On Mon, Sep 24, 2018 at 6:33 PM Shane Carey <[email protected]> wrote:
> > 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??? > It's probably the threshold. How your rivers compare to the ones derived on carved DEM? > > Thanks in advance - I think this method would will work well, if it were > able to "flood" all rivers. > > On Sun, Sep 23, 2018 at 12:55 PM, Shane Carey <[email protected]> wrote: > >> Thanks, I will compare them and let you know the differences. >> Thanks >> >> On Domh 23 MFómh 2018 at 02:09, Vaclav Petras <[email protected]> >> 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 <[email protected]> >>> 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 >>>> [email protected] >>>> https://lists.osgeo.org/mailman/listinfo/grass-user >>> >>> -- >> Le gach dea ghui, >> *Shane Carey* >> *GIS and Data Solutions Consultant* >> > >
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