Introduction

Yangtze Estuary is a giant river mouth，and the runoff discharge is steady about 900 billion m3 per year.Yangtze Estuary included four passages into the East Sea，and also lots of beaches around the river mouth.

The bathymetry of Yangtze Estuary was shown as below.

Fig.1　bathymetry of Yangtze Estuary and　the layout of navigation channel

Natural water depth of mouth bar area is only 5.5～6.0 m，for shipping development demands，a large-scale deep-water channel was conducted through mouth bar in the river mouth.The channel was nearly“50 km”long and“0.35～0.4 km”wide，and with 12.5 m depth，that made it navigable for 50，000 DWT ship.

Since 2010 after the engineering was finished，the 12.5 m deep-water navigation channel played a significant role in the economic and social benefits，but at the same time，the amount of sediment concentration phenomenon is also very prominent，maintenance dredging volume was huge and costed a lot.

In fact，even before project，in order to maintain water depth of North Passage up to 7.0 m，for 10，000 DWT ship，dredging volume is about 12 million m3 per year.According to statistics，in order to maintain water depth of North Passage up to 12.5 m，for 50，000 DWT ship，annual channel sediment siltation was up to 82 million m3 per year.