Simulation-optimization aids in resolving water conflict: Temecula Basin, Southern California

The productive agricultural areas of Pajaro Valley, California have exclusively relied on ground water from coastal aquifers in central Monterey Bay. As part of the Basin Management Plan (BMP), the Pajaro Valley Water Management Agency (PVWMA) is developing additional local supplies to replace coastal pumpage, which is causing seawater intrusion. The BMP includes an aquifer storage and recovery (ASR) system, which captures and stores local winter runoff, and supplies it to growers later in the growing season in lieu of ground-water pumpage. A Coastal Distribution System (CDS) distributes water from the ASR and other supplemental sources. A detailed model of the Pajaro Valley is being used to simulate the coupled supply and demand components of irrigated agriculture from 1963 to 2006. Recent upgrades to the Farm Process in MODFLOW (MF2K-FMP) allow simulating the effects of ASR deliveries and reduced pumping for farms in subregions connected to the CDS. The BMP includes a hierarchy of monthly supply alternatives, including a recovery well field around the ASR system, a supplemental wellfield, and onsite farm supply wells. The hierarchy of delivery requirements is used by MF2K-FMP to estimate the effects of these deliveries on coastal ground-water pumpage and recovery of water levels. This integrated approach can be used to assess the effectiveness of the BMP under variable climatic conditions, and to test the impacts of more complete subscription by coastal farmers to the CDS deliveries. The model will help managers assess the effects of new BMP components to further reduce pumpage and seawater intrusion.