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Geoelectrical and Electromagnetic Induction Delineation of Seep Origin at a US Army Earthen Dam
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  • Dan Glaser,
  • Ryan North,
  • Kevin Parkman,
  • Chandler Engle,
  • Meghan Quinn,
  • Chris Williams,
  • Shaun Stanton
Dan Glaser
USACE ERDC-CRREL

Corresponding Author:danney.r.glaser@erdc.dren.mil

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Ryan North
USACE ERDC-GSL
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Kevin Parkman
USACE ERDC-GSL
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Chandler Engle
USACE ERDC-CRREL
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Meghan Quinn
USACE ERDC-CRREL
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Chris Williams
USACE ERDC-CRREL
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Shaun Stanton
USACE ERDC-GSL
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Abstract

Earthen dam failures of high hazard dams are expected to cause downstream human life loss and economic and environment loss. Of the three most prevalent failure modes for earthen dams, seepage (or piping) failures account for approximately 40 percent. All earthen dams seep and it is not uncommon to observe some seepage on the downstream toe, but the flow rate of uncontrolled seepage should be negligible. In general, seepage occurs through the dam and/or its foundation. The cross section of the dam is designed to force the waterside head (pressure) to drop as the water flows through the cross section to the downstream toe. Uncontrolled or unexpected seepage can promote soil movement (i.e. piping) and cause a pipe or a cavity to develop within the earthen structure which can lead to a complete failure of the embankment. At present there are over 84,000 earthen dams throughout the United States many of which depend on the US Army Corps of Engineers for inspection, monitoring, maintenance, and repair. Recently a multi-method geophysical investigation, was performed at a site where a suspected seep outflow had increased ten-fold, warranting further investigation. Because the seep presented in a historically dry stream channel in the karst bedrock adjacent to the dam abutment there was some question as to whether the origin of the seep was indeed a result of piping or due to a naturally occurring seasonal spring. Electromagnetic induction measurements of terrain conductivity, as well as electrical resistivity tomography and mise-a-la-masse surveys were performed in an attempt to delineate the source water of the seep. The geophysical methods identified potential flow paths from the impoundment to the seep; however, a geochemical analysis of the seep outflow was compared to the same analysis of the impoundment water on the upstream side of the dam and found to be statistically different.