[GRASS-user] Stream power Index calculation?

[Markus Metz]

On Sun, Mar 1, 2015 at 8:15 PM, Helmut Kudrnovsky <hellik at web.de> wrote:
> Hi,
>
> in the book "Geomorphometry - Concepts, Software, Applications" I've found a
> short paragraph about the Stream power Index (SPI).
>
> the SPI can be used to describe potential flow erosion related to landscape
> processes.
>
>
> in the book SPI is defined as:
>
>     SPI = A x tan(beta)
>
> where A is the specific catchment area and beta is the local slope angle.
>
> in link [1] there is the SAGA GIS formula.
>
>
> sometimes SPI is also defined as:
>
>     SPI = ln(A x tan(beta))

This is also known as Topographic Convergence Index (TCI) or
Topographic Wetness Index (TWI). You can calculate this index with
r.watershed and r.terraflow. If you need the non-logarithmic form, you
can use r.mapcalc "SPI = exp(TCI)".

Markus M
>
>
> my idea for SPI calculation in GRASS GIS may be:
>
>
> A = {accumulation flow by r.watershed} x {ns resolution x ew resolution}
> beta = r.slope slope
>
>
> anyone ever used/calculated SPI in GRASS GIS? any hints for calculation?
>
> [1] http://www.saga-gis.org/saga_module_doc/2.1.4/ta_hydrology_21.html
>
>
>
> -----
> best regards
> Helmut
> --
> View this message in context: http://osgeo-org.1560.x6.nabble.com/Stream-power-Index-calculation-tp5190756.html
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