[GRASS-user] Calculate flooded area based on precipitation

[Laurent C.]

2017-02-15 18:38 GMT-06:00 Rich Shepard <rshepard at appl-ecosys.com>:
> On Wed, 15 Feb 2017, Laurent C. wrote:
>
>> The h_max output map of Itzï will correspond to the maximum water level
>> reached during the simulation.
>
>
> Laurent,
>
>   I did this to reveal water accumulation with un-blocked flows and did not
> see how to modify it to show blocked flow accumulations.
>
>> To simulate the blockage, you might need to change the DEM locally. But in
>> the case of a under-road culvert, just leaving the measured elevation of
>> the road might be enough.
>
>
>   I'll need to experiment with this to understand how to 'leave the road
> elevation' when the culvert's blocked. Perhaps increasing the DEM of all
> cells to that of the road elevation will do it.

Culverts usually don't appear on a raster DEM.
For instance, if you use LiDAR DEM, you will have only the elevation
of the road surface. Even bridges might appear as a dam on LiDAR data.
Itzï is not yet able to simulate pipe flow. To model a functioning
culvert, you will need to lower locally the DEM to let the flow pass.
Therefore, I'm not totally sure to understand how you modelled the
functioning culvert without changing the DEM.

But basically, yes, you need to have a DEM showing the actual
elevation of the road surface.


>> If you use direct rainfall, all the cells in the h_max map will appear wet
>> (although with very small depth). You will need to clean up the map using
>> r.mapcalc to keep only the cells with a water depth above a threshold of
>> your choice.
>
>
>   Don't completely understand this now; thinking about it and trying various
> simulations will probably help.
>
> Thanks,
>
>
> Rich
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