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.
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.
StreamPowerIndex
, DInfFlowAccumulation
, FD8FlowAccumulation
def sediment_transport_index(self, specific_catchment_area: Raster, slope: Raster, sca_exponent: float = 0.4, slope_exponent: float = 1.3) -> Raster: ...