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Making space for mooring on the waterway

A new marina for an old canal posed big challenges in working clay, piling and minimising traffic disruption

Project Saul Junction Marina
Client Land & Water Estates
Project manager Land & Water Services
Cost £2.5 million

A little over two hundred years ago, rich industrialists ploughed money into digging the canal network across the country to improve cargo links between the industrial production centres and ports.

But their heyday was brief and by the late 19th century the canals had been usurped by railways as the major transport routes of their day.

A renaissance for our inland waterways and an increasing demand for leisure boat moorings means new marinas are being built up and down the country.

One such development is under construction a few miles to the south of Gloucester near the village of Saul.

Here the junction of the Gloucester and Sharpness Canal, with its links to the tidal River Severn, and the Stroudwater Navigation, with its connection (once restored) to the Thames and Severn Canal and on to London, has prompted developer Land & Water Estates and its contracting arm Land & Water Services to invest £2.5 million in a 284-berth marina.

With access from the Stroudwater Canal, the new marina will have boat chandlers, docking, slipway and showering facilities, everything to keep the discerning boatie happy.

The outlook for inland marinas is so strong it has seen canal and river network manager British Waterways set up a New Marinas Unit to ease their development.

"There is definitely huge potential in their construction," explains Land & Water Estates director Neil Warren, who was one of the first to spot the potential for decent returns on investment. "Much of it is being pushed by British Waterways. For them it makes perfect sense to get boats off-line and into marinas, it helps free up the waterways themselves."

Mr Warren pinpointed Saul Junction as having development potential because of its proximity to a host of navigable waterways. It is now down to Land & Water Services project manager Phil Bollard to deliver what will be a key project for the company.

A keen boatman himself, albeit with more of a seafaring bent, Mr Bollard is excited about the potential for Saul Junction Marina and the development of more around the country.

Liquid assets

"Land & Water is keen to expand its business in this sector," he says. "We aim to be building at least two marinas a year for the next six years. We will work for other development clients as well as our own development arm."

At Saul one of the prerequisites was to keep off-site traffic movement down to an absolute minimum. Fortunately Land & Water and the earth moving subcontractor, Bristol-based Kelston Sparkes, were able to ensure that none of the 75,000 cu m of earth left the site.

"We were lucky in that the site is a greenfield site, but we still had to make sure there was enough material we could reuse," says Mr Bollard.

Site investigations had revealed that most of the material on site was of broken up limestone and sandstone as well as a mixed clay. It is this clay deposit that has been used to line the base of the marina by forming an impermeable layer between water and formation level.

"It's a re-engineered clay. It has had all the larger pieces of stone removed and it conforms to the British Waterways specification for puddle clay," says Mr Bollard.

That specification is notoriously tough and it needs to be. What no-one wants to see is either a leaky canal or one which could pollute the underlying water table or the canal water itself.

A specification which rules out the use of lime stabilised material can be difficult enough. Throw in a requirement for more than 65 per cent of the natural material to be finer than 0.06 mm and more than 40 per cent finer than 0.002 mm and it is clear the re-engineering of the clay is fundamental to the project's success.

"Of the 75,000 cu m of earth we dug out, we were able to re-engineer 18,000 cu m for use as the puddle clay liner layer," says Mr Bollard.

The material is excavated in 10 metre wide strips across the site to within 200 mm of formation level using GPS guided dozers and scrapers.

Keeping track

This ensures that the site team can keep track of where they are on the project and also means the formation is protected against damage by rain and construction traffic.

When enough material has been engineered into puddle clay, the final 200 mm is taken off before the puddle clay liner is laid in 250 mm layers and compacted using a sheep foot vibrating roller.

It is laid to a depth of one metre around the perimeter of the marina, tapering down to 700 mm across the rest of the site.

With only a limited amount of material suitable for use as puddle clay, the remaining excavated arisings are being used alongside a low-density plastic liner beneath the batters that form the basin's circumference. Any remaining material will be used for landscaping.

"The batters are preformed with 'no sharps' arisings and lined with a Nicoflex 800 LDPE plastic liner. It's an industrial heavyweight version of a pond liner really," Mr Bollard explains. "We are using stone-filled gabions for the wharf walls around the fuel docking, office and washroom facilities."

Row after row of steel columns are driven through the puddle clay liner to an embedment depth of three metres to help form the series of 1,200 mm-wide walkways and 750 mm-wide jetties, produced using 6.1 m span timber beams fixed to each column through a bolted galvanised crosshead.

These sit at 200 mm above final water level, which itself is 1.6 m above the final marina bed level.

Finding the right depth

"The draught on a canal barge is normally only about one -metre. Marinas more than 1.4 m deep are rare because of that, but here we are in close proximity to the tidal reaches of the -River Severn and the Gloucester-Sharpness canal is three metres deep.

"We wanted to give some of the keeled boats that use the waterway chance to use the berths," says Mr Bollard.

Boating enthusiasts have already given the scheme their approval, with more than a quarter of the berths snapped up after just one open day at Saul.

"We know there is a huge amount of potential in the project and I am confident it will be a success when it is completed in February next year," says Mr Warren.

Development unit to speed investment

British Waterways is so convinced of the commercial sense behind inland marina development that the canal network manager has set up its own marinas unit to help speed up their development.

"We work in a similar way to motorway services," explains Land & Water Estates director Neil Warren. "British Waterways agrees to supply the water and we pay them a percentage of our mooring fees."

The New Marinas Unit will offer guidance on the design and build of new facilities as well as supporting a new development through the relevant planning process, although it will withdraw that support if the development is not begun within a set period. This helps alleviate the problem of developers holding onto land with planning permissions in order to boost the value of that land.

For further details on British Waterways New Marinas' Unit see britishwaterways.co.uk/marinadevelopment

How the marina is filled

The only thing keeping gallons of water from flooding into the marina and draining the Stroudwater Canal is a clay piling mat at its entrance which acts as a plug.

The mat will be used by piling rigs to help form the curved concrete entrance walls to the marina.
But soon two rows of timber stop logs, set about a metre apart, will dam the water back until Mr Bollard and his team are ready to allow the marina to fill.

"Filling is carried out at an agreed, steady rate. It will take a few days," says Mr Bollard. "We can only fill when British Waterways allow us to as they will have to make sure the Gloucester/Sharpness canal is topped up."

Once filled, the two rows of stop logs will be replaced and the gap drained out, making the marina totally independent of the canals.

By monitoring the weather conditions and the water level over time, the team will be able to work out the rate of water leakage from the marina.

"There are no two ways around it. If there is a major leak it would be drain and start again," he says with a confident smile.