The effect of humans on rivers and river channels has been widespread throughout the period of habitation of this planet. Water supply and land drainage schemes were implemented as early as 3200 BC (Drower, 1954) whilst in Britain river regulation was widely used by Domesday (Cole, 1976). Concern for the human impact on rivers has been expressed in an abundance of research papers and since about 1970 the geomorphological study of river channels has been increasingly concerned with channel adjustments which are significant in relation to practical problems (e.g. Hails, 1977;Schumm, 1977;Gregory, 1979a). This has arisen because of the extensive distribution and in many cases the intensive nature of environmental problems and because of the realization that geomorphologists can extend the understanding of complexities of fluvial systems.At least four components of applied research related to river channels can be identified. First there is a need to establish the ways in which river channel stability has been affected by a range of impacts and at this stage it is necessary to identify the various types of effects that particular structures or changes could have. Although the direct effects of engineering structures have been acknowledged by engineers for many years the more widespread effects of these structures were less well appreciated. For example, the potential occurrence of scour immediately below dams had to be allowed for at the design stage and equations were developed to predict scour in relation to local environmental and hydraulic conditions (e.g. Komura and Simons, 1967). However, the downstream effects of dams were less immediately obvious but geomorphological research during the last decade has revealed a series of effects which can persist for very considerable distances below dams.A second component has been to investigate the magnitude and spatial extent of the effects which can be identified along individual river channels and this has produced valuable results. For example, below reservoirs in Britain channel capacities may be reduced to as little as 0.31 times those expected (Petts, 1980) whilst the effects of the Aswan High Dam on the channel morphology persist downstream for 965 km (Kashef, 1981). More recently a third component has emerged as it has been realized that there is a range of strategies available for the management of channel adjustment effects. The need for practical application has been advocated at Apollo Group -UOP on February 7, 2015 ppg.sagepub.com Downloaded from
