Tool Name	Topographic Wetness Index
Tool ID	20
Library ID	ta_hydrology
Version	1.0
Author(s)	O.Conrad (c) 2003

Description

Calculates the Topographic Wetness Index (TWI) using the supplied rasters for slope (Beta), specific catchment area (SCA), and optional transmissivity (T) when the soil profile is saturated:

TWI = ln(SCA / tan(Beta))

or with transmissivity

TWI = ln(SCA / (T * tan(Beta)))

References

Beven, K.J., Kirkby, M.J. (1979): A physically-based variable contributing area model of basin hydrology. Hydrology Science Bulletin 24(1), p.43-69.

Böhner, J., Selige, T. (2006): Spatial Prediction of Soil Attributes Using Terrain Analysis and Climate Regionalisation. In: Böhner, J., McCloy, K.R., Strobl, J.: SAGA - Analysis and Modelling Applications. Göttinger Geographische Abhandlungen, Vol.115, p.13-27. PDF

Moore, I.D., Grayson, R.B., Ladson, A.R. (1991): Digital terrain modelling: a review of hydrogical, geomorphological, and biological applications. Hydrological Processes, Vol.5, No.1. doi:10.1002/hyp.3360050103

Parameters

Name	Type	Identifier	Constraints
Input
Slope	grid, input	SLOPE
Catchment Area	grid, input	AREA
Transmissivity	grid, input, optional	TRANS
Output
Topographic Wetness Index	grid, output	TWI
Options
Area Conversion	choice	CONV	Available Choices: [0] no conversion (areas already given as specific catchment area) [1] 1 / cell size (pseudo specific catchment area) Default: 0
Method (TWI)	choice	METHOD	Available Choices: [0] Standard [1] TOPMODEL Default: 0