Abstract:

Previously measured data indicate differences in salinity variation at the water intake of reservoirs in the Changjiang Estuary during strong northerly winds and different tidal patterns. In this study, a three-dimensional numerical model of saltwater intrusion in the Changjiang Estuary was used to simulate the impacts of climatic winds and strong northerly winds at a speed of 10 m/s for 5 days during four tidal patterns (neap tide, middle tide after neap tide, spring tide, and middle tide after spring tide) on saltwater intrusion and the unsuitable water intake time of the reservoirs. Numerical experimental results showed that the maximum unsuitable water intake time at the water intake of the Qingcaosha Reservoir reached 15.87 days, an increase of 11.63 days compared to that under the climatic wind condition in the experiment of strong northerly wind in the neap tide. The maximum unsuitable water intake time in Dongfengxisha and Chenhang Reservoirs reached 20.12 and 7.95 days, with increases of 5.36 and 4.48 days in the experiments of strong northerly winds during the middle tide after spring tide and neap tide, respectively. Strong northerly winds amplified the landward net water and salt fluxes in the North Branch, with the effect being most pronounced during the spring tide experiment; the practical salinity units (psu) increased significantly in the upper reaches, with a maximum value of 6 in the neap tide experiment. In the South Branch, the seaward net salt flux increased and peaked at 20 t/s in the spring tide experiment. Furthermore, the water diversion ratio increased significantly under northerly winds, with an increase of 4.79% compared with that under the climatic wind condition. In the North Channel, the net water fluxes decreased the most, and a large amount of salt was transported landward in the neap tide experiment. Furthermore, the isohaline of 0.45 (the salinity standard for drinking water) crossed the water intake of the Qingcaosha Reservoir, and the impact of saltwater intrusion was the most serious in the middle tide after neap tide experiment. Additionally, the salinity in the middle-lower reaches increased significantly by up to 8 under the influence of the strong northerly wind in the neap tide experiment. The seaward net water and salt fluxes increased under strong northerly winds in the South Channel, with the maximum net water fluxes in the neap tide experiment and net salt fluxes in the middle tide after spring tide. In contrast, salinity in the middle-lower reaches decreased, particularly in the South Passage, due to the increased water diversion ratio. The net water and salt fluxes increased during different tidal patterns under strong northerly winds in the North Passage, with the most notable increase in the neap tide experiment. Moreover, salinity in the lower reaches increased in the neap tide experiment and middle tide after neap tide experiment. The seaward net water and salt fluxes increased in the neap tide experiment in the South Passage, and salinity decreased slightly in all experiments, with the most remarkable decrease observed in the neap tide experiment.

Key words: strong northerly wind, tidal pattern, Changjiang Estuary, saltwater intrusion, estuarine reservoir