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.