Description: : The catchment basin defines the area of all basins corresponding to a predefined set of seed points. At each confluence, a catchment basin is determined for each synthetic stream line forming the confluence. The area of each catchment basin is equal to the total upstream area minus the area of any upstream catchment basins. Each catchment basin is assigned a unique value and all of the cells in the basin carry that value. Catchments are derived by creating watersheds using the confluence points of synthetic streamlines as seed points. A typical catchment covers approximately 2 square miles. Each catchment is also assigned a Pfafstetter number that identifies the basin subdivision level, relates associated seed points and streamlines, and allows for analysis of upstream and downstream flow relationships with any other catchment or stream.