【作者】 李志龙；

【导师】 陈子燊；

【作者基本信息】 中山大学 ， 自然地理学， 2006， 博士

【摘要】 沙质海岸正遭受着侵蚀后退过程,此类海岸演变趋势和侵蚀机制已逐渐引起了人们的关注。岬间海湾是华南沿海广泛分布的一种地貌形态。本文就华南岬间海湾沙质海岸为研究对象,以现场实测资料为基础,采用多种研究方法,按不同时空尺度,探讨了华南岬间海湾沙质海岸的侵蚀演变机制与平面平衡形态规律。研究的目的在于探索海洋动力和近岸地形的变化规律,不同尺度动力与地形的相互作用模式,并且给出这样的模式一个物理解释。根据对控制过程的认识,从地形动力学与岸线形态规律出发,探求稳定的海滩状态与平衡岸线形态。波浪是沙质海岸的主要驱动力,了解岬间海湾沙质海岸近岸波浪场波要素时空分布特征是海滩侵蚀演变研究与岬湾形态规律机制分析的基础与前提。对粤东靖海湾波浪近岸传播变形进行了数值模拟并分析了近岸波浪场波要素分布特征。反映了岬间海湾破波波高存在自切线段指向遮蔽段递减的沿岸变化梯度。海滩前滨是海陆相互作用最直接的区域,其冲流蚀积过程是与横向输沙机制相联系的中、小空间尺度和时间尺度的海滩过程,是海滩蚀积规律最直接的反映。根据粤东后江湾实测海滩前滨剖面,选用了入射波频带波高、长重力波频带波高、垂岸流分量等7个动力因子,采用典型相关分析方法,分析了前滨海滩过程的四个作用模式,讨论了各模式的控制因子及其作用机制。同时,海滩前滨由于冲流作用是海滩最活跃的区域,冲流带海滩高频振动分析显示出滩面存在多个频段的周期振动。通过分析冲流带高频振动的影响动力因子,讨论了潮水位对海滩的影响机制与波能流对海滩变化的重要影响。从海滩地形动力学出发,以靖海湾海滩状态分析为例,讨论了华南岬间海湾海滩状态的空间差异与时间变化。台风大浪是影响海岸侵蚀的重要的因子。以粤西水东湾海滩对8616号台风的响应为例,探讨了台风大浪对岬间海湾沙质海岸侵蚀的影响。结果表明台风对海岸侵蚀影响是显著的,由于岬间海湾的海滩状态与形态特点,不同位置的海滩侵蚀受影响程度有所不同——耗散性海滩侵蚀较小,反射性海滩侵蚀较大,海湾切线段侵蚀较小,遮蔽段侵蚀较大。海平面上升是影响海岸侵蚀另一重要因子。应用奇异谱(SSA)分析方法,分析并讨论了华南相对海平面的变化趋势。以后江湾与水东湾为例,分别采用2.0mm/a与2.5mm/a两个预案,应用Everts剖面积分法预测了海岸对海平面上升的响应,表明微小幅度的海平面上升可造成大幅度的岸线退缩和大面积海滩被淹没。分析表明海平面上升也对水位极值分布推算有着显著的影响,而水位极值分布对海岸安全工程设计具有非常重要地意义。应用海门站31年的最高潮水位资料,求作了P-Ⅲ型和Gumbel型极值水位频率曲线,比较分析了海平面上升对极值水位推算的影响,表明由于海平面上升,导致多年一遇高水位增高。沿岸输沙是与长时间尺度的海岸侵蚀演变过程相联系的。常浪情况下,横向输沙只是把泥沙在近岸区来回搬运,从较长时间看并不引起海岸的侵蚀。沙质海岸的长期岸滩演变主要是由沿岸输沙所造成的。分析了波浪的沿岸输沙机理及沿岸输沙影响海岸侵蚀的作用机制,并以后江湾拟建拦沙堤为工程背景,根据沿岸输沙机理,建立了岬间海湾岸线演变的一线模型,预报拦沙堤建成之后的岸线变化,讨论了海岸工程建筑对沿岸输沙及岸线蚀积变形的影响。岸线变形动态模式(如一线模式)模拟更大的空间尺度和时间尺度岸线演变会产生较大的误差,而海湾平衡形态规律为研究更大时空尺度岸线的稳定性提供了有效的方法。当前的海湾岸线形态模型都是用特定的数学函数(如对数螺线函数,双曲线函数,抛物线函数)去拟合岸线。海湾演变问题是一个复杂的非线性动力系统问题,海湾平衡形态并非简单的数学函数关系能够描述的。考虑到BP神经网络具有处理复杂非线性函数的能力,以华南岬间海湾为学习样本,建立一个基于BP神经网络的岬间海湾平衡形态模型。针对当前海湾平衡形态模型定义主波向与下岬角所存在的不足之处,从入射波折射绕射机理上解释了静态平衡形态的形成及其影响因素,重新合理定义了主波向与“下岬角”并提出了其具体算法。应用模型对华南31个主要岬间海湾的稳定性进行了判定,并讨论了模型在海岸防护工程上的应用。更多还原

