The relationship between water level change and river channel geometry adjustment in the downstream of the Three Gorges Dam

doi:10.1007/s11442-018-1575-9

Abstract

Abstract:

In this study, data measured from 1955-2016 were analysed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam (TGD) after the impoundment of the dam. The results highlight the following facts: (1) for the same flow, the low water level decreased, flood water level changed little, lowest water level increased, and highest water level decreased at the hydrological stations in the downstream of the dam; (2) the distribution of erosion and deposition along the river channel changed from “erosion at channels and deposition at bankfulls” to “erosion at both channels and bankfulls;” the ratio of low-water channel erosion to bankfull channel erosion was 95.5% from October 2002 to October 2015, with variations between different impoundment stages; (3) the low water level decrease slowed down during the channel erosion in the Upper Jingjiang reach and reaches upstream but sped up in the Lower Jingjiang reach and reaches downstream; measures should be taken to prevent the decrease in the channel water level; (4) erosion was the basis for channel dimension upscaling in the middle reaches of the Yangtze River; the low water level decrease was smaller than the thalweg decline; both channel water depth and width increased under the combined effects of channel and waterway regulations; and (5) the geometry of the channels above bankfulls did not significantly change; however, the comprehensive channel resistance increased under the combined effects of riverbed coarsening, beach vegetation, and human activities; as a result, the flood water level increased markedly and moderate flood to high water level phenomena occurred, which should be considered. The Three Gorges Reservoir effectively enhances the flood defense capacity of the middle and lower reaches of the Yangtze River; however, the superposition effect of tributary floods cannot be ruled out.

Key words: low water level, flood water level, riverbed adjustment, cause analysis, Three Gorges Dam, middle and lower reaches of the Yangtze River

Yunping YANG, Mingjin ZHANG, Zhaohua SUN, Jianqiao HAN, Jianjun Wang. The relationship between water level change and river channel geometry adjustment in the downstream of the Three Gorges Dam[J].Journal of Geographical Sciences, 2018, 28(12): 1975-1993.

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Hydrological station and reach	Content	Period	Source
Yichang, Zhicheng, Shashi, Jianli, Hankou, Datong	Water, sediment, flow, water level	1955-2016	Yangtze River Middle and Lower Reaches Hydrological Yearbook
Songzikou, Taipingkou, Ouchikou, Chenglingji, Hukou, Huangzhuang	Water, sediment, flow	1955-2016
Yichang-Hukou Reach	Amount of river sediment	1987-2015
Yichang-Hukou Reach	Water level stations	1981-2014	Changjiang Waterway Planning Design and Research Institute
Yichang-Yangtze Estuary	Depth and width of the shipping channel	2002 and 2015	Changjiang Waterway Planning Design and Research Institute

Period of time	Reach	YZR	UJR	LJR	CHR	HHR
Period of time	Extent (km)	60.8	171.7	175.5	251.0	295.4
1981 to 2002	Low-water channel (%)	102.0	100.6	9.2	17.5	69.6
	Low beach (%)	-2.0	-0.6	-109.2	-117.5	-169.6
	High beach (%)	-2.0	-0.6	-109.2	-117.5	-169.6
October 2002 to October 2008	Low-water channel (%)	88.6	89.6	73.2	301.8	60.4
	Low beach (%)	1.7	2.2	11.6	-30.7	48.3
	High beach (%)	9.6	8.2	15.2	-171.1	-8.7
October 2008 to November 2015	Low-water channel (%)	96.4	94.0	95.4	95.3	115.0
	Low beach (%)	4.8	3.1	-0.4	5.8	-11.4
	High beach (%)	-1.1	2.9	5.0	-1.1	-3.6

Riverbed composition	Gravel and pebble river		Sandy river
Reach	Yichang-Zhicheng	Zhicheng-Dabujie	UJR	Chengjlingji-Hukou
Increasing amplitude (%)	91	65	3	2