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Researchers outline method to design daily functional-flow regimes for Central Valley rivers
Summary
UC Berkeley-led team described a method that converts unimpaired flow records and CalSim model outputs into daily, water-year–specific functional flow regimes; presenters said the approach will let analysts evaluate trade-offs across water users, ecosystems and climate futures and provide monthly water budgets for planners.
Ted Grantham, a professor at the University of California, Berkeley, told the California Environmental Flows Technical Work Group that his team developed a method to create daily "functional flow regimes" for Central Valley rivers by linking unimpaired-flow estimates with operations modeling and rule sets that scale flows by water-year percentile.
Grantham said the work, part of a project called CoEqual (the Collaboratory for Equity in Water Allocations), was funded through a state climate action initiative and was designed as a two‑year, actionable research effort. "What is our water future? How do we how do we decide, what what our water future is and who decides?" Grantham asked, describing the project’s equity emphasis.
The presentation explained the technical approach: use historical unimpaired flows to derive relationships among five functional-flow components (fall pulse, wet‑season base and peak flows, spring recession, dry‑season base), map those metrics to water‑year percentiles, then generate daily hydrographs for each water‑year type. The team runs scenarios in CalSim 3 (the operations model developed by the Department of Water Resources and the U.S. Bureau of Reclamation) and links outputs to ecosystem and socioeconomic models, including salmon life‑cycle models used by NOAA Fisheries.
Grantham said the project expands scenario scope beyond typical planning analyses by testing alternatives such as prioritizing the human right to water, implementation of SGMA (Sustainable Groundwater Management Act), adding conveyance projects, or restoring more natural flows. He noted technical limits: CalSim is typically run at a monthly time step and the team produces daily hydrographs from that coarser output.
Participants asked how the work would treat social and economic impacts. Amber Jamieson, of the Environmental Protection Information Center, urged broader valuation of cultural and subsistence impacts and said small organizations often cannot afford formal economic studies. Grantham replied the project seeks to highlight trade‑offs across ecological and socioeconomic dimensions and that values need not be expressed only in dollars and cents.
Other questions addressed groundwater and local application. A commenter asked whether groundwater pumping (for example, commercial pumping in the Shasta area) and surface–groundwater interactions would be included; Grantham said the scenario suite includes simulations tied to groundwater changes and that some groundwater interactions are represented in linked models, but that local, basin‑scale groundwater sustainability plan (GSP) models remain more finely resolved for local management.
The presenter said deliverables will include a public website hosting scenario data and that the team aims to make functional-flow products available as monthly water budgets and as daily hydrographs for roughly 17 Central Valley sites the group is evaluating. Grantham urged attendees to use the outputs to better characterize trade‑offs among water users and ecological objectives.
The meeting chair and staff noted follow-ups: the work group will pursue draft groundwater–surface water model products for particular watersheds through the fall and post presentation materials and the recorded meeting to the group website.
The presentation and audience questions focused on method design, scenario choices and planned linkages to salmon and socioeconomic models; no regulatory decisions were made at the meeting.
