Friday, December 19, 2008

What are the limitations of HEC-RAS???

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 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.

8 comments:

  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.

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  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.

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  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.

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  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.

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

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  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.

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  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!!

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    Replies
    1. Perhaps this will help identify the best variable to look at:
      http://hecrasmodel.blogspot.com/2009/03/sediment-output-variables-what-do-they.html

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