Self-potential investigation of moraine dam seepage |
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| Institution: | 1. University of Neuchâtel, Center For Hydrogeology and Geothermics (CHYN), 11 Rue Emile Argand, Neuchâtel 2000, Switzerland;2. DHI-WASY GmbH, Waltersdorfer Strasse 105, Berlin 12526, Germany;3. Gocad Research Group, Laboratoire GeoRessources, Université de Lorraine, Site de Brabois, 2 Rue du Doyen Marcel Roubault TSA 70605, Vandoeuvre-Lès-Nancy FR-54518, France;1. UMR 1114 EMMAH (INRA-UAPV), 301 rue Baruch de Spinoza, 84916 Avignon, France;2. Aristotle University of Thessaloniki, School of Geology, Lab. of Engineering Geology and Hydrogeology, 54124 Thessaloniki, Greece;3. Aristotelous 46, 57013 Thessaloniki, Greece;1. Süleyman Demirel University, Engineering Faculty, Department of Geophysical Engineering, West Campus, TR-32260 Isparta, Turkey;2. Bitlis Eren University, Faculty of Arts and Sciences, Department of Archaeology, TR-13000 Bitlis, Turkey;3. Career Research and Application Center, Bitlis Eren University, TR-13000 Bitlis, Turkey;4. Dokuz Eylül University, Engineering Faculty, Department of Geophysical Engineering, TR-35160 ?zmir, Turkey |
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| Abstract: | Self-potential (SP) and electrical resistivity measurements are used to investigate seepage at a remote moraine dam in the Sierra Nevada of California. The site is a small terminal moraine impounding roughly 300,000 m3 of water at ~ 3400 m a.s.l. Suspicious fine sediment in a small lake at the dam's downstream toe prompted initial concerns that anomalous seepage may be eroding matrix material from the moraine. 235 individual SP measurements covering the surface of the dam were collected in order to investigate electrokinetic current sources resulting from seepage, while resistivity soundings probed moraine stratigraphy and suggest that the till contains interstitial ice. Contoured SP data reveal a non-uniform voltage distribution over the moraine dam and two distinct negative SP anomalies. The first, located in the central area of the moraine, shows a broad negative SP zone around the crest and increasingly positive SP moving downhill towards both the upstream and downstream toes. This anomaly can be explained by shallow gravitational groundwater flow in the near subsurface combined with upward groundwater flux through evapotranspiration; numerical simulation of the combined effect matches field data well. The second SP anomaly has a tightly localized distribution and can be explained by vertically descending flow into a bedrock fault conduit. Our conceptual seepage model suggests that flow travels from Dana Lake first at the boundary of ice-filled moraine and bedrock before converging on a concentrated channel in the subvertical fault zone. Positive SP near the dam abutments results from groundwater inflow from adjacent hillslopes. Combined analyses suggest that seepage erosion is not currently affecting the moraine dam, and that the sediment observed on the bed of the downstream toe lake is likely a remnant of past outflow events. |
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