Tool Name	WETNESS
Tool ID	3
Library ID	ta_slope_stability
Version	1.0
Author(s)	A. Günther (c) 2012

Description

This tool calculates a topographic wetness index (TWI) following Montgomery & Dietrich (1994) that can be used to estimate the degree of saturation of unconsolidated, permeable materials above (more or less) impermeable bedrock. In contrast to the common TOPMODEL (Beven & Kirkby, 1979) - based TWI, this index differs in such that it considers hydraulic conductivity to be constant in a soil mantle overlying relatively impermeable bedrock. Also, it uses the sine of the slope rather than its tangens, which is more correct and significantly matters for steeper slopes that give raise to landslides. For computation, a slope (in radians) and a catchment area (in m2) grid are required. Additionally, information on groundwater recharge (m/hr), material hydraulic conductivity (m/hr), and depth to potential shear plane (m) are required that can be specified either globally or through grids. The tool produces a continuous wetness index (-) where cells with WI values > 1 (overland flow) set to 1, and optionally creates a classified WI grid rendering three saturation classes:.
0): Low moisture (WI smaller 0.1)
1): Partially wet (0.1 smaller WI smaller 1)
2): Saturation zone (WI larger 1)

References

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

Montgomery, D.R., Dietrich, W.E. (1994): A physically based model for the topographic control on shallow landsliding. Water Resources Research, 30, 1153-1171. PDF

Parameters

Name	Type	Identifier	Description	Constraints
Input
DEM	grid, input	DEM	A DEM
Min hydraulic conductivity grid (m/hr)	grid, input, optional	Cmin	A grid representing minimum material hydraulic conductivity (in m/hr)
Max hydraulic conductivity grid (m/hr)	grid, input, optional	Cmax	A grid representing maximum material hydraulic conductivity (in m/hr)
Min groundwater recharge grid (m/hr)	grid, input, optional	Dmin	A grid representing minimum groundwater recharge (in m/hr)
Max groundwater recharge grid (m/hr)	grid, input, optional	Dmax	A grid representing maximum groundwater recharge (in m/hr)
Min material depth grid (m)	grid, input, optional	Emin	A grid representing minimum depth to potential shear plane (in m)
Max material depth grid (m)	grid, input, optional	Emax	A grid representing maximum depth to potential shear plane (in m)
Output
WI values	grid, output	F	Resulting wetness index (-) grid
WI classes	grid, output, optional	G	Classified wetness (-) grid
Options
Min global material conductivity (m/hr)	floating point number	fCmin	Constant value if no raster set	Default: 2.700000
Max global material conductivity (m/hr)	floating point number	fCmax	Constant value if no raster set	Default: 2.700000
Min global groundwater recharge (m/hr)	floating point number	fDmin	Constant value if no raster set	Default: 0.001000
Max global groundwater recharge (m/hr)	floating point number	fDmax	Constant value if no raster set	Default: 0.001000
Min global material depth (m)	floating point number	fEmin	Constant value if no raster set	Default: 1.000000
Max global material depth (m)	floating point number	fEmax	Constant value if no raster set	Default: 1.000000
Parameter sampling runs	integer number	fH	Number of sampling cycles	Default: 1
Catchment Area Calculation	choice	METHOD		Available Choices: [0] Deterministic 8 [1] Rho 8 [2] Braunschweiger Reliefmodell [3] Deterministic Infinity [4] Multiple Flow Direction [5] Multiple Triangular Flow Direction Default: 4
Preprocessing	boolean	PREPROC		Default: 0