The Foundation of Martis Creek Dam: Revealed by Geophysical Imaging

Risk based evaluations of the U.S. Army Corps of Engineers (USACE) > 600 dam inventory has resulted in the identification of about 10 dams that received a Dam Safety Action Classification of DSAC I, indicating urgent and compelling safety concerns. Martis Creek Dam located in Truckee, California is one of these dams. The dam has a history of excessive seepage through the foundation and near the spillway, as well as a spillway deficiency that have combined to prevent the USACE from operating the dam at its full design function since its completion in 1972. Over the past few years the USACE has conducted intensive investigations of the foundation to improve our geotechnical understanding of the site. This paper will focus on highlighting some of the significant findings resulting from detailed geophysical surveys. Of primary interest are the findings of a capable fault found using airborne LiDAR imagery, detection of fault traces in seismic reflection data and their impacts on DC resistivity images, and the modeling of the top of confining layer using DC resistivity data. Three-dimensional imaging of these data reveals two paleochannels that may explain many of the seepage issues along the downstream toe. These surveys represent the culmination of a five-year program that has investigated the foundations of three dams and provides a state of the science case study on the application of geophysical methods for investigating geotechnical properties. 24 pp., 25 references.
Additional Keywords: Polaris Fault, Truckee, Martis Creek Dam, Geophysics, Paleoseimology, Tectonics