Watershed Modeling With HEC-HMS (Hydrologic Engineering Centers-Hydrologic Modeling System) Using Spatially Distributed Rainfall

Abstract

Simulation of the watershed runoff response to rainfall is an essential element of flood-warning and preparedness programs. The reliability of estimated runoff is an important aspect of successful programs. Methodologies for observing spatially distributed rainfall (radar rainfall) and for obtaining other gridded watershed data are continuously evolving. The increasing availability of spatially distributed data creates opportunity for improving rainfall-runoff modeling. The U.S. Army Corps of Engineers, Hydrologic Engineering Center (HEC) has developed a watershed modeling program, HEC-HMS, that has the capability to use spatially distributed rainfall and runoff parameters for runoff simulation. This capability and the associated applicability to flash floods are described. 2. Introduction The advent of Geographical Information System (GIS) technology has created opportunities to improve rainfall-runoff modeling techniques and thereby improve runoff forecast reliability and increase flood-warning time. Traditionally, using lumped parameters, the emphasis was on representing the runoff process and less attention was given to describing the physical system. Now, with readily available spatially distributed geographic and hydrometeorologic data, and the GIS tools to manage and manipulate these data, the emphasis has shifted. The availability of spatial data and GIS not only makes it possible to better defme the physical system, thus improving accuracy, but makes it much easier to develop physically-based parameters needed for runoff modeling. As an essential component of a sound flood-waming and preparedness program, distributed rainfall-runoff models can be applied to identifY flash flood prone areas, to characterize site-specific nature of the flooding, and to forecast flood threats. With this information, prudent plarming can save lives and property. The purpose of this paper is to describe a new distributed hydrologic modeling system, the use of GIS for model development, and model application for flood prone areas. 219 E. Grunt/est and J. Handmer (eds.), Coping with Flash Floods, 219-230.