Canals, and Levees
    • Spillway Safety Inspections
    • Landslides and Rockfall
    • Earthquake Engineering
    • Geologic Hazards
    • Geotechnical Site Characterization
    • Hydrogeology
    • Expert Witness
    • Concrete Dams and Locks
    • Geotechnical Instrumentation
    • Deep and Shallow Foundations
    • Geotechnical Manuals
  • Industries
    • Water Resources
    • Energy
    • Natural Resources
    • Industrial
    • Transportation
    • Ports and Airports
    • Expert Witness
  • Projects
    • Earth and Rockfill Dams >
      • Barney Reservoir
      • Frog Lake Reservoir
      • Iron Gate Dam Raise
      • McGuire Dam Raise
      • Bonneville Cofferdam
      • Bull Run No. 2 Seismic Stability Analysis
    • Levees and Canals >
      • Libby Dike Rehab.
      • St. Johns Dike Stabilization
      • Cowlitz River Levees
      • Swift Canal Failure
    • Earthquake Engineering >
      • Barney Dam Seismic Analysis
      • Fern Hill WTP Liquefacation Study
      • Bull Run No. 2 Seismic Stability Analysis
      • Mt. Tabor Seismic Stability Analysis
      • Port Westward Power Plant Seismic Design
    • Rock Slopes and Tunnels >
      • Libby Rockfall Mitigation
      • Sandy River Pipeline Tunnels
      • Ketchikan Third Avenue Extension
      • Sain Creek Water Supply Tunnel
      • Montana Rockfall Hazard Rating System
    • Foundations >
      • Port Westward Power Plant
      • Cascade Locks Casino
      • Air National Guard Hangar
      • Biglow Canyon Windfarm
      • Oakridge Water System Improvements
    • Concrete Dams and Locks >
      • John Day Lock & Dam
      • Marmot Dam Removal
      • The Dalles Dam
      • Willamette Falls Dam
      • Bonneville Dam
    • Transportation >
      • OTIA Cracked Bridge Geotechnical Baselines
      • Newburg Dundee Bypass Design DEIS
      • I-84 Sandy River Bridge Investigation
      • Tanana River Bridge Foundation, Tok, Alaska
      • Montana RHRS Implementation
      • Ketchikan Third Avenue Extension
    • Ports and Airports >
      • Navy CVN Drydock
      • Depoe Bay Seawall Distress
      • Willamette Falls Flow Control Structure
      • Air National Guard Hangar
    • Water and Wastewater >
      • Fern Hill Water Treatment Plant
      • Tualatin Valley North Transmission Line
      • Evaluation of 28 Water Storage Facilities
      • City of Sandy Water Treatment Plant
      • Mt. Tabor Reservoir No. 5 Cap Study
      • Oakridge Water System Improvements
  • Key Staff
    • Mike Meyer
    • Gerry Heslin
    • Brent Black
    • Ben George
    • Chris Carpenter
    • Charlie Hammond
    • Darren Beckstrand
    • George Machan
    • Tom Westover
    • Wade Osborne
    • Adam Koslofsky
    • Andy Kost
    • Aine Mines
    • Logan Allender
    • Anna Casady
    • Noah Kimmes
    • Aleyna Link
    • Justin McCarley
    • Michael Bunn
    • Larry Pierson
    • Andy Vessely
    • John Sager
  • Resources
  • Careers
    • Geotechnical Engineer
  • Contact Us