Supply and Demand Assessment (SDA) – San Gregorio Creek Watershed
Overview
The San Gregorio Creek Watershed is located within San Mateo County, extending from the Santa Cruz Mountains to the Pacific Ocean. The watershed area is approximately 51 square miles, with an elevation ranging from sea level to about 2,700 feet. Please note that the modeling domain includes San Gregorio Creek and some neighboring watersheds. This watershed has a Mediterranean climate and its primary land cover is forest and shrubland. The watershed has several dams and reservoirs, and much of the watershed is used for rangeland and other agricultural activities. Timber harvesting has historically played a substantial role in the watershed’s development as well. The San Gregorio Creek Watershed is listed under Section 303(d) of the Clean Water Act for excessive sedimentation. The watershed provides habitat for several threatened species, such as steelhead trout and coho salmon, and increases in erosion and sedimentation have impacted their habitats.
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Announcements
May 29, 2026 - San Gregorio Creek Watershed Model Work Plan - Now Available
The work plan from Paradigm Environmental for development of a hydrologic model for the San Gregorio Creek watershed is now publicly available in Model Development section below. Please email questions regarding the model development to DWR-SDA@waterboards.ca.gov.
Model Development
Outreach and Engagement
- San Gregorio Creek Watershed Fact Sheet – Coming Soon
Modeling in the San Gregorio Creek Watershed
The SDA Unit has continued to work on the models and tools developed for the Russian River Watershed during the State Water Board's 2021-2022 Regional Drought Response. These tools provided the necessary information for the Division of Water Rights (Division) to assess water availability and issue water right curtailments to ensure adequate, minimal water supplies for critical purposes under the emergency regulation.
To capture the water demand in the SDA Program Watersheds, water right demand estimates were incorporated based on information from annual reports of water diversion and use submitted to the Division. The SDA Unit continued to develop the Division's demand dataset methodology and converted it into a series of R scripts and manual review spreadsheets that apply data quality correction flags. For example, the scripts identified and corrected unit conversion errors, duplicate reporting, and misplotted points of diversion. The SDA Unit then uses a water allocation tool adopted from the UC Davis Drought Water Rights Allocation Tool (DWRAT) to allocate available supply amongst water right holders based on their respective water right priority and water demands. This version of DWRAT allocates water at the subbasin level and accounts for imported flows.
The SDA Unit's demand methodology, along with the supply scripts and the watershed specific versions of DWRAT, will be made available on the California Water Board Data Center GitHub page as separate repositories.
Supply and Demand Assessment Program Links
Supply and Demand Assessment Information
Project Watersheds:
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Contact Us
If you have questions or please email them to: DWR-SDA@waterboards.ca.gov
