黄河下游游荡段持续淤积及冲刷时平滩河槽形态调整规律

自1986年以来,由于上游来水来沙量不同程度的减少及小浪底水库的运用,进入黄河下游的水沙条件发生了较大变化.下游河道分别经历了持续淤积和持续冲刷的过程,其平滩河槽形态调整较为显著,尤其在游荡段.利用1986-2012年汛后实测淤积断面资料,统计了各年游荡段汛后28个断面的平滩河槽形态参数(平滩河宽、水深及面积等).然后,采用基于对数转换的几何平均结合断面间距加权平均的方法,计算了基于河段尺度的游荡段平滩河槽形态,并分析了这些参数的变化规律.计算结果表明:河段平滩河槽形态的调整与汛期及非汛期水沙条件都密切相关,且能与前期4年平均的汛期及非汛期的流量及来沙系数建立经验函数关系.该关系式可反映出流量、来沙系数对平滩河槽形态各参数的不同影响,并有较高的相关系数.

Variation in Bankfull Channel Geometry in the LYR Undergoing Continuous Aggradation and Degradation

Abstract: The flow-sediment regime entering the Lower Yellow River (LYR) has changed significantly since 1986 due to a reduction in the water and sediment volume and the operation of the Xiaolangdi reservoir, and the river channel downstream experienced continuous aggradation and degradation, respectively. Channel geometry adjustment of the LYR is most notable in the braided reach. In this study, the reach-scale bankfull channel dimensions (bankfull width, depth, area, et al) of the braided reach were calculated annually during the period from 1986 to 2012, based on the surveyed post-flood profiles at 28 sedimentation sections, using an integrated method which integrates a geometric mean based on the log-transformation with a weighted average based on the spacing between two consecutive sections. The results indicate that the magnitude of each reach-scale bankfull channel dimension responded well to the accumulative effect of incoming flow and sediment conditions during both the flood seasons and non-flood seasons. Empirical relationships for the braided reach were developed between the reach-scale bankfull channel geometry and the previous four-year average integrated incoming discharge-sediment condition. These relationships demonstrate different impacts of discharge and incoming sediment coefficient on the channel geometry, with relatively high correlation coefficients between them being obtained.