Near-bed sediment transport in a heavily modified coastal plain estuary

Abstract

Numerous estuaries of the world have been strongly modified by human activities. These interferences can make great adjustments of not only sediment transport processes, but also the collective behavior of the estuary. This paper provides a typical case of a heavily modified coastal plain estuary of Sheyang on the China coast, where a sluice barrage was built in 1956 to stop the intrusions of storm surges and saline water. Four sets of instrumented tripods were simultaneously deployed along a cross-shore transect to continuously observe near-bed flow currents and sediment transport. The in-situ surveys lasted over a spring and neap tide cycle when a strong wind event occurred in the neap tide. Comparisons of flows and sediment transport between tide-dominated and wind-dominated conditions demonstrated the important role of episodic wind events in flows and sediment transport. The wind-induced currents, bottom stresses, and sediment transport rates were significantly greater when wind was present than corresponding quantities induced by the tides. The long-shore sediment transport induced by winds exceeds the cross-shore component, especially near the river mouth bar. These results indicate the noticeable importance of wave-dominated coastal processes in shaping topographic features. A regime shift of estuarine evolution under highly intense human forcing occurs from fluvial to marine processes. This finding suggests that the management strategy of the estuarine system should focus on the restoration of estuarine processes, rather than the present focus on inhibition of marine dynamics.