TauDEM (Terrain Analysis Using Digital Elevation Models) is a suite of
Digital Elevation Model (DEM) tools for the extraction and analysis of
hydrologic information from topography as represented by a DEM. TauDEM
provides the following capability:

* Development of hydrologically correct (pit removed) DEMs using the
  flooding approach
* Calculates flow paths (directions) and slopes
* Calculates contributing area using single and multiple flow direction
  methods
* Multiple methods for the delineation of stream networks including
  topographic form-based methods sensitive to spatially variable
  drainage density
* Objective methods for determination of the channel network
  delineation threshold based on stream drops
* Delineation of watersheds and subwatersheds draining to each stream
  segment and association between watershed and segment attributes for
  setting up hydrologic models
* Specialized functions for terrain analysis

Note TauDEM also works fine with MPICH, so if you have it installed it
is not necessary to install OpenMPI.