Decadal variations in the erosion/deposition pattern of Nanhui muddy bank and their mechanism in the Changjiang Delta

HUO Miao; FAN Dai-du; LU Qi; LIU A-cheng

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HUO Miao, FAN Dai-du, LU Qi, LIU A-cheng. Decadal variations in the erosion/deposition pattern of Nanhui muddy bank and their mechanism in the Changjiang Delta[J]. Haiyang Xuebao, 2010, 32(5): 41-51.

Citation:

HUO Miao, FAN Dai-du, LU Qi, LIU A-cheng. Decadal variations in the erosion/deposition pattern of Nanhui muddy bank and their mechanism in the Changjiang Delta[J]. Haiyang Xuebao, 2010, 32(5): 41-51.

HUO Miao, FAN Dai-du, LU Qi, LIU A-cheng. Decadal variations in the erosion/deposition pattern of Nanhui muddy bank and their mechanism in the Changjiang Delta[J]. Haiyang Xuebao, 2010, 32(5): 41-51.

Citation:

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Decadal variations in the erosion/deposition pattern of Nanhui muddy bank and their mechanism in the Changjiang Delta

1.
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
2.
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China; Key Laboratory of Ministry of Education for Yangtze River Water Environment, Tongji University, Shanghai 200092, China
3.
State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China; Information Centre of East China Sea, East China Sea Branch, State Oceanic Administration, Shanghai 200137, China
4.
Information Centre of East China Sea, East China Sea Branch, State Oceanic Administration, Shanghai 200137, China

Received Date: 2009-09-28

Abstract

Abstract

Nanhui muddy bank shows its cyclic geomorphic evolution at different time scales.The nearly-a-centennial alternations of serious erosion and deposition are obvious from the bathymetrical data analyses of the longest time series (1842—2004) of charts available in the Changjiang Estuary.The erosion phase is characterized by "accretion on the northern and eastern flats,and erosion on the southern flat and the transition belt",while the deposition/erosion pattern is generally reversal during the deposition phase.The changing phases from erosion to deposition are inferred to highly relate to the shifting of the Changjiang main channel from the South Channel to the North Channel.There are much more and stronger storms in the erosion phases than the deposition phases.It is presumed that the pattern of"the higher flat erosion and the lower flat accretion" results from the iterative recording of bank erosion profiles by larger storms in the erosion phases; while the pattern of "the higher flat deposition and the lower flat erosion" is ascribed to the enhanced preservation of normal bank accretion landforms under weak wave conditions in the deposition phases.Net accretion/erosion regimes of the river delta are highly related to sediment discharge,but the morphodynamics is far from unification with the different delta sections undergoing dynamic erosion/deposition cycles at different tempo-spatial scales,which is jointly controlled by tides,waves,and river distributary processes through diverting riverine sediment toward/away from the study sections.There are at least three scenarios having been proposed for the critical sediment discharge (CSD) turning the delta from net accretion into net erosion.The higher and medium CSD values are considered to overestimate due to their deduction from segments instead of the entirety.The average annual sediment discharge has declined to 154 Mt/a since 2003 when the Three-Gorges Dam started its first phase operation,much lower than the lower CSD value of 184 Mt/a,but the Changjiang Delta is not observed to undergo the presumed change from net accretion into net erosion till now.Recent hydrologic data did not show the decrease of suspended sediment content in the estuary,either.It is partially due to the Changjiang Delta of tidal dominated type where tides play an important role in redistributing sediment within the estuary,resulting in lag response of delta to the sediment decrease.Synthetical studies are therefore proposed to improve complex processes in tide-dominated estuaries,and to elevate the accuracy for CSD scenario construction and the adaptability to potential disasters related to coastal erosion.
- Changjiang Delta,
- tidal flat,
- erosion/deposition cycles,
- estuarine processes,
- storms,
- Three-Gorges Dam,
- critical sediment discharge for delta shifting from net accretion into net erosion

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References(46)

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