Hi, Is there anyway of the algorithm just being able to create a floodlain for actual real rivers as opposed to the derived river dataset?
Thanks On Máirt 25 MFómh 2018 at 15:49, Shane Carey <careys...@gmail.com> wrote: > 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_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* >>>>> >>>> >>>> >> > -- Le gach dea ghui, *Shane Carey* *GIS and Data Solutions Consultant*
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