一个理想河口中拦门沙的存在对河口羽流扩展的影响

THE IMPACT OF A RIVER MOUTH BAR ON THE SPREADING OF RIVER PLUME IN AN IDEALIZED ESTUARY

河口羽流是河口冲淡水在陆架中扩展的主要形式,其扩展受到诸多动力与地形因素的影响,口门拦门沙就是其中之一。以一个理想化的河口为例,采用区域海洋模型(regional ocean modelling system,ROMS),研究口门拦门沙对河口羽流扩展的影响,具体包括拦门沙对羽流的出流状态、扩展范围以及远场区沿岸流淡水输运的影响。研究结果表明,拦门沙增加了口门处的水体分层,减小了羽流出流速度,增大了羽流凸出体的半径,减小了远场区沿岸流宽度,并进而减少了沿岸流中的淡水输送。本项研究对地形因素对河口羽流的扩展研究以及陆源物质的向海输运等均具有重要意义。

River plume is the form of riverine brackish water spreading in a continental shelf after leaving river mouth.The spreading of a river plume is affected by many external forcings and bathymetry near river mouth,of which mouth bar is an important one.Taking an idealized estuary as an example,we studied the effect of mouth bar using the ROMS ocean model on plume spreading in terms of outflow regime,extent of the plumes,and the transport of freshwater along coastal current in far-field region.Results demonstrate that the existence of the mouth bar decreases the outflow velocity but increases the stratification in estuary mouth and the exiting angle to downstream coastline.In addition,it decreases the radius of the plume bulge and the width of the coastal alongshore current.Eventually,it reduces the freshwater transport in the alongshore flow.This study provided an important reference for understanding the bathymetric effect on the spreading of river plume and the transport of terrestrial materials into the shelf.