I am currently working on an assignment where I need to model flood risk areas. Firstly I was asked to identify potential flood risk zones based on the following criteria:

  1. identify areas that I would consider to have steep slopes. I think I have completed this task. I used the Slope tool here.

  2. Identify a 20 year flood zone and base this on an estimated distance from rivers. Then repeat the task for a 100 year flood return. A guide value would be not to go beyond 2 kilometers for the 100 year and less for the 20 year. I have no idea how to even start this. I have googled different things have come up with extensions that can be used but we never went over any such extensions in the college practicals.


1 Answer 1


I would typically not base a flood zone on distance from the river, but instead on elevation (a very steep hill right next to a river is very low flood risk, for example). However, if you don't have elevation data, I guess distance can be a reasonable estimate.

Measuring distance from a river can be accomplished with the Buffer tool. Create a buffer of the size you think valid for a 20 year flood distance, and for a 100 year flood distance. (What that distance might be, I'd hesitate to even guess!)

  • Thank you, I never even thought of the buffer tool. I really appreciate your help here :)
    – user43548
    Commented Jan 3, 2015 at 18:32
  • Hope it gives you the results you need! :)
    – Erica
    Commented Jan 3, 2015 at 19:46

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