Human influence on the morphological adjustment of river channels: The evolution of pertinent concepts in river science

Whereas 6 decades ago little attention was accorded to the influence of human activity on affecting river channel adjustment, great progress has been made subsequently, with many contributions published in River Research and Applications. Many concepts have been involved, and this paper considers how they have arisen and developed during a sequence of complementary research stages. The first stage during the 1970s and 1980s, including research by Geoff Petts, involved "recognition of change" and saw the emergence of two separate research strands focused on different timescales: over shorter timescales river channel adjustments affected by the impacts of dams and reservoirs, channelization, land use changes, and urban effects; over longer timescales investigations of river metamorphosis. The second "realization" stage involved significant advances in understanding by considering interaction between these two timescales, more detailed investigations of changing processes, a more holistic catchment-based approach, and incorporation of ecological changes. These advances led into the third stage, "application" of results, stimulated by analysis of the effects of hard and soft engineering, development of international drivers such as the Water Framework Directive, and concern for what is "natural." This paper evaluates this sequence of stages, the concepts that have emerged, the extent to which they are consistent and sustainable, and how they can provide the foundation for evaluation of channel adjustments. The effects of urbanization in Fountain Hills, Arizona, USA provide an illustration. Finally, the future requirement for adaptation of existing concepts and the possible development of new ones is briefly considered in the context of global environmental changes.