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Flood Risk on Romney Marsh

 

 

Index Icon Introduction
Index Icon More Information

Index Icon Defend Our Coast
Index Icon Current & Future Plans

 
 

Introduction

The coastline and low lying land within the Romney Marsh area is one of the largest areas at risk from flooding in Southern England. Some of the areas are very vulnerable, with a 1 in 5 chance of flooding from the sea in any year.

Failure to manage the risk of coastal flooding on Romney Marsh would result in 14,000 homes and 9,603  hectares of agricultural land in danger of flooding. In addition, key infrastructure such as roads, rail links and utilities serving these assets would be  lost. The Internal Drainage Board has estimated the value of agricultural land on Romney Marsh to be £290m using land value rates.

There are a number of Environment Agency (EA) led schemes currently at the planning stage which when completed will raise the standard of protection across the Marsh in line with climate change/sea level rise predictions.

More Information

Defend Our Coast

The 'Defend Our Coast Association' is dedicated to holding the line, to keep the sea out and defend the wider Marsh.
It has been set up by local people living on the Romney Marsh following the previous lack of community involvement by Government Agencies during sea defence policy planning, Shoreline Management Plans and consultation with local stakeholders.

The aims of Defend Our Coast are: 

  • To act on behalf of all local communities on the Marsh in negotiations with various Government Agencies in order to maintain and improve our existing sea defences.
  • To liaise closely with all local Stakeholders, Businesses and Local Authorities to protect our communities from flooding.
  • To justify to Government the continued need for sustainable communities on the Marsh and to ensure that ‘managed realignment’ is not an option.
  • To work closely with all local communities to highlight coastal defence issues and associated effects of climate change.
  • To disseminate all relevant information on sea defence issues throughout our local communities, councils and educational institutions and generally improve coastal literacy.

You can find our more at the Defend Our Coast website.

Current Situation and Future Plans

Below we look at the current situation and future plans for the various sections of the Romney Marsh Coastline.
[information taken from a Shepway DC report dated September 2012].

Lydd Ranges

This frontage is part of the southern  shore  of  the  Dungeness  peninsula that is eroding due to a lack of sediment input from alongshore. The existing defences at Lydd Ranges comprise the shingle beaches and a secondary defence behind, consisting of an earth embankment known locally as the ‘Green  Wall’. At the western end, the  Green Wall is immediately behind the beach and at the eastern end is several hundred metres behind the beach. The defences have a 5% (1 in 20) to 10% (1 in 10) chance of failure in any one year where the likely failure mode would be a breach. There  have been occasional breaches of the wall in past years,repaired locally with shingle from the surrounding area.

Owing to a significant change of circumstances for the MOD the option and policy for defending the Lydd Ranges was changed from  ‘Managed Realignment’ to ‘Hold the Line’. The preferred scheme for Lydd includes improvements to the secondary defence (Green Wall), a rock revetment, shingle recharge, groynes (at the western end of the frontage) and a sheet piled wall(at the eastern end of the frontage). At £121m whole life costs, the scheme in its original form was more than £30m more expensive than the environmentally preferred option which was ruled out due to the loss of some MOD land. It could be argued that the additional £30m should be provided by the MOD defence budget and it is understood that negotiations are ongoing with them and other parties over scheme contributions. The EA is also considering how phasing of the work and beach maintenance options will impact upon delivery costs.

Denge Marsh Sewer to Dungeness Power Stations West

A shingle ridge provides the flood defence along this frontage. This is maintained by the EA through beach profiling. A tidal flap prevents sea water flowing along the Denge Marsh Sewer. The existing defences have a 20% (1 in 5) chance of failure in any one year, where the likely failure mode would be overtopping and breaching. This standard of protection will decrease over time if sea level rises as predicted.

This frontage is now included  within the Lydd Ranges frontage and the proposal here involves realigning the defence landward between the Denge Marsh Sewer and the Power Stations Switch House by improving the standard of protection and installing timber-clad plastic piling. This will limit the ingress of still water level flooding, whilst the shingle ridges and beach on the seaward side of the realigned defence will dissipate wave action. Realignment would improve the defences so that the risk of failure decreases to a 0.5% (1 in 200) chance in any one year up to 2108.

Dungeness Power Stations

A massive shingle embankment provides protection against a wave with a 0.01%  (1 in 10,000) chance of occurring in any one year, (essentially a tsunami  event). The embankment is designed to prevent the tsunami wave breaching the defences and overwhelming the power station. Tidal flooding, e.g. from a storm surge, is not understood to be a priority as the flood warning system would allow sufficient time to shut down the station in advance of an event.

Ongoing protection here involves sustaining the current standard of defences, taking account of predicted sea level rise. This would meet the safety case for the power stations until 2108 and covers the power stations generating and decommissioning phases. As the stations are decommissioned, the nature and location of the hazard requiring the 1:10,000 year tsunami protection will change. There will be ongoing reviews of the flood defence needs throughout decommissioning with management of the defences adapted accordingly.

Dungeness Shingle Recycling

The Environment Agency has been working with EDF Energy to submit a joint planning application to recycle shingle from Dungeness Point to maintain the flood defences around the power stations and along the Denge sea front.
Find out more at the Environment Agency website

Dungeness Power Stations to Greatstone

The coastline along this section is naturally accreting ie gradually increasing. At present, the shingle beach and ridges provide an appropriate standard of defence for the hinterland and there is no management intervention. ‘No active intervention’ is proposed along this frontage.

