From the State Water Resources Control Board:
This email contains updates regarding the State Water Board’s Watershed Supply and Demand Assessment Program, including updates on the status of water supply modeling and related work in current watersheds being modeled and additional watersheds selected for this effort.
Current Watershed Efforts
In June 2024, the State Water Board’s Division of Water Rights (Division) began developing water supply models and surface water demand datasets for 9 watersheds across California. The Division contracted with Paradigm Environmental for the development of surface water supply models. Staff have developed surface water demand datasets for each of the watersheds listed below and a summary of the model development status is provided in the table below.
| Watershed | Model Status | Update |
| Butte Creek | In Model Development | In the final phase of snow modeling calibration. |
| Gualala River | Staff Review | Draft model report completed and under review by staff. |
| Mattole River | In Model Development | Initial phase of model development underway, including watershed delineation and flowline development. |
| Napa River | In Model Development | A Memorandum of Understanding (MOU) between the State Water Board and Napa County Groundwater Sustainability Agency (GSA) was executed on May 6, 2025. Napa County GSA has shared its groundwater model, which will be coupled with our surface water model. |
| Navarro River | Staff Review | Surface water model and report are complete. |
| Putah Creek | In Model Development | Remaining model development is focused on Lake Berryessa reservoir modeling and calibration. |
| Salmon Creek (Sonoma County) | In Model Development | Model development is in calibration phase. |
| South Fork Trinity River | In Model Development | On temporary hold to merge this watershed with new effort to model the broader Trinity River watershed as a single model. |
| Tomales-Drake Bays | In Model Development | Initial phase of model development is underway, including watershed delineation and flowline development. |
The next steps for the watersheds listed above will be to complete water supply model development for each watershed, run the models monthly, and provide data visualizations that share information on water supply and demand in each watershed similar to what has been created for the Russian River watershed. For reference, the general steps in surface water supply model development are: (1) watershed delineation, (2) identification of flow lines (i.e., rivers and tributaries that contribute to surface flow); (3) collect and compile geological, meteorological, and streamflow (supply) data; (4) compile and clean up water use and diversion (demand) data; (5) calibrate and validate surface water supply model; and (6) develop model documentation and final model report.
The models will be available to the public so interested parties can evaluate different scenarios in a given watershed. The visualizations for each watershed will be updated monthly and available on the webpage for that watershed.
Additional Watersheds Selected for Modeling
In March 2025, Paradigm Environmental began developing water supply models and related demand information for the nine watersheds listed below:
- Big Creek
- Pescadero Creek
- Petaluma River
- Pismo Creek
- San Gregorio Creek
- San Lorenzo River
- Santa Maria River
- Sonoma Creek
- Trinity River (to be combined with South Fork Trinity River)
Similar to the initial watersheds, these nine watersheds were selected with consideration of various factors including: the watershed’s surface water demand, ecological significance, location, water rights complexity, and existing modeling efforts.
Please visit the Supply and Demand Assessment webpage for future updates and information on this effort. If you have questions, please email Supply and Demand Assessment Program staff at: DWR-SDA@waterboards.ca.gov.
