淮河洪泽湖入海（江）水沙变化对潮滩沉积地貌的影响

It is important material base for depositional physiognomy of tidal flat that sediment load into sea. The Huanghe river into Huanghai Sea by capturing Huaihe River in 1194, and Subei alluvial plain formation by huge amount of sediment, After the Huanghe River returned to Bohai Sea in 1855, sediment from river reduced, the effect of ocean dynamics enhanced, the tidal flat from siltation to erosion. The amount of water and sediment into Yangtze River is much more than into sea. Therefore, taking depositional physiognomy of tidal flat at estuary of abandoned delta of Huanghe River as example, this research analyzed characteristics of profile morphology and underwater topography based on remote sensing images and measurement data of water depth. And than, based on measured data of the runoff and sediment discharge, it is analyzed that the variation tendency of diversion ratios that water and sediment into Yangtze River and Huanghai Sea with by numerical modelling. Based on considerations of reducing sand into Yangtze River, increasing sand into Huanghai sea, meanwhile combining with the sediment sedimentation in Hongze lake, the maximum possible sediment flux into the sea is estimated in this research. Further, the influence of terrigenous materials increase is analyzed on depositional physiognomy of tidal flat by application of sedimentary dynamics and mathematical model. The purpose is to reveal whether it is possible to form a new Huaihe River delta, and the coastal erosion in the north of Jiangsu Province would be ended. These results should provide an important scientific reference for the exploitation and management of tidal flat resources, the protection of coastal zone and coastal environment and the construction of marine engineering.

入海泥沙是潮滩沉积地貌稳定的物质基础。黄河夺淮入海携带的巨量泥沙形成苏北冲积平原，黄河北归入渤海后，入海泥沙骤减，海岸由淤涨转为侵蚀。淮河洪泽湖水沙主要流入长江，入海泥沙数量很少。因此，本项目针对苏北废黄河三角洲需要大量入海泥沙改变海岸地貌侵蚀的现状，利用遥感影像、水深测量数据分析潮滩地貌剖面形态和水下地形特征，通过大量的实测资料和数值模拟分析淮河洪泽湖水沙进入长江和黄海的分流分沙的变化趋势。基于减少入江水沙，增加入海水沙的考虑，结合洪泽湖泥沙淤积量，估算最大可能的入海泥沙通量。应用沉积动力学与数学模型模拟陆源物质的增加对潮滩沉积地貌的影响。最终提出海岸沉积地貌由侵蚀改变为淤积的途径，形成新淮河三角洲，结束苏北海岸侵蚀的可能性。

入海泥沙是潮滩沉积地貌稳定的物质基础。通过布设固定监测断面，利用OBS-3A获得了浊度、盐度、水温等数据，利用ADCP获得了流速流向数据。通过野外实地调查，采集了岩芯沉积物，通过对水文监测站调研，获得了入海河流的流量、水位、含沙量、输沙率等历史数据。在此基础上，应用实验分析、空间分析、数值模拟等方法进行综合研究。从水沙变化趋势来看，除了年平均径流随时间变化呈缓慢下降趋势外，年平均输沙量、含沙量和输沙模数都表现为缓慢上升趋势。从水沙周期性规律来看，年平均径流量、年平均输沙量、含沙量与输沙模数等水文要素都表现为四年一个周期的变化特征。洪泽湖多年平均淤积327×104t，淤积率为50.1%，淮河干流来水来沙占洪泽湖总来水来沙的80％以上。沉积物以粉砂为主从低潮滩到高潮滩，随着潮滩逐渐淤高，从底部到表层表现为由粗变细的变化趋势，相应地沉积速率表现为下降趋势。根据地球化学元素的分布特征和富集系数，分析了物源指示意义，进一步利用物源定量识别的端元模型，估算了不同物质来源在岩芯沉积物不同层位的贡献率。沉积物来源的阶段性变化，在时间上与长江北支水动力的阶段性变化基本吻合。苏北废黄河三角洲经历了百余年的侵蚀演变过程，目前仍处在侵蚀演变中，水下斜坡的蚀退速率与海床的冲蚀深度均为南断面大。在10m水深处，底层存在较强的再悬浮和再沉积，存在向上和向下的流。在15—17m水深处，底层主要是向上的分量，只有上部存在向下分量，较深处可能较少发生沉积。