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根据长江口南汇近岸水域17个站的水文泥沙同步观测资料,阐述了该水域近底层泥沙的流速、悬沙浓度的分布和变化。经无量纲潮流动力值的计算表明,研究区存在一个包络南汇边滩先向东南继而向南延伸的舌状高能量区,与高悬沙浓度分布区相一致。通过对悬沙运动和涨、落潮周期流向的分析,揭示了长江口向杭州湾底层泥沙输移的规律,其底层泥沙输移主要集中在低潮位时段,输移时间约占潮周期的36%,其中以南汇边滩向杭州湾输移的时间为最长,大、小潮都在5h以上,与其相关联,在芦潮港水域下层存在着一股东西向的高悬沙浓度的水体。据盐度、潮流、悬沙浓度等要素,并结合絮凝沉降分析得出,南汇边滩的沉积强度是潮滩>潮下带>深水区;边滩舌尖前缘水域的泥沙沉积时间与水体出现向东偏南或向西流的时间一致,这可视为近年来南汇水下沙嘴向东偏南伸展的原因之一。
According to the synchronous observation data of hydrological and sediment at 17 stations in the offshore area of Nanhui, Changjiang Estuary, the distribution and variation of the velocity and suspended sediment concentration of sediment near the bottom of the water area are expounded. The calculation of the non-dimensional tidal current dynamic value shows that there is a tongue-like high-energy region enveloping the Nanhui side of the beach to the southeast and then to the south, consistent with the distribution of suspended sediment concentration. Through the analysis of the suspended sediment movement and the cycle of ebb and flow, the law of sediment transport from the Yangtze Estuary to the bottom of Hangzhou Bay was revealed. The bottom sediment transport mainly concentrated in the period of low tide, and the transport time was about the tide period 36%. Among them, the time of migration to the Hangzhou Bay by Nanhui beach was the longest, and the large and small tides were all over 5 hours. Associated with it, there was an east-west suspended sediment concentration in the lower part of Luchaogang. According to the factors of salinity, tidal current and suspended sediment concentration, the sedimentation intensity of Nanhui side beach is tidal flat> subtidal zone> deep water zone. Sediment deposition time of the front edge of the tongue beach is close to that of the water body It appears that the timing of the southward or eastward flow to the east is consistent, which can be considered as one of the reasons why the southward divergence sand spout extends eastward and southward in recent years.