Welcome to the RAS Solution › Forums › HEC-RAS Help › Obtaining cross sections using HEC GeoRAS

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  • July 18, 2014 at 9:06 am #5549
    Anonymous
    Guest

    Hello!

    I tried using HEC GeoRAS for my pre-processing and somehow, I am having troubles with the results.

    I am using a 3-degree conditioned DEM I downloaded from hydrosheds.usgs.gov. With such data, I followed the procedure for obtaining the cross sections (digitizing the river, banks, flowpaths and xcutlines.) When I am assigning now the elevations to the cross sections, I used DEM as my terrain.

    Now, when I view the results, somehow the stations are somehow to small. The actual width of the river is more than 5 meters while in my generated cross sections, I somehow get widths that are to small, not even half a meter. Even the distances between the stations are too small. They dont even reach a meter. Hence, my river was just a meter long, when in reality, the river is more than 100 meters long.

    Would you know where I went wrong? I also tried giving the DEM a new projected coordinate system, but it did not solve the problem.

    I hope you can help me with this. Thanks in advance!

    Regards,
    Chris

    July 20, 2014 at 6:58 am #8868
    cameron
    Participant

    What projection is the data in and what projection did you convert it too? What happens if you use the 3D Analyst tool in ArcMap to extract the elevations at one cross-section, does it give funny results also?

    July 21, 2014 at 9:17 am #8869
    Anonymous
    Guest

    Dear Cameron,

    Thanks! It says that the geographic coordinates is WGS 1984. I did not convert the DEM so that must be it. Based on your query, I think I still have to change the coordinates of the DEM? I think I will have to project it using another coordinates, say UTM, right?

    By the way, I am using a 3-second DEM. Do you know of any DEM source with finer resolution? Thanks!

    Chris

    July 21, 2014 at 9:34 am #8870
    cameron
    Participant

    WGS 1984 is in degrees and is probably why you are having a problem. I would convert it to UTM or Stateplane.

    If you are in the United States, you would check the USGS National Map website which can have down to 1/3rd arc seconds I believe.

    If you are out of the United States, your could try SRTM or Aster Data. Another place to look is Intermap

    http://www.intermap.com/en-us/home.aspx

    July 22, 2014 at 9:48 am #8871
    Anonymous
    Guest

    Thanks Cameron!

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