Supply and Demand Assessment (SDA) - Gualala River
Overview
The Gualala River Watershed is located on the Mendocino Coast. The watershed has a drainage area of approximately 300 square miles and flows for 40 miles before draining into the Pacific Ocean. The elevation ranges from near sea level to over 2,600 feet in the easternmost portion near Gube Mountain. The majority of the watershed is evergreen forest and shrubland, with the river being important habitat for native aquatic species and spawning ground for anadromous fish, especially steelhead trout. Increased sediment and stream temperatures have been linked to declines in salmonid populations over time. As a result, the U.S. EPA and North Coast Regional Water Quality Control Board established a Total Maximum Daily Load (TMDL) for sediments in the Gualala River and its tributaries in 2001.
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Announcements
July 13, 2026 –Gualala River Model Files – Now Available
The model files from Paradigm Environmental for the Gualala River water supply model are now publicly available to download in the Model Development section below. Video recording of LSPC model demonstration available on main Supply and Demand webpage. Please email questions regarding the model to DWR-SDA@waterboards.ca.gov.
Model Development
- Gualala River Workplan
- Gualala River Model Development Report – Describes data sources, calibration, and validation for model development
- Revised Gualala River Model Memorandum: North Fork Calibration – Describes updates to the Gualala River Model to improve performance in the North Fork Gualala River
- Gualala River Model Files – Folder containing model executable and weather data to run water supply scenarios
Outreach and Engagement
Modeling in the Gualala 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.
Additional Resources
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
