WETNESS
- Author: A. Günther (c) 2012
- Menu: Terrain Analysis | Slope Stability
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..
Montgomery D. R., Dietrich, W. E. (1994) A physically based model for the topographic control on shallow landsliding. Water Resources Research, 30, 1153-1171..
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 | Grid System | grid system | PARAMETERS_GRID_SYSTEM | - | - |
| 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 Directon
Default: 4 |
| Preprocessing | boolean | PREPROC | - | Default: 0 |
Command Line
Usage: saga_cmd ta_slope_stability 3 [-DEM ] [-Cmin ] [-Cmax ] [-Dmin ] [-Dmax ] [-Emin ] [-Emax ] [-fCmin ] [-fCmax ] [-fDmin ] [-fDmax ] [-fEmin ] [-fEmax ] [-fH ] [-F ] [-G ] [-METHOD ] [-PREPROC ]
-DEM: DEM
grid, input
-Cmin: Min hydraulic conductivity grid (m/hr)
grid, input, optional
-Cmax: Max hydraulic conductivity grid (m/hr)
grid, input, optional
-Dmin: Min groundwater recharge grid (m/hr)
grid, input, optional
-Dmax: Max groundwater recharge grid (m/hr)
grid, input, optional
-Emin: Min material depth grid (m)
grid, input, optional
-Emax: Max material depth grid (m)
grid, input, optional
-fCmin: Min global material conductivity (m/hr)
floating point number
Default: 2.700000
-fCmax: Max global material conductivity (m/hr)
floating point number
Default: 2.700000
-fDmin: Min global groundwater recharge (m/hr)
floating point number
Default: 0.001000
-fDmax: Max global groundwater recharge (m/hr)
floating point number
Default: 0.001000
-fEmin: Min global material depth (m)
floating point number
Default: 1.000000
-fEmax: Max global material depth (m)
floating point number
Default: 1.000000
-fH: Parameter sampling runs
integer number
Default: 1
-F: WI values
grid, output
-G: WI classes
grid, output, optional
-METHOD: 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: Preprocessing
boolean
Default: 0