133 / 2024-02-19 09:56:06

Simulation study of recharge fresh water for repelling saltwater intrusion in the Changjiang River Estuary in 2022

Changjiang River Estuary, Saltwater intrusion, Recharge fresh water, Drought event, Freshwater resource

Due to the extreme drought, the Changjiang River estuary experienced the most severe saltwater intrusion in nearly 50 years during the 2022 flood season. The cascade reservoirs, mainly the Three Gorges Reservoir, recharged a total of 4.063 billion cubic meters of water to the downstream, ensuring the safety of freshwater resources in the estuary. In this paper, we used a numerical model to quantitatively assess the effect of repelling saltwater intrusion, analyze the impacts of cold fronts and the timing of water recharge on water intake time of the reservoir in the estuary. The results show that recharge fresh water significantly repels saltwater intrusion in the Changjiang River estuary. The 0.45 isohaline in the North Branch, North Channel, and South Channel move downstream by 4 km, 18 km, and 31 km, respectively. The peak salinity at the water intake of Qingcaosha reservoir drops by 3, and the water intake time increases by 12.75 hours compared to no water recharge. Further research reveals that the wind-driven Ekman transport intensifies the direct saltwater intrusion in North Channel and significantly weakens the water recharge effect. Without cold front, the water intake time is 36.89 hours, which is 2.9 times than that with the cold fronts. Sensitivity analysis shows that when river discharge at Datong hydrological station increases, the salinity at the water intake begins to respond after 17.5 h on average, and the maximum decrease occurs after 6.1 d on average, which varies with the tide type. With cold fronts, the original water recharge timing has the best effect, the water intake time is 12.75 hours. Without cold front, the water recharge effect should two days in advance, the water intake time is 38.20 h. Recharge fresh water by the Three Gorges Reservoir effectively repelled saltwater intrusion in the Changjiang River estuary, while cold fronts reduced the effect.