河口挡潮闸对三角洲潮汐不对称时空变化的影响*

三角洲内部潮汐不对称性与三角洲地貌演变方向有重要关系。目前诸多研究关注海洋、陆地边界的改变对三角洲内的潮汐不对称性演变规律的影响。实际上, 大规模的河口工程也会对三角洲内的潮汐不对称性产生影响。在众多河口工程中, 河口挡潮闸由于直接削弱口门处海洋潮动力, 影响最为直接。荷兰三角洲是潮动力主导型三角洲, 受洪潮灾害影响较为严重, 为此在荷兰西南部修建了世界上著名的三角洲挡潮闸工程。文章以荷兰莱茵河-默兹河三角洲为研究对象, 分析以挡潮闸为主的河口工程对三角洲内河网潮汐不对称性演变特征的影响。选取莱茵河-默兹河三角洲13个潮位站点的50~60年的水文资料, 利用非平稳调和分析方法计算分析三角洲内部潮汐传播特性, 并进一步研究潮汐涨落潮历时不对称性演变特征, 揭示河口挡潮闸工程对潮汐河网中潮汐动力和潮汐不对称性的影响。研究表明, 莱茵河-默兹河三角洲为显著的涨潮占优型河口, 潮汐不对称现象总体向上游沿程增强。河口挡潮闸修建后受河网径流量和潮动力剧烈变化的影响, 封闭的南部通道内的潮波大幅度削弱, 潮汐不对称现象在下游增强在上游减弱。北部、中部通道其他站点则因为通道径流增大, 潮汐不对称现象增强, 中部站点变化更为显著。

Impact of estuarine storm surge barriers on spatiotemporal variation of tidal asymmetry in a delta*

Tidal asymmetry in a delta has a vital relationship with the evolution direction of the delta geomorphology. Many studies focus on the evolution of tidal asymmetry in a delta in response to the changes of seaward and landward boundaries. Large-scale estuary projects also affect tidal asymmetry in a delta. Numerous estuary works show that storm surge barriers directly weaken the ocean tidal power on the inlet. The Rhine-Meuse Delta of the Netherlands is a tidal-driven delta, subject to flood disasters. The world-famous delta project was built in the southwest of the Netherlands. We take it as the research target, and analyze the influence of storm surge barriers on the evolution of tidal asymmetry in the delta networks. In this paper, we apply a nonstationary harmonic model to 50 ~ 60 years of hydrological data from 13 stations in the Rhine-Meuse Delta to analyze the characteristics of tidal propagation and tidal duration asymmetry and the influence of the storm surge barrier. Analytical results show that the Rhine-Meuse Delta is flood-dominant, and tidal duration asymmetry gradually increases upstream. Under the impact of suddenly changed river discharges and tidal dynamics after the construction of the storm surge barrier, the tidal powers in the enclosed southern branches were greatly weakened, and tidal asymmetry increased in the downstream and weakened in the upstream. In the other channels of the northern and central branches, the tidal asymmetry increased due to the increase of river discharges, more significantly in the central sites.