ABSTRACT
Land has been shaped by water throughout geological history, with small streams linking to form rivers or with gullies joining to form broad flood channels. The terms used in technical literature to describe the water-surplus areas from which streams flow may cause some confusion since usage varies. In the USA, the whole area from which water drains into a river is described as the watershed. The most critical aspects of upper watershed management, which directly affect the lives and property of downstream users, are the effects on floods, on water supplies, and on sediment transport. Atmospheric disturbances that generate floods may occur over areas that are orders of magnitude greater than those of the watershed boundaries. The wet tropics are also vulnerable to misuse of land because of the violence of tropical rainfall and the very large amounts of water to be disposed of.
