[GRASS-user] r.sim.water - depth/discharge values

M S mseibel at gmail.com
Wed May 23 09:15:59 EDT 2007

Having lots of fun with the r.sim.water module.  very cool stuff!  Now if I
can understand the outputs a little more clearly.

My input data used were in a projection defined as feet, the elevations are
in feet, on a 5 foot X 5 foot grid.  I recognize that the outputs are in
meters (depth) and cubic meters (discharge), and that the inputs for
rainfall excess (6.6mm/hr) and rainfall infiltration excess ( 0mm/hr) are in
mm/hr.  The 6.3 documentation/manual indicates that the input data is
acceptable in feet for elevin, dxin, dyin.

At a critical downstream location, the elevation is 62 feet.  The output
values are (based on the input values provided above) at this location are
110 meters for depth, and 38,050 cubic meters for discharge.

Recognizing that for infiltration excess I inputted 0mm/hr needs to be
greater than zero for realistic results (still have to adjust that input
parameter).  The discharge in volume seems intuitive (but still validating
output), however, it is the depth that I do not understand.  As per the
manual, depth is an average and err is its RMSE.

Is the depth a relative or absolute value with regard to the elevation?
Meaning should my depth be something like 3 feet (1 meter) as a theoretical
result, which means at that location at the end of the event, the average
depth is 3 feet of water?  Or is the output in absolute elevation saying
that the water depth will be at this elevation, say 65 feet elevation (62 +
3 foot depth)?

Thanks for any clarification or help!

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