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

[Rich Shepard]

   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?

Rich