[GRASS-user] floodplain creation

[Shane Carey]

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 <wenzeslaus at gmail.com> wrote:

>
>
> 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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