河流三角洲地区河道形态自动调整机理及流路稳定性研究

River delta is a very important part of the terrestrial system and when rivers run into this area channel gradient decreases significantly and sediments deposit downstream continuously, making river channel morphology and flow course self-adjust frequently. These depositional rivers belong to non-equilibrium systems and their self-adjusting mechanisms and processes are very complex such that studies of the behavior of these systems are still dominated with empirical analyses, lacking convincing theoretical support. On the basis of equilibrium theory for alluvial rivers developed over the last more than 10 years, this project will investigate sediment transport，channel-form adjustment and flow course change in both meandering and straight channels. During this investigation, a mathematical-physical analytical approach will be used to develop theoretical modes for these depositional river systems and a cellular automaton model for simulating the process of flow course change. To examine if the theoretical modes are reasonable in reality mobile-bed flume studies will be carried out. Furthermore, this project takes the large delta of the Yellow River as a typical study area and evaluates the applicability of theoretical analyses in the channel adjustment along the lower reach and the mount of the Yellow River. Typically, a detailed assessment of the effects of flow and sediment discharge regulation, riparian vegetation composition and channel-control measures on channel morphology and stability of the present river course in the Yellow River delta will be undertaken.

河流三角洲是陆地表层系统的一个重要组成部分，当河流进入这一地区后随着河道比降逐渐变缓，携带的泥沙沿程不断沉积，致使河道形态及流路频繁地进行自动调整。这些沉积性河流属非平衡系统，其自动调整机理及过程极为复杂，对其演变规律的认识目前仍然以经验性分析为主，缺乏坚实可信的理论支撑。本项目以近十几年来发展起来的冲积河流平衡理论为基础，针对沉积性弯曲和顺直河道的泥沙输移、形态调整及流路摆动特征，利用数理分析方法构建沉积性河流河道形态自动调整理论模式，并通过动床水槽实验对这些理论模式的合理性进行检验，同时利用元胞自动机模拟分析流路的演变过程，以期在建立沉积性河流演变理论方面取得突破性进展。此外，还以广义黄河三角洲为典型研究区域，深入分析调水调沙、河道植被组成及河道整治工程对该地区河道形态和流路稳定性的影响，以及现行河道未来可能发生的调整趋势。

河流三角洲是陆地表层系统的一个重要组成部分，当河流进入这一地区后由于地表极为平坦，携带的泥沙沿程不断沉积，致使河道形态及入海流路频繁发生自动调整。但目前对这些河流演变规律的认识仍然以经验性分析为主，缺乏坚实可信的理论支撑。本项目以发展近十几年来建立起来的冲积河流平衡理论为主要目标，利用基于河道形态的变分分析方法解析沙洲发育机理，通过开展动床水槽试验确定河岸植被和河宽调整对河道形态发育的作用机理与过程，并以黄河下游和河口为典型研究区，采用遥感卫星影像、实际观测资料和计算机模拟相结合的分析方式，辨析近几十年来河道形态和入海流路对水沙变化的响应方式，并检验和改进河流平衡理论的实际应用性。研究结果表明，河道中沙洲的发育主要由汊道之间的比降差异所致，比降相同时则需要河底植被或基岩的支持。植被和高粘性物质能够抑制水流的侧向抗冲作用，是弯曲性河道发育的关键因子，反之将利于辫状或游荡性河道的形成。大洪水在含沙量较低时，黄河下游河道主槽发生冲刷而滩地承受淤积，河口入海流路延伸显著，而小洪水在含沙量较高时，黄河下游河道的主槽和滩地均发生淤积，河口入海流路淤堵不畅。此外，本研究还从河流演化机理和过程方面探讨了冲积河流平衡理论的哲学意义。