[GRASS-user] floodplain creation
wenzeslaus at gmail.com
Sat Sep 22 18:18:28 PDT 2018
These are steps based on:
You need r.stream.distance module from Addons:
Get drainage and streams from your DEM (your carved DEM):
r.watershed elevation=dem accumulation=flowacc drainage=drainage
Compute height above nearest drainage/stream (HAND):
r.stream.distance stream_rast=streams direction=drainage
elevation=elevation method=downstream difference=hand
Use r.lake not on the original DEM, but on the HAND and start flooding
("lake") from the streams:
r.lake elevation=hand water_level=3 lake=flood_3m seed=streams
Convert to vector if desired:
r.to.vect -s input=flood_3m output=flood_3m type=area
The difference to the r.grow+r.mapcalc method  is that this uses an
addon module (there should be no problem installing it) and that r.grow
uses euclidean distance for what is later used for height difference while
r.steam.distance follows drainage and further that r.lake floods only the
cells accessible to water unlike the r.mapcalc expression which just looks
at height. The two methodological differences can be summarized as "not
respecting the surrounding terrain enough." Anyway, the r.grow+r.mapcalc
method can get you quite far and I would be interested in the comparison
(will differ for different terrains).
On Fri, Sep 21, 2018 at 11:39 AM Shane Carey <careyshan at gmail.com> wrote:
> Hi All,
> I have used r.carve to carve out the rivers of a DTM - a really super job.
> I now need to pour 3meters of water into every cell in the river and see
> how for this water extends out - onto the floodplain.
> I was trying to use r.lake to do this, but unsure as to how r.lake will
> work to pour 3 meters of water in every cell along the river network.
> Any advice on this would be great. It is for the creation of a floodplain.
> Le gach dea ghui,
> *Shane Carey*
> grass-user mailing list
> grass-user at lists.osgeo.org
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