I'm having issues with flow direction in a reservoir heading in both directions. To try and correct this I think I need to add height to the portion of the DEM that currently represents the dam to force flow in one direction.

Is this possible in ArcGIS Desktop 10.3.1 and if so, what would be the best approach?

  • Welcome to GSE ! For questions for ArcGIS Desktop, it's better for an accurate answer to tell what is your licence level and extensions. Mar 18, 2019 at 22:52

1 Answer 1


sure. just make a vector polygon over the area with the value you want. Add a height value for the dam.

convert the polygon to raster using the height value and the original DEM resolution, projection, and as a snap raster.

merge the two rasters using your preferred method. I would use CON.

here is a similar answer

Account for bridge overpasses in a ground DEM to allow for water flow under the overpass

  • I would just fill sinks resources.arcgis.com/en/help/main/10.2/index.html#//… to make the area where the dam is come up to the lowest value that will allow outflow.. When processing hydrology with high resolution DEM data, especially from LiDAR, it's a good idea to do a little fill at the very least to smooth out little 'bumps' that cause havoc in hydrology modelling. Mar 18, 2019 at 23:03
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    @MichaelStimson I may or I may not. I would try it first. As you know, this will fill all sinks both real and spurious and for some reason, he or she may not want to fill other real sinks. In a traditional process though, yes you need to fill sinks. Next reason I may not is that with a dam it is game of chance filling sinks as it will not always work. With a large structure like a dam fill, sinks can make water take an alternate route that is not the true 'through the dam" flow, but I would try it first. Fill sinks has worked for me with smaller dams but not always larger ones. Mar 19, 2019 at 0:03

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