Effects of the Three Gorges Project operation on the recent variation in bankfull channel geometry of the Jingjiang Reach

In order to investigate the impacts of the Three Gorges Projects (TGP) operation on the recent channel adjustment in the Jingjiang Reach, bankfull channel dimensions at both section- and reach-scale were calculated annually from 2002 to 2013, with empirical relationships being proposed between these dimensions and the previous 5-year average fluvial erosion intensity during flood seasons at the Yichang hydrometric station. Hydrological data at this station were then estimated under the scenario without the TGP, and used to evaluate the corresponding bankfull dimensions. Differences were analyzed between the variations in bankfull dimensions under these two scenarios. The results indicate: ① after the TGP operation, the bankfull widths and depths at four typical sections increased gradually, with a remarkable increase in the width; ② the longitudinal channel slopes tended to flatten in the Jingjiang Reach, with an appreciable increase in the reach-scale bankfull depth and a slight change in the reach-scale bankfull width, which caused the geomorphic coefficient decreasing by 6.7%—10.3%; ③ Changes in bankfull channel geometry were slighter under the scenario without the TGP, with the increase ranges in the reach-scale depth and area accounting respectively for 16% and 18% of those under the scenario with the TGP. Thus, the TGP operation didn't alter the trend of the recent adjustment in bankfull channel geometry of the Jingjiang Reach, which tended to have a narrower and deeper channel geometry, but accelerated the adjustment process.