[GRASS-user] floodplain creation

[Shane Carey]

Super Vaclav - I am nearly there now - My last bit of the puzzle is to
create the flow direction raster. How do I reclassify in order to get the
stream direction using r.mapcalc? I am just coping in what you said from
your last email Vaclav so that you know which part I am stuck on. This is
really super - thanks again

[Since you already have the streams and you want to use them, you need to
convert them to raster and then also get stream direction for
r.stream.distance by reclassifying, e.g. with r.mapcalc]

Le gach dea ghui,
*Shane Carey*
*GIS and Data Solutions Consultant*


On Fri, Sep 28, 2018 at 3:02 PM Vaclav Petras <wenzeslaus at gmail.com> wrote:

>
> On Thu, Sep 27, 2018 at 12:10 PM Shane Carey <careyshan at gmail.com> wrote:
>
>>
>> Is there anyway of the algorithm just being able to create a floodlain
>> for actual real rivers as opposed to the derived river dataset?
>>
>
> Yes, just convert your streams to raster (presence-absence) and a raster
> for flow direction as I mentioned here:
>
> https://lists.osgeo.org/pipermail/grass-user/2018-September/079135.html
>
> However, you need to be cautious about fit between the existing streams
> and the DEM. Definitively check how your existing streams align with the
> derived ones (where there are both streams).
>
>
>>
>> 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.
>>>
>>
> To use the derived streams and get rid of parts you don't want, you could
> buffer the existing streams and preserve only the derived streams which are
> in that buffer.
>
> However, you should really look at why they are different and specifically
> what is closer to reality.
>
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