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|Title:||Geoelectrical survey performance and evaluation, Walter F. George Reservoir, Alabama-Georgia|
|Authors:||United States. Army. Corps of Engineers. Mobile District.|
Saucier, Roger T.
Walter F. George Reservoir
|Publisher:||U.S. Army Engineer Waterways Experiment Station.|
Engineer Research and Development Center (U.S.)
Abstract: A field demonstration of the Menard method of electrical resistivity surveying was conducted by the firm of J. J. Dury and Associates (Sondelec International Limited) at the Walter F. George Reservoir in December 1969. The test afforded the WES an opportunity to evaluate the effectiveness of the method in detecting and delinenting subsurface openings in which moving groundwater (underseepage) was present. The Menard method, similar in equipment, field procedure, and data-processing techniques to standard resistivity methods, proved to be effective in detecting anomalies caused by the electrofiltration effect that is created by moving groundwater. South of the left embankment, a horizontal resistivity profile was obtained that correlated reasonably well with a water-temperature profile that defined the path of underseepage. In the case of a vertical profile situated on the crest of the left embankment, an electrofiltration effect caused by a series of closely spaced grout columns prevented calculation of true resistivities but determination of potential anomalies was possible. A large and well-defined anomaly suggesting a multiplicity of electrofiltration effects was discerned along the profile in an area where no correlation with known conditions (i.e., a cavity) is apparent. When later furnished detailed subsurface data previously withheld, the engineering firm concluded that more precise correlations were possible if a horizontal distance error was assumed to be present because of a distortion in the electrical field caused by the electrofiltration effect. Under the circumstances, the advisability and validity of more precise correlations are questioned. It has been concluded that the geoelectrical method is superior to other techniques in detecting underseepage where it can be applied intensively in small areas; however, application in surveys of large areas with essentially unknown subsurface conditions probably would not be advantageous.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Miscellaneous Paper|
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