Tool Name	LS-Factor, Field Based
Tool ID	25
Library ID	ta_hydrology
Version	1.0
Author(s)	O.Conrad (c) 2013

Description

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

Böhner, J., Selige, T. (2006): Spatial Prediction of Soil Attributes Using Terrain Analysis and Climate Regionalisation. In: Böhner, J., McCloy, K.R., Strobl, J.: 'SAGA - Analysis and Modelling Applications', Göttinger Geographische Abhandlungen, Vol.115, p.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. doi:10.1080/00224561.1996.12457102

Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17:413-22. doi:10.1016/0098-3004(91)90048-I

Kinnell, P.I.A. (2005): Alternative Approaches for Determining the USLE-M Slope Length Factor for Grid Cells. Soil Sci. Soc. Am. J., 69: 674-680. doi:10.2136/sssaj2004.0047

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. doi:10.1002/hyp.3360050103

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.

Parameters

Name	Type	Identifier	Description	Constraints
Input
Elevation	grid, input	DEM
Fields	shapes, input, optional	FIELDS
Output
Field Statistics	shapes, output, optional	STATISTICS
Upslope Length Factor	grid, output, optional	UPSLOPE_AREA
Effective Flow Length	grid, output, optional	UPSLOPE_LENGTH
Upslope Slope	grid, output, optional	UPSLOPE_SLOPE
LS Factor	grid, output	LS_FACTOR
Sediment Balance	grid, output, optional	BALANCE
Options
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
Feet Adjustment	boolean	FEET	Needed if area and lengths come from coordinates measured in feet.	Default: 0
Stop at Edge	boolean	STOP_AT_EDGE		Default: 1
Rill/Interrill Erosivity	floating point number	EROSIVITY		Minimum: 0.000000 Default: 1.000000
Stability	choice	STABILITY		Available Choices: [0] stable [1] instable (thawing) Default: 0