A drainage divide, water divide, divide or (outside North America) watershed is the line separating neighbouring drainage basins (catchments). In hilly country, the divide lies along topographical peaks and ridges, but in flat country (especially where the ground is marshy) the divide may be invisible – just a more or less notional line on the ground on either side of which falling raindrops will start a journey to different rivers, and even to different sides of a region or continent.
Drainage divides are important geographical, and often also political boundaries. Roads (such as ridgeways) and rail tracks often follow divides to minimise grades (gradients), and to avoid marshes and rivers.
A divide is also known as:
- A watershed, the line between drainage basins – shedding is an old term for splitting or dividing, so it is the line which divides the water (however in North America "watershed" has come to mean the drainage basin itself);
- a water parting;
- a height of land (in Canada).
Drainage divides can be grouped in three types:
- A divide in which the waters on each side flow to different oceans (example: the Nile and Congo divide, Lunghin Pass triple divide)
- The waters on each side of the divide never meet again, but do flow into the same ocean (example: the divide between the Yellow River basin and the Yangtze)
- The waters part but eventually meet again at a river confluence (example: the Mississippi and Missouri divide)
Drainage divides are a hindrance to river navigation. In pre-industrial times water divides were crossed at portages. Later, canals were built to connect the adjoining drainage basins.