In case you
haven’t seen it, there has been a very popular LinkedIn discussion on the
Hydraulic/Hydrologic Modeler’s Forum debating the advantages, disadvantages,
and merits of HEC-RAS 5.0, TUFLOW, and DHI’s MIKE21. There was a lot of
great information (and some misinformation) and insight provided in that
thread. It is well worth the read. Some of the misinformation was
directed at the beta version of HEC-RAS Version 5.0. Enough that HEC
decided to publish a response to clear up any confusion.
At play is a
result of HEC-RAS’s 2D solution scheme using the full shallow water equation
where for highly dynamic events where flows severely contract, using too small
of a time step could lead to a divergence from the true solution, rather than a
convergence. This is not an issue when a computation interval is selected
within the guidance presented by HEC in their user’s manual. While HEC
disagrees that this is a necessarily a “problem” with its software, as some on
the discussion claim, HEC has elected to make this a non-issue by
“improving the portion of the full shallow water equation formulation, such
that user’s will be able to use very small time steps without the results
changing significantly.” I’ve included HEC’s response, written by Gary
W. Brunner, to the LinkedIn discussion below, but I highly recommend you read
the LinkedIn discussion first by clicking here:
I’m posting
this not just to allow HEC to reach a larger audience with their rebuttal, but
also because there is a LOT of great information in this document about how HEC-RAS 2D works and
how we, as HEC-RAS 2D modelers should use it. Please enjoy! A
downloadable pdf is available here.
The following text is copyrighted by the Hydrologic
Engineering Center and Gary W. Brunner:
