Geomorphic response of the Jingjiang Reach to the Three Gorges Project operation

摘要

Upstream damming often causes significant downstream geomorphic adjustments. Remarkable channel changes have occurred in the Jingjiang Reach of the Middle Yangtze River, since the onset of the Three Gorges Project (TGP). Therefore, it is important to investigate the variations in different fluvial variables, for better understanding of the channel evolution characteristics as an example of the Jingjiang Reach. Recent geomorphic adjustments in the study reach have been investigated quantitatively, including variations in sediment rating curve, fluvial erosion intensity, channel deformation volume and bankfull channel geometry. These fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the TGP operation. A focus of this study has been especially on variation in the bankfull channel geometry. Calculated bankfull dimensions at section- and reach-scale indicate that: (i) there were significant bank-erosion processes in local regions without bank-protection engineering, with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections; (ii) the variation in the reach-scale channel geometry occurred mainly in the component of bankfull depth, owing to the construction of large-scale bank-revetment works, with the depth increasing from 13.7m in 2002 to 15.0m in 2014, and with an increase in the corresponding bankfull area of about 11%; and (iii) the reach-scale bankfull channel dimensions responded to the previous 5-year average fluvial erosion intensity during flood seasons at Zhicheng, with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002-2012. Furthermore, these relations developed for the section- and reach-scale bankfull channel geometry were also verified by the observed data in 2013-2014, with encouraging results being obtained. Copyright (c) 2016 John Wiley & Sons, Ltd.