黄河洪水演进洪峰增值现象及其机理

2004～2006年小浪底水库异重流排沙期间,在小浪底～花园口区间出现了下断面的洪峰流量明显大于上断面洪峰流量的洪峰增值现象.本文详细描述了洪峰增值现象发生过程和主要特征.通过对黄河小浪底水库及其下游河道实测资料的研究和水力学理论分析认为,洪水发生洪峰增值的主要原因是河道糙率的大幅度减小.河道糙率与水流含沙量、悬沙级配、床沙级配、床沙床面形态、河道断面形态及河岸周界情况等因素有关.在小浪底水库异重流排沙之前有清水下泄过程,使河道床沙粗化,糙率大幅度增大,当异重流出库后,高浓度细颗粒泥沙使水流黏性增加、紊动削弱,河床被极细沙填附,河道糙率大幅度减小,导致后续水流流速加大,并赶上前方水流,发生洪峰叠加.

Analysis on mechanism of peak discharge increasing during flood routing in lower reaches of Yellow River

A flood peak discharge increasing phenoment occurred to the flood routing in the lower reaches of Yellow River in the periods of the Xiaolangdi Reservoir discharging sediment by density flow in 2004 to 2006. The analysis on observation data based on basic principle of hydraulics revealed that the flood peak increasing phenomenon was due to the significant reduction of river roughness in previous period. Since a period of clear water discharging from the Xiaolangdi Reservoir was always arranged prior to the discharging of density flow, the riverbed roughened due to the erosion of clear water. When the density flow discharged from the reservoir, the flow turbulence was reduced by high concentration of sediment and the flow was retarded by the roughened riverbed, but at the same time the riverbed was filled with fine grain sediment and the roughness of riverbed was greatly reduced, so that the subsequent flow was accelerated. The subsequent flow may catch up and joint with the preceding flow forming a higher flood peak discharge taken place at the Huayuankou river section downstream of the reservoir.