START : DEM processing and compute the Sediment Transport Index

Based on the data acquired from the Space Shuttle an enhanced Shuttle Land Surface model was released, having a spatial resolution of 1 arc-second, approximately 30 meters with elevation intervals of 1 meter. Additional details on this SRTM mission and product are described in Farr et. al. (2007). For this exercise the data at a coarser spatial resolution is used, again resampled to the same georeference as used in the previous exercises. Note that a Plate Carree projection is used, having a metric coordinate system and is equidistant, therefore distances in X and Y directions are equal. 

Note: 
that this is not the case when using maps with geographic coordinates as the Y distance changes over latitude! Furthermore this elevation model is corrected for sinks representing internal depression which create problems when trying to conduct hydrologic flow functions. 

The whole procedure has six steps (using the ILWIS 3.86 software)

First :

Calculate height differences in X-direction : DX
Calculate height differences in Y-direction : DY

Second:

Calculate a slope map in percentages from these maps DX and DY: 

Third:

calculate the slope in degrees, 

Fourth:

Calculate flow direction map

Fifth:

Calculate flow accumulation map

Sixth:

Calculate Sediment transport index