SEDIMENT SLUGS - LARGE-SCALE FLUCTUATIONS IN FLUVIAL SEDIMENT TRANSPORT RATES AND STORAGE VOLUMES

Variations in fluvial sediment transport rates and storage volumes hav e been described previously as sediment waves or pulses. These feature s have been identified over a wide range of temporal and spatial scale s and have been categorized using existing bedform classifications. He re we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of elas tic material associated with disequilibrium conditions in fluvial syst ems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by b asin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by loca l riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high-magnitude geomorphic events, and the impacts o n water and sediment production of tectonics, glaciation, climate chan ge and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment s lugs in fluvial systems. Attention is drawn to components of the fluvi al system where future research is urgently required to improve our qu antitative understanding of drainage-basin sediment dynamics.