Background & Project History

Geological History
History of Pevensey Levels
Geography Geology & Hydrology
History of Settlements
Levels of Importance
Coastal Processes
Sea defences

Geological History

Pevensey Bay is located in the softer sediments that lie between the Sandstones that form the ridge running through Ashdown Forest and meeting the coast near Hastings, and the Chalk of the South Downs. Pevensey Levels used to be an embayment open estuary when sea levels reached about the present day level ~5,000 years ago following the sea level rise during the Holocene. With this rising sea level, sand and gravel from the Channel floor was pushed landward and together with longshore drift from west to east created a shingle barrier similar to that seen today that closed the embayment by ~4,000 year before today. However, the bay did not stay closed, being opened at least once at ~2,500 years ago.

The image below shows schematically how sea levels have risen since the last ice age and that the sea only reached Pevensey about 5,000 year before today. Outcrops of chalk on the Channel floor are shown in pink, and it is flint from this chalk that is likely to have contributed to the beach material that was pushed northwards by the rising sea level.

Schematic change in sea level within the English Channel during the Holocene

The historic development of Langney Point and The Crumbles since the 16th Century can be seen following this link.

History of Pevensey Levels

The history of the lowland marsh area between Eastbourne and Bexhill, today known as the Pevensey Levels, is dominated by the changing relationship between land and sea. The first record of Pevensey, under its modern name, is in a charter of the 10th century - little is known about the earlier Roman settlement. There is no evidence of Roman occupation on the marshland behind the beach, presumed to be un-reclaimed, so that at high tide most of the level was a lagoon. Boats would have been able to moor at Pevensey Castle, which was located on a peninsula guarding the mouth of the estuary of the Pevensey Haven. At high tide there would still be many small islands of higher ground projecting above water level and evidence of this exists in place names that have the suffix 'ey' or 'eye' - the ancient term for an island (e.g. Manxey or Horse Eye).

Geography, Geology & Hydrology

The Pevensey Levels refer to the low lying area between Eastbourne and Bexhill-on-Sea, East Sussex. They are a wetland of national and international conservation importance and were awarded a Site of Special Scientific Interest (SSSI) designation in 1990 and a substantial part also became a Ramsar Site in 1999, designating it a Wetland of International Importance. They have also a high agricultural value. They are classified in the UK as wet grassland (RSPB et al, 1997) and were originally seasonally flooded. The Levels are a working landscape made up of a patchwork of livestock, arable farming and nature reserves. Different users have different needs for water level management.

The formation of the levels was dominated by the changing relationship between land and sea. The Levels themselves are a complex inter-bedded sequence of alluvial clays and peat. The peat layer is of variable thickness and fragmented in nature. It is generally overlain by at least one and a half metres of clay. The soils developed upon these substrates are described as "deep stoneless, mainly calcareous clayey soils of the Newchurch series of the Wallasea sub-group" (British Geological Survey, 1987).

The wetland catchment is delimited by the Chalk of the South Downs to the south-west, the foothills of the Weald to the North, composed mainly of Tunbridge Wells Sands, and outcrops of Wadhurst and Weald Clays to the east and west. The southern boundary is formed by a shingle barrier beach which isolates the wetland from the sea.

Two main watercourses feed the Levels; Pevensey Haven and Wallers Haven. Pevensey Haven is fed from streams to the west and north of the Levels and flows down to the Bay where it enters the sea through outfalls maintained by the Environment Agency. A network of small streams flowing south from the Ashdown Sands to the sea at Norman's Bay feed the Wallers Haven draining 600 ha of upland catchment in addition to 320 ha of grazing marsh. In summer months the Haven acts as a reservoir for public water supply. The amount of water allowed to flow out to sea has to pass through a sluice gate controlled by the Environment Agency. High levels are needed in the Walters Haven to ensure outlying ditches and streams are kept topped up to support the resident wildlife.

