荆江石首河段近50年河床演变分析

Fluvial processes of the Shishou reach in the Jingjiang Reach in recent fifty years

河道裁弯及三峡工程运用对荆江石首河段的河床演变产生了显著影响。结合实测水沙及地形资料分析,研究了该河段近50年来的河床演变特点,主要包括河床冲淤、平面及断面形态调整三个方面。分析结果表明:两次裁弯使得石首河段平面形态发生显著调整,1966-1975年该河段深泓平均摆幅达42.0m/a,且总体向左岸摆动。三峡工程运用后,大规模护岸工程的实施使石首河段的平面形态趋于稳定,深泓平均摆幅减小到29.8m/a,但北门口下段、调弦口弯道等位置的深泓摆动仍较为剧烈,使得这些局部河段岸线崩退现象十分明显。此外还分析了石首河段断面形态的调整过程,并建立了河段平滩河槽形态参数与前5年汛期平均水流冲刷强度的经验关系式,用于反映河段平滩河槽形态随水沙条件的变化趋势。

In recent 50 years,the Shishou reach has suffered significant channel evolution caused by the artificial cut-off and the Three Gorges Project(TGP).Based on the observed flow and sediment data,as well as the channel topographic maps,the characteristics of fluvial processes were investigated from the aspects of channel deformation,planform and cross-section adjustment in channel geometry.Analyses indicate that the Zhongzhouzi cut-off made the planform geometry adjust drastically and the reach-scale amplitude of thalweg shifting reach 42.0 m/a in 1966-1975.Large-scale revetment engineering made the bank-lines stable relatively and the shifting amplitude decreased to 29.8 m/a after the TGP operation.However,remarkable thalweg shifting processes still active in some local sub-reaches,such as the lower Beimenkou and Tiaoxiankou bend,which resulted in dramatic bank-retreat correspondingly.In addition,adjustments in cross-section geometry in the Shishou reach were also investigated,and empirical relationships were developed between the bankfull reach-scale channel geometry and the previous five-year average fluvial erosion intensity during flood seasons,which can be used to reproduce the adjustments in reach-scale bankfull dimensions.