[GRASS-user] Re: stream network from DEM

Dylan Beaudette dylan.beaudette at gmail.com
Mon Feb 26 22:59:05 EST 2007

On Sunday 25 February 2007 07:38, Xiaoyan Li wrote:
> hi,Dylan,
> I searched the following discusses about flow accumulation calculations on
> Internet. http://grass.itc.it/pipermail/grassuser/2006-May/034150.html
> http://grass.itc.it/pipermail/grassuser/2006-February/032744.html


Apologies for the late reply. Those messages should have some good hints on 
calculating flow accumulation.

> Do you think it is possible to do the same thing in GRASS as extracting
> stream network via detection of curvatures from DEM?

It might be, but I am not the one to tell you how to do it. You might have to 
contact some of the developers like Helena for the specifics. 

> I tried to do the same using following commands:
> Filling DEM:                 r.fill.dir
> Calculating tangential curvature:      r.slope.aspect
> Thresholding tangential curvature surface:   r.mapcalc (?guess)
> Thinning the result grid to get network segments: r.thin
> Run flowaccumulation function with network segments as weight to connect
> stream segments:    r.watershed or r.flow or r.terraflow Weight to connect
> stream segments?                r.mapcalc (?guess)

Seems like you are on the right track, but again I am not a hydrologist and do 
not have a lot of time to investigate further.

> I don't know about hydrology. Someone ask me help to implement this in
> GRASS. I am in a bit of quandary here:
> How to threshold tangential curvature surface?
> How to weight to connect stream segments?
> I had submitted a query to GRASS user mailing list, not get any answer
> reply until now.
> Any suggestions will help me greatly.

Try asking again, but with a more concise description of a part of the 
problem. Simple questions -- easier for more to answer.


Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis

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