Image attached shows rivers (black line) and floodplain of where it thinks there are rivers and in some cases where there may not be rivers.
Cheers Le gach dea ghui, *Shane Carey* *GIS and Data Solutions Consultant* On Tue, Sep 25, 2018 at 3:45 PM, Shane Carey <careys...@gmail.com> wrote: > Yes, this is the problem - there is not exact stream matching with the > ones derived on the carved DEM with the "Real" rivers. Any advice on how to > get around that? > > Thanks > > Le gach dea ghui, > *Shane Carey* > *GIS and Data Solutions Consultant* > > On Tue, Sep 25, 2018 at 3:53 AM, Vaclav Petras <wenzesl...@gmail.com> > wrote: > >> >> >> On Mon, Sep 24, 2018 at 6:33 PM Shane Carey <careys...@gmail.com> 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 <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_po >>>>> wer_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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