Hi All, This works well, but doesn't capture every river - is it a case of making the threshold value smaller or making a deeper carve in the rivers???
Thanks in advance - I think this method would will work well, if it were able to "flood" all rivers. Thanks Le gach dea ghui, *Shane Carey* *GIS and Data Solutions Consultant* On Sun, Sep 23, 2018 at 12:55 PM, Shane Carey <careys...@gmail.com> wrote: > Thanks, I will compare them and let you know the differences. > Thanks > > On Domh 23 MFómh 2018 at 02:09, Vaclav Petras <wenzesl...@gmail.com> > wrote: > >> These are steps based on: >> >> https://grasswiki.osgeo.org/wiki/From_GRASS_GIS_novice_to_ >> power_user_(workshop_at_FOSS4G_Boston_2017)#Hydrology: >> _Estimating_inundation_extent_using_HAND_methodology >> >> You need r.stream.distance module from Addons: >> >> g.extension r.stream.distance >> >> Get drainage and streams from your DEM (your carved DEM): >> >> r.watershed elevation=dem accumulation=flowacc drainage=drainage >> stream=streams threshold=100000 >> >> 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 [1] 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). >> >> Best, >> Vaclav >> >> [1] https://lists.osgeo.org/pipermail/grass-user/2018- >> September/079134.html >> >> On Fri, Sep 21, 2018 at 11:39 AM Shane Carey <careys...@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. >>> >>> Thanks >>> >>> >>> Le gach dea ghui, >>> *Shane Carey* >>> >>> _______________________________________________ >>> grass-user mailing list >>> grass-user@lists.osgeo.org >>> https://lists.osgeo.org/mailman/listinfo/grass-user >> >> -- > Le gach dea ghui, > *Shane Carey* > *GIS and Data Solutions Consultant* >
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