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Is there a way to find a flood zone from a stream using a DEM?

mcb9060mcb9060 Global Mapper UserPosts: 54Trusted User
I will try and describe what I am trying to achieve. I have a DEM and a course for a stream that is flowing downhill. I want to raise the water level in the stream by (for example) 2 meters. With this new water level, I want to see the areas affected by this increase in water level (flood zone). Is there a way to achieve this in Global Mapper? I am using version 22.1. Thanks very much, Mark   


  • Hi Mark,

    Have you turned on "Water Display" in Configuration (Spanner)/Vertical Options Menu as shown below? You can then raise/lower the water level by your pre-set increment via the + and - buttons on the Viewer toolbar.

    This tool alone is worth the cost of GM.  I use it for flood inundation studies frequently. 

    Hope this helps. Let us know if you have any problems with this.


  • mcb9060mcb9060 Global Mapper User Posts: 54Trusted User
    Hi CarrickCon, thanks very much for your reply to my query. The tools you mention are good for simulating for example rising sea levels as far as I understand. I was thinking more of being able to define a polygon that shows where the water would flood if water in a stream/river that is flowing downhill rises by for example 2 meters. Sorry if my explanation is not very clear. I have a path profile for the stream that flows from 272 meters above sea level to sea level. I would like to raise the water level parallel with the path profile by, lets say, 2 meters along the whole profile and see where the water would spread out along the banks of the stream using a DEM. Would this be possible in Global Mapper? Thanks very much, Mark
  • Hi Mark,

    Please see this earlier  discussion
    where forum member 946 explains how to use the Simulate Water Level Rise found in the Analysis toolbar.

    Please note that for flow along natural channels i.e. irregular/non-prismatic channels with varying slope, cross-sectional area, roughness etc. that a fixed flow depth (in your case 2 m) is completely an artificial or hypothetical condition as the actual depth and velocity will vary along the channel. Apologies if you already know this...

    If you need to model channel flows realistically you need to use hydraulic modelling software such as HEC-RAS, MIKE, FLOOD etc.


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