[GRASS-user] floodplain creation

[Shane Carey]

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 <careyshan at 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 <careyshan at 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 <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*
>>>>>
>>>>
>>>>
>>
> --
Le gach dea ghui,
*Shane Carey*
*GIS and Data Solutions Consultant*
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