Chapter Two Clastic Sediment Supply to the Shore: Processes and Palaeoenvironmental Considerations

Publisher Summary Much of the terrigenous sediment supply to the shore is provided by rivers, notably through trapping in the zone of density contrast between freshwater and saltwater. In addition to this density contrast in the supply of muddy or fine-grained sediment to the shore, the convergence of fluvial and marine bedload in estuarine and deltaic settings is an important mechanism in the supply of sand, and sometimes gravel, to the shore. The longshore redistribution of fluvial-supplied bedload from deltaic river mouths is, however, overwhelmingly dominated by wave-induced currents within the inner shoreface, while that of mud is linked to currents induced by waves, tides, wind activity, and density circulations. The amount of sediment supplied annually by the world's rivers has been estimated at 10–20 billion metric tons, although there is considerable uncertainty concerning volumes because of the effects of human intervention. A second important source of bedload sediment supply to the shore is the shoreface, especially in wave-dominated settings. Shoreline translation over the shelf during sea-level fluctuations provides a lower-order framework for further cross-shelf reworking of sediments, and this is a prime consideration in palaeoenvironmental applications of shore processes. This chapter deals with processes involved in supplying sediment to the shore. The first part examines the supply and convergence of sediment in transit through the fluvio-marine domain, while the second looks at sediment supply from the shoreface.