Tools for Assessing Groundwater-Surface Water Connectivity Under the Sustainable Groundwater Management Act

In 2014, California enacted the Sustainable Groundwater Management Act (SGMA), which requires local agencies to develop and implement groundwater sustainability plans (GSPs) in all groundwater basins designated by the California Department of Water Resources (DWR) as high or medium priority by 2020 or 2022, depending on basin condition. For the first time in California’s history, agencies managing groundwater under SGMA must assess the impacts of groundwater pumping on water supply and surface water flows and avoid “significant and unreasonable adverse impacts on beneficial uses of the surface water.”

SGMA’s legal and regulatory requirements pertaining to interconnected surface water – defined in SGMA as, “surface water that is hydraulically connected at any point by a continuous zone to the underlying aquifer and the overlying surface water is not completely depleted.” – represent a significant step forward in recognizing the interconnected nature of surface water and groundwater and for managing this resource accordingly. However, because groundwater-surface water connectivity was not a common management consideration prior to the enactment of SGMA, many basins lack data or models or technical capacity to adequately characterize interconnected surface water (ISW) and evaluate the impacts of groundwater pumping on these systems. Thus, meeting legal and regulatory requirements related to ISW may be hindered by a lack of information about both the location and timing of such waters, as well as the many beneficial uses and users that they support.

In March 2018, Water in the West, The University of Victoria, Foundry Spatial, The Nature Conservancy (TNC) and Environmental Defense Fund co-hosted a workshop on tools to assess ISW under SGMA. The workshop, which included a small, select group of hydrologists, water managers, water lawyers, nongovernmental organizations (NGOs) and academia, focused on four main areas:

1) Accounting for beneficial uses and users in GSP development and implementation;

2) Identifying physical or analytical approaches for characterizing, quantifying and monitoring ISW;

3) Using hydrological modeling to assess the effects of groundwater pumping on ISW and streamflow depletions; and

4) Understanding the functionality and use of decision support tools from other jurisdictions

This report summarizes key findings from the one-day workshop and a short questionnaire completed by workshop participants during the day. A list of workshop attendees, the workshop agenda and workshop questionnaire can be found in Appendices A-C, respectively.