Margate coastal scheme (2011 to 2012)

Margate is located on the north Kent coast in the district of Thanet. Margate’s wide sandy beach faces northwest and is sheltered from waves from the north and northeast by the Stone Pier, which is a Grade II listed structure owned and maintained by Thanet District Council.  The seawall was in a poor condition, dating back to Victorian times, and had been patched up over the years to maintain its integrity, although many of the most exposed sections had reached the end of their design life.

Whilst the majority of the town is elevated above the extreme flood level, there are parts of the seafront and areas immediately landward of this that are below this level, they are consequently at risk of flooding. The financial cost of damage to property in the Old Town area, resulting from a major flooding event, could have been as much as £70m affecting approximately 700 residential properties and 175 commercial buildings.

Under the East Kent Engineering Services Partnership, Thanet District Council approached colleagues at Canterbury City Council to design and supervise a scheme. Specialist input was provided by a flood risk management consultant who produced vital computer modelling which was used to steer the direction of the design work. A landscape architect and project artist were also appointed to the design team to help develop the structure.

The results of the physical modelling showed that a shallow sloping stepped revetment would reduce wave overtopping to below the critical threshold under the design event conditions. The preferred revetment configuration was the 1:4.5 stepped slope with a 2.7m wide mid-height berm.

The Environment Agency funded the £3.9m project which was awarded to J Breheny Contractors Ltd. Work commenced on site at the beginning of November 2011 and was completed by the end of March 2013. The scheme has reduced the risk of flooding from wave overtopping through four key improvements:

Strengthening works to the Grade II listed Stone Pier

The Stone Pier plays a vital part in protecting Margate and was strengthened as part of the works. This involved 295m of toe piling and stabilization of the loose chalk core by grout injection. Breheny brought in M & J Drilling as a specialist stabilization contractor to drill and grout the voided core structure. 930 holes around 10m deep were drilled on a 2m grid spacing, many formed at raking angles to avoid surface obstructions. Grout was injected under monitored pressure to fill and consolidate voids. In total 9,700m of drilling was carried out and approximately 400 tonnes of grout was injected in more than 10,000 stages.

Pre-cast concrete stepped revetment 

A major part of the new scheme is the new 220m long stepped revetment centred in the area of the King’s Steps on Marine Drive. The stepped revetment structure has over 400 precast blocks that were manufactured by Cornish Concrete Products Ltd. Each block weighs up to 15 tonnes and there are more than 60 different block types which make up the revetment structure. Each individual block was placed with a 2mm accuracy using a specially designed battery powered vacuum lifter. Contemporary LED lighting has been incorporated in the mid-berm.

New and raised seawalls either side of the revetment and new rear seawall with timber swing floodgates

The scheme also included the construction of new sea walls along the remainder of Marine Drive and The Parade either side of the revetment. The original Victorian Sturgeon lamps were all refurbished and placed on new pedestals. The last surviving section of Victorian handrail was also refurbished and incorporated into the scheme. Swing floodgates have also been installed at each end of the revetment and in the new rear wall at the back of revetment and will be closed in the event of a flood warning.

Hydraulic powered raising floodgate and wall across the Rendezvous frontage

A key element of the scheme is the 7m wide stainless steel hydraulic powered raising floodgate and section of sea wall across the Rendezvous frontage. The works in this area are required to divert overtopped sea water, back into the harbour via the slipway, which would otherwise flow behind the new defences to the Old Town flood compartment.