Impact of Emergent Water Supply of the Three Gorges Reservoir on Saltwater Intrusion in the Changjiang River Estuary in 2022

doi:10.11988/ckyyb.20240616

Abstract

Abstract:

During the flood season of 2022, the Changjiang River Basin experienced an unprecedented basin-wide drought. From September to October, the runoff at Datong Station fluctuated around 11,000 m³/s. Since September, the Changjiang River Estuary has faced severe saltwater intrusion due to typhoons, jeopardizing the water supply security of Shanghai. Based on analysis of measured runoff, wind speed, and salinity data, we conclude that low runoff combined with typhoons triggered the saltwater intrusion. We employed a three-dimensional estuary and coastal numerical model to quantitatively assess the impact of emergent water supply from cascading reservoirs. The emergent water supply mitigated saltwater intrusion in the Changjiang River Estuary, reducing the upward distance of saline water and shifting the 0.45 psu isohaline towards downstream by 17 km in the South Branch-North Channel section. This action reduced the salinity of reservoir water intake and extended the water intake window for the Qingcaosha Reservoir by approximately 6 hours. However, two cold fronts in October weakened the effectiveness of the water supply to some extent. To enhance the reliability of the water supply, it is crucial to strengthen comprehensive monitoring of hydrology, tides, and meteorology in the estuarine area, thereby ensuring the safety of freshwater utilization in Shanghai.

Key words: saltwater intrusion, reservoir operation, freshwater resources, saline-reducing effect, Three Gorges Reservoir, Changjiang River estuary

CLC Number:

P731.2

QIU Wei, LUAN Hua-long, QU Geng, LEI Wen-tao, LIN Mu-song, ZHU Jian-rong. Impact of Emergent Water Supply of the Three Gorges Reservoir on Saltwater Intrusion in the Changjiang River Estuary in 2022[J]. Journal of Changjiang River Scientific Research Institute, 2024, 41(10): 30-39.

Figures/Tables 14

Fig.1 Sketch of the Changjiang River estuary

Fig.2 Temporal variations in water level at measuring stations in the middle and lower reaches of Changjiang River from July to October, 2022

Fig.3 Temporal variations in river discharge, wind speed, wind vector and intake salinity from September to October, 2022

Fig.4 Computational domain and grids

Fig.5 Temporal variation in water level in August, 2021

Fig.6 Temporal variations in flow velocity and direction in January, 2021

Fig.7 Measured wind speed and wind vector at the weather station on Chongming eastern shoal in October, 2022

Table 1 Statistical indicators of water level simulation and observation values

水文站	CC	RMSE/m	SS
新村沙	0.98	0.05	0.93
崇西	0.97	0.10	0.92
堡镇	0.98	0.12	0.94

Table 2 Statistical indicators of flow velocity and wind speed simulation and observation values

站名	CC	RMSE/(m·s^-1)	SS
3^#浮标站	0.76(0.81)	0.43(0.26)	0.76(0.85)
5^#浮标站	0.82(0.84)	0.32(0.25)	0.86(0.89)
崇明东滩气象站	0.74	0.55	0.76

Fig.8 Distribution of unit width net water flux, unit width net salt flux during neap tide from 18 to 21,October

Fig.9 Distribution of salinity at ebb slack during neap tide

Fig.10 Distribution of salinity difference at neap tide ebb between before and after emergent water supply

Fig.11 Profile distributions of salinity and flow velocity along sections at ebb slack during neap tide

Fig.12 Temporal variations in salinity at the water intake of Qingcaosha reservoir

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