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Flood Simulation using GM 22

Dear Global Mapper friends,

I have a question:
I have an elevation model.
A river runs there.
The river has a slope. I can determine the slope from the lidar or elevation data.

Is it possible to create a flood simulation with Globalmapper, e.g. Water level (water higher) 1 m higher or differently 2 m ...? The water level functionality does not take into account any water gradient see attachment.

Hope you understand my problem?


  • Hi Gunter, greetings from Perth in Western Australia!

    I know exactly the question you are asking, but it boils down to the difference between "standing" water and "flowing" water. The GM Show Water Elevation tool only shows standing water i.e. water with a perfectly flat surface. It is very useful if you want to demonstrate the extent of flooding as a result of stationary water and I use this tool frequently.

    The only way that I know of to do what you are asking in GM is to create the sloping water surface using either field survey data or results from a hydraulic model (e.g. HEC-RAS, MIKE, FLOOD etc.)  and then increment that surface up/down depending on what you are trying to show. 

    However you need to be careful doing this (as you probably already know!) as water depth along a natural channel is non-linear with flow i.e. twice the flow does not result in twice the depth!



  • Hi CarrickCont thanks a lot.

    yes i know. And what you write, may be the right way.

    ?  hydraulic model = from River (?) (e.g. HEC-RAS, MIKE, FLOOD etc.) can i generate it from Lidar ?

    I have lidar data of the surface of the river.
    Can I generate it from it?

    With Global Mapper? But how ?

    And then assign other heights ??

    Thank you very much Günter

  • Hi Gunter,

    If you have LiDAR survey date for that stretch of the river you should be able to easily re-create the water surface within GM depending on how it has been classified. Sorry I can't instruct you long-distance how to use GM in detail, but I'd start by contouring the river surface and cropping it out using the contours overtop of the aerial imagery. You should end up with a fairly accurate surface that way...

    Best of luck,
  • 946946 Global Mapper User Posts: 167Trusted User
    You can do the following :

    Digitize the water surface and add elevation from terrain to resulting vector.
    Or just digitize the river centerline add elevation and use a small buffer value to create an area.

    Select the 3D polygon and use Water Rise Function.

    Use desired parameters and repeat the simulation with your increment

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