[GRASS-user] r.mapcalc: compare two maps [RESOLVED]

[Rich Shepard]

On Thu, 30 Mar 2017, Laurent C. wrote:

> If I understand well, you have a 'raw' DEM and you want to open the
> culvert in that DEM. If it is an under-road culvert, your 'raw' DEM will
> show the road elevation, and the culvert will not be shown. i.e the
> culvert is blocked. If you want to 'open' the culvert, you'll have to cut
> through the road. You can do this with r.carve, for example.

Laurent,

   Interesting observation. On the source DEM the elevation of the culvert
inlet is about 2 feet lower than the road and the elevation of the culvert
outlet is about 3 feet lower than the road.

   The attached .png shows the results of a 40-minute simulation of rainfall
accumulation. The two red dots are the culvert inlet and outlet. The
accumulation south of the road is because water pools in the swale below the
inlet until it reaches that elevation, then flows through and accumulates in
the deeper portion of the ditch on the north side.

   I expected to see something like this using the actual rainfall data I
have.

   Then, of course, if the culvert is blocked I expect water to accumulate
south of the road until it reaches that elevation, then overflow the road
and areas to the south.

Rich
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