I am trying to show the area of flooding that occurs when bodies of water increase by different increments, like 0.5, 1, 1.5 meters, etc.. for all of Tanzania. I have a DEM with all of the bodies of water clipped out and the inverse -the dem of just the bodies of water. My thought is to locate all of the connected pixels to the body of water locations above 0.5, 1, and 1.5 meters (above the particular water source).

I tried experimenting with the cost distance tool in ArcGIS but am not sure if it is the correct tool for the job.

I prefer to use python and/or ArcGIS.

Is there a good way to show what areas would be flooded nearby bodies of water? Is the approach I am considering valid?

enter image description here

  • What were the precise steps involved in your "experimenting with the cost distance tool in ArcGIS"? What was unsatisfactory about the result?
    – PolyGeo
    Commented Jan 19, 2017 at 22:29
  • @PolyGeo I kept receiving a raster with zero values. I tried putting the source raster as the DEM of just the water bodies and the cost raster as the DEM of non water bodies. I was not sure if I did it correctly.
    – timpjohns
    Commented Jan 19, 2017 at 23:09
  • Please use the edit button beneath your question to revise it with any requested information.
    – PolyGeo
    Commented Jan 19, 2017 at 23:13
  • I would recommend a different approach using the DEM and contours.
    – whyzar
    Commented Jan 19, 2017 at 23:27
  • @whyzar mind elaborating or linking to proposed method if you have time?
    – timpjohns
    Commented Jan 20, 2017 at 0:31

2 Answers 2


Although I have done a lot with rivers I would not consider myself a flood modeller and I suspect I have over simplified my answer.

There is the Expand tool that you could use to expand out the expansion of a lake 1 pixel at a time which you could then test to see if is below 1m or not. If it is, you keep it and then feed back the expanded lake? So this solution would involve a lot of looping which you would do in modelbuilder or python.

There is almost certainly a tool out there that does this but I guess it is finding the right search term, try flood modelling or flood routing?

For example the ever awesome Whitebox GAT gis system (which amazingly is free) has a tool call flood order...


A partial answer to my question was found here: Flood Elevation Setback. Partial due to preferring an arc based solution. I was able to create the following, using a flow accumulation grid for streams and a flow direction grid, all derived from a DEM. May play around with parameters a bit. enter image description here

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