Frog Lake Reservoir Landslide

Three Lynx,  Oregon

Frog Lake reservoir was built in 1953 as an addition to the Oak Grove Project near Estacada, Oregon, to produce electricity at peak times of usage. For decades, the reservoir leaked excessively and was unable to fulfill its purpose. In 1991, Landslide Technology determined that the reservoir was built on a massive, 3-square mile ancient landslide. Cracks and sinkholes developed as the slide moved due to the load of the reservoir and water leaking into the slide mass. Groundwater levels outside the reservoir rose and numerous springs appeared down slope as a result of the cracks and sinkholes.

Portland General Electric considered abandoning the facility. Landslide Technology recommended an alternative of building a central embankment and reducing the reservoir's load on the landslide. The new embankment avoids the troublesome area of the reservoir. Following reconstruction, groundwater and slope stability conditions have dramatically improved. The original intent of the project was reinstated, and the generation of peak electricity quickly recovered the cost of reconstruction.

Frog Lake Reservoir Following Reconstruction

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Services Provided:

• Geologic reconnaissance of landslide area
• Landslide hazard mapping
• Site investigation by borings and test pits
• Geotechnical Instrumentation
  
• Landslide hazard management and planning
• Evaluation of appropriate remedial options