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watershed — English
The boundary between two adjacent drainage basins (see “drainage basin”). It is an imaginary line in the landscape that joins all the highest points between two drainage basins. Rain that falls on the one side of the imaginary line flows in one direction, while that which falls on the other side of the line flows in the other direction. Often it is extremely difficult to see the watershed in the actual landscape, but gravity ensures that every drop of precipitation that becomes runoff (overland flow) “knows” exactly in which direction to flow. On a contour map a watershed can easily be indicated by joining the highest points to form a line. Interpolation is used to establish the height between any two points or contour lines (see “interpolation”).
