SWSI Environment and Recreation Needs and Priorities TRT Draft

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WatSIT Summary and Nature Conservancy Instream Flow Analysis The Water Supply Investigation Tool (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. Baseline available flows (user-input time series) can be supplemented with any combination of up to four available generic supply or demand management project alternatives: agricultural land transfer, reuse, consumptive use acquisition (non-agricultural), and conservation. WatSIT predicts reservoir storage 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 and reservoir operating constraints. A recent enhancement of WatSIT now provides the user with the ability to implement The Nature Conservancy's Range of Variability Approach (RV A) (Richter et al. 1997) to setting instream environmental flow targets in the context of water supply alternatives analysis. The user can investigate the impacts of these instream targets on reservoir firm yields, and/ or conversely investigate the impacts of new reservoirs on maintaining instream flow criteria. WatSIT calculates up to 18 of the 32 RV A metrics (Richter et al. 1997), as summarized in Table 7, for a given system based on a user-supplied "natural" flow time series. These flows can be calculated with existing water allocation models, like StateMod or ModSim, or they can be taken directly from appropriate historical measured USGS flow data. Those parameters not currently included in WatSIT are primarily daily values and thus not compatible with the model's monthly timestep. Future work may look to expand on the model's capacity in this regard. Table 7 Summary of RVA Analysis in WatSIT (18 out of 32 parameters) ~I-I-I~ Included in WatSIT TNC RV A Parameter -. Mean Monthly Flow (1 - 12) y Annual 3 Day Minima N Annual 1 Month Minima Y Annual 3 Day Maxima N Annual 1 Month Maxima Y Annual 7 Day Minima N Annual 3 Month Minima Y Annual 7 Day Maxima N Annual 3 Month Maxima Y No. of high pulses each year N Julian Month of Annual 1 Month Minima Y No. of low pulses each year N Julian Month of Annual 1 Month Maxima Y Mean duration of high pulses each year N Annual 1 Day Minima N Mean duration of low pulses each year N Annual 1 Day Maxima N Means on negative differences (consecutive days) N Means on positive differences (consecutive days) N ~5\^ISI S.lal~.....ide WeIer Supply Initiclive DRAFT CDIVI C:\DOCUMENTS AND SETTINGS\ROWANNC\DESKTOP\SWSI\RICKREDREC_ENV WHITE PAPER_1 Q-4-QS.DOC 15