The drainage basin perspective

Fluvial hydrosystems are the product of physical, chemical and biological processes operating throughout a river’s drainage basin and over a range of time-scales from a year to tens of thousands of years. A drainage basin is the area that gathers water from precipitation and delivers it to the river (Figure 1.2). Defined by a topographic divide, the basin is occupied by a drainage network which collects the runoff from hillslopes, together with its load of sediment, particulate organic matter and solutes. Thus, a river may be seen as the artery of a drainage basin conveying water, minerals and organic matter to the sea. A drainage basin perspective is also important because the flow regime and sediment loads determine the morphology of the channel which has a strong influence on the structure and function of fluvial hydrosystems as first recognized by Hynes (1970, 1975). However, drainage basins are complex geomorphological systems with a history. This chapter describes the characteristics of drainage basins and examines the ways in which the basin influences fluvial hydrosystems over a range of time-scales.