Tool Name	Topographic Wetness Index (One Step)
Tool ID	twi
Library ID	ta_hydrology
Version	1.0
Author(s)	O.Conrad (c) 2014

Description

Calculates the Topographic Wetness Index (TWI) based on the supplied Digital Elevation Model (DEM). Slopes (Beta), Specific Catchment Areas (SCA), and a depressionless DEM for SCA calculation are derived internally.

TWI = ln(SCA / 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.

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.

Parameters

Name	Type	Identifier	Constraints
Input
Elevation	grid, input	DEM
Output
Topographic Wetness Index	grid, output	TWI
Options
Preprocessing	choice	PREPROCESSING	Available Choices: [0] Fill Sinks (Wang & Liu) [1] Sink Removal Default: 0
Flow Routing	choice	FLOW_METHOD	Available Choices: [0] Deterministic 8 [1] Rho 8 [2] Braunschweiger Reliefmodell [3] Deterministic Infinity [4] Multiple Flow Direction [5] Multiple Triangular Flow Direction [6] Multiple Maximum Downslope Gradient Based Flow Direction Default: 0