A Study of Horizontal and Vertical transport Timescales in the Changjiang Estuary and its Adjacent Regions

The Changjiang Estuary is one of the largest estuaries in China. Because the geomorphology of the Estuary is very complex with multiple branches connecting to the open sea, an integrated residence timescale is not sufficient to reveal the temporal and spatial variability of the transport and flushing properties in the Changjiang Estuary. A three-dimensional hydrodynamic model was developed and utilized to investigate the long-term transport process and variations of estuarine circulation under the impacts of nature and the human activity in the estuary. The results show that the fresh water discharge plays a key role in controlling the long –time transport time. The water flows slower in the upper portion in the North Passage and South Passage due to the change of the freshwater discharge diversion and the increase of the friction in the downstream after the building the Deep Waterway Project. The water exchange between Changjiang Estuary and Hangzhou Bay exhibits a high spatial variation. Large water age is observed in the region near the southern coast, which is characterized by high pollutant deposition and low water quality observed in the field. The magnitude and direction of wind have a large impact on estuarine transport time . and play a critical role in the renewal of the water in Hangzhou Bay. The potential impact of the vertical transport time on the hypoxia in the Changjiang Estuary and adjacent regions will also be discussed.

Rereference

Gong, W., J. Shen, B. Hong. 2009. The influence of wind on the water age in the tidal Rappahannock River. Marine environmental research 68 (4):203-216.

Liu, Y., P. MacCready, B. M. Hickey. 2009. Columbia River plume patterns in summer 2004 as revealed by a hindcast coastal ocean circulation model. Geophysical Research Letters 36:L02601.doi:10.1029/2008GL036447.