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Thread: DEM Reconditioning problem.

  1. #1
    Muhammad Irfan
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    Default DEM Reconditioning problem.

    Hi all,
    I am using Aster DEM having 30m resolution n i wana use DEM reconditioning (AGREE) option. but i am little confuse with the following inputs;
    Stream buffer -------
    Smooth drop/raise --------
    Sharp drop/raise --------
    Kindly guide me that what should be the above inputs and which would be suitable for this DEM.

  2. #2
    Layla Bz
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    Post Re: DEM Reconditioning problem.

    Quote Originally Posted by mirfan09 View Post
    Hi all,
    I am using Aster DEM having 30m resolution n i wana use DEM reconditioning (AGREE) option. but i am little confuse with the following inputs;
    Stream buffer -------
    Smooth drop/raise --------
    Sharp drop/raise --------
    Kindly guide me that what should be the above inputs and which would be suitable for this DEM.
    Hi,
    Did you ever figure out what to put for those factors? I have the same issue. As far as I have understood, you can go as low as 2 buffer cells for "Stream buffer" input. Although I think 2 would give you a coarse result anyway but my understanding is that since we are using less cells in computation, it takes shorter time to do the DEM Reconditioning process.

    I am confused about smooth and sharp drop/raise too. I usually use 1ft for smooth, (I am working on a rather flat area (Florida)), but for sharp raise/drop I don't have any idea.
    My other problem is that I have NEGATIVE minimum elevations on my RAW DEM too. And I m not sure how to address them in my smooth and sharp drop/raise.

    Please let me know if you have figured out this.
    Thank you!

  3. #3
    Mark Boucher
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    Default Re: DEM Reconditioning problem.

    This post has some explanation.

    http://forums.arcgis.com/threads/521...l=1#post178866

    See also the link in my signature for other Arc Hydro tips.

  4. #4
    Layla Bz
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    Default Re: DEM Reconditioning problem.

    Yes, thanks I have seen that thread and checked out the links (only the second one opens for me though)
    I think I understand what smooth/sharp drop/raise are. But I am not sure how to figure out what number to use for each.
    I am working on Brevard County in Florida, which has a minimum of -30 ft and max of 150 ft in elevation. (I work on 5 separate sets of RAW DEM data that each have different min and max, but I provided the min and max for the whole county)

    My first question, is that since Florida is very flat (compared to a mountainous terrain) , do I need to take that into account when using default values for smooth (10 ft) and sharp(100ft) drop/raise factors?
    (For example, one of my sets of data has a min elevation of -4 ft and max of 55 ft )

    Second, Since I Have negative values for my minimum elevations in a few of my RAW DEM layers, do I need to take that into account when figuring out what values to use for smooth and sharp drop/raise?

    Thank you very much .

  5. #5
    Mark Boucher
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    Default Re: DEM Reconditioning problem.

    My SA license is not available for me to look at the commands in detail.

    My watersheds are generally not as flat as Florida. In the flat valley areas I do have, I find the need to "build" lots of walls to make the flows go in the right directions.

    I think there is an option in the burn streams tool that tells Arc Hydro to bring the negative dem values up to zero. If you do have zero values and can't find that option, but still want to see if the negative numbers make a difference, you could use the CON() function to make anything negative 0.0 or slightly above. Then you could use that raster for the rest of the process. I also don't recall negative numbers being a problem. I'm in the SF Bay area and my elevations aren't all that high. I use the default burn values which I think the deepest is 1000 ft. and I know many of my projects have gone to the bay and I've never had a problem.

    Since I have steeper terrain, my tendency is to minimize the width of the smooth and sharp rise values. The purpose of the smooth drop is to eliminate parallel stream right next to your main stream.

    It might be a trial and error situation for you to figure out what values to use. When I do trial and error, I do a trial noting the parameters I used, get out of Arc Map, delete the Arc Hydro file geodatabase and raster folder, start up Arc Map again and reprocess using different smooth/sharp drop values. Seems to be a few extra steps, but makes things run with fewer hiccups due to overwrite conflicts etc. This is where model builder comes in handy.

  6. #6
    Layla Bz
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    Red face Re: DEM Reconditioning problem.

    Quote Originally Posted by MBoucher21 View Post
    My SA license is not available for me to look at the commands in detail.

    My watersheds are generally not as flat as Florida. In the flat valley areas I do have, I find the need to "build" lots of walls to make the flows go in the right directions.

    I think there is an option in the burn streams tool that tells Arc Hydro to bring the negative dem values up to zero. If you do have zero values and can't find that option, but still want to see if the negative numbers make a difference, you could use the CON() function to make anything negative 0.0 or slightly above. Then you could use that raster for the rest of the process. I also don't recall negative numbers being a problem. I'm in the SF Bay area and my elevations aren't all that high. I use the default burn values which I think the deepest is 1000 ft. and I know many of my projects have gone to the bay and I've never had a problem.

    Since I have steeper terrain, my tendency is to minimize the width of the smooth and sharp rise values. The purpose of the smooth drop is to eliminate parallel stream right next to your main stream.

    It might be a trial and error situation for you to figure out what values to use. When I do trial and error, I do a trial noting the parameters I used, get out of Arc Map, delete the Arc Hydro file geodatabase and raster folder, start up Arc Map again and reprocess using different smooth/sharp drop values. Seems to be a few extra steps, but makes things run with fewer hiccups due to overwrite conflicts etc. This is where model builder comes in handy.
    thank you, I am very new to ArcHydro and I am still learning. I would have to read through everything you said and research more on it to be sure I understand what you said. I will get back to you. Thanks a lot.

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