Coarse-Grained Sediment Transport in Northern New England Estuaries: A Synthesis

Abstract

Although it is widely stated in the literature that estuarine river mouths are sediment sinks, northern New England estuaries are an exception to this model because they export coarse-grained sediment to the nearshore. The traditional view is that estuaries fill with sediment ranging from mud to gravel derived from fluvial or upland sources as well as from the inner continental shelf and adjacent shorelines. Fluvial sediments are deposited primarily in the inner and central portions of an estuary, although fluvial mud can be deposited in the outer estuary in some tide-dominated systems (e.g. sections of the Gironde River (France), Allen, 1991; Fly River (Papua New Guinea), Harris et al., 1993). The deposition of sediment in the inner and central portions of an estuary is due to the combined influences of a downstream decrease in the riverine current strength and clay flocculation produced by fresh and saltwater mixing. In estuaries having high sediment loads, fluidized mud can be an important component of estuarine sedimentation (Wells, 1983, 1995). Marine sediments enter the outer estuary due to residual, flood-oriented bottom currents and stronger flood than ebb tidal currents. This former flow pattern is caused by the seaward-flowing freshwater advecting the underlying saltwater producing a mass balance deficit of saltwater (Dyer, 1973).