Flood prevention and coastal protection work has recently been completed at a Kent UK seaside resort that has in the past, experienced the devastating effects that storm surges can have on towns not prepared for the worst.
On the north east tip of Kent, the seaside resort of Margate faces north at the narrow end of the funnel that comprises the Thames Estuary and southern North Sea. Devastating storms and subsequent flood damage have been recorded as far back as 1646, including the storm of January 1953 when gale force winds and high spring tides caused a storm surge that wreaked havoc and led to the loss of over 2,500 lives in countries bordering the southern North Sea, including the UK, Belgium and the Netherlands.
The old town area of Margate was flooded, with the whole coastline experiencing major damage. Half a century later, rising sea levels have again left the area at risk, resulting in a £3.5m project to increase flood defences to 1:200 for the next 50 years. The recently completed Turner Contemporary art centre sparked a regeneration of the old town area and another flood would have significant implications for the town beyond that of the 1953 event.
Needham Market based Breheny Civil Engineering was awarded the contract by Thanet District Council to reinforce the coastal flood protection provision in the area, while at the same time enhancing the landscape and amenity value of the seafront as part of the council’s regeneration plans.
The project involved two main areas of attention. Strengthening of the harbour arm (key to the protection of the old town) was essential but the main work was concentrated on the sea-facing Marine Drive and The Parade, the stretch of waterfront most exposed to north-westerly winds.
Basically, the height of the wall along the seafront needed to be raised and the work involved re-facing of the lower walls while the upper walls were removed and reconstructed using higher precast concrete units. The most visual aspect of the work involved construction of a 220m long shallow sloping stepped revetment in way of the most exposed part of the seafront, requiring sheet pile installation with capping beam. It was important to preserve the sea views and the inclusion of this innovative engineering solution removed the need for a high seawall along the more exposed stretch.
Work on the harbour arm included repointing the stone face walls and 295m of toe sheet pile installation with capping beam. The loose chalk core was stabilised with grout injection to a 2m grid. Resin bonded surfacing was also applied to the arm’s road surface. A ‘weak spot’ in the area’s defences is the slipway in the corner of the harbour. This provides important access to among others the RNLI lifeboats, housed ashore nearby for which uninterrupted access was provided throughout the works. Work carried out here increased the safety factor from flooding, including installation of a 7m wide stainless steel hydraulic raising floodgate and new raised seawall frontage in front of Turner Contemporary.
As always keeping control of costs was important and two value engineering solutions were adopted. Using rough cast casting of the sheet piles along with curtain grouting produced savings of £21,500 for Thanet Council. Programming of the work allowed for tidal working, especially during spring tides when mechanical work was restricted due to roosting birds. Public access to the stepped revetment, without compromising the flood defence element has been cleverly built in to the design with the inclusion of swing flood gates at access points.
