Soda Springs Dam Fish Passage Construction
Soda Springs Dam is part of the North Umpqua Hydroelectric Project owned and operated by PacifiCorp Energy. The dam is a combination concrete arch and gravity structure. The dam is 77 feet high and spans approximately 300 feet from abutment to abutment. As part of a recent FERC relicensing agreement, PacifiCorp agreed to construct fish passage structures at Soda Springs to facilitate juvenile and adult fish migration. Subsequently, PacifiCorp retained MWH Americas as the Prime Consultant, with Cornforth Consultants as the team’s Geotechnical Consultant.
The new facility included a fish ladder, juvenile fish screens, a new bridge to support the fish pipeline, and an evaluation building. FERC also required a reanalysis of the seismic stability of existing structures under updated ground motions. Cornforth completed detailed geologic mapping to characterize the site and provide data for foundation design, design of rock supports, and excavation shoring. Exploratory borings were performed in very difficult access locations to identify foundation conditions and to install instruments to characterize groundwater levels and landslide impacts. Slope stability studies and lateral earth pressures were evaluated to determine required design loads for permanent shoring walls. Bearing capacity and settlement calculations were completed for both shallow and deep foundation systems. Laboratory testing was completed on recovered overburden and rock core. Seismic ground motion studies were completed to determine site-specific response spectra to be used in a dynamic structural response analysis. Geotechnical work was summarized in geotechnical data reports and geotechnical analysis reports. Plans and specifications were prepared for geotechnical aspects of the project.
Cornforth Consultants provided key input to MWH and PacifiCorp on several last minute permit issues raised by FERC and the Oregon Department of Fish & Wildlife. Cornforth also provided full-time construction observation during installation of micropiles supporting the fish ladder intake and for installation of H-piles and tie-backs as part of the permanent retaining walls.