[GRASS-user] stream network

[Janet Choate]

Michel,
thank you - i'll try your r.mapcalc and vector suggestions.
Janet

On Thu, Mar 3, 2016 at 8:22 AM, Michel Wortmann <wortmann at pik-potsdam.de>
wrote:

> HI Janet,
> can you specify what you mean by 'fully connected stream network'?
> 'connected' doesnt mean much on a raster map or did you convert it a vector?
> I would try to build your stream network from the accumulation raster map
> by thresholding it with a certain catchment size (in cells). Eg.
> r.mapcalc exp='streams=if(accumulation>1000, 1, null())'
> That way you see what is happening in the accumulation map as a result of
> the DEM.
> Best,
> Michel
>
>
> On 03/02/2016 08:42 PM, Janet Choate wrote:
>
> Hi Will,
> When running r.watershed on a small 35 hectare watershed, it produces a
> fully connected stream network. However, when running r.watershed on a 6400
> hectare watershed, the stream network is not fully connected.
> No preprocessing with regards to merging different raster maps, however, I
> did try using r.fill.dir first to deal with any possible depressions that
> might be causing non-connected stream segments.
> thanks,
> Janet
>
> On Wed, Mar 2, 2016 at 11:22 AM, Will Fields <will.openfields at gmail.com>
> wrote:
>
>> Hi Janet,
>>
>> Can you give some more information about what you mean by larger
>> watershed basins?  Did you do any preprocessing of the elevation raster
>> before you tried to extract the stream networks?  Were you using an
>> elevation raster that had been merged from different rasters?  I've ran
>> into issues in the past where "seams" along the original edges of a raster
>> resulted in odd stream networks.
>>
>> Will
>>
>> On Wed, Mar 2, 2016 at 11:40 AM, Janet Choate < <jsc.eco at gmail.com>
>> jsc.eco at gmail.com> wrote:
>>
>>> Hi GRASS community,
>>> When creating a stream network with r.watershed, I end up with some
>>> isolated stream segments - particularly in larger watershed basins. Does
>>> anyone know how to generate a stream network that is fully connected, or
>>> how to correct this issue?
>>> thank you,
>>> Janet
>>>
>>>
>>>
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>>
>>
>
>
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> Tague Team Lab Manager
> 1005 Bren Hall
> UCSB, Santa Barbara, CA.
>
>
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-- 
Tague Team Lab Manager
1005 Bren Hall
UCSB, Santa Barbara, CA.
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