Hydrogeophysical investigations at Hidden Dam, Raymond, California

Journal of Environmental & Engineering Geophysics
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Abstract

Self-potential and direct current resistivity surveys are carried out at the Hidden Dam site in Raymond, California to assess present-day seepage patterns and better understand the hydrogeologic mechanisms that likely influence seepage. Numerical modeling is utilized in conjunction with the geophysical measurements to predict variably-saturated flow through typical two-dimensional dam cross-sections as a function of reservoir elevation. Several different flow scenarios are investigated based on the known hydrogeology, as well as information about typical subsurface structures gained from the resistivity survey. The flow models are also used to simulate the bulk electrical resistivity in the subsurface under varying saturation conditions, as well as the self-potential response using petrophysical relationships and electrokinetic coupling equations.

The self-potential survey consists of 512 measurements on the downstream area of the dam, and corroborates known seepage areas on the northwest side of the dam. Two direct-current resistivity profiles, each approximately 2,500 ft (762 m) long, indicate a broad sediment channel under the northwest side of the dam, which may be a significant seepage pathway through the foundation. A focusing of seepage in low-topography areas downstream of the dam is confirmed from the numerical flow simulations, which is also consistent with past observations. Little evidence of seepage is identified from the self-potential data on the southeast side of the dam, also consistent with historical records, though one possible area of focused seepage is identified near the outlet works. Integration of the geophysical surveys, numerical modeling, and observation well data provides a framework for better understanding seepage at the site through a combined hydrogeophysical approach.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Hydrogeophysical investigations at Hidden Dam, Raymond, California
Series title Journal of Environmental & Engineering Geophysics
DOI 10.2113/JEEG16.4.145
Volume 16
Issue 4
Year Published 2011
Language English
Publisher Environmental and Engineering Geophysical Society
Contributing office(s) Crustal Geophysics and Geochemistry Science Center
Description 20 p.
First page 145
Last page 164
Country United States
State California
City Raymond
Other Geospatial Hidden Dam