Our perceptions and concepts are increasingly structured by visual experiences. Figures i-viii illustrate a range of published images of river basins. Any hydrologist asked to draw one will produce a prototype hot air balloon, slightly crumpled and with a very simple stream network, possibly second or third order according to Strahler’s (1957) classification (Figure i). This is the small catchment beloved of water supply engineers and one over which land use control is relatively easily practised; it is also the largest scale used by experiments in hydrology—because of the unsuitability of larger units (say >100 km2) for controls and experimental treatments.
If we consider, however, that at another extreme the Amazon river basin may be fourteenth order on the Strahler scale, has a basin area of 5 Mkm2 and is in desperate need of efficient management under changing political and environmental circumstances, the hydrologist’s simplicity of concept may be dangerously illusory. The river manager, even on a small island like
Figure i The geomorphologist’s view of the river basin: ordered stream network within a defined boundary (Leopold, 1974)