I'm trying to generate flow accumulation using hec-geohms and I have already done some terrain processing using the DEM.

I was really confused what happened, why has the river channel been cut?

  1. what could be the possible reasons why this occurs?
  2. could this be a bigger error in my hydrologic model?

Here are the screen shots of what has been generated.

DEM overlain with river networks


Flow direction

Flow direction

Flow accumulation

Flow accumulation

Flow values enter image description here

  • Have you run the DEM through the FILL SINK tool first, this may fix the problem? – Hornbydd May 13 '14 at 14:45
  • Can you share the values in you flow direction. – If you do not know- just GIS May 13 '14 at 17:41
  • Is this the full extent of your DEM? Your DEM needs to encompass the entire watershed in order to generate a proper flow accumulation grid - it looks like you're modeling a pretty big stream. Also, are you using tools within GeoHMS to do this process or are you using spatial analyst? – thwllms May 13 '14 at 21:51
  • hi @thwllms . .i'm sorry for the late update. . i'm have this big river. . by the way, i'm using the tools wihthin GeoHMS. .the picutre is just a portion of what i see, has been encountering error. . – vklopt May 20 '14 at 0:27
  • hello @user27239 . .i'll be editing my post so i can add my flow direction values. . – vklopt May 20 '14 at 0:28
  1. Just the simple one first. Zoom in to the omitted area and double check it is not a rendering issue. You flow accumulation indicates it may just be this issue.

  2. If you have any other values than 1,2,4,8,16,32,64,128 in your flow direction you need to fix sinks first and rerun the entire process.

  3. I have had issues working in non-projected data (WGS 84 or NAD 83 for example) when creating hydrologic outputs. Try converting the original DEM in UTM or similar and run again and remember the fill.

  • hi @user. . i have already manage to follow your steps but the same thing happens. .this time the cut flow is on the other part of the river. . i have modified the DEM hoping this would work better. what I did is clipped certain area in the DEM where issues has been noticed, and add/subtract elevation from it. the clipped DEm is then mosaic to the original DEM in order to have a DEM of the full area. do you think this is acceptable? – vklopt Jul 24 '14 at 2:31

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