GRA SoCAL: Governance-First Integrated Modeling with GSFLOW

• Irvine, CA

In highly developed and conjunctively managed basins like the Russian River, traditional modeling approaches that examine groundwater levels or surface water in isolation are no longer sufficient to inform sustainable management. Effective water resource planning, particularly under the mandates of the Sustainable Groundwater Management Act (SGMA), requires a holistic water balance that begins with precipitation and accounts for the complex, nonlinear feedback between physical hydrology and operational rules.

This talk presents an integrated modeling framework using GSFLOW and MODSIM to provide a “governance-first” approach to watershed management. Fundamentally, these models partition precipitation into evapotranspiration (ET), surface runoff, infiltration, and baseflow to simulate the entire water portfolio. By simulating runoff and baseflow within the stream network, we can more accurately quantify critical surface water-groundwater interactions, such as the capture of streamflow by alluvial pumping and the annual replenishment of aquifers during high-flow events.

We will demonstrate how this integrated foundation allows for the evaluation of management strategies—including Forecast-Informed Reservoir Operations (FIRO) and Managed Aquifer Recharge (MAR)—while ensuring compliance with priority-based water rights and environmental flow requirements. By matching physical reality (precipitation-driven supply) with legal mandates (priority-based allocation), this framework provides a robust decision-support tool for navigating future hydrologic extremes in California’s watersheds.