Suspended material transport: Narragansett Bay area, Rhode Island

Abstract

Net circulation patterns and routes of suspended material transport in lower Narragansett Bay and its approaches were investigated utilizing sea-bed drifters, transmissometer measurements, grain size distributions, suspended material concentration data and compositional analyses. In general, seaward flowing near-surface currents carry silt through lower West and East Passages, west across the Bay mouths and then south along Point Judith Neck. Very fine silt is carried along this route with little deposition but medium silt settles toward the Bay mouths. At the entrances to Narragansett Bay, the landward-flowing direction of bottom currents is modified by coastal currents and topographic influences. Near-bottom suspended material is carried into all three Narragansett Bay passages as well as eastward and westward across the entrances. The westward setting component transports suspended matter from East and West Passage across the passage mouths, southward adjacent to Point Judith Neck and then westward into Block Island Sound. Coarse silt suspended by turbulence at East and West Passage mouths is deposited along this path in the sandy silt bed (McMaster, 1960) east of Point Judith Neck. Some of the very fine silt carried along this route may be deposited in the sandy silt bed as well as in Block Island Sound. The eastward component, influenced by the nearshore circulation in Buzzards Bay, flows along the south-eastern Massachusetts coast. Coriolis acceleration may cause the dextral movement of near-surface and near-bottom suspensates from the mouths of estuaries, based on results of this study and investigations of other workers.