In this chapter the aim is to set down those patterns and processes which lead us to the view of the drainage basin as a systematic physical whole. It is the key concept in the wider education of politicians, planners and the public that river systems are an interconnected transport system, albeit often working invisibly (as in the transfer of dissolved salts) or over extremely long timescales (as in the evolution of floodplains).
The ecosystem model of the river basin pays particular attention to the transfer system attributes, both sediment and water. Several of the spontaneous regulation functions of the basin rely for their operation on conservation of the natural dynamics of floodplains, wetlands, ‘wild’ channels and the slopes contributing water and sediment to those components. Climate is a major driving variable in the gross behaviour of the transfer system, controlling basin-scale inputs of water and (through plant cover) sediments, but the archaeological record and contemporary observations prove the progressive impacts of development. Humid zone basins are particularly vulnerable because of the influence of natural vegetation covers on evaporative loss and soil loss from slopes. By ‘progressive impacts’ we refer to the feedback mechanisms in the transfer system through which, for example, eroded slopes exhibit reduced infiltration capacity for rain and the resulting increase in runoff further increases slope erosion through gullying.
Professional perceptions are not without fault in their view of the basin system, particularly in terms of the timescales over which it comes to steady states and can therefore be managed by relatively simple, sustainable controls. Although remote sensing and interactive, real-time, mathematical modelling can now allow reactive as well as proactive control, the latter, as in river channel ‘training’ to improve land drainage, is still the least-cost solution in many cases to our exploitation of rivers or to protect ourselves from their extremes. There are, understandably, new professional viewpoints which see control of any kind as undesirable and river basin systems have become a focus for a variety of conservation and restoration approaches (see Chapter 6).