Basin Flooding/Sea Level Rise

Accessed with "Calculate, Drainage, Flood basin" menu choice. 

After you pick the point to start flooding from (or a shape file with multiple points), you will get the form below which lets you select options and parameters.

If you want to export this to a KML file, you must use a lat/long DEM. You can Reinterpolate a UTM DEM to lat/long:

These require that depths have negative z values.  You can quickly edit the DEM to multiply the depths by -1.

  • Reservoir top: flood up to this level (only level used for the "Flood" button).
  • Low level: for the movie option, the first level to depict.
  • Interval: amount to increase each frame of the movie.
  • Label maps: put the water level label on each map.
  • HTML:  copy the results of the Complex algorithm in the data grid into an HTML file.
  • Flood: flood a single water level.  The value will be in the "Reservoir top" edit box.
  • Movie: create animation with a variety of reservoir levels.  Frames are saved with the format selected on Directories tab of options form,
  • Start points: if you have a high resolution LIDAR image, you can start flooding from a number of points because bridges will act like dams.  Select a point database file, which you can create with the Create shapefile option (point shape file) on Annotate Map icon of map toolbar.   
  • Algorithm:  This choice only applies to a DEM map.  If you use an image, the Flooding algorithm will be used. 
    • Elevations: color codes elevations above the flood level green, and those below in blue.  Points (like Death Valley) will "flood" even if they have no path to the water.
    • Flooding: uses a fast graphical flood fill operation to rapidly find all points with a path to the water.  This uses the current screen resolution.  For maximum accuracy, you should be a 1:1 (100% zoom) level with the DEM, having a screen pixel size that is equal to or less than then DEM resolution.
      • create a white bitmap the same size as the map
      • set all points about the flood elevation to green
      • from all the starting points (one per point in the water that is separated by a bridge or peninsula from the others), flood fill to a green boundary, with blue fill
      • turn all the green to white, as those points are above the water
      • in blue the bitmap now has all the flooded points, which are below the top of the flooded level, and which have a clear path to the water
    • Complex: methodically computes all points with a path to the water.  It will be slow, but uses all points, and produces the table seen below.
Table from complex algorithm.

Save using HTML button

Movie showing flooding of downtown Annapolis with hurricane Isabel.

For this option, set:

  • Low level (m), for the water at the start of the animation.
  • Reservoir top (m), for the final water level.
  • Interval, the value in meters between frames in the animation.

There are some anomalies present due to the 2.5D nature of DEMs; bridges and some other features will block flooding, so you should use multiple starting points.

Larger example on web, and a KML model.

Caveats:


Last revision  2/9/2018