HR: 1340h
AN: H23A-1113    [Abstracts]
TI: Detecting Seepage Through a Natural Moraine Dam Using the Self-Potential Method
AU: * Moore, J R
EM: moore@decf.berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering, 440 Davis Hall, Berkeley, CA 94720 United States
AU: Sanders, J W
EM: jws@eps.berkeley.edu
AF: University of California, Berkeley, Department of Earth and Planetary Sciences, 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Clague, J J
EM: jclague@sfu.ca
AF: Simon Fraser University, Department of Earth Sciences, 8888 University Drive, Burnaby, BC V5A 1S6 Canada
AU: Glaser, S D
EM: glaser@ce.berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering, 440 Davis Hall, Berkeley, CA 94720 United States
AB: We conducted a self-potential (SP) survey of the Dana Lake moraine dam to investigate seepage flow through a natural moraine. Seepage erosion, along with overtopping, are the two primary mechanisms that cause moraine dams to fail. Specifically, localized seepage paths can entrain dam matrix material and may lead to undermining and partial collapse. Our survey included 200+ self-potential measurements spaced between 2 to 10 meters apart. The Dana Lake moraine dam is located in the Sierra Nevada, California. The moraine is likely between 4000 and 11,000 years old, and impounds approximately 3 x 10$^{5}$ m$^{3}$ of water. The moraine also has two small lakes (unofficially East and West lakes) at its downstream toe, which are fed in part by seepage from Dana Lake. Intriguingly, West Lake is primarily sand and silt bedded while gravel and boulders dominate the bed of East Lake, despite them being ~40 meters apart. We concentrated our study on the west side of the moraine dam because 1) we observed active seepage flow on that side and 2) the lake bed material difference between East and West lakes suggests seepage may be removing fines from the western side of the moraine. Preliminary analysis of our self-potential data indicates nonuniform seepage flow through the moraine. On the western side, a broad positive SP anomaly is spatially coincident with observed seepage outlets and a sub-moraine bedrock knob visible at the surface. Additionally, a large negative anomaly coincides with the edge of the bedrock knob and may represent a vertical seepage path. On the eastern side of the moraine, groundwater flow appears to originate at the lake margin and follows an arcuate path towards West Lake. Other localized positive SP anomalies indicate possible seepage outlets. Future work includes forward modeling to resolve seepage flow rates and resulting stresses for use in a full seepage erosion analysis of the moraine dam.
DE: 1824 Geomorphology (1625)
DE: 1829 Groundwater hydrology
DE: 1894 Instruments and techniques
DE: 0925 Magnetic and electrical methods
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting