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Publication Abstract

Streamflow Assessment Model for the Little Wabash River Watershed : Hydrologic Analysis Knapp, H. Vernon, and Michael W. Myers, 2001  Illinois State Water Survey, Champaign, IL,  ISWS CR 2001-14    Full Text Available
The Illinois Streamflow Assessment Model (ILSAM) is an analytical and information tool developed to predict the frequency of streamflows, and water use impacts on streamflows, for every stream in selected major watersheds in Illinois. The current version of ILSAM was developed to operate on a personal computer having a Microsoft Windows 95/98/2000/NT operating system. The model user can obtain streamflow frequency estimates for any location in the watershed by identifying the desired stream and location. The ILSAM has been developed for use with streams in five such watersheds: the Sangamon, Fox, Kaskaskia, Kankakee, and Little Wabash River. This report includes a description of the steps used to develop ILSAM for application to the Little Wabash River watershed, along with a description of the physical characteristics of the watershed, its surface water hydrology, and the factors that influence streamflow variability.

The Little Wabash River watershed is located in the southeastern portion of Illinois and has a total area of approximately 3238 square miles. The river and its major tributaries provide the source of water supply for all of the major communities in the watershed, either through direct withdrawals from the river or from the storage of water in impounding reservoirs. Many of these communities were forced to undertake emergency measures to sustain their water supply from these sources during the major droughts of the early- and mid-1900s. Thus, an understanding of the frequency of low flows and drought flows is critical for assessing surface water availability and yields for these communities. Streamflow frequency predictions produced by the model are also useful for evaluating instream flow levels for the protection of aquatic habitat, providing streamflow estimates for water quality analyses and regulations, and classifying Illinois streams by their hydrologic character for use in watershed management.

The hydrologic analyses used to develop the model include evaluating the flow frequency from all streamgage records in the Little Wabash River region, evaluating impacts to flow quantity from dams, water supply, and treated wastewaters, and developing regional equations to estimate flows at ungaged sites throughout the watershed. All streamflow frequency estimates produced by the model are representative of the long-term expected flow conditions of streams, reflecting hydrologic conditions over a base period of nearly 50 years (1952-1999).

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