State Water Board advances watershed supply-and-demand models for 18 basins

The State Water Resources Control Board on Sept. 3 updated the board on a multi‑watershed water supply and demand assessment program designed to produce hydrologic models, monthly supply estimates and public visualization tools for 18 watersheds across California. Philip Dutton, program manager in the Division of Water Rights, said the program grew from lessons learned during the 2021–22 Russian River drought and a $15 million contract with Paradigm Environmental to develop watershed models.

The models use the Loading Simulation Program in C++ (LSPC) framework, meteorological inputs, stream gauge records and a cleaned set of annual water‑use reports to simulate available supply and allocate water to surface‑water demands. "While we're not in drought now, this is important work being done following the last drought and will help [preparedness] in future drought years," Dutton said. Senior engineer Mohammad Sarabi described the calibration and validation approach used in the Navarro and Gualala River models and said those models showed "very good and good performance across all conditions and metrics."

Board members and staff said the tools are intended primarily to support local planning and decision making, and are expected to be used for: monthly supply and demand assessments; scenario evaluation for local water‑sharing and conservation strategies; analysis of potential wet‑season storage projects; and to support drought‑era board actions if needed. Dutton said that program staff will post draft model development reports for public review; the Navarro River draft report was open for comment through Oct. 9, 2025. Sarabi demonstrated a public dashboard now available for several watersheds that shows water‑use demand patterns, sub‑watershed demands and historical supply and demand estimates.

Board members emphasized outreach to local users, tribal governments, GSAs and NGOs so the models reflect local knowledge and improve water‑use reporting. Director Oppenheimer and board members noted the work dovetails with improvements to the board’s water‑rights data systems and pledged technical workshops to allow interested parties to run the LSPC models themselves. Dutton said staff expect to return with another program update in mid‑2026.

The program is ongoing and will continue to release technical reports, web dashboards and workshops as models reach the draft and final stages. Interested parties can sign up on the board's program web page for notifications of draft reports and technical workshops.