Seepage Investigation Using Geophysical Techniques At Coursier Lake Dam, B.C., Canada

Subsurface seepage flow at Coursier Lake Dam was identified by onshore<br>and offshore self-potential surveys, and electrical resistivity<br>profiles and soundings during a Deficiency Investigation by BChydro.<br>For typical seepage investigations baseline geophysical data are<br>collected at @llow-pool I1 level and the measurements are repeated when<br>high hydraulic gradient conditions exist. At Coursier Lake Dam a<br>rather unanticipated outcome of the low-no01 surveys was that<br>significant seepage beneath the structure'was detected. The low-pool<br>results were conclusive enough that, when combined with visual<br>inspection and observation of sinkholes on the embankment, an<br>immediate restriction was placed on the pool elevation. Thus, because<br>of the identified potential hazard, the remaining geophysical<br>investigations were conducted under a "minimum-pool" reservoir level<br>in order to complete the comparative study. Therefore, the dam was<br>studied under low- and minimum-pool reservoir conditions in the spring<br>and fall of 1993, respectively.