Numerical Study Of Geomorphic Evolution And Channel Improvement In The North Branch Of The Yangtze River

Estuary is the combination of the rivers and oceans where sea water was diluted by the land runoff. As the intersection area of the river power and marine dynamic, Estuary has a unique dynamic, deposition properties. The Yangtze Delta is sector on the coast which starts from Xiulujing down to the sand bar outside in the formation of three branching pattern of the four into the sea. The North Branch of Yangtze Delta was the main channel of the Yangtze River into the ocean18th century ago, then it shrink gradually. The reclamation and shrink narrow engineering and other factors lead to a sharp decline of the runoff in the North Branch, the split ratio has only2%nowadays, and the riverbed is silted up on the whole maintained. Researching the North Branch of water dynamic and sediment transport conditions and predicting the evolutionary trend of the riverbed will be helpful in making the comprehensive treatment of the estuary.Delft3D model used in this article to simulate the dynamic and sediment transport of the North Branch. The data of the water level, velocity,flow and suspended sediment concentration collected on2011February-March are used to authenticate the model. On this basis, the sensitivity analysis is used to obtain the reasonable model parameters, and then establish a long-cycle model of morphological evolution of the North Branch. Meanwhile, according to the status quo of the human activity in the North Branch, Remediation options are provided, and use the model to simulate the evolution of the riverbed of short cycles and long cycle scale under the condition of the remediation options.By the sensitivity analysis with Delft3D, the bathymetry, dimension and temperature and salinity of the flow were specified and tested. The result shows that the flow field is sensitive to the bathymetry. The influence of the dimension and the temperature and salinity is not obvious. Therefore, the reliability of topography is crucial for the sediment transport and morphological evolution modeling.Considering the human activities in the study area, four options have been designed for the Delft3D simulation:switching mode of crucial gate (closing during flood but opening during ebb), keeping the existing river bank and digging diversion channel in different regions. The modeling results show as follows:Sluices and canals have significant impacts on the flow field, sediment transport and geomorphic evolution in the north branch the Yangtze Delta. The sluices programs2and programs3and canals program5can be effective to ensure that salt water cannot be traced back along the river channel into the upper and middle reaches; program3to ensure a wider fairways; program5will enable the river’s tidal range smaller to avoid the riparian dangerous situation. Program6to expand the use of the water in north branch of the supply for production and living, Meanwhile it can also be use to improve the convenience of transportation in northern Jiangsu.