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Coastal defences: A new shield against the waves

littlehaven prom at night cropped

A complete realignment of a seawall and promenade has restored a picturesque piece of coastline in England’s north east.

 

Littlehaven is a little known beach in South Shields in the north east of England. It sits nestled inside the north and south piers at the mouth of the River Tyne and forms part of the coastal defences to the town behind.

However in 2012, the man-made vertical sea wall which formed the primary defence was at breaking point. Waves hitting the wall were reflected, creating turbulence at its base which scoured the sand away, exposing the supporting timber piles beneath. This in turn created voids in the structure and the loss of material was putting the concrete wall on a rapid path to collapse.

The original sea wall was built in the 1940s and also retained an area of higher ground which was built into the beach creating an unnatural protrusion. At high tide there was no separation of the land and the sea.

“In terms of the problem of the dereliction of the wall, it was for the most part due to the original alignment of the wall,” says Royal Haskoning DHV technical director Nick Cooper. “The old alignment stuck out into the bay, and that made it very vulnerable to any storm that occurred.”

It is not fully known why the additional land was created, however one theory was that the coal from the surrounding mines was brought to Littlehaven and then loaded onto boats at high tide straight from this elevated platform.

Now the area serves as a car park for surrounding businesses and visitors, but its low elevation meant that the sea would frequently break over the top of the wall and flood the area. Poor drainage would cause the water to pond and Tyneside City Council estimated that it needed to be closed to the public for at least 10% of the year.

Consultations on how to solve the problem suggested that the cheapest solution would be to pile large rocks in front of the wall to reinforce it. However, this would not have solved the flooding problem on the top and would have destroyed the council’s aspirations to create a continuous walkway along the coast.

The solution came from Royal Haskoning DHV who suggested that a complete remodelling of the beach would create a far more sustainable solution.

The team used historic maps to build up a picture of the evolving coastline due to the changing conditions to predict its response to future sea level rises. Along with crenulated bay theory, it was therefore able to create a new alignment for the beach. This involved removing the 1940s built up land, replacing the lost beach and putting in a new graded concrete apron set back from the shoreline as the new defence. The apron also doubled up as a continuous set of steps down from the new promenade to the beach giving direct access to it all the way along compared to only two previous access points.

Seeing the potential of the landscape which was to be created, the council jumped at the chance to regenerate the area. Landscape architect Oobe was employed to completely re-model and revamp the previously dilapidated sea front.

In breaking out the historic man made construction, huge quantities of rubble were created and sand excavated. The sand was used to reinstate the beach underneath the broken out 1940s build up and the rubble was relocated onto the land behind the newly formed alignment, raising its height and acting as an additional barrier to any extreme tidal events.

“The old car park was like a basin as it was much lower, so when waves came over the top, it just ponded,” says Cooper. “In the new car park area we raised the levels using some of this waste. Not only is it now better protected against waves coming over it in the first instance but on the rare occasions it does come over during a really big storm it is not as low lying and it is better drained.”

The new concrete “apron” was constructed behind the existing sea wall by excavating out the car park area in a strip, effectively forming a cofferdam in which the team could work. The apron has a sheet pile wall at its front which goes down 3m to protect its foundations from future scour. Originally the team envisaged that the structure would be constructed from precast concrete, however early on the purse strings were tightened and in a value engineering exercise it was proposed that it would be cast in-situ to save money.

Not satisfied with the potential drop in quality and surface finish that this may have, contractor Galliford Try suggested bringing the precast concrete manufacturer to the beach to create the same level of quality, but cast in-situ. Using steel as opposed to the more traditional timber formwork and a number of other techniques, a beautiful smooth finish was achieved.

“Normally you’re racing against the tide on every pour which is why many of these stepped apron systems are done with precast concrete,” explains Cooper. “But because we had this cofferdam, we brought factory workers onto site, we used steel shutters and lots of hand working post-pour.

“It was all done to a minute level of detail, filling in all of the holes and acid etching to get a really good quality of work.”

Today, sand has now been naturally deposited on the lower steps of the concrete apron by the tide and the area has been returned to its more natural form with the creation of 80m of new beach from the high tide line to the top of the apron. This ailing sea front has now been truly transformed with new elegant lighting, bespoke handrails and specially designed artwork which now grace the promenade. The area has become incredibly popular with local people and tourists alike.

“It is an area that people choose to go to rather than an area where people choose to avoid,” says Cooper.

 

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