小浪底水库运用前后黄河下游河道河型变化及成因分析

利用实测资料分析、理论判别和分形维数计算等方法,以黄河下游铁谢—伊洛河口、花园口—黑岗口和夹河滩—高村三个典型游荡性河段为研究对象,分析其1960年以来的主流摆幅、弯曲系数和主河槽宽深比等河势参数变化,以及小浪底水库修建前后下游游荡性河段的河型演化过程。结果表明,自20世纪90年代初,除花园口—黑岗口河段仍表现为游荡河性外,其他两个河段因整治工程不断完善其游荡性均有明显减弱,河型趋于限制性弯曲方向发展。自1999年10月小浪底水库拦沙运用以来,三个研究河段的整体游荡程度显著减弱,河势趋于规划流路方向发展,特别是夹河滩—高村河段河势基本稳定。小浪底水库长期下泄低含沙小流量过程,水流动力减弱,加之不断完善的河道整治工程,是河势游荡程度显著减小、河势归顺及河型发生变化的主要原因。

Evolution processes of river pattern in Lower Yellow River after commissioning of Xiaolangdi Reservoir

Since the commissioning of the Xiaolangdi Reservoir,the condition of water and sediment in the Lower Yellow River has undergone a drastic change.The matching of the water flow and sediment load within a year is different from that in the past.The river pattern of the Lower Yellow River is experiencing a change.The paper focuses on the evolution processes of the river patterns of the three reaches in the Lower Yellow River: Tiexie-Yiluo River mouth reach,Huayuankou-Heigangkou reach,and Jiahetan-Gaocun reach.The parameters of the river regime such as the wandering amplitude of the mainstream,bend coefficient and width-depth ratio of the channel are calculated since 1960.The development of these parameters in the past 50 years indicates that the river regimes of the three reaches are becoming regular.Especially,since the commissioning of the Xiaolangdi Reservoir,the wandering performance of the three reaches is inhibited markedly.In addition,the river patterns of the three reaches are identified by using the conventional method.As a comparison,the fractal dimension method is introduced to indentify the river pattern.The results of the two methods are coincident,which reflect the weakness of the wandering performance.The river pattern of the Lower Yellow River is experiencing the transition from the wandering river to the braided or the meandering river.Many factors are taken into account for the evolution processes of the river pattern.The low sediment-laden flow out of the Xiaolangdi Reservoir is the foremost factor and the improvement of the regulation works in the Lower Yellow River is helpful to regulate the river regime as the supporting factor.Under the current condition of water and sediment,more regulation works may contribute to regulate the river regime.