Abstract:

This research analyzed the general erosion-deposition characteristics of submerged delta front, the spatio-temporal changing pattern in different sub-regions, the geomorphological changes in the typical cross-sections, and the geomorphological evolution and corresponding controlled factors of the four important sub-regions (i.e., the eastern tidal wetland of Chongming-CM, the Hengsha shoal-HS, the Jiuduansha wetland-JDS, and the eastern tidal wetland of Nanhui-NH). Data sources include high-resolution DEM, sediment load data at Datong Station, and corresponding estuary construction information. Major findings are: (1) in general, the study area was slightly eroded (51.83% vs. 48.17%) in the past 30 years; specifically, it experienced an "erosion-deposition-erosion" pattern in the three periods; the geomorphological change was significant both spatially and temporally in the eight sub-regions, with an exception of the North Channel staying eroded; (2) the eastern and northern parts of CM and HS, the northern part of JDS, and the region within the 5m-isobath of NH were mainly dominated by the vertical deposition, while an opposite trend in southern CM and HS, and the region within the 5m-isobath of eastern and southern JDS; (3) on the whole, the envelop areas of 2 m and 5 m isobaths of the four important sub-regions kept increasing, and the average annual growth rates reached 10.42 km²/a and 7.99 km²/a respectively in the period of 1982-2010 (however, four sub-regions exhibited disagreements); the envelop area of 10m-isobath decreased in the whole region as well as sub-regions; the envelop area of 15m-isobath changed slightly during the period and remained stable; (4) influenced by the estuarine engineering, CM was the only station whose isobaths envelop area decreased, in accordance with the decline of the sediment load at Datong Station. Major conclusions are that estuarine engineering plays an increasingly important role in affecting the geomorphological change in the submerged delta under the macro-background of the reduction of sediment load, in terms of change in the envelop areas and the distribution of isobaths in the Submerged Delta. Along with the accelerating construction of Shanghai International Shipping Centre and reclamation engineering, the geomorphological evolution of submerged delta will become more complex and thus deserves frequent monitoring in the future.

Key words: Yangtze Estuary, submerged delta, erosion-accretion changes, sediment load, controlled factors