长江河口南汇嘴潮滩圈围工程前后水沙运动和冲淤演变研究

Research on the movement of water and suspended sediment and sedimentation in Nanhui spit of the Yangtze Estuary before and after the construction of reclamation projects on the tidal flat

南汇嘴潮滩地处长江河口拦门沙地带，是上海陆沿海岸滩淤涨速度最快的滩地，也是促淤圈围土地最频繁的地带。在1994—2003年期间实施了大规模低滩筑堤促淤圈围工程，圈围土地约15000hm。。由此，也必将对潮滩水沙过程和冲淤变化产生影响。工程实施期间，促淤坝田淤积速率明显增大，最大淤积区年淤积厚度在1．0m以上，一般淤积区年淤积厚度在0．3～0．8m，而促淤堤外侧浅滩受坝田外泄清水影响，滩面发生不规则的冲刷，一般冲刷深度0．3m左右，最大冲刷区达到1．0m左右，在水深大于3m的浅滩区仍以淤涨为主；圈围工程完成后，由于圈围工程堤线保持了原有格局，对水流流势影响较小，在流域来沙量出现锐减，而河口区再浮悬泥沙和海域来沙量有所增大的环境下，南汇嘴潮滩水体含沙量仍较高，大潮汛实测潮周期平均含沙量为1．67kg／m^3左右，小潮汛为0．92kg／m^3左右，而且浅滩水流输沙方式有利于促使潮滩淤涨发育过程。

Located on the mouth bar of the Yangtze River, Nanhui spit was of the fastest accreted rate in the tidal flats of Shanghai. The actions of reclamation and enclosure in Nanhui spit were also the most frequently occurred in Shanghai. Filled and accreted project in the low tidal flat of Nanhui spit had been carried out to a great degree during 1994 -2003, which created lands of 15, 000 hm^2 and was the largest action of reclamations in history. Therefore, the movement of water and suspended sediment and changes of sedimentation in Nanhui spit can be definitely influenced by these actions. The accreted rate of the filled field was evidently increased during the period of silted engineering, where the silted area has been accreted 0.3 - 0.8 m in thickness every year and the biggest was over 1 m. However, the seaward shoal of the accreted groyne was affected by the drained clear water from the silted field, which made the irregular erosion of the beachface. The shoal was usually eroded about 0. 3 m in thickness and the biggest was about 1 m. The accreted areas of the shoal occurred mainly in the area with the flow depth more than 3 m. Meanwhile, the inhered movement patterns of water and suspended sediment were remained after the filled and enclosed projects were finished, which had minor influence on the hydrological dynamics in Nanhui spit. Thus, although the quantity of water and sediment of the Yangtze Estuary from drainage basin were rapidly decreased, the concentration of suspended sediment in water of Nanhui spit area, at which the turbidity maximum is located, was maintained relatively high value. Presently, the average concentration of suspended sediment of a tidal cycle in Nanhui spit area was about 1.67kg/m^3 during the spring tide and 0.92kg/m^3 during the neap tide, respectively. Thereafter, the movement of water and suspended sediment in the shoal had been restored to the previous state without reclamation projects, which can oblige the change of tidal fiat into new growth processes of fast accretion.