Spatial averaging of land use and soil properties to develop the physically-based green and ampt parameters for HEC-1

The computer hydrologic model HEC-1, developed by the Hydrologic Engineering Center (HEC), has been used for many years by hydrologists and engineers to estimate surface water runoff caused by rainfall events. Besides the rainfall data itself, the most sensitive set of input parameters in a runoff model are the rainfall loss parameters. The SCS (NRCS) Curve Number approach is commonly used to compute rainfall losses. Another method available for computing rainfall losses in HEC-1 is the Green and Ampt approach. However, this method is used infrequently because of the difficulty in obtaining the soil data needed to derive the Green and Ampt parameters. The purpose of this study is to present an automated method of computing Green and Ampt parameters using digital soil and land use data. Studies were performed with data that compare this automated method with another nonautomated method of computing Green and Ampt parameters. Parameters computed using the automated method were consistent with the parameters computed using the non-automated method. Furthermore, by taking advantage of Geographic Information System (GIS) overlay capabilities, significant time was saved in computing the Green and Ampt parameters.