三峡工程运用前后沙市段河床形态调整特点

为研究裁弯工程实施及三峡工程运用对沙市段河床演变的影响,依据近50 a实测水沙及地形资料,采用河段平均的方法计算了沙市段河段尺度的深泓摆幅及平滩河槽形态参数,定量分析了该河段河床平面及断面形态的调整特点。结果表明:下荆江裁弯后1966—1987年该河段深泓摆动剧烈,平均摆幅约为30.8 m/a;1987—2002年深泓较为稳定,平均摆幅减小为19 m/a;三峡工程运用后2003—2015年深泓摆动有所加剧,平均摆幅约为32.6 m/a。太平口心滩及金城洲处典型断面形态在三峡工程运用前调整幅度较大,运用后相对稳定,而三八滩处典型断面形态在运用前后均发生了明显调整。总体上,三峡工程运用后沙市段平滩河槽形态调整以平滩水深及面积的增加为主,而河宽变化较小。建立了河段尺度平滩河槽形态参数与前5 a汛期平均水流冲刷强度的幂函数关系式,用于反映河槽形态随水沙条件的变化过程。

Riverbed Geomorphic Adjustments in the Shashi Reach before and after the Operation of Three Gorges Project

Over the past five decades, the Shashi reach has undergone significant channel evolution due to the artificial cut-off and the operation of the Three Gorges Project (TGP). According to the measured hydrological and topographic data in the past five decades, the variations in reach-scale amplitude of thalweg shifting and bankfull dimensions are calculated in order to quantify the adjustments in channel planform and cross-sectional profiles in the Shashi reach.Results show that: (1) after the artificial cut-off project in the lower Jingjiang River, the mean amplitude of thalweg shifting at reach-scale was 30.8 m/a in 1966-1987, indicating a drastic adjustment in river regime; in 1987-2002,the thalweg was relatively stable, with the mean shifting amplitude reducing to 19 m/a; afterwards, the mean shifting amplitude increased to 32.6 m/a in 2003-2015 owing to the operation of the TGP. (2) Bed deformation was remarkable at some typical sections of Taipingkou point bar and Jincheng island before the operation of TGP, but became relatively insignificant after the TGP. However, obvious bed deformation continuously occurred at the typical sections of Sanba central bar. (3) After the TGP operation, bankfull channel adjustment in the Shashi reach was mainly represented by increases in bankfull depth and cross-sectional area, with an insignificant increase in bankfull width. In addition, power function relationship was established between the reach-scale bankfull dimensions and the five-year average fluvial erosion intensity during flood seasons, which can be used to reflect the adjustments in reach-scale bankfull dimensions.