SacWAM (Sacramento Water Allocation Model)

Criterion	Explanation
General Description	The Sacramento Water Allocation Model (SacWAM) is a hydrologic and system operations model developed by the Stockholm Environment Institute (SEI) and State Water Resources Control Board (State Water Board) to assess potential revisions to instream flow and other requirements in the Bay-Delta Watershed including the current Phase 2 review and update of the 2006 Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary (2006 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. The model website is at: https://www.waterboards.ca.gov/waterrights/water_issues/programs/bay_delta/sacwam/
Model Domain	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.
Developer	The model developers are the Stockholm Environment Institute (SEI) and State Water Resources Control Board (State Water Board).
Hardware computing requirements	SacWAM runs on Microsoft Windows.
Code language	Information not available.
Original application	SacWAM is an application of the WEAP model.
Public/proprietary and cost	The source code is proprietary. To run SacWAM, you must obtain a WEAP license. License fees vary from free to $3000 for two years use.
Physically or empirically based	The model is physically based.
Mathematical methods used	SacWAM calculates a water mass balance for every node and link in the system on a monthly time step. Water is dispatched to meet instream and consumptive requirements, subject to demand priorities, supply preferences, mass balance and other constraints.
Input data requirements	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 user enters data under the following categories: Key Assumptions, Demand Sites, Hydrology, Supply and Resources, Environment, and Other Assumptions.
Outputs	The model estimates: Flow conditions under a range of alternative regulatory requirements Changes in water diversions for use in an evaluation of the impacts of alternative regulatory requirements on agricultural resources, water suppliers, and groundwater Changes in reservoir storage for use in an analysis of the impacts of alternative regulatory requirements on hydropower generation, recreation, fisheries and water supply
Pre-processing and post-processing tools	The model is integrated with a Graphical User Interface (GUI), which allows for pre- and post-processing.
Representation of uncertainty	The basic PEST tool (pest.exe) is included in the WEAP installation. PEST (Parameter ESTimation) is a free software package for Model-Independent Parameter Estimation and Uncertainty Analysis.
Prevalence	SacWAM is used by the State Water Board.
Ease of use for public entities	There are no barriers to the widespread use of the model. The model is well-documented.
Ease of obtaining information and availability of technical support	There is an active on-line user forum for WEAP. Training course are offered periodically.
Source code availability	The source code is proprietary.
Status of model development	In 2016, the Delta Science Program (DSP) facilitated an independent scientific review of SacWAM to assure transparency and confirm the adequacy of SacWAM to simulate flows that will be used in a comparative analysis of alternatives related to updates of the Bay-Delta Plan. Model refinement was undertaken to address DSP recommendations.
Challenges in integration	Monthly time step output from SacWAM may be used to estimate the changes in water supply and agricultural resources resulting from potential BayDelta Plan modifications. Addressing potential impacts to in-Delta fisheries on a monthly time step is also adequate. Impacts on resources that occur on a sub-monthly time scale may need to be assessed using other approaches.

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