HEC-HMS is a Hydrologic Modeling System that is designed to describe the physical properties of river basins, the meteorology that occurs on them, and the resulting runoff and streamflow that are produced. This model is produced by the Hydrologic Engineering Center of the US Army Corps of Engineers in Davis, CA, http://www.hec.usace.army.mil/ A GIS preprocessor called HEC-GeoHMS is also available from the HEC for creating the basin model describing the physical characteristics of the watershed in HEC-HMS.