珠江磨刀门河口径潮动力异变格局下余水位的形成变化机制

The process of mutation driven by intensive human interventions has become a new challenge for studying the evolution of estuarine system all over the world. In particular, the change or transformation of tide-river dynamics affected by mutation is the key issue to study the evolution of estuarine system. Understanding development and variation of residual water level, as a result of nonlinear interaction between tide and river flow, is important to explore the complex tide-river dynamics affected by mutation and to develop the corresponding regulation of techniques for estuaries. In this study, the Modaomen estuary in the Pearl River is selected as the study area to examine the development and variation of residual water level affected by mutation of tide-river dynamics. To understand the complex pattern of residual water level induced by the complex tide-river interplay with a wide range of spatial-temporal scales, a new analytical model building on the previous works is employed to assess the impacts of width convergence, depth variation, salinity gradient and external forcing (tide and river) on the spatial-temporal variations of residual water level. On the basis of the analytical results for key factors that control the pattern of residual water level, the influences of various tidal constituents and branching channel on the change of residual water level are explored using a numerical model. Subsequently, the potential impacts of sand excavation and estuary mouth regulation on the residual water level pattern are numerically modelled. Based on numerical analyses, in combination of scaling analysis and decomposition of residual water level used in the analytical method, the mechanism governing the development and variation of residual water level affected by mutation is revealed, which is particularly useful for the integrated regulation and water resources management in the Modaomen estuary.

强人类活动驱动的河口系统超自然过程异变是全球河口演变研究面临的新挑战，异变格局下的径潮动力结构变化或转换已成为河口演变的焦点。余水位是河口径潮动力非线性作用的典型结果，其成因及变化机制是河口异变格局下复杂动力结构研究的重要科学问题，也是研究河口治理技术的有效靶点。选取珠江磨刀门河口为研究靶区，针对河口径潮动力过程的复杂性及其时空多变性导致的余水位复杂变化问题，基于申请人已有解析解重新构建一维余水位解析模型，探讨河宽、水深、盐度梯度和不同径潮组合对余水位形成变化的影响；在探明余水位关键影响因子基础上，通过数值模拟探讨不同分潮族及河道分汊对磨刀门河口余水位时空变化的影响，并模拟以河道采沙和口门整治为代表的强人类活动对余水位格局变化的影响；在数值模拟的基础上，结合解析模型无量纲分析及余水位的分解方法，揭示径潮动力异变格局下余水位的形成变化机制，并为磨刀门河口的综合整治及水资源配置等提供科学依据。

强人类活动驱动的河口系统超自然过程异变是全球河口演变研究面临的新挑战，异变格局下的径潮动力结构变化或转换已成为河口演变的焦点。余水位是河口径潮动力非线性作用的典型结果，其成因及变化机制是河口异变格局下复杂动力结构研究的重要科学问题，也是研究河口治理技术的有效靶点。项目选取珠江磨刀门河口为研究靶区，针对河口径潮动力过程的复杂性及其时空多变性导致的余水位复杂变化问题，基于实测资料分析，指出磨刀门河口主要受高强度采砂等强人类活动对河道地形的影响，水位为适应地形改变而做出调整，其中上游水位大幅下降，马口站多年平均余水位下降0.84m，而下游水位变化较小，三灶站仅有0.01m的变化，导致水位坡度变缓，年均余水位坡度减缓4.83e-6，从而减弱潮波振幅的衰减效应。通过构建径潮动力耦合条件下潮波传播的一维水动力解析模型，从理论机制上探讨径潮动力非线性作用下余水位的多时空尺度变化，指出余水位呈现明显的大小潮和洪枯季变化，其形成变化机制可通过分离控制余水位变化的三个主要因素（即径流、潮流和径潮相互作用因子）进行阐释。在探明余水位关键影响因子基础上，通过流量驱动的数据驱动模型，对磨刀门河口沿程主要站点长时间日均水位序列进行分解，分解出由地形和海平面边界共同驱动以及仅由上游马口站流量边界驱动引起的日均水位变化。结果表明甘竹至灯笼山河段春夏两季日均水位变化主要由河道挖砂引起，日均水位下降约0.26m；秋冬两季则由口门围垦与海平面边界控制，日均水位抬升约0.07m。仅由上游马口站流量边界驱动的结果表明：春夏秋三季日均水位变化主要由水库蓄水主导，日均水位下降约0.13m；冬季日均水位变化受水库调枯影响，日均水位抬升约0.03m。项目系统揭示径潮动力异变格局下余水位的形成变化机制，可为磨刀门等河优型河口的综合整治及水资源配置等提供科学依据。基于项目资助成果，共培养硕士研究生4名，以第一或通讯作者发表相关论文19篇，其中SCI论文12篇，超额完成研究目标。