[GRASS-user] Watershed delineation

[Hamish]

Laura (author of r.terraflow) wrote:
  http://article.gmane.org/gmane.comp.gis.grass.devel/1442
Aleksey Naumov wrote:
> (b) BTW, what controls the size of those subwatersheds saved in the
> "swatershed" map? (Something similat to "threshold" in r.watershed
> may be nice...)
Laura:
"In Terraflow the watershed of a sink represents the *entire* area that
flows into the sink.  Basically each sink-watershed represents a bucket
in the ground that will fill with water when it rains (long enough).
Each sink-watershed is well-defined, and does not depend on the choice
of a threshold. Selecting all the sinks in the terrain and computing
their watersheds defines a partition of the terrain into
sink-watersheds.

In general a watershed can be defined by an outlet point. Depending on
how the outlet point is chosen, the  watershed is larger or smaller.
r.watershed solves a more general problem of partitioning the terrain
into watersheds of arbitrary outlets (not necessarily sinks) and of a
given (approximate) size.  The problem is how to choose the  outlets
in order to have the watersheds define a partition and have
approximately the specified size. This is a different problem that
computing flow direction and flow accumulation. r.terraflow does not do
that (yet) -- but we are working on extending it with this
functionality."


hope it helps.

Hamish


ps- I think it would be nice to write a r.catchment script from
r.watershed streams map + r.cost/r.drain + r.report + r.mapcalc/r.patch
to connect watershed basins from r.watershed into greater catchment
areas. ie convert fractal basin areas to integrated hydrologicaly
connected areas.



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