Seepage Investigation Using Geophysical Techniques at Coursier Lake Dam, B.C., Canada
Phil Sirles*, MicroGeophysics Corporation, Wheat Ridge, Colorado
Paper – [pdf] DAMS_Sirles_1997 SAGEEP-SP seepage_investigation
Low-pool data indicated very high resistivities (3000 to 5000 ohm-m) throughout the embankment indicating a coarse-average grain size, probably unsaturated sands and gravels. Higher resistivities (>5000 ohm-m) were obtained within the foundation deposits along the
Results from low-pool SP surveys, performed both on-shore and offshore, indicate a dispersed or sheet-flow seepage occurring nearly 1100 feet upstream of the intake. Therefore, apparently the seepage source begins far upstream of the embankment within the foundation deposits. Modeling the SP data indicated a number of anomalous areas interpreted as concentrated seepage flow paths within the foundation and lower portion of the embankment.
The minimum-pool data, acquired when only a stream entered the intake structure, confirmed the low-pool electrical and SP interpretations. Remediation of the seepage problems at Coursier Lake Dam was completed in 1996 utilizing a combination of an upstream cutoff trench to reduce the seepage flow through the foundation, and placement of a geomembrane (tied into the cutoff trench) over approximately two thirds of the core to reduce the flow gradients within the embankment.