Using "Simulate Water Level Rising/Flooding..."

DionybellDionybell Global Mapper UserPosts: 33Trusted User
edited March 2015 in Elevation Data
Hello,

I have a Raster DSM of an area and what Im trying to do is to recreate a flood by a tropical storm in 1998. All I have are photographs taken from an helipcoter of the same area, where you can appreciate the flood.

I used the 3D View on GM and start rising the water above sea level until what I see on the 3D view looks just about the same as the photos. I managed to do that by rising the water level on 3D view by 6.8 meters above sea level.

But now Im playing with other tools of Global Mapper and what to do some calculations or something.

I tried using the "Simnulate Water Level Rising/Flooding" which is supposed to do the same thing, but I don't understand how it works. I want to rise the water level 6.8 meter to get a flood area just as I got on the 3D View. The results don't match, it fills just a part of the area, but the rest is not filled.

This is what I get on 3D View by rising water level 6.8 meters.

Inundacion.jpg

This is what I get with the Simulate tool

ddddd.jpg

What am I doing wrong? I set the Water Level Increase Amount to 6.8. Unchech the "Increase from Selected Areas" and Check "Increase from Elevation"

Any help/explanation on how to properly use the tool will be appreciated.

Also what can I do with that polygon? Is there a way to calculate the water volume above ground level? or any other calculation?

Thanks in advance.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited July 2014
    The water rise tool would select all areas that flow in to the selected area features from a height less than 6.8 meters above the height at the polygon edge. So any areas that were flooded but that didn't flow in to your area wouldn't be highlighted.

    If the flood was from sea level you probably want to do the water rise over a larger area that includes the ocean and increase from the sea level height of 0. The difference in the water rise tool and the water level display tool is that the water rise tool takes obstructions in to account. For example, if you looked at a map of the entire US and set the water level to 0, places that are below sea level, like Death Valley, would show as flooded even though the water can't get there. With the water rise tool if you started at the ocean polygons and raised sea level by say 10m it still wouldn't flood Death Valley. You would have to raise it enough that the water can get over the lowest path to reach Death Valley.

    In many simple coastal scenarios you can get a pretty good sense just from the water height display and that is much faster. The water rise tool is useful in more precise scenarios where you have earthworks that may block flow, like perhaps levees.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • DoncheDonche Global Mapper User Posts: 5
    edited August 2014
    Hi Mike,

    Sorry for bringing in the unrelated stuff to this thread.
    I just got registration done and like to know how I can add new thread. I can't find the Add New Thread button anywhere.

    Thanks

    Don
  • JeffH@BMGJeffH@BMG Global Mapper Developer Posts: 322Trusted User
    edited August 2014
    Donche wrote: »
    Hi Mike,

    Sorry for bringing in the unrelated stuff to this thread.
    I just got registration done and like to know how I can add new thread. I can't find the Add New Thread button anywhere.

    Thanks

    Don
    Hi Don,

    All that you should need to do is to pick the appropriate subforum (e.g., "Technical Support", "Bug Report"), and then click on the button that says "+Post New Thread", which should be to the top/left of the subforum.

    Hope this helps,

    ~Jeff
  • DoncheDonche Global Mapper User Posts: 5
    edited August 2014
    Awesome! Thanks Jeff. It works.

    Don
  • AlbertalbernAlbertalbern Global Mapper User Posts: 1
    edited September 2014
    Good work...
    It's very helpful for everyone.
  • AGRAYAGRAY Global Mapper User Posts: 4
    edited March 2015
    Is there a way to calculate the height of the water above the ground using the polygon from "simulate water level rising/flooding" output?
  • bmg_bobbmg_bob Global Mapper Programmer Posts: 1,970
    edited March 2015
    Hello,

    After you run the Simulate Water Level rise, you can use the Raster Calculator to produce a grid containing the depths:

    1) Select the output area from the Simulate Water Level process using the digitizer.
    2) Choose the Analysis->Raster Calculator - Apply Formula... menu item. The Set up Apply Formula window will be displayed.
    3) Under Set up Formulas for Each Band of Output, select the Add Custom Formula radio button and type "<water level increase>-B1, replacing "<water level increase>" with the height that you used when you simulated the water level rise. For example, if you simulated a water level rise of 13, type "13-B1". Click the Add Band button to add your formula to the list.
    4) Select output band settings as desired. The defaults are probably OK. Make sure that the units match the units of your elevation layer.
    5) On the Export Bounds tab, select the Crop to Selected Area Feature(s) radio button near the bottom of the window.
    6) Click OK. Global Mapper will create a new elevation grid layer using your formula.

    Note that this assumes that, when you ran the Simulate Water Level Rise tool, you used the Increase from Elevation option, and specified a base elevation of zero.

    Cheers,

    Bob
  • AGRAYAGRAY Global Mapper User Posts: 4
    edited March 2015
    Thanks, Bob!
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