Use HEC-HMS to perform calculations similar to those of HEC-1, covering a variety of precipitation and runoff processes.

Precipitation Modeling
Model hypothetical storm events based on frequency.
Use the U.S. Army Corps of Engineers standard project storm for hypothetical storms in the U.S. east of the Rocky Mountains.
Consider historical storm events through cell-based precipitation data.
Import precipitation data from other sources.
Specify gages and a method of weighting the gages, including user-defined and inverse distance-squared weighting.
 

Basin Modeling
Compute sub-basin runoff in either a lumped or linearly distributed fashion.
Determine losses based on several methods, including Green & Ampt, SCS Curve Number, gridded SCS Curve Number, and the Initial/Constant method.
Transform precipitation to runoff through either unit hydrograph methods (Clark, Snyder, or SCS) or Kinematic Wave methods.
Route hydrographs using Kinematic Wave, Modified Puls, Muskingum, or Muskingum-Cunge.
Divert flow, either losing the diverted hydrograph or adding it back in further downstream.