Greatstone to Romney Sands

There are sand dunes along much of this frontage that form the flood defence and provide an appropriate standard of protection. The dunes have a 0.1% (1 in 100) chance of failure in any one year, where the likely failure mode would be erosion leading to breach.

Shepway DC has responsibility for this frontage and since 2009 have successfully bid for funding to maintain the Greatstone dune system (£15k/annum). Maintenance comprises managing pedestrian traffic through the dune system by fencing to prevent erosion. The sand fencing also increases accretion of the dunes at the base rather than the tops.

Greatstone Dunes to Littlestone South

There are no formal defences in this area and the beach provides a low standard of protection with a 2% (1 in 50) chance of failure through breach in any one year. The frontage lies between the Greatstone Dunes in the south and Littlestone beach in the north where there is a seawall and shingle beach.

The preferred option on this frontage is for a beach recharge to raise the beach crest between the Varne Boat Club and the southern end of the sea wall at Littlestone in line with climate change/sea level rise predictions. The EA is currently in discussion with Southern Water with regard to the possibility of constructing a rock groyne around an extension to the sea outfall. It is estimated that this scheme will require an external contribution of  around 75% of scheme costs in order to proceed. There are also issues around the Bathing Water Directive which may be difficult to resolve. An ‘insitu’ compensatory habitat would also need to be provided should the scheme progress.

Littlestone to St Mary’s Bay

A coastal defence scheme for this frontage was completed in 2004 by the EA. The scheme comprised substantial recharge of the shingle beach, strengthening and raising of the seawall, placement of rock, construction of a new promenade and the construction of a terminal rock groyne south of the Jesson Outfall. The scheme allowed for future recycling of shingle that accretes against the terminal rock groyne, back across the frontage. The net drift rate is northerly; however,in practice the movements of shingle have been driven by a series of north easterly sea states (i.e. the shingle is moved towards the south west), resulting in little recent accretion at the terminal rock groyne. The defences here have a 1% (1 in 100) chance of failure in any one year, where the likely failure mode would be overtopping and erosion of the beach.

The proposed option for this frontage is to Hold the Line by continuing to maintain the current scheme for the first 50 years and then sustaining the existing defences so that risk of failure remains at 0.5% (1 in 200) chance of failure in any one year,up until 2108. The EA is considering the possibility of combining this frontage with the adjoining frontages which could prove beneficial in beach management terms.

2014/15
Littlestone is to get new flood defence work in 2014/15. £1.5million has been provided to upgrade the beach defences to protect some 4,500 homes.

St Mary’s Bay

The defences along this frontage consist of extensive concrete stepped revetment, a promenade and concrete wave return wall. The defences are in good condition, having been constructed in the mid 1990s by the EA.

The proposed option for this frontage is to Hold the Line by continuing with the existing scheme until the end of its design life (about 35 years), then by improving the existing defences. This option maintains the landscape character of the area whilst addressing the increasing flood risk over time due to climate change/sea level rise. The standard of protection would be increased so that the risk of failure is 0.5% (1 in 200) or less in any one year until 2108.

High Knocke to Dymchurch

This frontage, know as the Dymchurch Wall, is divided into two sub-sections. Frontage A begins at the north end of High Knocke and extends north for approximately 2.3km. Frontage B begins at this point and extends for approximately 2.5km to Dymchurch Redoubt. Frontage A defences comprise a raised and strengthened seawall and a stepped concrete revetment. The Frontage B defence structures are similar to those along Frontage A, with the addition of a rock revetment along the lower part of the structure to improve wave energy dissipation. Prior to the completion the Frontage B scheme in 2011, the existing defences had a  0% (1  in  10)chance of breach in any one year. Currently, the risk of failure is reduced to 0.5% (1 in 200) in any one year, up until 2108.

The new schemes for Frontages A and B will continue to fix the coastline in position, reducing its ability to respond to natural processes. The policy is to maintain the current standard of defence at 1 in 200 through general maintenance.

Hythe Ranges

The existing defences comprise a shingle beach with timber groynes. Rock has been placed along sections but is does not form a structural revetment ie protection. These defences have a 5% (1 in 20) chance of failure in any one year through overtopping and breach. This standard of protection will decrease over time if sea level rises as Predicted. The defences here are managed by the MOD in order to protect the Hythe Ranges training facility.

The original Hold the Line option here was to improve the existing defences by constructing a new rock revetment. The structure would incorporate a track along its crest to facilitate access for the MOD. This would remain in place for 50 years, after which the defences would be realigned along the seaward side of the A259 road that borders the range complex (an option that is only viable if the MOD  no longer required the ranges for operational purposes for the latter part of the strategy appraisal period). The scheme will increase and sustain the standard of protection with the risk of failure decreasing to a 0.5% (1 in 200) chance in any one year. The EA is now considering a phased approach to this scheme – Phase 1 at the western end incorporating the Dymchurch Redoubt frontage and the first 600m of the Ranges and Phase 2, the remainder of the Ranges from the 600m  point to Fisherman’s Beach. As with Lydd, the EA is in discussion with the MOD and other stakeholders with regard to funding contributions.

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