Interacting effects of multiple factors on the morphological evolution of the meandering reaches downstream the Three Gorges Dam

doi:10.1007/s11442-017-1434-0

Abstract

Abstract:

Elucidating the influence of dams on fluvial processes can inform river protection and basin management. However, relatively few studies have focused on how multiple factors interact to affect the morphological evolution of meandering reaches. Using hydrological and topographical data, we analyzed the factors that influence and regulate the meandering reaches downstream the Three Gorges Dam (TGD). Our conclusions are as follows. (1) The meandering reaches can be classified into two types based on their evolution during the pre-dam period: G1 reaches, characterized by convex point bar erosion and concave channel deposition (CECD), and G2 reaches, characterized by convex point bar deposition and concave channel erosion (CDCE). Both reach types exhibited CECD features during the post-dam period. (2) Flow processes and sediment transport are the factors that caused serious erosion of the low beaches located in the convex point bars. However, changes in the river regime, river boundaries and jacking of Dongting Lake do not act as primary controls on the morphological evolution of the meandering reaches. (3) Flood discharges ranging from 20,000 to 25,000 m3/s result in greater erosion of convex point bars. The point bars become scoured if the durations of these flows, which are close to bankfull discharge, exceed 20 days. In addition, the reduction in bedload causes the decreasing of point bar siltation in the water-falling period. (4) During the post-dam period, flood abatement, the increased duration of discharges ranging from 20,000 to 25,000 m3/s, and a significant reduction in sediment transport are the main factors that caused meandering reaches to show CECD features. Our results are relevant to other meandering reaches, where they can inform estimates of riverbed change, river management strategies and river protection.

Key words: reaches downstream dams, meandering river, morphological evolution, Three Gorges Dam

Jianqiao HAN, Wei ZHANG, Yongyang FAN, Mengqing YU. Interacting effects of multiple factors on the morphological evolution of the meandering reaches downstream the Three Gorges Dam[J].Journal of Geographical Sciences, 2017, 27(10): 1268-1278.

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Data type	Station	Measured time	Sources
Hydrologic data	Shashi Jianli	2003-2013 1996-2015	CWRC
Sectional velocity	Six typical sections	August 2014, January 2015	CWPDRI
Sectional profiles	Laijiapu reach	2003-2016	CWPDRI
Sectional profiles	Eight typical sections	1996, 2003, October 2016	CWRC