Challenges of Land reclamation at Royal Pier Waterfront (RPW), Southampton

Forming new property from the sea has gotten sophisticated, even as the relentless tides are a force to be reckoned with. But it’s worth the investment.

The new scheme at Royal Pier in Southampton will be constructed partly on existing land at Mayflower Park and Town Quay, and partly on land reclaimed from the sea. It is this reclaimed land that presents the major challenge for Lucent Group ("Lucent") on this project.

As participants in a joint venture land opportunity know, any work undertaken on the coastline is always going to be difficult, but the scale of the reclamation at Royal Pier Waterfront ("RPW") presents its own trials. In essence Lucent will build a dam out into the Test Estuary using sheet piling that stretches from the existing Red Funnel ferry terminal right out to the tip of the old pier structure, then returning back in a straight line to the western end of Mayflower Park. This will create a 13 acre lagoon, and the next step will be to pump out most of the sea water which will leave a large ‘hole’ – ideal to be made into a large basement and exactly what Lucent plans to do.

There are a number of issues in doing this, not least of which is installing the sheet piling in the first place. This requires long ‘W’ section steel sheets to be driven into the sea bed from a floating barge, and these sections must interlock through a system of clutches to create a reasonably water tight seal with its neighbour. Once the sheet piling is complete the water can be pumped out.

The next challenge is keeping the water out so that work can commence on the basement structures. This is done by using ‘dewatering’ plant, which consists of sinking a number of tubes into the seabed around the perimeter to create a system of wells from which the remaining water can be pumped away. This lowers the water table and creates a dry working area. Because there is a lot of porous gravel under the seabed, water pressure from the tide causes the ground water level to fluctuate throughout the day, placing a varying demand on the dewatering plant during the course of 24 hours.

Once the ground water is under control, a level platform needs to be created on the seabed.  This level platform is called a piling mat. This consists usually of a thick layer of crushed rubble and provides a stable working area so that plant and machines can begin constructing the basement.

The sheet piling installed earlier now needs to be stabilised to prevent it from being damaged by the action of the waves. One of the traditional ways to do this would be to sink ‘sacrificial’ piles into the seabed and connect these to the sheet piles using steel tie rods. However because we are creating a basement, we can use the concrete floor slab to stabilise the piles instead, while a reinforced waterproof concrete wall is constructed behind the sheet piles. Investors in joint venture partnerships want to know they are building on a solid foundation, literally and figuratively. By this point we should have 13 acres of reclaimed land on which to commence construction.

Of course the alternative for our land fund managers would be to build a traditional revetment sea wall and back fill the whole space with dredged material, but that wouldn’t be much fun would it?