【作者】 段凌云；

【导师】 王张华；

【作者基本信息】 华东师范大学 ， 自然地理学， 2006， 硕士

【摘要】 长江入海泥沙约30％向南输移影响杭州湾和浙闽沿海，并形成巨大的浙闽泥质条带，这种输移主要通过枯季的再悬浮作用实现。另外长江口外存在多级锋面，对长江泥沙的扩散输移有重要作用。本文将利用春季在长江口外进行的水文泥沙调查，确定盐度锋的分布，揭示锋面不规则高速流现象，分析其产生机制，计算锋面泥沙输移通量，探讨不规则高速流对长江泥沙向南输移的意义。 本论文主要依据2004年5月在长江口外进行的水文泥沙调查。调查区域位于121°57.5′E~122°30′E，30°50′N-31°42′N共9个站位，分三条船同步观测，每个站位连续观测13-25小时。利用ADP、直读式海流计观测流速流向，利用OBS观测温度、盐度、浊度，同时采集水样，带回实验室分析含沙量和悬沙粒径。 根据温度、盐度和含沙量的分布，把调查区域分为3个区：Ⅰ)高度混合区位于南支口门外，10m等深线以内(S3、M3、S2和M2)，高温，低盐，高含沙量，且混合较均匀。Ⅱ)表层冲淡水、下层高盐水区位于南支口外，20m等深线附近(S1和M1)，低温，高盐，含沙量较低，水深约4m处出现盐跃层和温跃层，垂向盐度梯度最大达2.9／m。Ⅲ)苏北沿岸流水主导区位于启东一线的区域(N2和N3)，低温，高盐，含沙量较低。另外从Ⅰ区的S2、M2到Ⅱ区S1、M1之间的表层盐度梯度达0.4／km～0.6／km。因此可以确定，S1和M1两站位于盐度锋区。 调查显示，Ⅱ区(S1和M1)在高高潮涨潮初期都出现了不规则的高流速现象，流速分别达到了160cm／s，200cm／s，高流速主要发生在表层6m水深以上；这种不规则流和涨急相继发生，使高流速流持续时间长达约7小时。据S1站观测资料，发现涨潮初期高流速时段，该站表层5m水深以上由低盐高温冲淡水主导，而底层由29‰的高盐水控制。我们推测这种不规则的高流速是锋面过程所致。 调查期间还发现，M2在低低潮落急时流速高达220cm／s，流向东南；S2在两个潮周期内的涨落急流速均高，尤其落急流速(168cm／s和150cm／s)明显高于涨急(136cm／s和110cm／s)，推测为径流或沿岸流和落潮流的叠加所致。 对各站13～25小时泥沙输移通量的计算显示，本区S2站净输沙量最大，达0.37kg／m~2／s，方向东南；其次为S3，向西北净输沙0.28kg／m~2／s。其次，在高流速的作用下，S2、M2、S1三站的瞬时输沙量都表现出东南向异常高值，分别达到2.28kg／m~2／s，1.36kg／m~2／s，1.06kg／m~2／s。第三，盐度锋区的S1站25小时的净输沙量值较低，为0.17kg／m~2／s，方向东南，但高高潮涨潮初期瞬时输沙量最大达1.06kg／m~2／s。上述结果反映了高流速潮流对本区海底泥沙强烈的再悬浮以及向东更多还原

【Abstract】 About 30% Changj iang suspended sediments are dispersed southward to the Hangzhou bay and the coast of Zhejiang and Fujian to form the mud wedge extending from the Yangtze River mouth southward off the Zhejiang and Fujian coasts into the Taiwan Strait. The resuspension in the winter plays a critical role on this kind of transportation. Several salinity fronts occur off the Changj iang estuary, which significantly influences the suspended sediment dispersal. The present study carried out a sea investigation off the Changj iang estuary during the spring season. The objectives of this study includes: 1) to determine the location of the salinity fronts; 2) to reveal the occurrence and formation mechanism of the high-speed current at the salinity front; 3) to compute the sediment flux at the frontal area; and 4) to discuss the implication of the high-speed current on the suspended sediment transportation.On 8-14 May 2004, a hydrologic and sediment logical investigation was conducted off the Changing river mouth (121°57.5’E ~122°30’E, 30°50’N~31°42’N). Nine sites were set for continuous observation of 13-25 hours. During the investigation, 3 boats observed in phase according to the tidal fluctuation. At each site, temperature, salinity, and turbidity were measured by OBS; current speed and direction were examined by ADP and direct-reading current meter. Besides, water samples were taken at the surficial, middle and bottom layers. The water samples were then tested for suspended sediment concentration (SSC) and grain size.According to the distribution of the temperature, salinity and the sediment concentration, the studied area was divided into 3 regions: I) well-mixed estuarine water dominates in an area shallower than 10m (sites S3, M3, S2 and M2). This area is characterized by high temperature and SSC, low salinity; II) diluted water at the surface water column versus salt water at the lower water column within the area of water depth from 10 m to 20 m (sites S1 and M1). The water of this area is featured by low temperature and SSC, high salinity. A halocline and thermocline occur at water depth of about 4 m with the highest salinity gradient reaching 2.9/m; III) Subei coastal current water (sites N2 and N3). The water of this area is characterized by low temperature and SSC, and high salinity. The salinity gradient reached 0.4~0.6/km on the sea surface between the region I (S2 and M2) and the region II (SI and Ml). Therefore, sites S1 and M1 are located in the frontal area.During the investigation, anomalous high-speed currents (160cm/s and 200cm/s) were found at the initial stage of the flooding of the higher high water. This high speed occurred generally at the upper water column shallower than 6 m and lasted for about 7 hours. Diluted water of lowest salinity and highest temperature dominated in the upper water column of site S1 at the initial stage of the flood tidal, whilst salt water of 29‰ occupied the lower water column. Therefore the anomalous high-speed current is suggested to be caused by the salinity front.High speed current also occurred at site M2, reaching 220 cm/s at the max. ebb tide of the lower low water, and directing southeasterly. Both max. ebb and max. flood were found of high speed at site S2. The speed of the max. ebb tide (168cm/s and更多还原