4.2             Flow Grid

 

Flow Direction outputs an encoded grid with the neighboring cell direction to which the steepest descent is found using D8 algorithm [O'Callaghan and Mark (1984)]. The encoding is 1 - east, 2 - North east, 3 - North, 4 - North west, 5 - West, 6 - South west, 7 - South, 8 - South east.

Flow Accumulation outputs an accumulation grid that contains the accumulated number of cells upstream of a cell, for each cell in the input grid using a recursive procedure explained in (Mark, 1988).

Fig x.x shows the Flow direction and Flow accumulation calculations performed on a synthetic DEM grid.

 

 

In the Input section of the dialog browse the Pit Filled Grid generated by the step 4.1. In the Output section browse the file names to which the flow direction and flow accumulation grid could be saved. At this point the module is ready to run; select Run to start processing. Please be patient until it completes processing. The text browser at the bottom of the dialog should provide information related to any error or processing. If the Load in Data Frame is checked the Flow Direction Grid and Flow Accumulation Grid will be automatically loaded in the Qgis window. After the processing is complete you need to press Close to proceed to next step.