[GRASS-user] floodplain creation

[Shane Carey]

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_po
>>>>> wer_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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