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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Sediment management and morphodynamics : Effects of the three gorges project operation on the variation in bankfull channel geometry in the j...
Effects of the three gorges project operation on the variation in bankfull channel geometry in the jingjiang reach
Upstream damming often changes the downstream channel geometry. Significant channel evolution has occurred in the
Jingjiang Reach of the Middle Yangtze River, because of the operation of the Three Gorges Projects (TGP), which has
led to longitudinal variability in the cross-sectional geometry. Therefore, it is necessary to use an appropriate method to
describe the effects of the TGP operation on the recent adjustments in bankfull channel geometry at section- and reachscales.
In this study, the Jingjiang Reach covering the Upper Jingjiang Reach (UJR) and Lower Jingjiang Reach (LJR) is
selected as a study region, with the recent fluvial processes in these reaches being also presented. An integrated
approach to calculating reach-scale bankfull channel dimensions is then outlined, based on the measured section-scale
bankfull geometry. The reach-scale bankfull channel dimensions in the UJR and LJR were calculated annually from
2002 to 2013 by means of the integrated approach and the surveyed post-flood profiles at 171 sections. In addition, the
processes of bank retreat at typical sections in the study reach were also investigated. Calculated results with the TGP
operation indicate that: (i) the channel evolution in the UJR and LJR occurred mainly in the component of bankfull depth
because of the construction of large-scale bank revetment works, although there were significant bank erosion processes
in local regions without bank protection engineering; (ii) the reach-scale bankfull depth increased respectively by 1.6 m in
the UJR and 0.7m in the LJR, with an average increase in the reach-scale bankfull area of about 8%; (iii) empirical
relationships were developed to predict the accumulated widths of bank retreat at four typical sections over the period;
and (iv) similar relationships for the UJR and LJR were also developed between the reach-scale bankfull channel
dimensions and the previous five-year average fluvial erosion intensity at Yichang during flood seasons, and higher
correlations for the bankfull depth and area were obtained when calibrated by the measurements from 2002 to 2013. In
order to investigate the effects of the TGP operation on the bankfull channel geometry in the study reach, the natural
flood-averaged discharges and suspended sediment concentrations at Yichang were returned under the scenario without
the TGP, based on the methods of artificial neural network and regression analysis, and the corresponding bankfull
channel dimensions at section- and reach-scales were estimated using the developed empirical relations and the
returned flow and sediment conditions. These estimated results without the TGP show that: (i) the processes of bank
retreat at typical sections in local regions would be reduced significantly; and (ii) the channel in the Jingjiang Reach
would experience an insignificant degradation process, which could lead to a negligible increase in the reach-scale
bankfull depths and areas of the UJR and the LJR.
File Size : 2,914,877 bytes
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Sediment management and morphodynamics
Date Published : 18/08/2015
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