Author(s): Meirong Zhou, Junqiang Xia, Shanshan Deng, Fenfen Lin
Linked Author(s): Meirong Zhou
Keywords: Geomorphic adjustments, flow and sediment regime, bed-material coarsening, gravel-sand bed reach, Three Gorges Project
Abstract: Since the onset of the Three Gorges Project (TGP), remarkable geomorphic adjustments have occurred in the Yizhi reach (YZR) downstream of the dam. Due to the differences in channel pattern and bedform, the YZR is divided into the Yichang reach (YCR) and the Yidu reach (YDR). A special attention has been paid on the variation in bankfull channel geometry. The section-scale bankfull dimensions were firstly calculated annually from 2002 to 2015 in these two reaches, and then a reach-average method is adopted to calculate the reach-scale bankfull channel dimensions. Calculated results indicate that: (i) the reach-scale bankfull widths changed slightly; (ii) the adjustments in channel geometry occurred mainly in the component of bankfull depth, with the value increasing respectively by 1. 57 m and 3. 28 m in each reach, as well as a corresponding increase in bankfull cross-sectional area of about 6% and 17%. Furthermore, empirical relationships for the YCR and the YDR are developed between these reach-scale bankfull dimensions and the previous 5-year average fluvial erosion intensity during flood seasons at Yichang. It is found that: (i) the relationships between the reach-scale bankfull width and the previous flow and sediment conditions are relatively weak in these two reaches, with the corresponding correlation degrees of 0. 16 and 0. 04; (ii) the bankfull depth and cross-sectional area responded well to the altered flow and sediment regime, with the correlation degrees both being equal to 0. 98 in the YDR, which are higher than those of 0. 61 and 0. 71 in the YCR where the bed material suffered significant coarsening process. Therefore, a comprehensive empirical relationship both the concerning previous flow and sediment regime and the bed material coarsening process is further proposed, with much higher correlations of 0. 93 for bankfull depth and 0. 91 for bankfull area being obtained in the YCR
Year: 2017