一个概化的潮汐河口羽状流动力学的初步研究

Preliminary Studies on the Dynamics of the Plume in a Schematized Tidal Estuary

基于区域陆架海水动力-生态耦合模型(COHERENS)中的三维水动力模型,对一个概化的潮汐河口羽状流动力学进行了初步研究。在均一水深和无风的理想条件下,模拟得到了一个潮周期内概化的潮汐河口表层水体:a)羽状流流场和盐度场的平面分布;b)3种不同河流径流量作用下的羽状流流场和盐度场的平面分布;c)4种不同底床粗糙长度下的羽状流流场和盐度场的平面分布。结果分析表明:a)羽状流的长度在潮汐的作用下递增,而其最大宽度近似呈周期性的变化;b)羽状流的长度和最大宽度都随着河流径流量的增大而分别变长和变宽;c)羽状流的长度和最大宽度都随底床粗糙长度的增大而变小;d)无潮情况下羽状流的凸起明显并存在沿岸流,然而在有潮情况下凸起不明显且无沿岸流;e)水平扩散可能限制了沿岸羽状流的发展。

Under the constant water depth and no wind condition, a three-dimensional numerical model modified after the COHERENS （A Coupled Hydrodynamical-Ecological Model for Regional and Shelf Seas）, is used to study dynamics of the plume in a schematized tidal estuary. Modeled results （for surface layer） include a） variations in its plane shape; b） horizontal distribution of tidal velocity vectors; and c） horizontal distribution of salinity fields within the plume over one tidal cycle. Effects of three different river discharges, tides and four different bottom roughness lengths on its development are examined. Results suggest that a） under tidal actions, the plume length increases gradually but its maximum width shows approximately periodic variations; b） both the plume length and the maximum plume width increase with the increasing river discharge; c） both the plume length and the maximum plume width decrease with the increasing bottom roughness length; d） both the bulge and coastal currents of the plume are more evident under amphidromic conditions than under tidal actions; and e） the horizontal diffusivity would constrain the development of the coastal plume.