河流平面型态在干旱区的转化机理及临界条件研究-以塔里木河为例

Channel planform pattern (channel pattern) is one of a trans-discipline research topic and also a hot scientific question in both Fluvial Morphology and River Dynamics. Grasping mechanism of channel pattern transformation bears theoretic and realistic significance in understanding fluvial processes and guiding scientific training of rivers. Due to its great complexity, studies on this topic are still dominated with empirical analyses, lacking convincing theoretical support, and especially short of attention on dryland rivers which mostly belong to non-equilibrium system. With the aim of examining the suitability of equilibrium theory for alluvial rivers which developed over the last more than 10 years on non-equilibrium river in arid regions, with a case study of Tarim River which located in a hyper-arid region in Northwest China, and combing field observation and theoretic analysis, this research will investigate the dynamic relations between channel pattern and flow-sediment processes, riparian vegetation and valley morphology to explore the causes of channel pattern development along Tarim River; then determine the key factors pushing channel pattern transformation and their threshold ranges, and set up a coupling model between channel pattern and the key factors to reveal the mechanism behind channel pattern transformation and determine the thredhold which inducing channel pattern transformation. Finally, the future fluvial processes and possible channel pattern transformation direction of the Tarim River under the impacts of large-scale human interventions will be also discussed. The potential outputs of this project will broaden the knowledge of dryland rivers on fluvial morphology feature, evolution causes and processes; meanwhile, it will be helpful to comprehensive management of the Tarim River and sustainable development of the Oasis in the basin.

河流平面型态（河型）是河流地貌学和河流动力学的一个交叉研究领域和热点问题，认识河型转化机理对于理解河流演变规律，指导河流科学治理有重要理论和现实意义。由于问题的复杂性，有关的认识仍以经验性为主，缺乏坚实可信的理论支撑，且以往对多处于输沙非平衡态的干旱区河流关注不够。以检验近年发展起来的冲积河流平衡理论在输沙非平衡态干旱区河流演变中的应用性为目的，本研究以地处干旱区的塔里木河为主要对象，实际观测和理论分析相结合，将阐明河道型态与水沙过程、滨河植被及河谷地貌等的动态响应关系，探求塔里木河河型发育成因；确定推动河型转化的关键因子及阈值范围，建立河型与关键因子的耦合模型，揭示河型转化机理，明晰触发河型转化的临界条件。最后，探讨人类活动影响下塔里木河地貌未来演变趋势和可能的河型转化方向。项目成果将拓展对干旱区河流地貌特征、发育成因和演变规律的认识，并为塔里木河综合治理和流域绿洲可持续发展提供参考。

为认识河流平面形态在干旱区的转化机理和临界条件，本项目以地处干旱区的我国南疆塔里木河为主要对象，基于系统的野外踏勘调查、采样，结合遥感影像、重点水文站点水沙数据、区域历史文献和经济社会发展资料等，实际观测和理论分析相结合，对河道型态与水沙过程、滨河植被之间动态响应关系以及河型发育和转化机理等开展了研究。.通过四年的研究工作，较好完成了研究计划拟定的工作任务，取得的主要成果包括：（1）深入认识塔里木河的地貌演变及其成因：人类活动作为主要驱动因素显著影响塔里木河的水系变迁、河道水沙过程和地貌演变；塔里木河上游河床总体淤积抬升，强烈波动；平均河宽和辫状系数呈下降趋势；现状河道蜿蜒系数显著低于废弃河道。（2）阐明了塔里木河水沙动态、滞后效应及其成因。塔里木河输沙-流量过程呈现较好的幂函数关系。有效流量过程（以日计）发生频率在0.5-2%（平均持续时间2-7天/年），说明泥沙运动主要集中于汛期中-高流量过程。不同时期的有效输沙流量存在差异。塔里木河的水沙关系主要为顺时针曲线，但逆时针和“8”字型曲线也有发生，其河岸的崩岸过程可能是形成后两类滞后关系曲线的主要原因。（3）初步揭示塔里木河中游弯道动态变化、河型转化成因及临界条件。塔里木河中游弯曲河道横向摆动显著，河道裁湾发生频率高。塔河河岸泥沙构成主要为细沙和粗粉沙，缺少粘性物质成份，河岸抗冲强度极低，而汛期水沙过程集中，这可能是导致塔里木河干流河道摆动幅度较高和改道频繁的主要原因。（4）明晰了滨河植被在塔里木河中游弯道发育中的作用。基于BSTEM (Bank Stability and Toe Erosion Model)模型，定量分析和模拟了旱区典型滨河植被（胡杨、红柳和芦苇）根系对塔里木河弯曲河道地貌发育和演变的影响。滨河植被是维持塔里木河中下游弯曲河道的必要条件之一。.本项目成果将丰富和扩展干旱区河流地貌的研究体系，并为塔里木河和其它干旱区河流的科学管理和调控提供参考和借鉴。