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  • Studies on Storm-induced Sediment Transport
    Author:   | Date:2006-03-14   | Click Rate:    | 【Close
    Typhoon is a severe disaster to the economy and environment in coastal areas. On the one hand, the sea level rise induced by a storm, a companion of typhoon, frequently causes enormous economic loss and claims tens of thousands of people’s lives. On the other hand, storm-induced sediment motion may possibly block waterway and harbor berth only in days or even hours. A paradigm was found in the Yangtze River Estuary, where people had to give up the South Channel for navigation due to the legacy of a vast sedimentation left by Typhoon 8310, and resorted instead to dredging the North Channel for shipping. By coupling a storm surge flow model with the sediment transport model based on the new understanding of burst and flocculation effect, the group of environmental fluid, Institute of Mechanics, CAS, has investigated storm surge flows and the accompanying sediment transport laws for cases of different typhoon parameters and benthal topography. Some new findings have been drawn as follows. The current speed variation lags behind wind speed due to the duration needed for momentum transfer from air to water body. Therefore, such a time lag can approximately be estimated by momentum conservation law. Sediment concentration rises up and drops down following current speed variation with a time lag as well. The retarded dynamic process to balance sediment entrainment and settling in the benthal layer may convincingly account for thtis time lag. Investigations on the sediment motion in a harbor demonstrate significant impact of typhoon tracks on sea bottom evolution. While the typhoon track’s direction determines erosion or deposition in the harbor, the relative position of the track regulates the magnitude of erosion/deposition. It is the magnitudes and directions of the current vectors at the mouth and the time lag between sediment concentration and current speed that dominantly regulate sediment delivery processes between the harbor and open sea. Generally speaking, the northward typhoon results in harbor erosion, and the southward or westward one causes deposition. Both erosion and deposition take place along the coastline. Little variation of bed happens nearby the harbor center. These results can serve as a guideline for predicting typhoon disasters and designing waterway and environment protection project. [Ref: Journal of Waterway, Port, Coastal and Ocean Engineering-ASCE, 2005, 131(1): 25-32]
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