water divide

A drainage divide, water divide, or simply divide is the separation between neighbouring drainage basins (catchments). In hilly country, the divide lies along topographical peaks and ridges, but in flat country or on a high plateau (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 country or continent. Drainage divides are important geographical, and often also political, boundaries. Roads and rail tracks often follow divides to minimise grades (or gradients) and the need for bridges.
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