Time of concentration and storage coefficient values for Illinois streams

Values of time of concentration and storage coefficient, two unit hydrograph parameters, are presented for 194 and 120 basins in Illinois. Tabulated values consist of those computed by previous investigators as well as those computed for 98 basins as part of this investigation. These additional values were computed by calibration of the U.S. Army Corps of Engineers Flood Hydrograph Package (HEC-1). The significance of differences in method used by each investigator to compute these unit hydrography parameters was evaluated by statistical comparison of four sets of time of concentration values and three sets of storage coefficient values. Because no difference due to method was identified, it is concluded that all of the values tabulated in this report can be used in any application for which time of concentration and storage coefficient are required.