This tool calculates the sediment transport index, or sometimes, length-slope (LS) factor, based on input specific contributing area (As, i.e. the upslope contributing area per unit contour length; `sca`) and slope gradient (β, measured in degrees; slope) rasters. Moore et al. (1991) state that the physical potential for sheet and rill erosion in upland catchments can be evaluated by the product R K LS, a component of the Universal Soil Loss Equation (USLE), where R is a rainfall and runoff erosivity factor, K is a soil erodibility factor, and LS is the length-slope factor that accounts for the effects of topography on erosion. To predict erosion at a point in the landscape the LS factor can be written as:

> LS = (n + 1)(As / 22.13)n(sin(β) / 0.0896)m

where n = 0.4 (`sca_exponent`) and m = 1.3 (`slope_exponent`) in its original formulation.

This index is derived from unit stream-power theory and is sometimes used in place of the length-slope factor in the revised universal soil loss equation (RUSLE) for slope lengths less than 100 m and slope less than 14 degrees. Like many hydrological land-surface parameters sediment_transport_index assumes that contributing area is directly related to discharge. Notice that As must not be log-transformed prior to being used; As is commonly log-transformed to enhance visualization of the data. Also, As can be derived using any of the available flow accumulation tools, alghough better results usually result from application of multiple-flow direction algorithms such as `DInfFlowAccumulation` and `FD8FlowAccumulation`. The slope raster can be created from the base digital elevation model (DEM) using the slope tool. The input images must have the same grid dimensions.

## Reference

Moore, I. D., Grayson, R. B., and Ladson, A. R. (1991). Digital terrain modelling: a review of hydrological, geomorphological, and biological applications. Hydrological processes, 5(1), 3-30.

## See Also

`StreamPowerIndex`, `DInfFlowAccumulation`, `FD8FlowAccumulation`

## Function Signature

`def sediment_transport_index(self, specific_catchment_area: Raster, slope: Raster, sca_exponent: float = 0.4, slope_exponent: float = 1.3) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW