Channel change and sediment transport in regulated U.K. rivers

Abstract

AbstractThe history of investigations of channel change consequent upon river regulation is traced from the late 1960s until the present. The associated sediment transport and depositional processes are also reviewed. Conveniently the approaches adopted historically have fallen into three basic groups, these are: (1) analyses of the changes in channel networks as evident in adjustments to hydraulic geometry related to catchment area; (2) analyses concerned with sediment transport processes and channel adjustments at the reach scale (typically utilizing regime‐type concepts), and finally; (3) more recent attempts at an integrated approach utilizing holistic concepts of channel change over extended time periods.A major conclusion drawn from this review is that each reservoir‐catchment system is unique, producing singular responses that cannot easily be integrated into a basic general model except at a facile level. The continuing lack of complete theoretical models of channel adjustment is a hindrance in predicting regulation effects and may be related to limited understanding of such factors as sediment supply dynamics and bank collapse mechanisms. Emphasis is placed on: the importance of the aggregational as well as the well‐known degradational response of channels below dams; the recognition of suitable temporal frameworks; the potentially destabilizing effect of rare large floods; and the local effects of unregulated tributary inflows. In addition more sophisticated theory and analysis needs applying to the transport and subsequent deposition of suspended sediments in gravel‐beds whilst the three‐dimensional facies relationships of regulated river alluvial suites need clarification in the light of recent initiatives concerning the sedimentary architecture of other alluvial systems.