Friday, December 19, 2008

What are the limitations of HEC-RAS???

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © 2008. All rights reserved.

There are certainly some limitations to HEC-RAS: Steep bed slopes (User's manual says >10%), multi-dimensional flow characteristics, complex pipe systems, etc, etc. However, I recently discovered that HEC-RAS is capable of handling enormous data sets. I put together a model of the ice age Missoula Floods, simulating the "breaking" of an epic-sized ice dam near the Montana-Idaho border. In short, the resulting flood wave traveled through the pan-handle of Idaho, south through Eastern Washington, through the Columbia River gorge with a side trip up the Willamette River in Oregon, and finally out to the Pacific Ocean. The overall simulation was about 1 month long, and it took 7 days for the flood wave to travel from the ice dam to the Pacific Ocean. So I guess the lesson learned is, as long as you work within the bounds of HEC-RAS's applicability, there is really no model too large for it to handle. For more details, you can check out the paper I presented at the EWRI2008 conference in Honolulu.


  1. Hello. Is there anyone who run Sediment Transport capacity with SI Units?
    I am trying to do that (specially with MPM) but independent from Flow (m3/s), I got a result (tonnes/day) just with Laursen (Copeland) function (and its very high values, there may be wrong as well). All other results are Zero. Although settings is SI Units, I am wondering if the units are really correct. I tryed already many things but still doesnot work.
    Please, can anyone help me.
    Thank you for your feedback.

  2. I will post this in the forum as well, to see if anyone else has experience with this. I did some playing around with sed transport capacity using SI units and I was able to get similar problems. Only difference is I got results for Toffaletti and none of the others. Anyway, I submitted a bug report to HEC about this. We'll see what they say. You could always try running the new sediment transport (not sediment transport capacity) in HEC-RAS and see if you can get anything that way. I know that most of HEC's sediment focus is towards the full-blown sediment transport capabilities, and not the sediment transport capacity function in the HD area.

  3. Hello,

    To determine sediment transport capacity I've had to go back to using HEC-RAS Version 3.1.

    I haven't had any success with getting version 4 or 4.1 to work.

  4. Version 4.0 had some bugs, but I was able to use it. Version 4.1 has most of those bugs fixed, and I've had no problems. Not sure why you're not having luck with 4.1.

  5. when i take data from HECgeoRAS & GIS to HECRAS all station data is coming 0..
    any one can help me.

  6. Did you run through all of the attribute steps in GeoRAS for the stream centerline and cross sections? Sounds like maybe you skipped a step.

  7. Hello, back to the sediment problems.. I’m modelling sediment transport in HEC-RAS and I introduced a boundary condition of sediment load series (tonnes) at river first section each 24 hrs for 41 days with a peak of 90.000 tonnes in 24 hours. After running the model the output variables are shown but the sediment discharge (tons/day) at river first section are very different from the boundary condition with a peak of 280.000 tons/day.
    I don’t know which is the variable that shows the sediment load. I thought it was sediment discharge, but results are quite different.
    The convertion.. 1 tonnes to tons 1.1023.
    NO variable shows the values of the Sediment Load of the boundary condition that I put upstream.
    Thank you!!

    1. Perhaps this will help identify the best variable to look at: