Littlehampton River Arun Tidal Walls

Purpose

With the tidal River Arun running through its heart, more than 2,000 residences and businesses were at risk of flooding. New and raised defences were needed on the east bank Arun Parade near the river mouth, through the town centre to north of the A259.

What we did

The 2.5km of new defences were designed to accommodate 100 years of predicted sea level rises and protect the town from a 1-in-300 year storm surge. We installed nearly 450m of sheet piled walls, raised the existing promenade and raised and reprofiled earth embankments. We reconstructed the Arun View pub which backs onto the river and is part of the defence line, and carried out hard and soft landscaping works.

We installed the sheet piles on programme during difficult winter conditions. This meant less disruptive works could proceed during the busier summer season. We also drove king piles with intervening steel sheet piles into the underlying chalk bedrock, using crane suspended vibratory and impact hammers.

Access constraints were overcome by placing our 160t crane on a floating barge. Where access permitted working from the riverfront, we engineered two temporary steel platforms and shingle access ramps, to bridge over weak ground and site our crane and other plant.

We completed the walls by backfilling behind the sheet piles with granular fill, including reusing 400t of shingle from our access ramp, before placing concrete coping beams and pouring concrete insitu.

Disruption to residents, businesses and tourists was minimised, by avoiding weekend working and erecting noise barriers. We delivered much of the work just a few metres away from homes or businesses. Although we had to shut Pier Road and Arun Parade for periods, we minimised disruption to businesses by maintaining safe pedestrian access.

Despite very small losses of inter-tidal mudflat, we achieved a net gain of 0.75 hectares of inter-tidal habitat, by creating 0.27 hectares of new mudflat and 0.7 hectares of new saltmarsh. We achieved this, through managed realignment works in an area where the embankment was set back and bioengineered, to form a new embankment along the highway.

Project successes

We beat the target cost and programme and met the client’s aspirations to open early. The completed scheme has improved the standard of tidal defence, created new valuable intertidal habitat and regenerated the main tourist area, providing economic benefits for years to come. The 2.5km of upgraded tidal defence, now has a 1 in 300 years (0.33%) standard and the works protect 748 residential and 340 commercial properties.

The new defences incorporated enhancements to the promenade and riverfront area, with hard and soft landscaping providing an attractive environment for shoppers and tourists. This included stepped seating areas, wider pathways, additional lighting, planted areas and coloured concrete finishes. The scheme fulfilled a long-held council wish, to provide an uninterrupted link between the town centre and the sea front.

Our focus on meeting the needs of local people and visitors, during construction was recognised with a Considerate Constructors Scheme Gold award and an Environment Agency Project Excellence Award for Customer Service. Positive feedback received from the community included: ‘A great project for all that live and work here’; ‘Very necessary work and effectively carried out’; ‘Aren’t we lucky!’