Hydrologic Analysis for Kankakee River Watershed Streamflow Accounting Model

Abstract:

Streamflow frequency is used for in-stream flow needs evaluation, water supply planning, water quality analysis, and stream classification, among other purposes. The Illinois Streamflow Accounting Model (ILSAM) was developed to predict the streamflow frequency for Illinois streams and has the capacity to explore anthropogenic impacts on streamflow frequency. Over the past two decades, ILSAM has been applied to ten major watersheds in Illinois. This study updates the hydrologic analysis for the Kankakee River watershed. The hydrologic analyses used to develop the model involved evaluating streamflow records from gaging stations and developing regional equations to estimate flows at ungaged sites throughout the watersheds. Impacts to flow quantity from dams, water supplies, and treated wastewater effluents are examined. The baseline flow condition is the flow record at gaged sites which includes historic anthropogenic effects. The unaltered flow condition, influenced primarily by climate, topography, hydrogeology, and land use, is determined by separating the effects of historic human impact. The effects of the various human modifications to flow in the basin have changed substantially over the history of the available streamflow records. The present flow condition is determined by assuming that current human impact extends back throughout the history of available streamflow records, and statistical estimates are computed accordingly. Flow frequency estimates for each gaging record are adjusted to account for differences in the period of record and other factors such as the hydrologic persistence of low flow. For ungaged sites, a regional regression based on unaltered flow conditions is developed to estimate flow frequency, and adjustments are made to account for human impacts to represent the present flow condition for all sites.