曲流串沟型江心洲形成机制与演化探讨

曲流串沟型江心洲是现代河流水利学研究关注的重要河流要素，不同于曲流河点坝和辫状河心滩，但在油气储层沉积学研究中鲜有关注。选取现代松花江典型河段，开展基于水动力学的沉积数值模拟，恢复曲流串沟型江心洲的演化过程，建立了曲流串沟型江心洲演化模式。研究结果表明:1）洪水期曲流河发生漫滩冲刷，串沟发育扩张，截弯取直，形成分汊河道及江心洲地貌；2）分汊偏移角、相对梯度优势可用于预测短期汊道存在的稳定性；3）串沟型江心洲形成于曲流点坝残余沉积之上，发育洲头侵蚀、洲尾加积、翼部双侧积，但垂向加积主要发育在顶部，不构成沉积主体结构。通过上述研究建立了曲流江心洲沉积模式，揭示了曲流河江心洲内部结构及分汊河道水动力特征，对现代河流治理和地下河流沉积储层刻画有指导意义。

Mechanism and Evolution of Ditch-scouring to Form Mid-channel Bar in Meandering River: A case study in modern Songhuajiang River

Studies of ditch-scouring to form mid-channel bars in meandering rivers have rarely been reported， although it is an important element in modern river hydrodynamics research. This mechanism differs from braided bars and point bars. In this study， a typical section of the Songhua River was selected for hydrodynamics-based numerical simulation modeling of sediment deposition to reveal the evolutionary process of ditch-scouring forming a mid-channel bar. It was concluded that （1） the floodplain of a meandering river is scoured and the scoured ditch is developed and expanded； the meandering section is cut， forming a branching channel and a mid-channel bar develops during flood periods； （2） the bifurcation offset angle and relative gradient advantage were used to predict the stability of short-term bifurcation； （3） in the ditch-scouring bar formed on the remaining meandering point bar， head-erosion， bar tail accretion， and bilateral accretion all develop. Vertical accretion is commonly developed at the bar top， and is not the major reservoir architecture in the main body. In this study， a model of a sedimentary ditch-scouring mid-channel bar was established， and the architecture and hydrodynamic characteristics of the bar were revealed. This has guiding significance for modern river regulation and the characterization of subsurface river sedimentary reservoirs.