| In order to improve the economic and social development of the river area,the Yellow River navigation needs to be further improved,in which the sandy branching type river section is the important and difficult point in the Yellow River channel improvement project.The characteristics of the Yellow River sandy branching type river section are affected by the branching form and its own water and sand conditions are complex,the riverbed Quality is mostly coarse sand,the river channel is easy to wash and easy to silt,frequent changes,the river bank is not very stable,the river bank side beach will also be scoured and deformed during the flood season.Therefore,by studying the obstructive characteristics of the sandy branching river in the Yellow River,and then carrying out pilot studies on channel improvement projects,we propose a solution to solve the obstructive problems and improve the navigation conditions of the channel,in order to promote the economic and social development of the areas along the river,and also to provide a reference for similar channel improvement projects in the future.In this study,based on the channel improvement project of about 90 km from Zhonghui Shapotou water conservancy hub to Zhongning County Baima Township Sandaohu Village,the one-dimensional mathematical model of the long river section was nested with the two-dimensional mathematical model of the beach dangerous river section and combined with the physical model test to analyze the navigable water flow conditions of two key beach sections,Zaolinwan to Shentan section and Matan to Yingpantan section,as well as the study of improvement measures to propose improvement measures to meet the scale of Class V channel and navigable water flow conditions,in order to achieve the purpose of smooth navigation.The main results were as follows:(1)Through the analysis of the prototype observation and the topographic map data of the past years,the Yellow River Zhongwei section was a sandy branching type shallow riverbed,influenced by the shoreline management project,the shoreline boundary conditions did not change obviously,the continental beach was developed,and gradually formed a multi-channel wide and shallow channel pattern;along with the construction of upstream reservoirs,the upstream incoming sand gradually decreased,and the riverbed was scoured and undercut,especially the concave bank side of the river channel was easy to form a significant deep channel by the mainstream top wash.In the dry period,the river channel was narrow and shallow,and was often obstructed by insufficient water depth;in the middle flood period,the river was obstructed by steep and rapid water,high waves and turbulent flow patterns.(2)Two typical sandy branching shallow riverbeds,Zao Lin Wan to Shen Tan and Matan to Ying Pan Tan,were selected for the pilot study of channel remediation,the former using physical model tests and the latter using two-dimensional numerical simulation tests.The water flow characteristics under natural conditions were analyzed,and it was found that the water flow was concentrated in the local area,the flow velocity is large,and there were bad flow conditions such as plunge water and scissor water in some sections,which made the navigation of ships difficult and need to be improved.Taking into account the characteristics of the shallow shoals,the causes of shoal hazards,the channel regulation standards and the natural flow conditions of the channel,the regulation principles of "controlling the river potential,stabilizing the shoals,selecting the channel,low water regulation,and taking into account" were proposed,and the regulation parameters of the studied river section were determined by calculation.(3)By analyzing the water flow characteristics of Zao Lin Wan to Shen Tan section and Matan to Ying Pan Tan section under natural conditions,it found that the major difficulty of typical branching type sandy shallow river section was the selection of navigable branching channels.In the section from Zao Lin Wan to Shentan,the 1# and2# beaches of Zhongwei Yellow River Bridge were seriously obstructing navigation,and the water flow was divided into left and right branches in the middle and dry periods,with the left branch being the main branch,but the water depth was large,the water flow was rapid,the specific drop was large,the flow pattern wad disordered,and the navigable water condition was poor,while the flow velocity of the right branch was small and the water depth was insufficient.In the section from Matan to Yingpan Tan,the navigation was seriously hindered by the Tian Tan,and under the condition of medium dry water,the diversion ratio of the left branch was more than 80%,and the same problem exists in the left branch with steep and rapid water flow,and the right branch with small flow speed and insufficient water depth.By comparing and analyzing the effect of different remediation schemes in each dangerous beach section,it was proposed that the selection of navigable branching channels in the sandy branching shallow beach section should follow the direction of riverbed evolution and be arranged on the main branching side of the river,which was conducive to maintaining the longterm stability of the channel and reducing the channel maintenance cost.(4)For the sandy riverbed,the remediation idea of "cutting the beach mainly and filling the channel as a supplement" was proposed.By comparing and analyzing the water flow conditions and dredging range of different remediation programs,the recommended channel and remediation program was proposed for two serious obstruction beaches.The left branch of 2# beach was selected as the navigable branch,the left branch of 1# beach was dredged and cut,the right branch was improved,and the local filling and dredging are combined with the form of compound section to improve the bad flow pattern,the water surface was smooth and the navigation depth was sufficient after the remediation,which satisfies the scale of Class V channel and the requirements of navigable water flow conditions.Tiantan section of the channel layout selected left branch for the navigable branch,while the overall channel navigation depth was not enough to take dredging measures,the overall flow pattern in the channel after remediation was good to meet the requirements of navigability. |
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