Tool LS-Factor, Field Based
Calculation of slope length (LS) factor as used for the Universal Soil Loss Equation (USLE), based on slope and (specific) catchment area, latter as substitute for slope length. This tool takes only a Digital Elevation Model (DEM) as input and derives catchment areas according to Freeman (1991). Optionally field polygons can be supplied. Is this the case, calculations will be performed field by field, i.e. catchment area calculation is restricted to each field's area.
References
- 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, 115, 13-27.
- Desmet, P.J.J. & Govers, G. (1996): A GIS Procedure for Automatically Calculating the USLE LS Factor on Topographically Complex Landscape Units. Journal of Soil and Water Conservation, 51(5), 427-433.
- Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17:413-22.
- Kinnell, P.I.A. (2005): 'Alternative Approaches for Determining the USLE-M Slope Length Factor for Grid Cells. soil.scijournals.org, 69/3/674 http://soil.scijournals.org/cgi/content/full/69/3/674.
- 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.
- Moore, I.D., Nieber, J.L. (1991): Landscape assessment of soil erosion and nonpoint source pollution. J. Minnesota Acad. Sci., 55, 18-25.
- Wischmeier, W.H., Smith, D.D. (1978): Predicting rainfall erosion losses - A guide to conservation planning. Agriculture Handbook No. 537: US Department of Agriculture, Washington DC.
- Author: O.Conrad (c) 2013
- Menu: Terrain Analysis|Hydrology|Topographic Indices
Parameters
| | Name | Type | Identifier | Description | Constraints |
|---|
| Input | Elevation | Grid (input) | DEM | - | - |
| Fields (*) | Shapes (optional input) | FIELDS | - | - |
| Output | Field Statistics (*) | Shapes (optional output) | STATISTICS | - | - |
| Upslope Length Factor (*) | Grid (optional output) | UPSLOPE_AREA | - | - |
| Effective Flow Length (*) | Grid (optional output) | UPSLOPE_LENGTH | - | - |
| Upslope Slope (*) | Grid (optional output) | UPSLOPE_SLOPE | - | - |
| LS Factor | Grid (output) | LS_FACTOR | - | - |
| Sediment Balance (*) | Grid (optional output) | BALANCE | - | - |
| Options | Grid system | Grid system | PARAMETERS_GRID_SYSTEM | - | - |
| LS Calculation | Choice | METHOD | - | Available Choices:
[0] Moore & Nieber 1989
[1] Desmet & Govers 1996
[2] Wischmeier & Smith 1978
Default: 0 |
| Type of Slope | Choice | METHOD_SLOPE | - | Available Choices:
[0] local slope
[1] distance weighted average catchment slope
Default: 0 |
| Specific Catchment Area | Choice | METHOD_AREA | - | Available Choices:
[0] specific catchment area (contour length simply as cell size)
[1] specific catchment area (contour length dependent on aspect)
[2] catchment length (square root of catchment area)
[3] effective flow length
Default: 1 |
| Stop at Edge | Boolean | STOP_AT_EDGE | - | Default: 1 |
| Rill/Interrill Erosivity | Floating point | EROSIVITY | - | Minimum: 0.000000
Default: 1.000000 |
| Stability | Choice | STABILITY | - | Available Choices:
[0] stable
[1] instable (thawing)
Default: 0 |
| (*) optional |
Command-line
Usage: saga_cmd ta_hydrology 25 [-DEM <str>] [-FIELDS <str>] [-STATISTICS <str>] [-UPSLOPE_AREA <str>] [-UPSLOPE_LENGTH <str>] [-UPSLOPE_SLOPE <str>] [-LS_FACTOR <str>] [-BALANCE <str>] [-METHOD <str>] [-METHOD_SLOPE <str>] [-METHOD_AREA <str>] [-STOP_AT_EDGE <str>] [-EROSIVITY <double>] [-STABILITY <str>]
-DEM:<str> Elevation
Grid (input)
-FIELDS:<str> Fields
Shapes (optional input)
-STATISTICS:<str> Field Statistics
Shapes (optional output)
-UPSLOPE_AREA:<str> Upslope Length Factor
Grid (optional output)
-UPSLOPE_LENGTH:<str> Effective Flow Length
Grid (optional output)
-UPSLOPE_SLOPE:<str> Upslope Slope
Grid (optional output)
-LS_FACTOR:<str> LS Factor
Grid (output)
-BALANCE:<str> Sediment Balance
Grid (optional output)
-METHOD:<str> LS Calculation
Choice
Available Choices:
[0] Moore & Nieber 1989
[1] Desmet & Govers 1996
[2] Wischmeier & Smith 1978
Default: 0
-METHOD_SLOPE:<str> Type of Slope
Choice
Available Choices:
[0] local slope
[1] distance weighted average catchment slope
Default: 0
-METHOD_AREA:<str> Specific Catchment Area
Choice
Available Choices:
[0] specific catchment area (contour length simply as cell size)
[1] specific catchment area (contour length dependent on aspect)
[2] catchment length (square root of catchment area)
[3] effective flow length
Default: 1
-STOP_AT_EDGE:<str> Stop at Edge
Boolean
Default: 1
-EROSIVITY:<double> Rill/Interrill Erosivity
Floating point
Minimum: 0.000000
Default: 1.000000
-STABILITY:<str> Stability
Choice
Available Choices:
[0] stable
[1] instable (thawing)
Default: 0