[GRASS-user] Algorithm in flow direction

[Markus Metz]

margherita wrote:
> Hi all
>
> i have some question about the commands r.watershed and r.terraflow. 
> By using both commands i obtained from a DEM a flow accumulation with 
> the algorithm of the single flow direction and a flow accumulation 
> with the algorithm of the multi flow direction. In both cases i did 
> not enter the treshold of cell (i.e. in the flow accumulation if a 
> grid cell value exceeds a certain threshold, it's part of the river, 
> if not, it isn't)
>
> Please can you let me know if there are default values of this 
> threshold and, if yes, what they are, and if that value can be changed 
> by the user and how.
This threshold can be set with the option threshold=some_value in 
r.watershed (details are in the manual, please read it). r.terraflow 
doesn't have such an option (details are in the manual, please read it).

If the option threshold=some_value is given for r.watershed, you can 
also get basins, half basins, and stream segments. Maybe these stream 
segments are what you are looking for.

Good luck,

Markus M