小浪底水库对下游游荡河段河床形态与过流能力的影响

Influences of the Xiaolangdi Reservoir on the channel geometry and flow capacity of wandering reach in the Lower Yellow River

小浪底水库蓄水拦沙以来,进入黄河下游的泥沙大幅度减少,引起了下游河道的再造床过程。以黄河下游游荡河段1986-2015年实测大断面资料为基础,从河床冲刷量、平滩河槽形态、平滩流量等方面分析了小浪底水库运行前后黄河下游游荡河段的河床调整过程及过流能力变化,并还原了无小浪底水库时的平滩河槽形态参数及平滩流量。研究结果表明:小浪底水库运行后,黄河下游河道持续冲刷,累计冲刷量为18. 6亿m^3,其中游荡河段所占比重达到72%。典型断面及河段尺度的平滩河槽形态调整明显,平滩河宽与水深增加,河相系数逐年递减,横断面形态总体向窄深方向发展。主槽过流能力明显增加,河段平滩流量都有不同程度增加,游荡河段内三个分河段的增幅分别为3 381 m^3/s、4 450 m^3/s及4 590 m^3/s。还原了无小浪底水库条件下2015年汛后游荡河段的平滩面积及平滩流量计算值,分别为有小浪底水库时的64%和80%。

Sediment load in the Lower Yellow River( LYR) had reduced significantly since the operation of the Xiaolangdi( XLD) Reservoir,which induced channel processes in the LYR. Based on the observed postflood cross sections and hydrological data,the channel adjustments and flood discharge capacity were studied in terms of the volume of channel evolution,bankfull channel geometry and bankfull discharge in the wandering reach of the LYR during the period from 1986 to 2015. The bankfull channel geometry and bankfull discharge were calculated by an empirical formula under the scenarios without the XLD reservoir. The results indicate that the river channel has experienced continuous degradation after the operation of the XLD reservoir,and the cumulative volume of channel scour in the braided reach was 1. 86 billion m^3,accounting for 72% of the LYR. The cross and reach-scale bankfull channel geometry varied remarkably,and the bankfull width and depth increased greatly with the geomorphic coefficient decreasing gradually,which caused the cross-sectional profiles to be narrow and deep. There was an increase in the bankfull area and flood discharge capacity of the channel,leading to the bankfull discharges in three sub-reaches increasing by 3 381 m^3/s,4 450 m^3/s and4 590 m^3/s,respectively. The bankfull area and bankfull discharge calculated by the empirical equations in the braided reach under the scenario without the XLD reservoir were only 64% and 80% of those under the condition with the XLD reservoir by 2015.