The hydrology is dominated by the dynamics of the relationship between stream inflow, rainfall, outflow to the sea and evapotranspiration. Groundwater movement is not important, since a clay layer effectively isolates the Levels from the underlying chalk aquifer. Meteorological data collected at the Horse Eye Meteorological Station suggest that the mean annual rainfall (between 1941-1970) was 800mm (Southern Water Authority, 1971a). Comparisons with the 1961-1990 mean annual rainfall value has suggested a 5 % increase in recent years (National Rivers Authority, 1993), although several droughts in the past 25 years have been significant. There is an eastwards decrease in rainfall; prevailing south-westerly winds loose a considerable proportion of rainfall when passing over the South Downs, 15 kilometres due west of the wetland. Annual evapotranspiration calculated by the Penman method (1941-1970) estimate values of 550 mm/yr on the seaward side of the wetland and 525mm elsewhere on the wetland assuming a surface albedo of 0.25 (Southern Water Authority, 1971b).

In addition to the natural input, seven Sewage Treatment Works (STWs) discharge into the Pevensey Levels. Water from these sources can account for large proportions of inputs to the wetland water budget, particularly during dry summers. Contributions from these sources are an import to the hydrological system, water having originated in the Arlington Reservoir, in the catchment of the Cuckmere River, directly to the West of the Pevensey Levels.

Water moves through the Pevensey Levels by a complex network of ditches. Water levels in the ditches are controlled by a series of pumping stations and sluices operated by the Environment Agency for the benefit of agriculture and conservation. In many of the ditches water can flow in either direction.

Farmers use ditches instead of fences to prevent cattle and sheep from straying. In some areas water levels in the ditches have been lowered to grow crops.

History

The earliest records describing the Pevensey Levels date from Roman Times. At that time, all land below 4mO.D. (Ordnance datum) was submerged at high tide and the area was a wide, tidally-influenced bay studded with an archipelago of small islands or eyots. These areas have retained their names to the present day with the suffix 'ey' or 'eye' (eg. Horse Eye, Chilley, Manxey and Pevensey). The Roman garrison fort of Anderida was sited in a peninsula jutting out into the bay and it was here that William the Conqueror landed in 1066. It is commonly thought that even in Roman Times, some form of shingle beach existed roughly on the line of the present shore. There would have been significant gaps in the beach to allow out the flow of the forerunners of the Pevensey and Wallers Havens. High tides would have also entered through these gaps in the beach and into the tidal lagoon behind allowing boats to have moored where Pevensey Castle stands today.

There is evidence to suggest that salt making was an important occupation in the area at the initial stages of the economic exploitation of the marsh. Attempts to reclaim the marsh date as early as 772. Evidence from two Anglo-Saxon charters of the time and records from the castle demesne suggest that the land was ploughed, sown and harvested at this time, albeit on a small scale. Only in the 10th century is Pevensey first mentioned in a charter and the Domesday Book (1086) records that the edges of Pevensey Marsh reputedly supported 100 salt works so that it can be assumed that salt water still inundated much of the present marsh area.

Reclamation in earnest began in the Middle Ages and was achieved by progressively enclosing portions of the marsh within sea walls. The main factor that allowed the reclamation of the Pevensey levels was undoubtedly the development of the Crumbles shingle ridge.

By the time of the Great Flood, in 1287, almost all of the present marshland had been reclaimed. The flood affected a large area and two years later resulted in the appointment of the first recorded Commissioners of Sewers for the Sussex Coast. From the first 'inning' to the end of the 14th century all the Levels drained out to sea to a point due south of the castle. In the latter part of the 14th century a large cut was made to replace the former outlet. Another cut was made due west, diverting the Ashbourne stream to provide more effective water evacuation and groynes were built into the shingle ridge to stabilise it. Ditches were constructed to connect with these main channels and by 1696 the "innings of the Pevensey Levels" had been completed.

The underlying problem faced throughout history has been that as soon as the marsh is dammed off to prevent the sea coming in, it is only possible to discharge freshwater out to sea at ebb tide. This then leads to the risk of flooding the land behind the sea wail.

