California SGMA Groundwater Modeling for Groundwater Sustainability Planning

Water stands as a highly valued resource in California, vital for public well-being, a strong agricultural and industrial economy, and environmental health. Groundwater makes up a significant portion of the state’s water resource supplies, accounting for up to 60% of California’s total annual supply during years of prolonged drought. With increasingly frequent dry spells, excessive pumping of California’s groundwater has been largely unregulated, leading to a dramatic fall of California’s aquifers–and emptying them faster than natural systems can recharge them. With over 30 million Californians reliant on groundwater, safeguarding sustainable management of this resource is essential for California’s future hydrological needs.

The Sustainable Groundwater Management Act (SGMA) of 2014 set forth to ensure the preservation of this resource, addressing overexploitation, overdraft, and imbalances of the state’s aquifers. SGMA dictates Groundwater Sustainability Plans (GSPs) for over 100 groundwater basins across the state. The GSPs must characterize the current state and trends for groundwater supplies in each of those basins. The statewide framework works towards building a resilient water supply in the face of prolonged drought and anticipated climatic changes. With an overarching vision that the process be locally driven at the groundwater basin level, the development of the GSPs is overseen by newly constituted Groundwater Sustainability Agencies (GSAs) for each basin. Typically, the GSAs engage private consultants to develop the GSPs. The GSPs are underpinned by a wide range of technical analyses to understand basin hydrogeology and water budgets, to support development of sustainability metrics, and to develop and evaluate alternative projects and management actions that may help the basins achieve long-term sustainability.

Key Lynker staff have supported SGMA since the early stages of the framework’s development, including offering comments on the draft regulation developed by the California DWR per SGMA mandate. Subsequently after rules adoption, we have been involved with GSPs for five basins in the central part of the state. Our work generally involves integrating the best available geologic, hydrologic, meteorologic, and land use data into detailed basin water budgets and groundwater flow models that GSA water managers can rely on for evaluating basin conditions and actional pathways to long- term sustainability. For example, working closely with the prime GSP contractor, our team led the “soup-to-nuts” development of the groundwater flow model for the Santa Ynez River groundwater basin Eastern Management Area.