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London Gateway in the pipeline

On the north bank of the Thames Estuary, a £1.5bn project to dredge, reclaim and build Europe’s newest deep-sea container port is underway.

On an ordinary, grey day in Stanford-le-Hope - a part of Essex on the north bank of the Thames Estuary - three large vessels are steadily dredging a channel, and using the material to reclaim a huge area of land from the Thames.

This is the £1.5bn London Gateway port project, covering 600ha of land east of London on the former Shell Haven oil refinery site.

When completed, the London Gateway will comprise deep-sea container port capacity for the world’s largest cargo ships, and Europe’s largest logistics park offering more than 860,000m² of space.

36,000 jobs

The project is conceived as a transformative asset that will create 36,000 new jobs, contribute £3.2bn to the UK economy annually, and negate millions of road miles of freight transport each year by offering a port and logistics park in close proximity. It will add 3.5M twenty-foot equivalent units (TEUs) to the nation’s port capacity.

The project is being developed by DP World, one of the globe’s largest marine terminal operators, which is calling this the most significant UK port development for 20 years.

It is certainly the largest private foreign direct investment (FDI) project in the country, and it is hoped that the port will serve as a catalyst for further FDI in the future. “We have no grants at all from UK bodies,” says DP World London Gateway chief executive Simon Moore - although he says some money has come from the EU.

“All this stuff we’re standing on has been created by dredging and moving large quantities of land. It’s quite spectacular”

Vince Cable

Visiting the site in October, business secretary Vince Cable praised the reclamation efforts. “All this stuff we’re standing on has been created by dredging and moving large quantities of land. It’s quite spectacular,” he said.

“The sheer size and scale of this project is staggering.”

And so it needs to be. The size of vessels that London Gateway will be able to accommodate is equally huge.

Since the start of containerisation in the 1950s, ships have substantially grown from an average length of 200m and hull draft (the vertical distance between waterline and keel) of less than 9m to the 397m lengths and 15.5m drafts of today.

First phase

Laing O’Rourke and Dredging International are the companies contracted for the first phase of construction, which comprises the reclamation of 2.7km of land to form the port; the construction of a new jetty; the installation of a quay wall; and dredging to deepen the existing navigation channel, which will be 100km long and 300m wide.

The existing northern approach channel to the Thames Estuary will be dredged to a depth of 14.5m in the inner channel and 16.5m in the outer, to accommodate the large container ships.

Dredging will be carried out using 9,000m³ capacity trailer suction hopper dredgers, which draw seabed deposits into a drag head and up through a pipe just under 1m in diameter, from where they are pumped into a hopper.

Valves return water and fine sediment to the estuary, and the rest of the material is then taken to London Gateway and discharged into the reclamation area either by bottom dumping or by being pumped through a pipeline.

Additional dredging will be done by a cutter suction dredger, which will discharge into the reclamation by pipeline. Up to three dredging vessels can be on site at any one time.

The discharge pipelines for both types of dredger will initially connect to a spreader pontoon to enable the material to be placed precisely in layers. Once areas within the reclamation footprint have been completely enclosed, pipeline discharge will become direct.

Two phase reclamation

Shell still has an active bitumen plant on the London Gateway site, so the reclamation was split into two stages meaning that work could commence on the eastern half of the reclamation while a jetty was completed further along the coast. Now that the concrete and steelwork for the new jetty are finished, the western half of the reclamation can begin on the site of the old jetty when required.

The reclamation stages are divided into a series of cells. The spreader pontoon diffuser head creates a bund, which forms a cell outline to be infilled. The first stage of the reclamation comprises four cells.

Construction of the quay wall will begin later, in 2011. It will be 42m deep and constructed as a 1.25km long diaphragm wall, using a Hydrofraise machine to excavate a trench which is filled with bentonite to support the sides. A steel cage is dropped in and then concrete is pumped in to displace the slurry.

Laing O’Rourke says that the high water table in the area means 400,000 band drains must be used to draw up water and disperse it laterally once the dredged material is reclaimed, in order to expedite ground settlement.

The ground will need to settle up to half a metre and the band drains will accelerate that settlement.

Work started on site in March and approximately 25% of the dredging and land reclamation is already complete, with work continuing 24 hours a day. Six million tonnes of dredged material has gone into the reclamation so far. This first phase of London Gateway construction will be completed in 2012, says Moore, although dredging will continue into 2014. No maintenance dredging is expected to be necessary, says Dredging International environmental manager Daniel Leggett.

“The known sand banks tend to stay where they are. We don’t anticipate problems after we finish.”

Environmental impact

Environmental impact is one aspect of construction which has had to be taken very seriously on the project, owing to the ecological and archaeological sensitivity of the estuary.

An ecological advisory group (EAG) has been formed to provide a forum for discussions between DP World and stakeholders including the statutory regulators, the Port of London Authority and the Environment Agency. New wetlands have been created nearby for wildlife, and inter-tidal mud flats are being replaced.

So far, says Leggett, the EAG is happy with London Gateway’s attention to the environment. “No-one would try to say there are no effects from an operation on this scale, but thus far we are keeping effects to a minimum,” he says.

In addition, dredging operations are being intensively monitored. Twelve monitoring buoys are spread along the dredge channel to measure sediments and water turbidity. A four-person monitoring team is dedicated to watching the buoy readings. “Simon Moore gets immediate notification by text if it’s too high so he can amend dredge operations accordingly,” says Leggett.

Pollution minimisation

All plant on site also uses biodegradable oils, meaning that in the event of any leaks, the impact of pollution in the estuary will be minimised.

The London Gateway represents one of Europe’s largest brownfield reclamation projects. Shell invested over £50M in clearing the site after it closed its Shell Haven oil refinery in 1999, although some further remediation is still required.

Over 100 workers are currently on site clearing the site of animals and old infrastructure including Shell bitumen pipelines.

Overall, London Gateway is a complex project that still has a long way to go. The 300 workers on site at the time of NCE’s visit will swell to 700 by Christmas, building on the good progress made so far.

The dredging, reclamation, new jetty and quay wall are only the first part of the project - still to come are the construction of port infrastructure and the whole of the logistics centre. “There are projects within projects,” says Leggett.

But the work happening on site now is setting a benchmark of responsible and efficient construction, which promises to deliver an important new asset for the UK.

Readers' comments (1)

  • Great stuff. No indication of the volume or rate of material shifted by this dredging/pumping method?

    The advancing technology should be used to de-silt some of the world's great reservoirs, many of those built in the 1960's being half silted up. One at least (in the Indus basin) has become run of the river. On the principle of using some power fed back to achieve this (as with carbon capture elsewhere), a dredger could work around the reservoir and pump the silt downstream past the dam. Half the head would be available there already. As the reservoir level varies seasonally, different parts of it could be de-silted. Some of the arisings may be useful as aggregate, fill etc. or for agriculture.

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