Weng Mengyong: Dredging the Deepwater Channel at the Yangtze River Estuary
It is well-known that Shanghai is a city connecting the Yangtze River to the sea, and connecting China to the outside world for trade. Being an international shipping port of long-standing significance, Shanghai and the Yangtze River Estuary are indispensable for the economic development of the Yangtze River Delta region.
Since the 1970s, the transport departments have carried out large-scale dredging projects to maintain the Yangtze River Estuary at a water depth of 7 meters in order to improve navigation. By the 1990s, the annual maintenance dredging volume reached 15 million cubic meters, and the dredging intensity constantly increased. However, a 7-meter depth couldn’t meet the demands of large-scale vessels entering and leaving Shanghai Port.
In the 1980s and 1990s, vessels berthed were severely subject to size restriction. At that time, the gross tonnage of vessels sailing the Yangtze River Delta region already surpassed that of the entire inland waterways of Europe, but the Yangtze River, three times the length of the Rhine River, had less than one tenth of the Rhine in terms of freight volume.
The reform and opening up and the rapid development of China's economy made dredging the stronghold part of the Yangtze River Estuary more urgent than ever.
In 1992, the plan for the Yangtze River Estuary deepwater channel regulation and preliminary technical and economic demonstrations were rolled out for the first time.
“At that time, different opinions on the governance of the Yangtze River Estuary were held by academics, but they finally reached agreement in scientific and technological project under the 'Eighth Five-Year Plan’: Firstly, the Yangtze River Estuary was manageable: and secondly, from the hydrological data accumulated over the years, the condition of the Yangtze River Estuary was stable and it was a good time for management,” Weng Mengyong recalled.
On April 22, 1997, then Premier Li Peng presided over ta State Council meeting and agreed to implement the Yangtze River Estuary deepwater channel regulation project. Considering the complexity of engineering technologies, the project was phased in with dynamic management. Remediation and dredging were carried forward simultaneously, and finally the objective of a 12.5-meter deep channel was achieved.
The Yangtze Estuary deepwater channel regulation project is hailed as the “Underwater Great Wall”. Two long dikes with a total length of more than 100 kilometers guide the river and resist the quicksand like a Great Wall submerged at the bottom of the sea. Nineteen spur dikes, which are placed horizontally on the inner sides of dikes, carefully safeguard the channel.
Foreign experts described the project as a “mission impossible”
Sandbars pose severe challenges. Each year, 480 million tons of sediment are continuously deposit in the estuary, forming a turbid shoal up to 60 kilometers wide.
Projects of this kind are always time-consuming. The 13.7-meter deep waterway project of the Mississippi River in the United States took more than 150 years, the 13.6-meter deep waterway project of the Mersey River in the United Kingdom lasted for 45 years, and the 12.5-meter deep-water channel project in the Yangtze River estuary took the Chinese builders 12 years. Yet it was achieved against all the difficulties.
In March 2000, just after the completion of the 8.5-meter waterway of the first phase of the project and the announcement of navigability by the Ministry of Transport, five typhoons attacked unexpectedly. In just six months, water depth from 8.5 meters dropped to 7.3 meters due to sediments. The Yangtze River Estuary Deepwater Channel Engineering Construction Command worked around the clock. Finally, on January 1, 2001, the water depth was restored to 8 meters.
The second phase of the project then began. The first batch of 16 semicircular caissons, each 20 meters long and weighing more than a thousand tons, was installed in a line. But the first strong gales of winter blew away all the caissons and the levees were broken to pieces.
The third phase was mainly to dredge the north channel to increase the water depth from 10 meters to 12.5 meters, but the siltation during the excavation process was much more voluminous than predicted.
Statistics show that 74 innovative engineering technologies were applied in the Yangtze River Estuary channel regulation Project, including 49 original innovations. These advanced technologies in large-scale estuary channel dredging were originally created by China and unrivaled in the world.
On March 14, 2010, Weng attended the handover ceremony. “The completion of the Yangtze Estuary Deepwater Channel Regulation Project is of great significance in the water transport engineering sector in China. It is a milestone in the history of the industry,” said Weng.
The Yangtze Estuary Deepwater Channel Regulation Project was a “golden key” to open the "Golden Waterway" of the Yangtze River.
In 2016, benefiting from the deepwater channel of the Yangtze River Estuary, the passenger throughput of cruises berthed at Shanghai Port was 2.9 million tons, a year-on-year increase of 76.2%, making it the fourth largest cruise port in the world.
Weng said that the dredging of the Yangtze River Estuary is of nation-wide significance as the estuary does not belong only to Shanghai, but to the entire country.
A total of 15 billion yuan was invested in the three phases in the Yangtze River Estuary Deepwater Channel Regulation Project and the annual maintenance costs after operation have brought huge economic benefits.
It is estimated that since the opening of the 12.5-meter deep-water channel in the Yangtze River Estuary, the annual average economic benefit generated has exceeded 10 billion yuan. The annual GDP growth generated by freight volume exceeded 100 billion yuan, and the annual fiscal revenue growth boosted by the freight volume exceeded 20 billion yuan. Over 100,000 jobs have also been created each year.
Weng is very satisfied with the achievement. “The Yangtze Estuary Deepwater Channel Regulation Project has been continuously optimized from construction and operation to management.”
The project has also withstood the test of time for ecological and environmental protection and to date no adverse effects have been discovered.
The Yangtze River Estuary Project is located in the Jiuduansha Wetland Nature Reserve. In order to protect the largest and best-developed estuarine tidal flat wetland in Shanghai, no construction workers were allowed to dig sand, hunt or fish in Jiuduansha. They were also banned from cutting down vegetation or collecting benthic organisms. The construction units also subsidized restoration of aquatic ecosystems.
Channel dredging inevitably produces soil, and the Yangtze River Estuary is no exception. The average annual maintenance of dredging generates about 60 million cubic meters of dredged soil. Instead of being dumped into estuaries or the sea, which is harmful to the ecology, the dredged soil was utilized by Shanghai municipal government for land reclamation. As a result, more than 60^ of the dredged soil has been recycled.