Abstract. Estuarine saltwater intrusions are mainly controlled by
river discharge and tides. Unexpectedly, an extremely severe saltwater
intrusion event occurred in February 2014 in the Changjiang estuary under
normal river discharge conditions. This intrusion cut off the freshwater
input for 23 d into the Qingcaosha reservoir, which is the largest
estuarine reservoir in the world, creating a severe threat to water safety
in Shanghai. No similar catastrophic saltwater intrusion has occurred since
records of salinity in the estuary have been kept. During the event, a
persistent and strong northerly wind existed, with a maximum speed of 17.6 m s−1, lasting 9 d and coinciding with a distinct water level rise. Our study demonstrates that the extremely severe saltwater intrusion was caused by this northerly wind, which drove substantial landward net water transport to form a horizontal estuarine circulation that flowed into the northern channel and out of the southern channel. This landward net water transport overpowered the seaward-flowing river runoff and transported a
large volume of highly saline water into the northern channel. The mechanisms of this severe saltwater intrusion event, including the northerly wind,
residual water level rise, landward water transport and resulting horizontal circulation, etc., were systematically investigated.
Abstract. Estuarine saltwater intrusion is mainly controlled by river discharge and tide. Unexpectedly, an extremely severe saltwater intrusion event in February 2014 occurred in the Changjiang Estuary under normal river discharge conditions. It cut off the freshwater input for 23 days into the Qingcaosha Reservoir, which is the largest estuarine reservoir in the world, creating a severe threat to water safety in Shanghai. Such catastrophic saltwater intrusion has not occurred since recorded salinity in the estuary. During the event, a persistent and strong northerly wind existed, with a maximum speed of 16 m s−1, lasting ten days and coinciding with a distinct water level rise. Our study demonstrates that this extremely severe saltwater intrusion was caused by a persistent and strong northerly wind, which drove substantial landward Ekman transport to form a horizontal estuarine circulation that flowed into the North Channel and out of the South Channel. This process surpassed seaward runoff and brought very large amounts of highly saline water into the upper reaches in the North Channel. An ordinary cold front passing over the estuary cannot produce strong saltwater intrusion; only a strong northerly wind lasting 8 days can produce a severe saltwater intrusion in the Changjiang Estuary. The revealed dynamic mechanism is important to ensure safety of freshwater resource utilization in estuaries.
Estuaries are areas where runoff and tide interact. Tidal waves propagate upstream from river mouths and produce tidal currents and tidal level variations along rivers. Based on the hydrological frequency analysis of river discharge in the dry season and flood season at the Datong hydrological station over the past 70 years, a three-dimensional estuary numerical model was used to produce the quantitative relationships between the tidal current limit, tidal level limit and river discharge in the Changjiang River estuary. The positions of tidal current limit and tidal level limit depend not only on river discharge but also on river topography. When river discharge varies from a hydrological frequency of 95% to 5%, the relationship between the tidal current limit and river discharge is y=2×10−13x3+3 × 10−8x2− 0.0074x+359.35 in the flood season, with a variation range of 90 km, and y=−4×10−10x3−1 × 10−5x2−0.1937x − 1232.9 in the dry season, with a variation range of 200 km. The relationship between the tidal level limit and river discharge is y=6×10−8x2−0.0096x+775.94 in the flood season, with a variation range of 127 km, and y=0.3428x2−17.9x+777.55 in the dry season, with a variation range of 83 km, which is located far upstream of the Datong hydrological station.
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