Fluvial Processes And Navigation Conditions Of Lishui-Songzi Rivers In The Hunan Reach

The Lishui-Songzi River in the south of Hunan refers to the river network formed by the Lishui River entering the lake and the Songzi River System(inside Hunan).It is an important navigable water system connecting the Yangtze River,Lishui,and West Dongting Lake.With the development of the Yangtze River and the development of water transportation,it is imperative to improve the navigation conditions of the Lishui-Songzi River in the southern part of Hunan.Due to the double influence of natural conditions and human activities,in the context of the operation of the Three Gorges Reservoir,the changes in water and sediment from the Yangtze River have changed the hydrological conditions and river bed evolution process of the Lishui-Songzi River in the Hunan section to a certain extent.The navigation conditions of the southern section of the Songzi River in Hunan have also undergone new changes.To improve the level of the channel of the water system and improve the navigation conditions,it is necessary to understand the changes in hydrological data and terrain.Therefore,it is of great significance to sort out the water and sediment changes,flood encounters and channel evolution of the Songzi River after the Three Gorges Reservoir is impounded,and to study its evolution law,which is of great significance to the promotion of the Lishui-Songzi River Hunan Channel construction project and the improvement of the channel management plan.Using numerical simulation methods to study the hydrodynamic conditions of the Lishui-Songzi River Hunan Channel,analyze the effects of the channel construction,and draw the following main conclusions:(1)The hydrological conditions in the southern section of Lishui-Songzi River are affected by the double layer of the upper reaches of Lishui and the Yangtze River.Affected by the decrease in upstream water flow,the average flow during the flood season in 2003-2013 decreased by 18.5%,and the average flow during the mid-water period decreased by 42.1%During the dry season,the Guanyan River(the west branch of the Songzi River)was affected by Lishui topping.The average flow increased from-24.9 m3/s to-13.43 m3/s.Lishui was dispatched by the upstream Yanzhou Reservoir,and the flow increased by 8%.(2)From 2002 to 2011,the average annual erosion volume of the Songzi estuary was 170.7×104m3,and the riverbed erosion was concentrated on the left bank.The average annual erosion depth from 2002 to 2006 was 0.92m,and the average annual erosion depth from 2006 to 2011 was 0.15m.The intensity decreased year by year.The performance of all river sections is in the state of erosion,with an average annual erosion volume of 814.8 × 104m3 from 2003 to 2011,and the deceleration rates in flood,intermediate and dry seasons are 374.3× 104m3/a,351.6×104m3/a and 137.7 × 104m3/a,respectively.In 2009-2011,the Songzi River as a whole exhibited siltation of 219 ×104m3,and part of the tributary of the southern section of the Lishui-Songzi River in Hunan.From 2005 to 2011,the Guan'an River(the west branch of the Songzi River)and the Autonomous Bureau River(the middle branch of the Songzi River))The annual average siltation volume is 53.1×104m3 and 33.8×104m3,respectively.(3)A two-dimensional hydrodynamic mathematical model is used to simulate changes in flow velocity,water level,and flow pattern before and after remediation under low-water and mid-water periods.On this basis,the impact of the remediation project on the river section was calculated and analyzed.During the dry season,Wangjiazhou and Zhang Jiutai re-planned the channel to increase the bending radius,and the water depth of Pei Huangzhou,Maojiadu,and Qinglongjiao channels reached 2.4m.It has reached the level ? navigation standard.During the mid-water period,the average flow velocity at the Zhangjiutai bend was reduced from 1.5m/s to 1.05m/s,reducing the risk of the ship spending to enter the bend.The optimization scheme is aimed at the problem of slight siltation of the Guan'an River section and easy clogging of the river section.Actual engineering excavation may be considered to increase the depth of the Guanyuan section by 1m.