珠江河口口门区滩槽演变及对泄洪的影响研究

受流域来水来沙和高强度的人类活动的影响,珠江河口口门滩槽演变规律复杂,对泄洪安全的影响有待深入研究。本文阐明了珠江河口滩槽近期演变总体特征,揭示了河口拦门沙演变动力机制,评估了不同类别大型涉水工程对泄洪的影响和贡献率,提出了珠江河口径潮控制敏感区的划分方法,量化了涉水工程防洪影响关键控制指标。研究发现:(1)在来沙大幅减少背景下,珠江河口滩涂存在侵蚀后退的可能,滩槽近期演变总体上有利于口门泄洪;(2)季风成沿岸流和洪水径流是塑造磨刀门拦门沙东、西汊发育的主动力,洪水与波浪共同作用是形成拦门沙内、外坡冲刷,拦门沙顶淤高的主要成因;(3)涉水工程对河口洪潮水位、分流比、净泄洪量、纳潮量等影响的群体效应,伶仃洋东四口门桥梁工程群对潮位影响贡献率大于围垦工程,而在西四口门围垦工程对潮位影响更大;(4)引入径潮动力比概念,提出珠江河口径潮控制分区,识别了防洪敏感河段,建立基于单宽流量概念的工程阻水效应判断方法,划分防洪影响敏感水域;(5)综合分析提出了各敏感河段或水域的涉水工程的允许壅水高度,基于口门均衡断面的河相关系,提出涉水工程引起的潮量减幅应控制在1%~2%以内。

The impact of channel-floodplain evolution on the flood release in the mouths of Pearl River Estuary

Regional security of flood control is highly related to the clearness of estuarine mouth. Due to the impact of variable flow and sediment load and intensive human activities, the rule of channel-flood-plain evolution is complicated in the Pearl River Estuary. Hence, regional security of flood control should be further explored. This paper characterizes the evolution of channel-floodplain in the Pearl River Estuary and reveals the hydrodynamic mechanism of river mouth bar evolution. Besides, the influence of multiple large-scale wading projects on flood release is evaluated. The classification of estuarine sensitive region un-der the control of runoff and tide is presented and the influential factor of flood control is quantified. It is found that:(1) with significantly decreasing sediment load, the floodplain has the potential of erosion, which may provide advantage for flood release;(2) alongshore current driven by monsoon and flood flow are the main influential factors of east and west channel evolution of river mouth bar, and the interaction of flood and wave leads to the erosion of inner and outer slope and siltation of crest for river mouth bar; (3) wading projects exert group effect on the water level, flow division ratio, the load of flood release and tidal prism, and the variation of water level is more sensitive to bridge constructions than reclamation proj-ects in the four eastern mouths while it is reverse in the four western mouths;(4) according to the ratio of runoff and tide, unit discharge and the effect of water block, regional classification is proposed to distin-guish the flood risk of different channels;(5) the height of water block in the sensitive part of channel is calculated. Base on the transverse hydraulic geometry, the decrease of tidal prism caused by wading proj-ects should be less than 1%-2%.