Paleohydrologic Controls on Alluvial Deposition: A Process-Simulation Approach to Reconstruct Aquifer Heterogeneity

Stanford University, Stanford CA

Investigators

Abstract

0207177 Gorelick. Physical process simulation can be used as a too] to help reconstruct the spatial pattern of sediments comprising aquifers used for water supply. Sedimentary evolution is simulated using a process-imitating model, based on large-scale mathematics, that describes hydrologic, sedimentary, and tectonic events which have occurred over hundreds of thousands of years. The specific processes of interest are major floods, sedimentation, erosion, compaction, subsidence, sea-level variation, and regional-scale fault motion. The product is a quantitative too] to study aquifer stratigraphy and its evolutionary link to paleohydrology and tectonic conditions. This tool can be used in hydrogeologic investigations where the large-scale pattern of relative flow paths and flow barriers is important. The field area for application is the Santa Clara Valley in northern California, which is Approximately 240 mi2 Groundwater provides approximately half of the public water supply in Santa Clara Valley, yet pumping has caused a serious problem of land subsidence due to clay compaction. In most areas, the controls on groundwater flow and land subsidence imposed by aquifer heterogeneity and confining bed geometry are poorly understood. The Valley occupies a structural depression within a block bounded on the cast and west by the Hayward-Calaveras and San Andreas Fault systems. Respectively. The multiaquifer system consists of coalescing alluvial fans interfingered with estuarine deposits that have been formed over the past 600,000 years. The sedimentary process simulation model results will be compared to geologic and hydrogeologic data covering certain portions of the Valley. The goal is to use the model to interpret the roles played by various past hydrologic and geologic processes on the development of alluvial-bay aquifer architecture.