Research On The Characteristics Of The Channel And The Navigable Conditions In The Typical Rapids During The Dry Season From Chaotianmen To Fuling

With the increasing development of shipping,the number of navigable ships is increasing year by year,and the deadweight tonnage of ships is rising,which requires stable navigation conditions in the Yangtze River channel.During the dry season,some rapids of the channel from Chaotianmen to Fuling block navigation,and rapids of Guangyangba,Dajiantan and Wangjiatan are shallow and dangerous,which makes ships are susceptible to accidents such as running aground and ship broken during navigation.Researching on the flow change,trend development and ship navigation flow in the dry season of the Yangtze River channel,is to provide referential data for the flow forecast of the Yangtze River channel,improve the accuracy of the flow forecast,alleviate the unstable navigation conditions of the channel,and help the ships navigate safely in the dry season.This thesis mainly carries out historical data investigation,obtains historical low water level information,and estimates the corresponding low-level flow.The hydrological predict methods are used to analyze the daily runoff series data of Cuntan station from January to April in 1960 to 2020,and then study the changes in the dry season of the Yangtze River and speculate the trend.A 2D flow mathematical model is established to simulate the flow of Chaotianmen-to-fuling channel in the Yangtze River under historical low water conditions.Typical rapids are selected,and changes of channel elements of which are analyzed.With the daily runoff series data of Cuntan station from January to April in 1960 to 2020,flow in the channel is simulated by the mathematical model.Representative ships are selected to study and analyze the self navigation ability in rapids.Finally the following research results are obtained:(1)Through the investigation of historical dry-season water literature,the thesis found that the Baiheliang dry-season water inscription contains relevant records for more than 1,200 years since the Tang Dynasty.The water level record range is 137.41m-138.55 m,and the corresponding low water flow range is estimated to be 2217.91m3/s-2620m3/s.Combining the historical estimated low water flow with the runoff series from January to April in 1960 to 2020,a Pearson type III curve is drawn,and the low water flow with a return period of 1000 years is about 2200 m3/s.With hydrologic analytical methods,the trend and periodic changes of the daily runoff data of Cuntan Hydrology Station from January to April in 1960 to 2020 is analyzed.The results show that the runoff of the Yangtze River channel is on the rise from January to April,the first main period of the series is 39 a,and the second main period is 20 a.(2)A 2D flow mathematical model is established,and the Chaotianmen-Fuling channel is selected as the calculation area to simulate the changes of water level,water depth,flow velocity and gradient of the channel under historical low water conditions.The error of the simulated water level verification does not exceed 0.1m,and the error of the flow velocity is not beyond 10%,indicating that the model can simulate the changes of water flow.According to the simulation results,guangyangba,dajiantan,luoqi,Wangjiatan and niushiqi are selected as typical rapids to analyze the changes of channel elements under historical low water conditions,and variation range of which is obtained.(3)Combined with the measured hydrological flow data of Cuntan station from January to April in 2010 to 2016,the channel flow simulation is carried out.Based on simulation results,2000 t,3000t and 5000 t freight ships are selected as representative ships to analyze the self-propulsion ability in each rapid from January to April,and finally the self-propulsion flow range and adverse flow range are obtained.