Dynamic mechanism of extremely severe saltwater intrusion in the Changjiang Estuary occurred in February 2014

Abstract

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.