A Study of Coastal Morphodynamics on the Muddy Islands in the Changjiang River Estuary

Yang Shilun

Abstract


Based on field work for morphology and collected data on hydrodynamics, winds as well as artificial structures, this article deals with characteristics of coastal profiles, shoreline migration, erosion-accretion cycles and influence of human activities on coastal development. Due to silt-dominated sedimentary environments and current-dominated hydrodynamic conditions, coastal morphology in the studied area is different from that on sandy beaches. On the other hand, the ringlike shoreline of the islands and the strong influence of river discharge make the coastal processes more comprehensive than normal muddy coasts. Coastal profiles in the islands were classified as three types: channel bank, tidal beach and shoal head. In the light of these terms, three kinds of erosion-accretion cycles were explored;

(a) several years cycle, controlled by the changes in the offshore river channels; (b) annual cycle, influenced by the seasonal variations in winds, sea level, tidal range and nearshore suspended sediment concentration and (c) storm cycle caused by typhoons or cold waves. Due to the protection of vegetation, morphological process in the marsh was apparently different from that in the adjacent bare flat. Protective structures have stoped the retreat of the erosive coasts and slowed the migration of the islands, while reclaimation on accretional coasts greatly narrowed intertidal profiles and speeded the advancement of shorelines. The potential impacts of sea-level rise and reduction in sediment supply in the next century were also related.


Keywords


Coastal profile; erosion-accretion cycle; muddy tidal flat; sediment island; the Chang-jiang River estuary; China.

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