Module WETNESS

This module 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 module 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..

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

• Author: A. Günther (c) 2012
• Specification: grid
• Menu: Terrain Analysis|Slope Stability

Parameters

Command-line

Usage: saga_cmd ta_slope_stability 3 -DEM <str> [-Cmin <str>] [-Cmax <str>] [-Dmin <str>] [-Dmax <str>] [-Emin <str>] [-Emax <str>] [-fCmin <str>] [-fCmax <str>] [-fDmin <str>] [-fDmax <str>] [-fEmin <str>] [-fEmax <str>] [-fH <num>] [-F <str>] [-G <str>] [-METHOD <str>] [-PREPROC <str>]
  -DEM:<str>    	DEM
	Grid (input)
  -Cmin:<str>   	Min hydraulic conductivity grid (m/hr) 
	Grid (optional input)
  -Cmax:<str>   	Max hydraulic conductivity grid (m/hr) 
	Grid (optional input)
  -Dmin:<str>   	Min groundwater recharge grid (m/hr) 
	Grid (optional input)
  -Dmax:<str>   	Max groundwater recharge grid (m/hr) 
	Grid (optional input)
  -Emin:<str>   	Min material depth grid (m)
	Grid (optional input)
  -Emax:<str>   	Max material depth grid (m)
	Grid (optional input)
  -fCmin:<str>  	Min global material conductivity (m/hr)
	Floating point
	Default: 2.700000
  -fCmax:<str>  	Max global material conductivity (m/hr)
	Floating point
	Default: 2.700000
  -fDmin:<str>  	Min global groundwater recharge (m/hr)
	Floating point
	Default: 0.001000
  -fDmax:<str>  	Max global groundwater recharge (m/hr)
	Floating point
	Default: 0.001000
  -fEmin:<str>  	Min global material depth (m)
	Floating point
	Default: 1.000000
  -fEmax:<str>  	Max global material depth (m)
	Floating point
	Default: 1.000000
  -fH:<num>     	Parameter sampling runs
	Integer
	Default: 1
  -F:<str>      	WI values
	Grid (output)
  -G:<str>      	WI classes
	Grid (optional output)
  -METHOD:<str> 	Catchment Area Calculation
	Choice
	Available Choices:
	[0] Deterministic 8
	[1] Rho 8
	[2] Braunschweiger Reliefmodell
	[3] Deterministic Infinity
	[4] Multiple Flow Direction
	[5] Multiple Triangular Flow Directon
	Default: 4
  -PREPROC:<str>	Preprocessing
	Boolean
	Default: 0