The sediment transfer system is normally laid bare for us to see; regulators of the system, both spontaneous (natural) and imposed are observable even if we choose to ignore their influence, but it is more difficult to apply the ecosystem concept to patterns and processes of runoff. Hydrology is a young science and, while its early days were preoccupied with surface processes, hydrologists now admit that many of the key points of the runoff system are hidden—in soil, in rock or in plants. Hydrological process studies are a feature of the last thirty years and we remain in ignorance about many of the key controls; we may assert the obvious—that land use and land management influence runoff and water quality—but proving the point remains difficult, especially when another human influence (the direct one of damming and piping water) is less subtle. Few hydrologists are prepared to take an ecological or ‘land/water’ approach to their publications (with some exceptions, for example, Falkenmark and Chapman, 1989).
As we have previously observed, ‘water and land’ best represents the driving force behind the hydraulic civilisations, their use of the land being controlled by the availability of water and the efficiency of the distribution network. Just as the controlling variables of fluvial geomorphology may change their status as dependent or independent according to timescales (see Chapter 2), so land and water have become reversed in order of influence—with our use of land having first priority, at least in the humid zones in which development has been rapid.
An example will illustrate the rapidity with which the balance may change. One of the preoccupations of water resource managers in the UK between 1930 and 1970 was that human recreational pressure might damage reservoir and river water quality and lead to the spread of disease, e.g. typhoid. During the 1970s recreational facilities were slowly developed on both reservoirs and rivers, with the purification costs borne by the water suppliers. By 1990 the situation had reflexed totally and recreational water users were being warned that reservoir and river water threatened them as the result of algal blooms!