Major Tasks Completed

  • Technical and Strategic Support to the seven GSAs in the Cosumnes Subbasin
  • GSP Development and Implementation
  • Numerical Groundwater Model Development and Application
  • SGMA Compliance

Groundwater Sustainability Plan and Managed Aquifer Recharge for Groundwater Sustainability

Client

Department of Water Resources, Sacramento County

Location

Cosumnes Subbasin, CA

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EKI has been actively working in the Cosumnes Subbasin (basin) since 2017.  For the past 20 years, groundwater storage in the basin has declined on average by about 10,000 acre-feet per year (AFY). EKI assisted the seven Groundwater Sustainability Agencies (GSAs) in the basin to develop and finalize their Groundwater Sustainability Plan (GSP). The GSP identifies projects and management actions to eliminate the chronic decline in storage by 2042 and provide a sustainable water supply over a 50-year planning horizon. A key component of the strategy includes implementation of managed aquifer recharge (MAR) via the controlled flooding of dormant farm fields with winter runoff from local surface water sources.

Potential MAR sites in the basin were identified and the complex cause-and-effect relationships between recharge, changes in water table elevation, changes in seepage to and leakage from interconnected surface water features, changes in subsurface inflow and outflow across basin boundaries, and the resulting benefit to groundwater storage were evaluated. These relationships were quantified using a regional numerical surface water groundwater model that EKI developed collaboratively with neighboring basins north of the Cosumnes (the South American Subbasin and North American Subbasin) and a pre-existing model of the neighboring basin south of the Cosumnes (the Eastern San Joaquin Water Resources Model developed for the Eastern San Joaquin Groundwater Subbasin). The groundwater model is being applied to facilitate optimization of P/MA implementation, including assessing the effectiveness of demand management measures and recharge basin development, and is supporting data gap filling efforts. EKI is also supporting public and stakeholder outreach, including preparing and giving presentations, and facilitating landowner and other stakeholder meetings.

Outcome

As the technical advisor to the GSAs, EKI continues to assist the seven GSAs in the basin to develop and implement a comprehensive strategy for SGMA compliance, including preparation and implementation of a single, coordinated GSP. Part of EKI’s GSA administration support are developing meeting agendas, 3-month “look ahead” schedules to facilitate timely decision making, and meeting presentations; supporting the formation and management of several ad-hoc committees; and providing regular reporting and data management system.