[GRASS-user] floodplain creation

[Vaclav Petras]

On Mon, Sep 24, 2018 at 6:33 PM Shane Carey <careyshan at 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 <careyshan at 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 <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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