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Publication Abstract

Fox River Streamflow Assessment Model: 1999 Update to the Hydrologic Analysis Knapp, H. Vernon, and Michael W. Myers, 1999  Illinois State Water Survey, Champaign, IL,  ISWS CR-649    Full Text Available

The proper management of surface water resources in a watershed requires an understanding of both the expected streamflow characteristics within a river basin and the effects of various potential water-use practices on those flow characteristics. In many circumstances, potential conflicts exist between the uses of streams for domestic, industrial, and agricultural water supplies and the natural functions of the streams, which include providing habitat for aquatic and terrestrial biota. Sufficient information to evaluate these potential conflicts and other water resource questions is seldom available in a useful form.

The Illinois Streamflow Assessment Model (ILSAM) was developed to provide needed streamflow information to watershed managers and planners. This specialized software program was developed for use on a personal computer to provide estimates of the long-term expected magnitude of streamflow at various frequencies for any stream location along a major stream in a watershed. The effects of potential or hypothetical water resource projects on the quantity of water in streams also can be examined using options available in the model. For the purposes of this model, major streams are considered to be those having upstream contributing drainage areas that exceed 10 square miles in size.

To date, the sets of hydrologic data used by the model have been developed for four major watersheds in Illinois: the Sangamon, Fox, Kaskaskia, and Kankakee River Basins. Hydrologic data sets also are currently being developed for the Little Wabash and Rock River Basins.

The purpose of this study was to update ILSAM for the Fox River Basin, a model originally developed in 1988. Over time, climate variability and changes in human factors, such as land and water use, and water resource projects, can greatly affect the quantity and distribution (both in space and time) of surface waters in a river basin. For this reason, the data sets used by ILSAM were designed to be updated periodically, perhaps every 5 to 15 years. The frequency of and need for updates are governed by the rate at which streamflow conditions in the watershed change over time. The model update for the Fox River Basin addresses four areas that influence the flow frequencies and their estimation:

  • Increases in population, overall water use, and the resulting effluent discharges.
  • A new public water supply withdrawal from the Fox River and increases in magnitude of existing withdrawals.
  • General increases in streamflow magnitude caused by climatic variability and the overall increase in average precipitation.
  • Adoption of improved regional equations from which to estimate flow at ungaged sites.

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