When the first Commissioners dammed off the Pevensey Haven (somewhere near the current Pevensey Bridge) they also had the additional problem of the Haven silting up, thus reducing the capacity for vessels entering the port.

The reason so much time and money was spent on reclaiming the marshland was because the value of the recovered land was greater than the established upland, as it was far more fertile. Indeed, during the 14th century the area was considered to contain some of the most valuable arable land in the county, supporting a large population. However, the land began to suffer more and more from freshwater flooding and by 1402 the entire area was again under water. To cure this problem a new cut was made from what is now Middle Bridge on the A259 to a new outfall at Normans Bay. This was a forerunner of the Wallers Haven.

Whilst the risk of freshwater flooding has been alleviated, the power of the sea began to cause problems. The Commissioners at this time were not responsible for the maintenance of the sea walls since they were monastic properties. With the dissolution of the monasteries the sea walls were neglected and drifting shingle blocked the tidal channels resulting in the area between Pevensey and Bexhill returning to salt marsh.

The battle to keep the Haven mouth open to shipping continued until 1st November 1694, when an engineer, William Markwick, was engaged to build a new sluice at the mouth of the Haven and cut off all the remaining tidal creeks which were soon drained. From time to time major works have had to be carried out to balance the risks of freshwater and tidal flooding. Examples of this are the construction of the Pevensey New Cut and Sluice in 1748 and in the period between the late 1950s and 1980 a number of schemes were implemented to improve the drainage of the marshland, enabling the land to be used for arable production and to guard against flooding during periods of tide-lock.

Since much of the area is significantly below high tide level (typically +2m above mean sea level, compared to high tides of up to +4.2m), it is not possible to discharge floodwaters at high tide. Drainage schemes are necessary to ensure the land is usable.

Pearson, A F (1999) Building Anderita Late Roman Coastal Defences and the Construction of the Saxon Shore Fort at Pevensey Oxford Journal of Archaeology 18 (1), 95 - 117.
Dulley, A J F (1966) The Level and Port of Pevensey in the Middle Ages. Sussex Archaeological Collections, 104, 26-45
Salzmann, L F (1910) The inning of Pevensey Levels. Sussex Archaeological Collections, 53, 30-60
 

Levels of Importance

This low-lying marshland supports a rich community of plants and animals including the rare Fen Raft Spider (Dolomides plantarius) which is widespread on the Levels. With a white stripe down the side of its abdomen, the Fen Raft Spider can be confused with a similar species, but as Britain's largest spider it is easy to recognise when it is fully-grown.

Twenty-one of Britain's 38 dragonfly species have been recorded on the Levels including the nationally scarce hairy dragonfly (Brachytron pratense) and variable damselfly (Coenagrion pulchellum). Twenty per cent of Sussex' breeding population of yellow wagtails nest there.

Four of Britain's rarest freshwater snails (molluscs) also like the conditions on Pevensey Levels where they make their homes in the lime rich drainage ditches. The Little Whirlpool Ram's horn, Shining Ram's-horn, the Large-mouthed Valve Snail and the False Orb Pea Mussel all appear on threatened species lists.

Pevensey Levels offer the water vole a great habitat with an extensive network of ditches and drainage channels, but there were only three records of water voles in the 1980s. If you spot any surviving colonies on the Levels or anywhere in Sussex contact your local Environment Agency office.

Sadly, there has been a decline in the numbers of breeding and wintering birds over the last 30 years and today, despite its extensive area, the Pevensey Levels no longer support any species in nationally important numbers.

It is widely believed that the decline in wet grassland species such as wintering wigeon, teal and snipe and breeding redshank, lapwing and snipe resulted from the installation of pumped drainage in the late 1960s.

The Environment Agency has an important role in helping to improve the condition of the Pevensey Levels SSSI by adjusting the management of water levels within the ditches. A survey in 2006 by Natural England, showed that whilst large areas of the marsh were already in favourable condition for notified species (ditch flora and fauna), year round target water levels of 30cm below field level were needed to improve areas in poor condition.

