# Sediment transport index

This tool can be used to calculate the sediment transport index (STI) described by Moore and Burch (1986). 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. The index combines upslope contributing area (*As*), under the assumption that contributing area is directly related to discharge, and slope (*B*). The index is calculated as:

*STI* = (*m* + 1) × (*A*_{s} / 22.13)^{m} × sin(*B* / 0.0896)^{n}

Where *A*_{s} is the specific catchment area (i.e. the upslope contributing area per unit contour length) estimated using one of the available flow accumulation algorithms in the Hydrology toolbox; *B* is the local slope gradient in degrees; the contributing area exponent, *m*, is usually set to 0.4 and the slope exponent, *n*, is usually set to 1.4. Notice that *As* must not be log-transformed prior to being used; *As* is commonly log-transformed to enhance visualization of the data. The slope image can be created from the base digital elevation model (DEM) using the **Slope** tool. The input images must have the same grid dimensions.

Grid cells possessing the **NoData** value in either of the input images are assigned **NoData** value in the output image. The output raster is of the* float* data type and *continuous* data scale.

## See Also:

## Scripting:

The following is an example of a Python script that uses this tool:

```
wd = pluginHost.getWorkingDirectory()
```

caFile = wd + "contributing area.dep"

slopeFile = wd + "slope.dep"

outputFile = wd + "output.dep"

caExponentValue = "1.0"

slopeExponentValue = "1.3"

args = [caFile, slopeFile, outputFile, caExponentValue, slopeExponentValue]

pluginHost.runPlugin("SedimentTransportIndex", args, False)

This is a Groovy script also using this tool:

```
def wd = pluginHost.getWorkingDirectory()
```

def caFile = wd + "contributing area.dep"

def slopeFile = wd + "slope.dep"

def outputFile = wd + "output.dep"

def caExponentValue = "1.0"

def slopeExponentValue = "1.3"

String[] args = [caFile, slopeFile, outputFile, caExponentValue, slopeExponentValue]

pluginHost.runPlugin("SedimentTransportIndex", args, false)

## Credits:

- John Lindsay (2012) email: jlindsay@uoguelph.ca