[GRASS-user] footprint of a given volume of water.

[Glynn Clements]

Jeroen Wortel wrote:

> > I've used r.lake to answer the question "What land is inundated given
> > a X meter high dam?". In this case however, X is the unknown so I'm
> > trying to answer the question "How high does the dam have to be in
> > order to hold Y cubic meters of water?"  as well as to determine the
> > "inundation footprint".
> > 
> > I'm familiar with some engineering models that require much more
> > detailed cross-sectional information than we have available...
> > currently we have a high-res DEM as our sole source. Are there any
> > GRASS modules or scripts that I should take a look at?
> 
> I would use r.mapcalc and calculate water volume slices from the deepest
> point of your basin in, say, 1 meter steps. As the resulting volume
> exceeds Y cubic meters of water (your threshold), you know how high your
> dam should be. This can be easily scripted. You can adjust the step size
> (1 meter) according to your accuracy needs.

As the relationship between height and volume is monotonic, you can
use bisection, which will be faster.

-- 
Glynn Clements <glynn at gclements.plus.com>