Topographic Wetness Index
- Author: O.Conrad (c) 2003
- Menu: Terrain Analysis | Hydrology | Topographic Indices
Description
Calculates the Topographic Wetness Index (TWI) using the supplied rasters for slope (Beta), specific catchment area (SCA), and optional transmissivity (T) when the soil profile is saturated:
TWI = ln(SCA / tan(Beta))
or with transmissivity
TWI = ln(SCA / (T * tan(Beta)))
References
- Beven, K.J., Kirkby, M.J. (1979): A physically-based variable contributing area model of basin hydrology. Hydrology Science Bulletin 24(1), p.43-69.
- Boehner, J., Selige, T. (2006): Spatial Prediction of Soil Attributes Using Terrain Analysis and Climate Regionalisation. In: Boehner, J., McCloy, K.R., Strobl, J.: 'SAGA - Analysis and Modelling Applications', Goettinger Geographische Abhandlungen, Vol.115, p.13-27.
- Moore, I.D., Grayson, R.B., Ladson, A.R. (1991): Digital terrain modelling: a review of hydrogical, geomorphological, and biological applications. Hydrological Processes, Vol.5, No.1.
Parameters
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | Slope | grid, input | SLOPE | - | - |
| Catchment Area | grid, input | AREA | - | - |
| Transmissivity | grid, input, optional | TRANS | - | - |
| Output | Topographic Wetness Index | grid, output | TWI | - | - |
| Options | Grid System | grid system | PARAMETERS_GRID_SYSTEM | - | - |
| Area Conversion | choice | CONV | - | Available Choices:
[0] no conversion (areas already given as specific catchment area)
[1] 1 / cell size (pseudo specific catchment area)
Default: 0 |
| Method (TWI) | choice | METHOD | - | Available Choices:
[0] Standard
[1] TOPMODEL
Default: 0 |
Command Line
Usage: saga_cmd ta_hydrology 20 [-SLOPE ] [-AREA ] [-TRANS ] [-TWI ] [-CONV ] [-METHOD ]
-SLOPE: Slope
grid, input
-AREA: Catchment Area
grid, input
-TRANS: Transmissivity
grid, input, optional
-TWI: Topographic Wetness Index
grid, output
-CONV: Area Conversion
choice
Available Choices:
[0] no conversion (areas already given as specific catchment area)
[1] 1 / cell size (pseudo specific catchment area)
Default: 0
-METHOD: Method (TWI)
choice
Available Choices:
[0] Standard
[1] TOPMODEL
Default: 0