Bedload-sediment transport through the Connecticut River estuary

Abstract

The Connecticut River is the third-largest river on the east coast of the United States, and its estuary is microtidal and sand dominated. Discharge of the river annually varies from tens to thousands of m 3 /s, and circulation in the estuary spans the full range of estuarine mixing modes. During half of the year, the estuary is partially mixed with mutually evasive tidal currents established between the flood-dominated channel and ebbdominated shoal margins. The distribution, orientation, and tidal modification of large bedforms in the estuary demonstrate that there are major pathways of bedload-sediment transport through the estuary to Long Island Sound. Calculations of shear stress on the bed, based on current-velocity measurements at 47 stations through full tidal cycles during low-discharge conditions, indicate that most of the estuary is essentially ebb dominated with respect to bedload-sediment transport. Observations of bedform occurrence and orientation during high discharges indicate that bedload transport is ebb oriented throughout the entire estuary. Analysis of dredging records and historic charts of the estuary since 1915 show little net change in bathymetry and suggest that the bed of the estuary may be in equilibrium with its sediment supply. The combined evidence argues that the Connecticut River estuary is not a site of significant bedload storage, and that it is a conduit of sand into Long Island Sound.