清水冲刷条件下长江中下游江心洲汊道重塑机制研究

Channel bar development is extremely prominent in the middle and lower Yangtze River due to the dual effect of water and sediment process and river bed morphology, whereas channel bar branch and its evolution would inevitably constrain river regime development and frequently trigger disaster issues on river flood control and navigation guarantee measures. As the construction of large and medium reservoirs in the upper and middle Yangtze River radically altered the original water and sediment process, the reconfiguration pattern of controlling channel bar under clear-water scouring in the lower reach has become a key problem to be solved. This project highlight the critical water and sediment condition of channel bar growth or recession and reconfiguration process and characteristics of induced disasters of various type channel bars under clear-water scouring aiming at the response to water and sediment regulation and disaster dynamics of channel bar branches in downstream from the Three Gorges Reservoir based on prototype observation, laboratory experiment and theoretical analysis. Investigating the evolution law of downstream channel bar branches and establishing the relationship between water-sediment distribution of branches and stable development of channel bars under clear-water scouring, morphological evolution mechanism of channel bar branches in downstream of the dam under clear-water scouring is thus revealed. This study will provide theoretical basis of researching the response to erosion and deposition of river bed morphology in braided reaches of the middle and lower Yangtze River and different subtypes and technical support to guide the floodplain-channel regulation, navigation guarantee, diversion works and embankment projects in downstream of the dam.

长江中下游河道受来水来沙与河床形态组成的双重作用，洲滩发育极为突出，而江心洲汊道及其演变过程必将制约着河势发展，并在防洪、航道等方面频繁引发灾害问题。长江上游修建运行的大中型水库从根本上改变了原有的来水来沙过程，下游河段控制性江心洲汊道在“清水”冲刷条件下的重塑规律已成为急需解决的关键问题。本课题以原型观测、室内试验及理论分析为基础，针对三峡水库下游河段江心洲汊道对水沙调控的响应与致灾动力，突出研究江心洲生长与消退水沙临界条件、不同类型江心洲“清水”冲刷下的重塑过程及其诱发灾害特征，以探明江心洲汊道段“清水”冲刷条件下的演变规律，建立“清水”冲刷条件下汊道段水沙分配与江心洲发育稳定关系，从而揭示“清水”冲刷条件下坝下游江心洲汊道形态演变机理。本研究将为长江中下游汊道段及其不同亚类的河床形态冲淤响应研究提供理论基础，为指导坝下游河段的滩槽治理、航道保障、引水工程、堤防工程的建设提供技术支撑。

本项目采用原型观测分析、遥感解译、室内试验、数值模拟及理论分析等综合技术手段，以三峡水库下游长江中下游江心洲汊道段为研究对象，开展了坝下游8个重点江心洲的遥感解译分析和5个典型江心洲汊道的形态演变分析，揭示了水沙变异条件下坝下游不同类型江心洲汊道形态演化特征和规律；开展了顺直分汊和弯曲分汊江心洲概化水槽试验，研究了不同流量、减沙系列、清水系列等条件下江心洲汊道水动力条件及河床冲淤变化，揭示了清水冲刷条件下坝下游江心洲汊道重塑过程和机制；选取长江下游大型江心洲汊道——黑沙洲为典型案例，结合原型资料分析和数值模拟，研究了汊道分汇流水流特性与汊道演变的响应关系；最后，总结分析了三峡水库蓄水以来长江中下游崩岸总体情势变化及乌龟洲、世业洲、太平洲等典型崩岸险情发生原因，初步提出了江心洲河段重塑影响下的水沙灾害发生规律与治理对策。项目研究成果有力支撑了长江中下游重点江心洲汊道段河势控制、航道整治及崩岸险情应急治理等工程，指导优化了典型河道治理方案，在保障防洪安全、河势稳定、航道畅通及岸滩利用等方面发挥了重要作用。