人工沙坝和鱼礁潜堤养护下浪控海滩地貌形态演变机制研究

Beach nourishment is an eco-friendly and effective method for beach restoration with extensive application worldwide. In recent years, artificial reef and sand bar instead of traditional submerged breakwater have been employed in beach nourishment projects for nearshore ecological environment considerations. This research is focused on the wave-dominated morphodynamic system consisting of nourished beach, artificial reef and artificial sand bar. A series of movable bed experiments will be setup to quantify the relation between the spatial characteristic of wave energy and sediment transport, and to investigate the function of short wave, bound long wave and undertow on morphological evolution. As a result, the hydrodynamic factors are prioritized by the degree of accounting for the morphological evolution in three sub-regions of artificial reef, artificial sand bar and beach face. The morphological evolution is analyzed in terms of processes induced by erosive big waves, accretion small waves and storm waves derived from records from an offshore wave station. According to the analysis of regular field measurement, a new equilibrium profile function considering artificial reef and artificial sand bar can be obtained to predict the morphology of the whole system. Based on the acquired mechanism, non-hydrostatic wave model is adopted to include the nonlinear short and long wave effects. The bedload and suspended load modes are reconstructed based on the study of existing sediment transport modes and a morphodynamic prediction model is established to simulate the morphological evolution in the system. The anticipated achievements will be great theoretical progress in coastal dynamic geomorphology and coastal numerical modelling and also provides the theoretical basis and technical support for the use of artificial reef and artificial sand bar in beach nourishment project.

人工养滩作为一种环境友好的有效修复侵蚀砂质海滩的方法在世界范围内广泛应用。近年来鱼礁潜堤、人工沙坝因其近自然的保护海洋生态环境的原因，代替传统的离岸潜堤在人工养滩中被采用。本项目以鱼礁潜堤—人工沙坝—海滩系统为研究对象，通过水槽动床试验研究人工养护下浪控海滩系统的波能空间分布特征与泥沙输运的定量关系，分析短波、长波和底部回流对地貌形态演变的作用方式，分离出鱼礁潜堤、人工沙坝和滩面三个子区域的主次动力因子；结合现场观测资料对比分析侵蚀浪、恢复浪和风暴浪三种典型波况下的地貌形态演变过程，获得鱼礁潜堤和人工沙坝养护下的海滩平衡剖面预测公式。在此基础上，采用非静压波浪模型模拟非线性的长波和短波的动力过程，重构悬移质和推移质输沙模式，建立人工沙坝和鱼礁潜堤养护下海滩系统的地貌形态演变预测模型。预期成果可丰富海岸动力地貌学和数值模型的理论，为人工养滩中鱼礁潜堤和人工沙坝的应用提供理论依据和技术支撑。

人工养滩作为一种环境友好的有效修复侵蚀砂质海滩的方法在世界范围内广泛应用。鱼礁潜堤和人工沙坝因其近自然地保护海洋生态环境，代替传统的离岸潜堤在人工养滩中被采用，但在它们养护下砂质海滩地貌形态演变机制仍不清楚。本项目以鱼礁潜堤—人工沙坝—海滩系统为研究对象，采用现场试验、水槽动床试验和数值模拟相结合的方法，系统研究了人工沙坝和鱼礁潜堤作用下短波、长波和底部回流的作用方式及泥沙输运特点和风暴侵蚀与恢复机制，揭示了海滩地貌形态演变机理，推导了包含人工地貌单元的砂质海滩平衡剖面形态预测公式。研究发现鱼礁内部湍流结构主要受水平对称的涡结构控制，迎流面开孔后侧涡度形状为偶极子型，由两对旋转方向相反的高涡度云组成。鱼礁潜堤提高了随机波的高频和低频波能比重，耗散系数>透射系数>反射系数，其消浪作用取决于鱼礁潜堤的孔隙结构；人工沙坝促进随机波低频波能比重增加和谱峰频率减小；鱼礁潜堤与人工沙坝组合下，鱼礁潜堤抑制了人工沙坝前坡反射，进而大幅减小海滩处低频能量。鱼礁潜堤和人工沙坝重构了水沙输运过程，促进了海滩动力地貌模式向反射型海滩状态转变。建立了一个指数模型定量描述海滩侵蚀陡坎蚀退过程，获得了海滩上破波沙坝高度与位置的线性定量关系。风暴潮期间风致增水>气压致增水>波致增水，冲流作用和海滩前滨泥沙离岸输运是砂质海岸风暴侵蚀的主要机制，而风暴后常浪作用下泥沙向岸输运是海滩恢复的主要机制。基于最大信息熵原理和抛物线函数，推导出背景剖面和人工地貌剖面叠加形式的海滩平衡剖面预测公式，并由现场测量数据验证了适用性。构建了风、浪、流、潮共同作用下的含人工地貌节点单元的泥沙输运和海床演变模型，模拟了多重动力作用下的砂质海滩和人工地貌节点单元的泥沙输运和海床演变过程，预测了多个典型海滩生态修复工程下的动力地貌演变规律。项目研究成果丰富了海岸地貌动力学理论，为砂质海滩的生态修复提供了理论依据和技术支撑。