The Environment Agency's has developed and implemented a Water Level Management Plan to target these poor condition areas. Many of the water control structures on the marsh have been replaced, refurbished and automated to offer a greater degree of control over water levels. These actions, alongside many landowners actively encouraging shallow winter flooding and sensitive ditch management, should result in greater numbers of wintering birds and ditch flora and fauna generally.

Flood Defence

The Environment Agency operates within the flood defence policy and guidance set out by the Department for Environment, Food and Rural Affairs (Defra). Regional and Local Flood Defence Committees oversee and authorise the Agency's flood defence work. A majority of local authority members make up the Sussex Local Flood Defence Committee.

Before it can take action the Agency must gain the approval of the Flood Defence Committee. Where capital investment is proposed, approval from Defra is also needed. Planning permissions are often required.

The Flood Defence Committee decides how much levy to raise on the local councils to fund the work. In Sussex the levy is raised on the West and East Sussex County Councils and Brighton and Hove Unitary Authority. This money is later refunded to the local authority from Central Government.

In addition to the local authority levy, money can also come from Defra as grant aid specifically for major capital works. It can be up to 65% of the cost, with the remainder coming from the local council levy.

The responsibility for looking after the problems of flooding and erosion along our coastline is complicated.

The legal position behind the various powers, duties and obligations has evolved over hundreds of years, involving the Environment Agency, local authorities and local landowners.

Most of the coastal work carried out by the Agency and Local Authorities can be divided into sea defence and coast protection.

Sea defence works generally reduce the risk of low-lying land flooding from the sea. Coast protection works generally reduce the rate of erosion of cliffs by the sea. While the Environment Agency does not have a duty to provide sea defences, it does have permissive powers to take action. District councils and unitary authorities can undertake coastal protection work. The Environment Agency works closely with these authorities to ensure that where action is taken it is coordinated along the coastline.

Powers to do work exist but strict economic and environmental criteria have to be met. They are linked to what are called 'benefit to cost studies' and 'environmental assessments.' This process ensures the Agency and local authorities invest wisely on behalf of the nation. It these criteria are met and the necessary external approvals obtained, the scheme will enter the Flood Defence Committee programme and be undertaken when funds permit, according to the priority assigned to the scheme.

The Pevensey Bay Coastline

The coastline along Pevensey Bay has changed naturally in the past leading to large scale long term changes that can bee seen in historic maps. Even over decades and on a smaller and localised scale, the coastline is changing its position across a coastal zone. The mechanisms and processes behind these changes still operate today and will do so in the future so that to maintain the coastline in the position that it has been fixed by present day settlements, these processes have to be counterbalanced by management activities.

Pevensey Coastal Defence Ltd maintains the Pevensey Bay coastline on behalf of the Environment Agency . The land to the west is looked after by Eastbourne Borough Council and consists of the higher land of the urban area of the town.

To the east Rother District Council looks after the low cliffs fronting the town of Bexhill. In practice the Agency, Eastbourne and Rother work together very closely to protect the coastline. The entrance to Sovereign Harbour is a breach in the coastline that prevents shingle movement along the coast.

Coastal Processes

As the coastline is exposed to the power of the sea it tries to adapt to minimise the effects. For example waves from the southwest will move beach material northeastwards to create a beach alignment that is more parallel to the waves; this can be seen to work very efficiently within the groyne embayments at Eastbourne. Another example is that during a storm the beach will flatten which result in a profile that reduces the wave energy reaching the top of the beach. This change is known in the short term as 'coastal processes' and over longer times scales as 'geomorphological change'. It may not be possible to provide sea defences that will survive in the longer term and costs will increase as sea levels continue to rise and in the face of an increase in storms or a change in their directions.

