枢纽下游河岸强约束型分汊河段主支汊易位的演变规律研究

Braided reach is widely existed in nature, and its evolution law is quite complicated.the alternatively shifting of main & tributary branches is the main river evolution characteristic of braided reach. River bed adjustment is acuity with the construction of project，which will leads to the problems on river regime, flood control, irrigation and navigation, etc. So the law of the alternatively shifting of main & tributary branches is the one of the key factors to research on the evolution rule of braided river. At present, the researches about this issue are not enough in depth, and also lack of effective prediction method..This research project focuses on the braided river with strong constraint riverbank, and conceptual flume experiment and GIS technoligy are taken as the main technical means combined with field data analysis and matrix operations of multiple regression analysis. The research includes twe aspects, the first is to reveal the evolution mechanism of main & tributary branches alternatively shifting in braided river under different boundary conditions, the second is to identify the main factors which affect the main & tributary branches alternatively shifting in braided river, and refine the discriminant model of main & tributary branches alternatively shifting. The results would promote the intersection of river dynamics and fluvial geomorphology; enrich the theoretical system of subjects, and provide scientific basis for solving the safety problems of river engineering.

分汊河段广泛存在，演变规律复杂，其主要的特征就是主支汊易位。枢纽修建后分汊河段的河床调整较自然状态下更为剧烈，河道是否会发生主支汊易位关系到河势、防洪、灌溉及航运等诸多问题。对主支汊易位演变机理的深刻认识，是探索分汊河段河床演变规律的关键所在。目前对主支汊易位的演变规律还缺乏系统深入的研究，也缺少有效的预测方法。本项目以河岸强约束型分汊河段为研究对象，采用实测资料分析、概化模型试验并结合GIS技术、多元回归分析等多种手段，研究环流作用下分汊河道的水流运动特性，进而揭示枢纽下游不饱和水流作用下分汊河段的主支汊易位演变规律，识别影响主支汊易位的条件和因素，建立不同影响因素与主支汊易位临界条件的定量关系，提出基于主要影响因素的主支汊易位判别模式，研究成果将促进河流动力学同河流地貌学的学科交叉，丰富学科理论体系，可为解决河流中的工程安全问题提供科学依据。

在国家自然科学基金项目的支持下，本项目以河岸强约束型分汊河段为研究对象，采用实测资料分析、概化模型试验并结合GIS技术、多元回归分析等多种手段，研究年内非交替型和交替型分汊河道区分条件，分析环流作用下分汊河道的水流运动特性，进而揭示枢纽下游不饱和水流作用下分汊河段的主支汊易位演变规律，识别影响主支汊易位的条件和因素，提出基于主要影响因素的主支汊易位判别模式，取得了较为系统的创新性成果。.（1）对长江中下游河段分汊河段就年内非交替型和交替型进行了分类并分析了原因；以三峡工程下游的关洲河段和世业洲汊道段作为水流动力轴线年内交替型和非交替型分汊河道的典型代表，根据其多年实测资料，分析研究了两河段在三峡水库蓄水运用前后的冲淤变化情况，总结出两类分汊河段的河床演变特点及冲刷调整的一般规律。据此，提出了两类分汊河道的水流和河道边界区分条件。.（2）建立水流动力轴线年内交替型和非交替型分汊河道的概化模型，设计试验方案和测量内容；通过定床模型试验，研究了不同流量级下两类分汊河道的流速分布，水流动力轴线，水面形态，分流区的分流比、横向环流等水流运动特性的变化，剖析了入流角度对分汊河道的影响；通过动床模型试验，研究不同流量级下分汊河道的纵剖面深泓形态、典型横断面形态、洲滩形态等冲淤变化规律。.（3）系统分析了来水来沙因素（驱动因素）和河床边界因素（阻力因素）两个方面因素对分汊河道主支汊易位的影响，指出了主支汊易位的主导因素应为来流动力轴线的变化和各个汊道过流（沙）能力的相对关系，提出了来流动力轴线摆动向支汊一侧和洲头形态变化引起支汊过流能力增加两类分汊河道主支汊原位交替的判别模式。