Tool Name	SHALSTAB
Tool ID	2
Library ID	ta_slope_stability
Version	1.0
Author(s)	A. Günther (c) 2012

Description

This tool is a realization of the SHALSTAB (Shallow Slope Stability) model from Montgomery & Dietrich (1994). The model computes grid cell critical shallow groundwater recharge values (CR in mm/day) as a measure for relative shallow slope stability, utilizing a simple model that combines a steady-state hydrologic model (a topographic wetness index) to predict groundwater pressures with an infinite slope stability model. For computation, a slope (in radians) and a catchment area (in m2) grid are required. Additionally, information on material density (g/cm3), material friction angle (°), material hydraulic conductivity (m/hr), bulk cohesion (MPa) and depth to potential shear plane (m) are required that can be specified either globally or through grids. The minimum and maximum grids (or global values) specify the range of values from which each soil parameter is sampled. The number of sample runs determines how many values for each soil parameter are randomly taken from the range of values found for each grid cell. Finally, the mean value of the samples taken is calculated (per cell) and used as the soil parameter value in the stability equations. This introduces a probabilistic component in addition to the spatial variability of the soil parameters. If you want to work with static values, enter the same value for minimum and maximum and set the number of samples to one.
The tool produces a continuous CR (mm/day) raster with unconditionally stable cells blanked, and unconditionally unstable cells as CR = 0. Optionally, a classified CR grid can be calculated representing seven stability classes.

References

Montgomery D. R., Dietrich, W. E. (1994): A physically based model for the topographic control on shallow landsliding. Water Resources Research, 30, 1153-1171. doi:10.1029/93WR02979

Parameters

Name	Type	Identifier	Description	Constraints
Input
Slope grid (rad)	grid, input	A	A slope angle grid (in radians)
Catchment area grid (m2)	grid, input	B	A catchment area grid (in square meters)
Min Density grid (g/cm3)	grid, input, optional	Cmin	A grid representing minimum material density (in g/cm3)
Max Density grid (g/cm3)	grid, input, optional	Cmax	A grid representing maximum material density (in g/cm3)
Min Hydraulic conductivity grid (m/hr)	grid, input, optional	Dmin	A grid representing minimum material hydraulic conductivity (in m/hr)
Max Hydraulic conductivity grid (m/hr)	grid, input, optional	Dmax	A grid representing maximum material hydraulic conductivity (in m/hr)
Min Thickness grid (m)	grid, input, optional	Emin	A grid representing minimum material thickness (in m)
Max Thickness grid (m)	grid, input, optional	Emax	A grid representing maximum material thickness (in m)
Min Friction angle grid (degree)	grid, input, optional	Fmin	A grid representing minimum material friction angle (in degrees)
Max Friction angle grid (degree)	grid, input, optional	Fmax	A grid representing maximum material friction angle (in degrees)
Min Bulk cohesion grid (MPa)	grid, input, optional	Jmin	A grid representing minimum bulk cohesion
Max Bulk cohesion grid (MPa)	grid, input, optional	Jmax	A grid representing maximum bulk cohesion
Output
CR values	grid, output	G	Resulting critical recharge (m/day) grid
CR classes	grid, output, optional	H	Classified critical recharge (-) grid
Options
Global minimum density (g/cm3)	floating point number	fCmin	Constant value if no raster set	Default: 1.600000
Global maximum density (g/cm3)	floating point number	fCmax	Constant value if no raster set	Default: 1.600000
Global minimum conductivity (m/hr)	floating point number	fDmin	Constant value if no raster set	Default: 2.700000
Global maximum conductivity (m/hr)	floating point number	fDmax	Constant value if no raster set	Default: 2.700000
Global minimum thickness (m)	floating point number	fEmin	Constant value if no raster set	Default: 1.000000
Global maximum thickness (m)	floating point number	fEmax	Constant value if no raster set	Default: 1.000000
Global minimum friction angle (degree)	floating point number	fFmin	Constant value if no raster set	Default: 33.000000
Global maximum friction angle (degree)	floating point number	fFmax	Constant value if no raster set	Default: 33.000000
Global minimum bulk cohesion (MPa)	floating point number	fJmin	Constant value if no raster set	Default: 0.000000
Global maximum bulk cohesion (MPa)	floating point number	fJmax	Constant value if no raster set	Default: 0.000000
Number of sampling runs	integer number	fK	Number of sampling cycles	Default: 1