SAGA-GIS Module Library Documentation (v2.1.3)

Module SAGA Wetness Index

The 'SAGA Wetness Index' is, as the name says, similar to the 'Topographic Wetness Index' (TWI), but it is based on a modified catchment area calculation ('Modified Catchment Area'), which does not think of the flow as very thin film. As result it predicts for cells situated in valley floors with a small vertical distance to a channel a more realistic, higher potential soil moisture compared to the standard TWI calculation.

References
- Boehner, J., Koethe, R. Conrad, O., Gross, J., Ringeler, A., Selige, T. (2002): Soil Regionalisation by Means of Terrain Analysis and Process Parameterisation. In: Micheli, E., Nachtergaele, F., Montanarella, L. [Ed.]: Soil Classification 2001. European Soil Bureau, Research Report No. 7, EUR 20398 EN, Luxembourg. pp.213-222.

Parameters

 NameTypeIdentifierDescriptionConstraints
InputElevationGrid (input)DEM--
Weights (*)Grid (optional input)WEIGHT--
OutputCatchment areaGrid (output)AREA--
Catchment slopeGrid (output)SLOPE--
Modified Catchment AreaGrid (output)AREA_MOD--
Topographic Wetness IndexGrid (output)TWI--
OptionsSuctionFloating pointSUCTIONthe lower this value is the stronger is the suction effectMinimum: 0.000000
Default: 10.000000
Type of AreaChoiceAREA_TYPE-Available Choices:
[0] absolute catchment area
[1] square root of catchment area
[2] specific catchment area
Default: 1
Type of SlopeChoiceSLOPE_TYPE-Available Choices:
[0] local slope
[1] catchment slope
Default: 1
Minimum SlopeFloating pointSLOPE_MIN-Minimum: 0.000000
Default: 0.000000
Offset SlopeFloating pointSLOPE_OFF-Minimum: 0.000000
Default: 0.100000
Slope WeightingFloating pointSLOPE_WEIGHTweighting factor for slope in index calculationMinimum: 0.000000
Default: 1.000000
(*) optional

Command-line

Usage: saga_cmd ta_hydrology 15 -DEM <str> [-WEIGHT <str>] [-AREA <str>] [-SLOPE <str>] [-AREA_MOD <str>] [-TWI <str>] [-SUCTION <str>] [-AREA_TYPE <str>] [-SLOPE_TYPE <str>] [-SLOPE_MIN <str>] [-SLOPE_OFF <str>] [-SLOPE_WEIGHT <str>]
  -DEM:<str>         	Elevation
	Grid (input)
  -WEIGHT:<str>      	Weights
	Grid (optional input)
  -AREA:<str>        	Catchment area
	Grid (output)
  -SLOPE:<str>       	Catchment slope
	Grid (output)
  -AREA_MOD:<str>    	Modified Catchment Area
	Grid (output)
  -TWI:<str>         	Topographic Wetness Index
	Grid (output)
  -SUCTION:<str>     	Suction
	Floating point
	Minimum: 0.000000
	Default: 10.000000
  -AREA_TYPE:<str>   	Type of Area
	Choice
	Available Choices:
	[0] absolute catchment area
	[1] square root of catchment area
	[2] specific catchment area
	Default: 1
  -SLOPE_TYPE:<str>  	Type of Slope
	Choice
	Available Choices:
	[0] local slope
	[1] catchment slope
	Default: 1
  -SLOPE_MIN:<str>   	Minimum Slope
	Floating point
	Minimum: 0.000000
	Default: 0.000000
  -SLOPE_OFF:<str>   	Offset Slope
	Floating point
	Minimum: 0.000000
	Default: 0.100000
  -SLOPE_WEIGHT:<str>	Slope Weighting
	Floating point
	Minimum: 0.000000
	Default: 1.000000