How are drainage-basin boundaries identified?
A drainage divide follows ridges and topographic highs that send precipitation into different river systems.
Formation process and geographic mechanism
On contour maps, lines form upstream-pointing V shapes in valleys, and divides follow high ground between them. Digital elevation models calculate cell-to-cell flow direction and delineate basins automatically. Changing the outlet changes the defined sub-basin. Flat land, closed depressions and artificial canals can make boundaries uncertain.
Spatial outcomes, measurement and management
Surface and groundwater basins do not always match; karst conduits can carry water beneath a topographic divide. Roads, dams and drainage works may reroute small flows. Basin boundaries are basic units for flood modeling, water quality and management. Field observations and high-resolution data should verify automated maps.