Thursday, 10 November 2005 - 9:00 AM
316-5

Regional-Scale Hydrologic Modeling of Flow and Reactive Salt Transport in the San Joaquin Valley, Ca.

Jan W. Hopmans, University of California Davis, Department Land, Air and Water Resources, 123 Veihmeyer Hall, Davis, CA 95616, Gerrit Schoups, Stanford University, Geological and Environmental Sciences, Stanford, CA 94305, Chuck Young, None, 2706 Rondo Place, Davis, CA 95616, Jasper Vrugt, Los Alamos National Laboratory, Earth adn Environmental Sciences Division, Mailstop T003, Los Alamos, NM 87545, and Kenneth Tanji, University of California, Department Land, Air and Water Resources, Davis, CA 95616-8628.

A hydro-salinity model was developed to integrate subsurface hydrology with reactive salt transport for a 1,400 km2 study area in the San Joaquin Valley, CA. For the first time, such a modeling framework was used to reconstruct historical changes in salt storage by irrigated agriculture over the past 60 years. We show that patterns in soil and groundwater salinity were caused by spatial variations in soil hydrology, the switching from local groundwater to snowmelt water as the main irrigation water supply, and by occasional droughts. Gypsum dissolution was a critical component of the regional salt balance. Although results show that the total salt input and output were about equal for the past 20 years, the model also predicts salinization of the deeper aquifers, thereby questioning the sustainability of irrigated agriculture.

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