Soft defences of sand and shingle can be very effective in absorbing and breaking up the power of the waves. This is particularly so where flood protection rather than erosion prevention is the main aim. Groynes can help to retain the shingle and maintain a coastline that is out of a natural alignment but open beaches are more effective in some circumstances and while they might have higher maintenance costs, the capital investment into structures that eventually needed to be replaced are much smaller and future adaptations to the location of the coastline within the coastal zone are easier and less costly to implement from an open beach.

The Pevensey Bay Sea Defences

Pevensey Bay's shingle sea defences are 9 km long. The crest of the sea defences lies at about 6mO.D. and in most cases the shingle bank extends seawards around 45 m. The beach seaward of the defences is sand and of shallow gradient. Over the period 1973 - 96 there was no discernible change in crest height and the shingle ridge was overall as wide as it had been for a number of years. In 2000 there were over 150 timber groynes along the frontage, many of which were in a relatively poor state of repair. As they fail, groynes are being removed so that ultimately only ten or so will remain, which will be needed to maintain major discontinuities in beach alignment.

The sea defences provide protection from the permanent flooding of a 50 square km area including Pevensey Bay, Normans Bay, Langley, Westham and parts of Pevensey itself. Within this area there are more than 10,000 properties, important recreational and commercial sites, transport links (main road and railway), wetlands of international importance and two important nature reserves (Hooe Flats and Pevensey Levels). Should there be a serious breach of the sea defences then all these sites could be flooded.

Reduced Risk of Flooding

It is important to remember that the Pevensey Bay sea defences were built to reduce the risk of flooding to the low-lying land across the Pevensey Levels. Many current developments, such as caravan sites on low lying land and indeed properties built into the crest of the sea defences, are to a degree incidental to this. The defences were not built with protecting these developments in mind.

The Environment Agency maintains the Pevensey Bay frontage to reduce the risk of Pevensey Levels again becoming a lowland tidal marshland. In this way the Agency reduces the risk of flooding and damage to property, roads, railway and the unique ecology of the Levels. Given the nature of the construction there has always been a risk of defence overtopping and temporary breach. As a result there has been a long history of temporary flooding problems with the last reported major flood being in October 1999 when overtopping of the defences caused damage to some of the crest top properties. On Christmas Eve 1999 many local residents were evacuated because of the prospect of high tides and high winds. A change of wind direction provided some relief and the worst fears were to prove unfounded. There are records of similar events in 1926, 1935 and 1965. Nevertheless, the future of this area is likely to be affected by problems of high sea level and storms.

Sea Defence Options

Future defence options for Pevensey Bay were examined in an Agency study in the mid 1990s. The document, which examined options from doing nothing through to such structures as rock islands, concluded that it was possible to defend Pevensey Bay for the foreseeable future. This level or defence could prevent the Levels from returning to permanent salt marsh. It would not guarantee protection against temporary breaches or overtopping of the defences at any location.

Although most of the options studied would do the job, the preferred option has to comply with strict economic guidelines. These guidelines require that the costs of such a scheme must be exceeded by the potential flood damage thereby avoided. The Strategic Study for Pevensey Bay concluded that an 'open shingle beach' solution would satisfy these economic criteria whilst other options involving large rock groyne structures could not be justified. Against this, it must be remembered that it is impossible to stop all flooding. Pevensey Bay although well defended will always be at some risk from both overtopping and breach of the defences.

In addition to this the Government requested that the Agency look at the possibility of providing sea defences through a private financial initiative (PFI). It was following this that the Agency selected Pentium Coastal Defence Ltd (now Pevensey Coastal Defence Ltd) to manage the sea defences on behalf of the Agency for 25 years at a cost of 30 million.

In summary, the future defences at Pevensey Bay will be managed as a more open beach with fewer groynes. Pevensey Coastal Defence Ltd will carry out periodic shingle replenishments, the maintenance of some strategic groynes, recycling of material around the beach and reprofiling during and after storms.

Pevensey Coastal Defence Ltd, Westminster House, Crompton Way, Segensworth West, Fareham, Hampshire, PO15 5SS
Registered in England, Company No. 03776520