Flow direction values of 1 - 255. Why is this happening?

Question

I am using a practice data set to practice the delineation of watersheds. I have been following the manual and so far everything is going well. However, when using the "Flow Direction" tool, the output has values ranging from 1 to 255.

Although it shows the value between 1 - 255, should I be worried? Why is it showing so many values?

JayantaPoddar · Answer

Adding to Dan, There are eight valid values of flow direction (1,2,4,8,16,32,64,128) depending on the direction a water can flow from a particular pixel.

If a cell's (or spatially connected cells') flow direction cannot be assigned one of these eight values in a flow direction raster, it becomes a Sink.

DanPatterson_Retired · Answer

That is what would be expected... see How flowdirection works