[GRASS-user] r.lake: understanding variable 'water_level'

[Anna Petrášová]

On Thu, Oct 6, 2016 at 6:59 PM, Rich Shepard <rshepard at appl-ecosys.com> wrote:
>   The elevation map (be_metric) has minimum and maximum elevations of 45.17
> and 51.32 m. This command:
>
> r.lake elev=be_metric water=50 lake=pop coord=2295821.12321,175257.829078
> --overwrite
>
> produces the output map with this commentary:
>
> Lake depth from 0.000000 to 4.833561 (specified water level is taken as
> zero)
> Lake area 357082.807803 square meters
> Lake volume 409786.922884 cubic meters
> Volume is correct only if lake depth (terrain raster map) is in meters
>
>   My interest is in a specific, much smaller area. However, when I re-run
> the command with much smaller water_level values there is no output:
>
> r.lake elev=be_metric water=0.01 lake=pop coord=2295821.12321,175257.829078
> --overwrite
>  100%
> ERROR: Given water level at seed point is below earth surface. Increase
>        water level or move seed point.
>
> r.lake elev=be_metric water=0.1 lake=pop coord=2295821.12321,175257.829078
> --overwrite
>  100%
> ERROR: Given water level at seed point is below earth surface. Increase
>        water level or move seed point.
>
>   If the entire 36 sq. km. is covered with water when water_level is set to
> 50 (just below maximum elevation), yet input values of 0.01 and 0.01 are
> underground, how do I specify small elevations above that of the 'dam' which
> is at an elevation of approximately 48.25m?

I am not exactly sure what are you asking, but water_level is the
absolute level of the water, not relative height above the elevation
of the seed. If you want to use the relative height, user r.what to
query the elevation of the seed and add it to your relative height.

Anna

>
> Rich
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