Output 3: Flow Accumulation Raster

The flow accumulation raster uses the flow direction raster to determine how many upstream cells flow into a certain location. In the flow accumulation raster, the value in each grid cell is equal to the number of upstream cells that flow into it. In the raster example images below, we can view the flow accumulation raster to see where we have concentrated flowpaths. 

Flow direction, flow accumulation rasters

For example, in the watershed image below, as upstream cells begin to converge their flow, the path is shown in green. As the flow accumulates more, the path is shown in blue. This raster output allows us to view flowpaths within the watershed and see where channels may begin. 

Hillshade of surface in yellow with small watershed outlined in navy, two smaller flowpaths outlined in green and cobalt.

Tool Summary

Inputs:

  1. Unfilled DEM (DEM + inHUC) (Required)
  2. USER DECISION: Z-Factor (Required)

Outputs:

  1. D8 Flow Accumulation raster (D8FlowAcc + inHUC)