【Abstract】 Sandy coasts are suffering from erosion, which gradually is attracting people’s attention to. The headland bays are a ubiquitous morphologic form in the south of China. Headland sandy bays in South China as studying object, based on field measured date, adopted various means, according to different scales of temporal and spatial, erosion mechanisms and equilibrium shapes of headland sandy bays in South China were studied in this paper.The main objectives of the analysis were to probe into the variety rule of sea dynamics and morphology, the interaction patterns of dynamics and morphology in various scales of temporal and spatial, and provide such patterns a physical interpretation, based on the understanding of morphordynamics processes, seek the stable beach states and the form of static equilibrium shoreline.Waves are primary dynamics of sandy coasts. To understand the distributing characteristics of wave factors in nearshore is precondition of studying beach erosions and equilibrium shoreline shapes. The wave fields of Jinghai Bay were numerically simulated and wave distribution characteristics were analyzed. The results showed that the broken wave heights tended to ascend from shadow zone to tangent zone in headland bay coasts.Foreshores are the firsthand interaction area of lands and seas. The morphodynamic processes in the foreshore, which are intermediate or small scales relating cross-shore sediment transport, straightly reflect erosion-deposition mechanism of beach. Based on the measured data of beach profiles and waves in houjiang Bay, selected seven factors of dynamics, adopted canonical correlation analysis, four patterns of foreshore governing processes was explained, and the governing factors of each pattern were discussed. On the other hand, foreshores are the most drastic area of beach. The analysis of high-frequency beach oscillation in the swash zone indicated that beach face oscillation had several different frequency periods. Mechanisms which tide level effect beach and important effect of energy flux in the variation were discussed.Based on Morphodynamics, through analysis of beach state of jinghai Bay, It was discussed that beach state diversity of headland sandy bay in South China in temporal and spatial.Storm is an important factor of effecting coast erosion. Taken shuidong Bay as an example, response of shuidong Bay to 8616 typhoon was analyzed. The result showed that the effect of storm in coast was obvious, because of difference of beach state and shape, degree of erosion was different to the beach in different location of bay: degree of erosion was greater reflective beach than dissipative beach and tangent zone than shadow zone.Effect of sea level rise in erosion of coast is other important factor. Applied singular spectrum analysis, trend of sea level change was analyzed and discussed. Taken houjiang Bay and shuidong Bay as examples, adopted two project of 2.0mm/a and 2.5mm/a, applied Everts integral method, response of coast to sea level rise was forecasted. The result showed that a litter rise of sea level could make shoreline retreat large. Effect of sea level rise in calculation of extreme level distributing is obvious too. Applied extreme high level date of 31years in haimen station, frequency curve of P-Ⅲand Gumbel were calculated. Through comparing and analyzing, the result showed that sea level rise caused extreme high level become higher.Longshore sediment transport is relational with coastal erosion processes of large temporal scale. Under normal waves condition, cross-shore sediment transport only takes sediment inside-and-outside, and can’t cause coast erode in a long period. Sandy coast erosion is caused by longshore sediment in a long period. Mechanisms of longshore sediment transport and effect of longshore sediment transport in coast erosion were analyzed. Taken groynes being built as background, based on mechanism of longshore sediment transport, one-line model of headland bay was built. Change of shoreline was forecasted applying the model, and the effect of structure near shore to shoreline changing was discussed. The shoreline evolvement model as one-line model will bring great deviation, when simulating shoreline evolvement of larger temporal and spatial scale. However, equilibrium shapes rule of bay offers availability means for shoreline stability assessment of large temporal and spatial scale.Shoreline shapes model of nowadays all applied specifically function, such as logarithmic spiral, parabolic, hyperbolic and so on, to simulate shoreline. Problems of bay evolvement are complex and nonlinear, consequently, simple function can’t describe the shape of equilibrium bay. Considered the back propagation artificial neural networks have the capability to deal with complex nonlinear problem, taken headland bay in the south of china as sample, a back propagation artificial neural networks model concerning equilibrium shapes of headland bay was built. In addition, definiens of front orientation and downcoast tip for shape model of nowadays was not reasonable. Through analyzing forming mechanism of static equilibrium shape, front orientation and downcoast were defined reasonably and the calculating means were provided.At last, applied the model to estimate the stability of 31 headland bays in South China, and discussed the application of coast-defend engineering更多还原