Sacramento Water Allocation Model (SacWAM)

SacWAM is a hydrologic and system operations model developed by the Stockholm Environment Institute (SEI) and State Water Board to assess potential revisions to instream flow and other requirements in the Bay-Delta watershed, including the current Sacramento/Delta review and update of the Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Watershed (Bay-Delta Plan). SacWAM was developed using the Water Evaluation and Planning (WEAP) software platform, and is intended to be user-friendly and usable for efficient comparison of multiple scenarios.

Stream flows estimated by SacWAM are used to inform various types of analyses as part of the State Water Board’s assessment of potential alternative regulatory requirements:

• Estimates of flow conditions under a range of alternative regulatory requirements.
• Estimates of changes in water diversions for use in an evaluation of the impacts of alternative regulatory requirements on agricultural resources, water suppliers, and groundwater.
• Estimates of changes in reservoir storage for use in an analysis of the impacts of alternative regulatory requirements on hydropower generation, recreation, fisheries and water supply.
• To inform other analyses or models, such as delta hydrodynamics, temperature and economic.

SacWAM is used in a comparative manner in which a model scenario is compared to a model base condition and the difference in model outputs is used to assess potential impacts of proposed regulatory actions.

The model represents the Sacramento River Hydrologic Region, the Trinity River watershed above the Lewiston gauge, and the northern part of the San Joaquin River Hydrologic Region downstream from the gauge at Vernalis. The model includes the entire Sacramento-San Joaquin Delta (Delta), and the Delta eastside streams comprising the Cosumnes, Mokelumne, and Calaveras Rivers. The model simulates pumping plants in the Delta, the California Aqueduct and Delta Mendota Canal, as well as San Luis Reservoir.

On August 19, 2026, the State Water Board released the latest version of SacWAM (version 2026.05.29). Current and prior versions of SacWAM are available on the Board’s file transfer protocol (FTP) site. To request a copy of the models or modeling results, contact Bay-Delta@waterboards.ca.gov.

• Model Version 2026.05.29 Documentation
• FAQ (last updated September 2023)

• December 12, 2025 – Release of SacWAM version 2025.08.28
• August 22, 2025 – Release of SacWAM version 2025.08.22
• September 28, 2023 – Release of SacWAM version 2023.06.12
• November 22, 2019 – Release of SacWAM version 2019.11.22
• August 16, 2019 – Release of SacWAM version 2019.08.16
• October 4, 2017 – Response to Peer Review Comments
• December 19, 2016 – Transmittal Letter from Delta Science Program to State Water Board
• December 2016 – Delta Science Program Independent Peer Review Report on SacWAM
• October 19, 2016 – Delta Science Program Independent Peer Review Meeting
• October 4, 2016 – Workshop on Introduction to SacWAM
  • Presentation 1
  • Presentation 2
• September 2016 – Draft Hydrological and Operations Modeling Considerations for Phase II Update of 2006 Bay-Delta Plan
• September 19, 2016 – Email Announcement Publicly Introducing SacWAM