CHARACTERIZING DAM LEAKAGE/RESERVOIR SEEPAGE USING ELECTROMAGNETIC INDUCTION AND D.C. RESISTIVITY, SOUTHEAST TEXAS

Dam leakage/reservoir seepage is examined in a newly built residential subdivision in southeast Texas using Electromagnetic Induction (EM) and two multiple electrode configurations of the D.C. Resistivity method. A man-made lake was constructed for the use of the residents within the new community. The water covers an area of approximately 24 acres. The lake was filled for the first time in December 2002 and has subsequently lost several meters of water table elevation. A resistivity survey was conducted using a Wenner array in a constant spread traverse configuration with an “a” spacing of 15 meters. Resistivity lows were noted along the south and southwest portions of the dam. This is the response expected in an area with high moisture content possibly due to leakage. The EM data indicates a conductivity high that corroborates with the resistivity in the southwest section of the dam but is inconclusive with regards to the southeast portion. There may be evidence of an alternate path of water loss along the west shore of the lake. Both the EM induction and resistivity surveys exhibit an anomaly on the west side of the lake that may connect to an active seep that terminates at the shore of the nearby Brazos River. A great amount of concern has been expressed with regards to the source of water from the seep because the area between the west shore of the lake and the seep include currently occupied residential lots. Future work on this problem include a dipole-dipole resistivity survey to locate specific leakage points of the dam. Results of the dipole-dipole survey can then be used to direct remedial grouting operations should they be necessary. EM mapping of the areas between the west shore of the lake and the seep will be conducted to see if the source of the seep and the man-made lake are related.