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.
| | 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 | Grid System | grid system | PARAMETERS_GRID_SYSTEM | - | - |
| 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 |