Publication Date
4-8-2008
Abstract
In a stream with a managed impoundment, the frequency, magnitude and duration of flows may be altered. Reservoir release policies attempt to preserve the essential quality of the aquatic environment while simultaneously satisfying the needs of a growing human population. The Connecticut Institute of Water Resources (CTIWR) has developed a simulation model to help resource managers quantify the impacts of release policies on both downstream flows and water supply reliability. The model, developed using STELLA, contains a single artificial reservoir with configurable rating curves. Input flows are simulated using either actual streamflow data, or by a synthetic flow with the hydrologic attributes expected to exist in some future climate change scenario. Water leaves the reservoir in one of four ways: direct evaporation, withdrawal for human use, spillage, or through an actively managed release. The current version of the model contains three main types of release rules and each rule has several configurable settings that control the amount and timing of release flows. A “Fractional Release” rule sets the managed release to some percent of the natural inflow, with the percent perhaps varying by season. A “Fixed Release” rule sets the release to some constant rate, regardless of the amount of flow into the reservoir, but that rate may vary by season. A “Pulse Release” rule requires the manager to punctuate periods of very low release with a few days of higher flows. The model may be used to estimate safe yield for each configured system, for either current conditions or some future hydrologic regime. Other model outputs such as the downstream hydrographs and storage timeseries may be post-processed to quantify the frequency of drought conditions and the degree of alteration in flows and storage resulting from each policy. Model outputs for selected release scenarios and Connecticut basins will be presented.