Geography Reference
In-Depth Information
Usage:
r.lake [-no] dem=name wl=value [lake=name] [xy=east,north]
[seed=name] [--overwrite]
Flags:
-n
Use negative depth values for lake raster map
-o
Overwrite seed map with result (lake) map
--o
Force overwrite of output files
Parameters:
dem
Terrain raster map (DEM)
wl
Water level
lake
Output raster map with lake
xy
Seed point coordinates
seed
Raster map with seed (at least 1 cell > 0)
The command is pretty straightforward. Notice that we can choose to
assign negative values to the lake map using the
-n
option. This means
that if we query a given cell, the value will be negative, indicating a
depth from the surface of the lake.
The seed coordinates specify the starting point of the calculations. We
could use a raster map as a seed as long as it has one cell with a value
greater than zero. Why would we want to do this? If we wanted to create
a series of maps showing an increasing water level, we could use the
previous output as the seed for the next map. Another important point
is that the water level must be specified in DEM units—in our case,
meters.
To flood our DEM, we pick a point in the southwest corner somewhere
and use the following command:
r.lake dem=ancc6_dem lake=ancc6_lake_100m xy=258686.903427,1298819.69314 wl=100
on the next page. Each flooded cell in the raster has a value indicating
the depth, while those that are above water are set to null. This means
the underlying layer(s) on our map are visible so we can see what land
remains.
If you look carefully at the newly create lake, you can see the original
river course underneath. It flows from the top center of the map down
and then to the west. This was the extent of the water before we flooded
the area, apart from a few lakes in the southwest quadrant of the map
that are now completely underwater. You can see from the result that
raising sea level 100 meters isn't a good thing. We flooded several lakes,
along with a bunch of subdivisions and a town or two.
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