Dune convergence/divergence controlled by residual current vortices in the Jade tidal channel, south-eastern North Sea

详细信息    查看全文

• 作者：Adam Kubicki ; Frank Kösters ; Alexander Bartholomä
• 刊名：Geo-Marine Letters
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：37
• 期：1
• 页码：47-58
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Geology;
• 出版者：Springer Berlin Heidelberg
• ISSN：1432-1157
• 卷排序：37

文摘

A field of large to very large subaqueous dunes was investigated in the Jade tidal channel, south-eastern North Sea, between January 2006 and October 2011. A ground-truthed sidescan sonar sediment map shows that the dunes, which are located on top of a consolidated clay surface, are composed of medium to coarse sand. A series of 35 consecutive high-resolution bathymetric surfaces collected by multibeam echosounder revealed a complex migration pattern induced by the reversing tidal currents. Various parts of the dune field are under the influence of either ebb- or flood-dominated currents, as indicated by dune asymmetries. Although some dunes migrate at a pace exceeding 100 m/year, the majority are displaced by 30 m/year in the direction of the locally dominant current. In the deepest part of the channel, however, dunes were observed to converge head-on, resulting in practically zero net transport with minor oscillations of symmetrical dunes at the apex. Applying the numerical UnTRIM model for the simulation of the fair-weather hydrology, a simplified map of residual current vectors over the dune field was generated. The residual flow vectors are found to perfectly match the derived dune migration vectors, suggesting that dune convergence is controlled by two counter-rotating residual current vortices caused by the local shape of the tidal channel. As no sediment build-up is observed, a mechanism of sediment bypassing with potential recirculation must exist, but has not yet been identified.