植被作用下河口湿地海域水动力特性及泥沙输运机制研究

The cognition of interaction and coupling effect on wave, current, sediment and wetland vegetation could help to understand hydrodynamic properties in wetland estuaries and reduce the damage from marine natural disaster. Because of the complicated interactions among variables mentioned above, the underlying interaction mechanisms and coupling effects among them remain largely unknown, the relate studies become the hotspot and difficulty in wetland estuaries, and they have attracted more and more attention in recent years..The wetland of Liao River Estuary has been listed as the largest coastal wetland at the high latitude in China. Taking the coastal wetland of Liao River Estuary as the object of study, three methods of field observation, remote sensing technique and numerical simulation are used in this project. The field observation data is used to derive the empirical formula for wave attenuation over vegetated waters, the dynamic responses of suspended sediment under variable wave and tide conditions in wetland vegetated waters are explored as well. The hydraulic properties and flow structure are investigated in wetland estuaries using the numerical models, the effect mechanism for the hydrodynamics and the energy dissipation caused by wetland vegetation are reached in this study. The processes of the tide flooding and ebb in wetland vegetation domain are calculated under the condition of the land-ocean interaction, the resistance effect caused by wetland vegetation is obtained considering the flooding and ebb tide processes using a high-resolution numerical model. Considering the coupling processes of hydrologic connectivity in river and estuary, the dynamic variation of suspended sediment in wetland domain is numerically analyzed in the process of tide periodic flooding and ebb, and the exchange mechanism of suspended sediment between the vegetated domain and estuary is obtained in this study, the main driving factors of the morphological evolution at research coastal waters are understood in this study..This research results have important theoretical value and practical significance for analyzing and evaluating the influences of water ecological environment, the disasters prevention induced by extreme waves and the functions of stabilizing and protecting beach by planting wetland vegetation on the shoreline.

对湿地植物与波浪、潮流、泥沙之间相互作用和耦合效应的认知有助于了解河口湿地海域水动力特征，减少海洋自然灾害带来的危害，而上述因子相互作用复杂，耦合机制尚不明确，因此成为河口湿地海域研究的热点和难点。本项目以国内高纬度面积最大的辽河口滨海湿地为研究对象，结合现场观测、遥感技术与数值模拟三种方法，解析湿地植被的消波经验公式，探寻植被区悬移泥沙在变化波流条件下的动态响应；研究湿地海域的水动力特性和流动结构，揭示湿地植被对水动力及波浪能量衰减的作用机理；模拟海陆相互作用下植被区出现的潮水漫滩过程，解析植物阻力在涨落潮过程中的阻滞效应；耦合河海的水文连通，分析在潮流周期性淹没与退水过程中植被区悬移泥沙的动态变化，查明植被区和河口区悬浮泥沙的交换机制，确定湿地潮滩地貌演变的主要驱动因子。研究成果对分析评价湿地海域的水环境变化、极端波浪引起的灾害防治、湿地植物固滩护堤功能等具有重要理论和应用价值。

辽河口潮滩生长大量盐沼植被，大规模的海洋开发活动使辽河口局部海岸冲淤严重，湿地出现退化现象。盐沼植物能消减水流和波浪能量，进而影响泥沙输运与潮滩地貌演化。但目前学术界对盐沼植物的护岸机制认识不足，相关研究亟需开展。本项目主要研究内容包括：悬移泥沙对波流变化的动态响应、水动力变化特征、潮滩漫滩的动力过程及悬移泥沙的输运特性研究。针对上述研究内容，本项目结合现场观测、遥感技术与数值模拟三种方法，取得了以下研究成果：（1）辽河口潮滩湿地淹没存在一定的周期性，在接近高潮位时植被区的悬浮泥沙含量较高，退潮时植被区的悬浮泥沙含量显著降低，盐沼植被能够捕捉部分悬浮泥沙；（2）解译了辽河口潮滩盐沼植被的空间分布，盐沼植被对辽河口潮滩湿地区域的流速与流场结构影响明显，相对盐地碱蓬，芦苇对流速衰减较盐地碱蓬更大；（3）辽河口潮滩区域的淹水时间的分布不均匀，盐沼植被类型与分布对潮滩淹水过程影响不大，盐地碱蓬植被的适宜淹水时间为0.79-3.22小时/天，淹水时间过长或过短均不利盐地碱蓬的生长与发育；（4）在周期性淹没与退水过程中植被区的悬沙浓度变化明显，盐沼植被植株形态特征对悬浮泥沙的输运和截留影响较大，考虑波流耦合作用时，模拟的悬沙浓度较纯流工况呈增大趋势。预期研究成果有助于加深对盐沼植物与波浪、潮流、泥沙之间相互作用和耦合效应的认知，对盐沼植物的海滩防护等方面具有重要的理论和科学价值。