HydroCAD v HEC-RAS (for water surface elevation evaluation)

[DE Yakr]

I'm trying to write out a statement for our in-house designers why HEC-RAS should be used for a water surface evaluation difference between a pre and post condition in a streambed. A few years ago, Peter wrote, "a reach is intended only for modeling normal flow with a constant cross section", so I'm presuming since a natural streambed has variable cross sections and variable friction forces, than that should be a good enough reason for 'dictating' HEC-RAS?

On the flip side, if I had a 'constructed' ditch/swale with a constant cross section and constant n value (per say), would HydroCAD be acceptable for evaluating a water surface elevation difference in that?

THANKS!!!!

 

[psmart]

If you're modeling normal flow with a (reasonably) constant cross-section, a HydroCAD reach will do the job. For a variable cross-section you may need a more detailed water surface profile, as done by HEC-RAS. It all depends on the uniformity of the cross-section and the accuracy that you require. Remember that a reach routing in HydroCAD is intended primarily to generate an outflow hydrograph, rather than evaluate the exact water surface profile. HEC-RAS, on the other hand, is a steady-state analysis which is able to evaluate a more complex channel, but it's not a hydrograph-routing model. Different tools for different purposes.

Peter Smart
HydroCAD Software

http://www.hydrocad.net