[GRASS-user] floodplain creation

[Shane Carey]

Thanks, I will compare them and let you  know the differences.
Thanks

On Domh 23 MFómh 2018 at 02:09, Vaclav Petras <wenzeslaus at 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 <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.
>>
>> Thanks
>>
>>
>> Le gach dea ghui,
>> *Shane Carey*
>>
>> _______________________________________________
>> grass-user mailing list
>> grass-user at 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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