Littlehampton Tidal Flood Defences, UK | 2014

The Comprehensive Project for Protecting Littlehampton Against Predicted Sea Level Rise in the UK

Working in partnership with Arun District Council, West Sussex Council and Littlehampton Harbour Board, the Environment Agency is improving the tidal flood defences along the East Bank of the River Arun in Littlehampton, on the South Coast of England. The work is being carried out by VolkerStevin and CH2M Hill and is budgeted at £14.1million.

Completed at the end of 2014, the scheme protects 2,000 residential properties and businesses against 75 years of predicted sea level rise as well as enhancing the riverside walkway between the town and the beach.

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Typical cross section Tidal Flood Defences River
Littlehampton, UK © High Camera Ltd
Littlehampton, UK © High Camera Ltd
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Two types of retaining wall were considered for the structure which has to withhold upto 6.9 m soil and ground water without lateral support. Initially a tubular wall in combination with AZ® steel sheet piles was thought to be the most economical but on consideration of the long design life, the HZ® / AZ® combined wall system from ArcelorMittal was found to be the most economic and technically feasible solution. 

It utilises large HZ®-M (HZ 1180M A-sol.12 & HZ 1180M D-sol.12) beams with welded interlocks, which are installed by panel driving techniques down to the required levels before AZ 26 sheet piles are driven to connect the beams into a continuous wall. The beams carry the vast majority of the bending moments and have the advantage that the face of the beam is small in comparison with a tubular solution.

Soils typically consisted of made ground with overlying chalk of varying strength. The made ground was the result of previous port construction (and activity) and was very varied. It included obstructions and cobbles. The chalk was weak in the upper layers, but increased in strength with depth and had flints and cobbles within the matrix.

The installation was carried out by VolkerStevin. Very robust driving frames have been constructed such, that the lower frame was close to high tide level and then the wall was installed with a combination of vibratory techniques (PVE 40VN) and noise shrouded percussive techniques (BSP CX85 in 7 Tonne mode and BSP CX110 in 9 Tonne mode). All equipement was heavily shrouded with double skin acoustic shrouding to keep noise levels to a minimum.

The site worked through some very difficult conditions with the wettest winter for some years, in conjunction with long periods of gale force winds. The installation works on Reaches 1 & 2 have been successfully completed with piling work moving to higher reaches using conventional AZ® sheet pile walls.