Coarse sediment connectivity in river channel systems: a conceptual framework and methodology

Identification of coarse sediment connectivity down river-channel systems is important for understanding the linkages between river reaches, the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change. A conceptual framework is developed in which several types and degrees of connectivity are proposed. It is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions. A method of identifying the status of reaches is developed, based on field mapping of morphology and sedimentology. The analysis is exemplified by two channels: one an ephemeral channel in SE Spain; the other a perennial channel in NW England. Questions arise over whether reaches that lack channel stores transfer coarse sediment. Three scenarios are suggested: (1) lack of flux due to lack of competence of the reach; (2) flushing through of sediment due to high competence; and (3) potential transport of coarse sediment but exhaustion or lack of availability. Changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage. Short-term variations in connectivity can be identified by repeated mapping. (C) 2003 Elsevier Science B.V. All rights reserved.