山东半岛海湾对泥沙的捕获机制--以威海湾为例

The Yellow River is the main sediment source that affects the sedimentary pattern of the eastern margin of China, but there is still a lot of controversy on the redistribution flux after the Yellow River sedimentation. Shandong Peninsula coastal area is the main channel of sediment transportation of the Yellow River to the Yellow Sea. There are many bays in the coastal area in Shandong Peninsula, a total area of the Gulf (excluding Laizhou Bay) is about 2500km2. Due to the reduction of precipitation and the change of the underlying surface caused by human activities, the flow of short-source rivers is rapidly declining or even drying in the Gulf and the outer sediment is the main source of sediments in present. The mechanism for the trapping of sediment in the Shandong Peninsula Bay is still rarely reported. The project plans to select the study of the hydrological and sediment observation at the bay mouth during the winter and summer events and the extreme events (storms and floods), and to find out the process of catching the sediment under normal sea conditions and extreme events. Combining with the three-dimensional mathematical model of Mike3, this paper simulates the effects and contributions of the dynamic factors and human factors on the capture of sediment in the bay, reveals the key sedimentary dynamic processes and mechanisms of the Gulf catching sediment. The research results will enrich the scientific connotation of "source - sink" about the transportation process of sediment of the large rivers.

黄河是影响中国东部边缘海沉积格局的主要物质来源，但在黄河泥沙入海后的再分配通量问题上至今仍有很大争论。山东半岛沿岸海域是黄河入海泥沙向黄海输送的主要通道，近岸分布有众多海湾，海湾（不包括莱州湾）总面积约2500km2。受降水减少和人类活动导致的下垫面变化影响，海湾内入海的短源河流径流量急剧下降甚至断流，湾外泥沙成为目前海湾沉积物的主要来源。关于山东半岛海湾捕获泥沙的机制至今还鲜有报道。本项目拟选择山东半岛威海湾为研究对象，冬夏季和极端事件（大风浪和洪水）期间分别在海湾口门进行水文泥沙观测取样，查明正常海况和极端事件下海湾捕获泥沙的过程和通量；结合Mike3三维数学模型，模拟探讨不同时空尺度的动力因素和人为因素对海湾捕获泥沙的作用和贡献，揭示海湾捕获泥沙的关键沉积动力过程和机制，探讨海湾在黄河入海泥沙“源-汇”过程中扮演的“角色”。研究成果将丰富发展大型河流入海泥沙“源-汇”过程的科学内涵。

黄河是影响中国东部边缘海沉积格局的主要物质来源，但在黄河泥沙入海后的再分配通量问题上至今仍有很大争论。山东半岛沿岸海域是黄河入海泥沙向黄海输送的主要通道，近岸分布有众多海湾，受降水减少和人类活动导致的下垫面变化影响，海湾内入海的短源河流径流量急剧下降甚至断流，湾外泥沙成为目前海湾沉积物的主要来源。关于山东半岛海湾捕获泥沙的机制至今还鲜有报道。本项目采用座底三脚架底边界层观测、多站位水文泥沙同步观测、钻探和表层沉积物取样测试分析及数值模拟等方法开展了研究。主要内容包括威海湾水文泥沙对夏季台风和冬季大风过程的响应；海湾口门近底层悬浮泥沙浓度潮周期和天气尺度变化规律及动力机制；威海湾内外水沙交换过程和机制；海湾泥沙来源和演化趋势。研究结果表明：（1）夏季水体层化显著，湾内存在明显上升流现象；表层悬浮体浓度一般小于5mg/L；底层悬浮体浓度明显升高。冬季研究区水体混合强烈，风浪天气下悬沙浓度约是平静天气下的3倍。（2）夏季，北侧和南侧口门沉积物再悬浮分别受控于潮流和波浪，近底层平均单宽泥沙通量0.773 g/m2/s和-0.130 g/mh2/s。（3）冬季，潮流和波浪共同控制北侧口门处再悬浮过程；南侧口门沉积物再悬浮则主要受控于波浪，北侧和南侧口门站位近底层平均单宽泥沙通量分别为0.657 g/m2/s和1.515 g/m2/s。（4）威海湾北侧口门沉积物输运取决于余流，由湾内指向湾外；南侧口门沉积物输运受控于潮泵效应，泥沙净输运方向指向湾内。（5）强北风期间，北侧口门余流减弱，南侧口门余流增强；北风减弱或转向后，北侧口门处沉积物输运仍受控于余流，南侧则由潮泵效应占主导。（6）威海湾的泥沙输运存在类似“夏储冬输”的特征，“捕获”过程不仅发生在夏季，也存在于冬季北风间歇期。成山头附近再悬浮的沉积物是湾内悬沙的主要来源，而水平浓度梯度引起的平流输运是泥沙捕获的重要机制。研究成果对于海湾泥沙来源和输运机制研究具有借鉴意义，对海湾合理开发利用和可持续发展具有指导意义。