[GRASS-user] Calculate flooded area based on precipitation

[Laurent C.]

Hello Rich,

The h_max output map of Itzï will correspond to the maximum water
level reached during the simulation.
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. The water will accumulate
behind the road until it overtops it (or the rain stops).
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.

Regards,
Laurent


2017-02-15 17:20 GMT-06:00 Rich Shepard <rshepard at appl-ecosys.com>:
>   My client needs maps that show flooded areas above a specified elevation
> based on precipitation rate and time. I can approximate precip rates based
> on daily measures at nearby weather stations and can assume saturated soils.
> The topography is flat: 0-3% slope is the characteristics of this soil map
> unit, and the ~40 ha area is essentially flat.
>
>   Precipitation flows off this land through an under-road culvert with a
> known invert elevation. If the culvert is blocked he needs to know the area
> inundated with a given precipitation rate for a specified time (e.g., one
> day).
>
>   I've looked at the hydrologic models and don't see any that appear to
> provide answers to this question. It's not landscape level analyses, nor are
> there any defined stream channels, or noticeable slopes. r.lake shows
> inundated areas at specified water heights above a given elevation, but
> this is independent of precipitation rates and time.
>
>   Laurent's Itzi model calculates accumulation at various elevations for
> a specified precipitation rate and time, yet I'm not seeing how to use this
> if there is blocked at a specified coordinate along the drainage path.
>
> Pointers needed,
>
> Rich
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