HEC-RAS can model precipitation and infiltration over 1D (river reaches and storage areas) and 2D flow areas. Precipitation can be modelled with precipitation grids or point gage data. If point gage data are used the data is interpolated to a grid before use by the computational engines. To learn how to add precipitation data into HEC-RAS, please review the 2D User's Manual.

In addition to precipitation, modelers can now account for infiltration over 1D reaches, storage areas, and 2D Flow Areas. Currently the infiltration is subtracted directly from the precipitation hyetograph, and HEC-RAS is not performing infiltration based on the depth of the water on the land surface. There are three available infiltration methods in HEC-RAS, they are: Deficit and Constant Loss method; the Curve Number method; and Green and Ampt. For details on how to use the Infiltration methods, please review the HEC-RAS 2D User's Manual. Here is a short technical description of each of the three methods.