Working toward Sustainable Groundwater Resources in an Uncertain Future
Pajaro Valley Water Management Agency
Groundwater overdraft and seawater intrusion are two serious threats to the sustainability of groundwater resources in the Pajaro Valley. Located adjacent to the Monterey Bay in Central California, the Pajaro Valley is home to some of the most productive agricultural land in the country, producing more than $900 million/year of high value fruit, vegetable, and flower crops on approximately 28,500 irrigated acres. Average water usage in the valley is 55,000 acre-feet/year (AFY), with groundwater providing over 95% of the supply. Decades of groundwater overdraft have induced seawater intrusion, which was first documented in 1953. The Pajaro Valley Water Management Agency (Agency) was formed by an act of state legislature in 1984 to “efficiently and economically manage existing and supplemental water supplies in order to prevent further increase in, and to accomplish continuing reduction of, long-term overdraft.” The Agency developed its first Basin Management Plan (BMP) in 1993 and has updated twice since that time to reflect changing conditions. The BMP guides PVWMA’s efforts to reduce groundwater production and develop supplemental water supplies in an effort to balance the basin and halt seawater intrusion. Implementation of BMP projects occur in phases as funding allows. Between 2000 and 2009, the Agency constructed a managed aquifer recharge and recovery facility, a water recycling facility, and over 20 miles of distribution pipeline. While these projects reduced the magnitude of groundwater overdraft and seawater intrusion affecting the basin, they were not able to solve these problems entirely. In 2010 the Agency set out to identify the next phase of projects and programs needed to solve the water resource issues affecting the basin. The Agency’s extensive monitoring program, which includes among other things the metering of production wells and collection of groundwater levels, provided valuable data for the development of a regional scale hydrologic model that was used to estimate the basin’s water budget. The Pajaro Valley Hydrologic Model (PVHM), is an integrated hydrologic flow model that uses MODFLOW-OWHM, a code which fully couples the simulation of the use and movement of water throughout the hydrologic system, was created to help inform water resource management decisions. Stakeholder driven committees were formed to guide development of a suite of projects and programs to address a shortfall in the simulated water budget of ~12,000 AFY. The PVHM was later used to evaluate the effectiveness of proposed solutions toward attaining the co-equal goals of balancing the groundwater basin and stopping seawater intrusion. Following nearly two years of meetings, the planning committee decided on a suite of seven projects and programs that include conservation (5,000 AFY), optimizing the use of existing supplies (3,000 AFY), and developing new supplies (4,100 AFY). Projects being implemented in phases. If basin monitoring shows continued overdraft and/or seawater intrusion following the completion of each phase, additional projects identified in the BMP Update will be considered for implementation.