Supply and Demand Assessment (SDA) - Petaluma River Watershed
Overview
The Petaluma River is one of the major tributaries to the San Pablo and San Francisco Bays. The watershed covers approximately 198 square miles, and its elevation ranges from sea level to approximately 2297 feet. The headwaters and tributaries of the Petaluma River originate on the southwest slopes of Sonoma Mountain, the southern slopes of Mecham Hill, and the eastern slopes of Weigand's Hill and Mount Burdell. The river flows through the city of Petaluma, then continues south-southwest into the northwest portion of San Pablo Bay. The watershed has a Mediterranean climate with distinct wet and dry seasons, and the land cover is mainly grassland and developed.
The Petaluma River watershed represents an important habitat for native aquatic species and spawning ground for anadromous fish, especially chinook salmon and steelhead trout. The decline in anadromous fish populations within the Petaluma watershed has been linked to increases in sedimentation, habitat degradation, and elevated stream temperatures. The Petaluma River has appeared on the Clean Water Act's 303(d) list of impaired waters due to elevated levels of fecal indicator bacteria. The river is also listed as impaired due to excessive algae growth, known as eutrophication, a process that depletes oxygen levels and degrades aquatic habitats caused by high nutrient concentrations. These factors led to the development of a Total Maximum Daily Load (TMDL) for bacteria in 2019.
- Click on Map to Enlarge
Announcements
May 29, 2026 - Petaluma River Watershed Model Work Plan - Now Available
The work plan from Paradigm Environmental for development of a hydrologic model for the Petaluma River 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
- Petaluma River Watershed Fact Sheet - Coming Soon
Modeling in the Petaluma River 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:
Stay Informed
Email Subscription List
Subscribe to the SDA Information email topic to receive notifications and the latest updates.
Contact Us
If you have questions or please email them to: DWR-SDA@waterboards.ca.gov
