AppendixF

• Basin: Statewide
• Title: SWSI Phase 1 Report - Appendix F
• Date: 11/15/2004
• Author: CWCB
• SWSI - Doc Type: Final Report

WatSIT (Water Su~ply Investi~ation Tool~
a water allocation screening model
1.) Overview:
WatSIT is a screening level water allocation model designed to provide quantitative
comparisons of water supply alternatives with respect to yields, storage requirements, and
return flows. It is intended to be used as an initial step in a water supply alternatives
analysis for a basin, sub-basin, water district, or individual user. The model can operate at
monthly or annual timesteps for up to 100 years of simulated hydrologic record. Any
combination of up to four available generic project alternatives can be simulated:
agricultural land transfer, reuse, consumptive use (non-ag) acquisition, and conservation.
WatSIT predicts reservoir storage, or instream flow, and return flows as functions of
baseline inflows, additional supply provided by project alternatives, and calculated
demands. The model has proved to be particularly useful for quantifying firm yields
associated with streamflow time series as functions of total reservoir storage.
The model is written in Visual Basic for Applications (VBA) and framed in a straight-
forward and easy-to-use Excel-based interface. This structure makes the model well-
suited for client use and supporting new business pursuits.
2.) Model Inputs and Outputs:
Model inputs and outputs are summarized in Table 2-1. Not all of the listed inputs are
required for any single simulation run.
A snapshot of the "Main" input screen is shown in Figure 2.1. Through this screen, the
user selects whether to run the model at monthly or annual timesteps and whether the
direct source of water is a reservoir or a reach (i.e. where the water is ultimately drawn
from). The simulation duration can be from 1 to 100 years.
Baseline inflows must be specified for each timestep for the full simulation duration.
These baseline inflows represent "natural" or historical available flows without additional
supply alternatives. For simulation durations greater than one year, monthly or annual
baseline inflows are input on a separate sheet, which are automatically created when the
user selects a"POR" (period of record) simulation rather than a single year simulation.
The user can also select up to four (4) generic proj ect alternatives (in any combination) or
none at all. The alternatives either provide "new" water to the system (ag transfer and
non-ag acquisition) or reduce user demand on the water already available (conservation
and reuse). Each come with their own set of inputs, organized in separate worksheets.
In the "Use" input sheet, the user must define the baseline gross total water usage of the
water users at either monthly or annual timesteps. This parameter represents the actual