Abstract: 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.

Key words: riverbed adjustment, bar evolution, Three Gorges Project, plane morphology, sectional morphology, Shashi reach