【作者】 曹颖；

【导师】 孙志林； 林炳尧；

【作者基本信息】 浙江大学 ， 港口海岸及近海工程， 2010， 硕士

【摘要】 河口拦门沙处在河流入海的咽喉部位,是海陆动力相向作用的产物,也是水沙运动、河床变化最为剧烈的地带。河口区是人类社会经济更为发达的区域,因而历来倍受关注。因不同河口山潮水势力对比的不同,河口拦门沙以堆积部位在河口口门内或口门外而划分为沙坎和拦门沙。本文以钱塘江河口多年积累的实测资料为基础分析了钱塘江沙坎年内、年际的变化规律及其与各自然要素之间的相关关系,以期初步建立钱塘江河口河床自动调整体系及沙坎平衡态的概念。钱塘江河口沙坎的组成物质是细颗粒泥沙,沙坎顶部在七堡～盐官之间,沙坎高程及位置的变化是河口河床自动调整体系中重要的一环,用以保持河口径、潮流的平衡。沙坎年内呈现明显的洪冲潮淤;年际间则丰冲枯淤,连续丰水年沙坎顶点位置偏靠上游,沙坎高程相对较低;连续枯水年沙坎位置下移,沙坎高程淤积抬升。文中以深泓沙坎和平均沙坎两个指标进行分析,经比较,平均取值随机性相对较小,更能突显深槽地形的趋势性和规律性。沙坎顶点部位则因河口段多个弯道深槽的存在,其位置的变化是不连续的,因而与径、潮流等动力因子之间的相关性较差。本文研究了沙坎对钱塘江河口大规模人类活动的响应,新安江建库后,沙坎顶点刷低下移,变幅有所减小。河口治江围涂对沙坎的影响是冲刷下移,变幅增大。基于一维动床模型,模拟了不同径流条件下河口冲淤量的变化,进而建立了河口沙坎与径流和冲淤量之间的相关关系。钱塘江河口不同的水文周期对应于不同的沙坎平衡态。大规模的人类活动会破坏原有的平衡,并形成新的平衡。引入钱塘江河口断面山潮水系数M,分析径流～沙坎～潮汐关系,发现控制沙坎高程的主要动力是上游径流,潮流仅仅是维持河口沙坎平衡的一个因素,相对于径流而言明显处于次要地位。沙坎高程受径流影响发生改变,沙坎的变化造成低潮位随之发生改变,从而改变进潮量,影响河口的径潮流动力比。更多还原

【Abstract】 Mouth bar is a production of runoff and tidal dynamics, it is located at the throat on the way from river to sea. The change of runoff and tidal dynamics and sediment is quite big in estuary area. At the same time, human society and economy are more developed in this area, thus estuary always has been concerned. Mouth bar located at inside or outside of the river mouth induced by the difference of the runoff/tide ratio of the estuary. This article analyzed the annual transformation and long term evolution of the Qiantang mouth bar based on long time data in the estuary, and built the relationship between natural factor and the mouth bar elevation, try to set up a self-adjustment system of the estuary riverbed and the balance of the mouth bar.Qiantang mouth bar is mainly combined with fine-grained sand. The vertex of the mouth bar located from Qibao to Yanguan, The evolution of mouth bar was an important factor to keep the balance between runoff and tide in the self-adjustment system of the estuary riverbed. Qiantang mouth bar was eroded during flood season and deposited during dry season in a year, and was eroded during flood years and deposited during dry years in a long period. The vertex of the mouth bar was promoted to the downstream in continuous dry years, and back upstream in continuous flood years. The channl elevation and the average elevation of the mouth bar were compared. The result shows that the average elevation can better express the regularity of the riverbed evolution. The location of the mouth bar was discontinuous because of the the existing of several bend in the estuary, thus it won’t have a good relationship with the runoff/tide dynamics.The response of the mouth bar on human impact was studied. After the Building of the Xin’anjiang Reservoir, the mouth bar was eroded and the transformation decreased. After the reclaiming in the estuary, the mouth bar was eroded and the transformation increased. A 1D numerical model was built to analyze the quantitative relationship between the runoff, the erosion/deposition evolution and the mouth bar. Different hydrodynamics corresponding to certain balance of the mouth bar. Human activities will destroy the original balance, and form a new balance. M was defined as a coefficient of the runoff/tide ratio at the cross section in the estuary. The vertex elevation of the mouth bar was mainly controlled by the runoff according to the analysis of the relationship between runoff and tidal dynamics and the mouth bar. The tidal current is just a factor to keep the balance of the mouth bar. The elevation of the mouth bar changed with the runoff, and it caused the change of the low tide level, then the tidal prism changed, the runoff/tide ratio of the estuary changed at the end.更多还原