The influence of source composition and flow on the morphological change of meander river based on flume sedimentation simulation experiment
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摘要: 河流沉积广泛发育于自然界地层中,而曲流河沉积则是河流沉积的重要组成部分。由于曲流河发育过程中河道的频繁迁移,发育大量侧积体,导致点坝内部沙体叠置关系复杂,因此对曲流河演化过程的分析一直是沉积学研究重点,分析曲流河形态变化的控制因素对于地质历史时期的古气候演化、大陆风化强度等研究以及油气储层勘探开发均具有重要意义。前人学者观察现代河流沉积对产生曲流河的初始条件进行了总结,研究了不同黏土矿物含量、植被覆盖以及河床初始饱和度对曲流河发育的影响,但自然界中河流沉积发育周期过长,通过实地考察与解剖露头不能很好地观察河流动态沉积过程,记录过程易受环境因素干扰,同时缺乏定量数据支撑。本文通过水槽沉积模拟实验研究单因素条件下曲流河发育过程中河道迁移和坝体发育的影响,本次研究设置了不同粒度、流量和黏土矿物含量条件下的实验共三组,采用高精度3D激光扫描仪将数据转换成高程模型,用于定量化研究剖面结构与河床沉积变化。实验结果表明:(1)供源沙粒径直接影响曲流河弯曲度,在黏土含量保持不变且流量恒定的条件下,沙粒粒径越小,形成的曲流河弯曲度越大,不同粒度条件下河岸坍塌沙体结构存在明显差异;(2)流量影响曲流河发育时泥沙输移平衡和河岸所受水流冲击力,当泥沙输入速率和搬运速率处于动态平衡,河岸维持向外侧扩张侵蚀,河道向曲流河形态发育;(3)河岸添加黏土矿物提升河道堤岸抗渗透强度,在供源沙粒度和流量保持不变的条件下,黏土矿物含量越高,河道宽深比越低。Abstract: Fluvial deposit is widely developed in natural strata, and meandering river deposit is an important part of fluvial deposit. Due to the frequent channel migration during the development of meandering river and the development of a large number of lateral deposits, the superposition relationship of sand bodies inside the point dam is complicated, so the analysis of the evolution process of meandering river has been the focus of sedimentological research. The analysis of controlling factors of meansional river morphology is of great significance to the study of paleoclimate evolution, continental weathering intensity and the exploration and development of oil and gas reservoirs. Previous scholars summarized the initial conditions for the generation of a zigzagging river by observing modern river sediments, and studied the effects of different clay mineral content, vegetation cover and initial saturation of river bed on the development of a zigzagging river. However, the development period of river sediments in nature is too long, and the dynamic sedimentation process of river cannot be well observed through field investigation and dissected outcrop, and the recording process is susceptible to interference by environmental factors. And lack of quantitative data support. In this paper, the effects of channel migration and dam body development on meander river development under single factor conditions were studied through flume sedimentation simulation experiments. In this study, three sets of experiments under different particle size, flow and clay mineral content were set up, and high-precision 3D laser scanner was used to convert the data into an elevation model for quantitative study of profile structure and bed sediment changes. The experimental results show that: (1) the particle size of the source sand directly affects the curvature of the meander river. Under the condition of constant clay content and constant flow, the smaller the particle size of the sand, the greater the curvature of the meander river formed. There are obvious differences in the structure of bank collapse sand bodies under different particle size conditions; (2) When the discharge affects the sediment transport balance and the flow impact force on the riverbank during the development of meandering river, when the sediment input rate and transport rate are in dynamic equilibrium, the riverbank maintains outward expansion and erosion, and the channel develops into meandering river form; (3) The addition of clay minerals to river banks can improve the permeability resistance of river banks. Under the condition that the source sand grain size and flow rate remain unchanged, the higher the clay mineral content, the lower the width to depth ratio of river channels.
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