[GRASS-user] Stream power Index calculation?

[Helmut Kudrnovsky]

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))


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



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best regards
Helmut
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