本文着重研究黄河水沙情势、冲积河流水沙运动特性、黄河下游宽河段最佳输沙河槽宽度、弯曲型整治工程布局对“两道防线”治理方案的必要性等关键问题。首先，进行黄河水沙情势研究。基于自组织映射-K均值聚类耦合方法，对黄河中游潼关站1919—2019年和1987—2019年的年径流量和年输沙量组合进行分类，并结合流域降雨量和产沙量的变化趋势，得到潼关以下河段年径流量和年输沙量的特征值，有助于深入了解黄河中下游水沙变化特点；进行新情势下黄河中下游河段设计洪水计算，有助于进一步研究黄河治理的对策和工程布局。其次，研究泥沙扬动与输移特性、起动流速、水流阻力等基本问题。分析泥沙扬动与输移特性发现，为提升河道输沙能力需维持较大的水流动力；以李保如泥沙起动流速公式的物理图形为基础，将摩擦系数的函数修正为由“隐蔽”影响项和重力作用项两项组成，推导出李保如泥沙起动流速修正公式；以相对流速反映水流强度和床面泥沙运动状况，以浑水卡门常数反映挟沙水流内部能耗状况，以近壁层流层厚度与床沙中值粒径之比反映河床近壁区相对摩阻状况，构成综合影响系数，建立能够反映水流特性和河床边壁情况对床面糙率影响的水流阻力公式。验证结果表明，本文建立的起动流速公式和阻力公式均具有较高精度，可以满足实际需要。再次，基于本文建立的起动流速公式和水流阻力公式，联立广泛应用于黄河的水流挟沙力公式，得到黄河沙质河段河槽宽度与糙率关系曲线，基于阻力最小、输沙效率最高概念提出黄河沙质河段主槽稳定宽度计算方法，其计算结果与下游现行的整治河宽相符；提出一种计算滩地宽度发生变化后复式断面水沙因子分布情况的方法，表明适当缩窄滩地的宽度有利于主槽与滩地冲淤平衡状态的形成。本文为河道整治宽度的确定提供了新方法，能够为黄河治理方案的制定提供依据。最后，黄河下游典型游荡型河段模型试验表明，大洪水使河势下挫或趋直后的地形上，在2500~3000 m3/s中常流量持续作用与工程控导下，整体河势能够逐渐靠溜，“两道防线”治理方案能够适应中常洪水的作用；在中常洪水过程中主流被限制在河道整治工程构成的外包线之内，按治导线开展的工程布局可成为“第一道防线”的基本依托，形成对“第二道防线”的有效保护；中常洪水流量下平均主槽宽度与平均水深测量值和本文主槽稳定宽度与水深理论计算值颇为接近。

This thesis focuses on several key theoretical and technical issues of the Yellow River, including variation of runoff and sediment load in the Yellow River, water and sediment dynamics in alluvial rivers, optimum main channel width for sediment transportation in the lower Yellow River, and the key roles of the layout patterns of meandering regulation projects in the “two-boundary” river training mode.Firstly, a coupled clustering method based on the self-organizing maps and K-means clustering is developed and adopted to the annual runoff and sediment load data (1919-2019 and 1987-2019) at Tongguan station to reveal the characteristic patterns of runoff-sediment. Combining the variation trends of the rainfall and sediment yield in the Yellow River basin, the characteristic values of annual runoff and sediment load in the middle and lower Yellow River reaches below Tongguan are obtained. To further support the management strategy and the projects’ overall arrangement, the design flood of the main stream in the middle and lower Yellow River under new conditions are calculated.Secondly, the dynamics of the uplift, transport, and incipient characteristics of sediment, and flow resistance are investigated in detail. Analysis on the uplift and transport characteristics of sediment indicates that relatively large flow energy should be maintained to improve the sediment transport capacity. Based on the physical diagram of Li Baoru’s sediment incipient velocity equation, the function of the incipient coefficient is modified to concern the following effects: the viscous sublayer effect and the gravitational effect. This improvement leads to a modified version of Li Baoru’s sediment incipient velocity equation. A new flow resistance equation with the ability to reflect the effect of the flow characteristics and sidewall conditions on the bed roughness of sand-bed rivers is developed by relating a proportionality coefficient to a comprehensive influence coefficient represented by a combination of the relative velocity (an indicator of the flow intensity and bed material movement), von Karman constant of sediment-laden flows (an indicator of the energy consumption condition in sediment-laden flows) and the ratio of particle size to viscous sublayer thickness (an indicator of the relative friction condition in the near-wall region). Based on the field data, the performance of the two proposed equations are validated to achieve the best accuracy in the calculation.Thirdly, the graphical relations between the main channel width and Manning’s roughness coefficient in the sandy reaches of the Yellow River are obtained through the combination of the proposed incipient velocity equation, flow resistance equation and a widely used suspended load carrying capacity equation. The main channel width under the minimum Manning’s roughness coefficient is treated as the optimum main channel width for sediment transportation. The optimum main channel width for sediment transportation is consistent with the current river training width of the lower Yellow River. A method to calculate the water and sediment factors in compound channels under various floodplain widths is proposed. The results show that proper shrinkage of the floodplain width is conducive to the formation of the equilibrium state in the main channel and the floodplain. The above results provide an alternative approach of the determination of the channel width ranges and can be used to support the river training strategy of the Yellow River.Finally, a physical model of the typical wandering reach of the Yellow River is conducted in this thesis and the results indicate that after the depletion process of the heavy flood that can straighten the river or reduce the river slope, the regular flow route patterns can basically recover under the condition of constant frequent flood discharges ranging from 2500 to 3000 m3/s and the guidance of regulation projects, indicating that the “two-boundary” river training mode is applicable in frequent flood cases. And the main flow can be confined to areas between the first boundaries so that it cannot scour the Grand Levees, suggesting that the regulation projects following the regulation line lay the foundation of the first boundaries of the “two-boundary” river training mode and effectively protect the second boundaries. Besides, the average main channel widths and depths of the cross sections match well with the calculated optimum main channel widths for sediment transportation and the corresponding flow depths under the frequent flood discharges.