Incorporating Surface Storage and Slope to Estimate Clark Unit Hydrographs for Ungauged Indiana Watersheds

Abstract

Application of Soil Conservation Service’s (SCS) dimensionless unit hydrograph method for ungauged basins in Indiana yields very high peak flows and short time to peaks for the northern region, thus producing unrealistic flow estimates for design purposes. It is hypothesized that the overestimation of peak flows in northern region using SCS method is due to the flat terrain and high surface storage caused by the Wiconsinan glaciations. To incorporate the slope and storage characteristics, the application of Clark synthetic unit hydrograph (SUH), which incorporates time of concentration ( tc ) and a storage parameter (R) to produce runoff hydrograph, is explored for Indiana. A statistical analysis of 29 geomorphic attributes and past storm hydrographs for thirty watersheds in Indiana show that watersheds in north, central and southern regions are statistically different in terms of slope and storage characteristics. A statistical comparison of Clark parameters ( R and tc ) estimated for past storm events a...