Question

How to give the threshold value for flow accumulation in arcgis?

Answer 1

The Flow Accumulation tool calculates accumulated flow as the accumulated weight of all cells flowing into each downslope cell in the output raster. If no weight raster is provided, a weight of 1 is applied to each cell, and the value of cells in the output raster is the number of cells that flow into each cell.

In the graphic below, the top left image shows the direction of travel from each cell and the top right the number of cells that flow into each cell.