Flood Risk Assessment in the Pevensey Levels

The Pevensey Levels are a 4,300-hectare drained coastal marsh stretching between Eastbourne and Bexhill-on-Sea, much of which lies below the level of a high spring tide and is held back from the sea only by the shingle bank at Pevensey Bay. Almost the whole area sits in Flood Zone 3. A flood risk assessment in the Pevensey Levels has to treat the marsh for what it is, a defended floodplain, where the tide, the rainfall the land cannot shed by gravity, and a high water table all have to be reconciled on the same site.

Unda prepares flood risk assessments in the Pevensey Levels for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies. We know this landscape and the bodies that govern it, the Environment Agency, East Sussex County Council as lead local flood authority, and the Pevensey and Cuckmere Water Level Management Board, and we turn their requirements into a report that holds up to scrutiny.

Behind the Pevensey Bay defences sits land low enough that, in a worst-case breach, an estimated 36,500 residents and more than 2,000 properties could be affected, which is exactly why a site here has to be judged on its residual risk, not just its flood-zone label.

Speak to one of our experienced flood risk consultants for a free, no-obligation quote. We reply to every enquiry within 60 minutes. Call +44 (0) 1293 214444 or start a quote online.

• Where it is. A 4,300-hectare grazing marsh between Eastbourne and Bexhill, spanning the Wealden, Rother and Eastbourne planning areas.
• Flood zone. Predominantly Flood Zone 3, the highest-probability zone on the Environment Agency’s Flood Map for Planning.
• Dominant risks. Tidal and coastal flooding held back by sea defences, surface water that cannot drain by gravity from the marsh, and groundwater on low-lying ground.
• The defences. The Pevensey Bay shingle bank, maintained to roughly a 1-in-400-year standard through continual replenishment.
• Who governs it. The Environment Agency for the sea and main rivers, East Sussex County Council as lead local flood authority, and the Pevensey and Cuckmere Water Level Management Board for the internal drainage network.
• Protected status. A Site of Special Scientific Interest, Ramsar wetland, Special Area of Conservation and National Nature Reserve, so the Habitats Regulations apply to development.

Check flood risk anywhere in the Pevensey Levels

The Pevensey Levels are outlined below. Screen any postcode against Environment Agency data for rivers and the sea, surface water and the planning flood zones, with a climate outlook to 2125. It is an indicative first pass to orient a site, not a substitute for a site-specific assessment.

Flood risk in the Pevensey Levels: a defended tidal floodplain

The Pevensey Levels flood for the same reason they exist as farmland: the land is too low to drain itself. The sea is kept out by the Pevensey Bay shingle bank, rainwater is moved off the marsh through a network of ditches and pumps, and groundwater sits close to the surface. Most sites face more than one of these at once, so a single map rarely tells the whole story.

The sea, the shingle and the Pevensey Bay defences

The marsh is shielded from the English Channel by the shingle barrier at Pevensey Bay, an 8.5km frontage maintained to roughly a 1-in-400-year standard. From 2000 the beach was managed under a 25-year Environment Agency contract delivered by Pevensey Coastal Defence Ltd, which ended in March 2025; the work now continues under the Pevensey Bay to Eastbourne Coastal Management Scheme. Its short-term phase, running from 2025 to 2027, manages the Pevensey Bay frontage and protects more than 3,000 homes and businesses, with the longer-term scheme aiming to safeguard up to 18,000 properties from coastal flooding and erosion over the next century. Maintaining the beach depends on continual shingle replenishment and recycling, because sea levels in southern England are projected to rise by more than a metre this century.

None of this removes the risk. Defences reduce the probability of flooding, not the possibility of it, and a defended site can still flood through a breach, overtopping or asset failure. The Environment Agency’s Flood Map for Planning shows the floodplain as if the defences were not there, which is why the Levels remain in Flood Zone 3 on paper. That residual risk is usually where a planning application here is won or lost, so it is the heart of any credible assessment. Our explainer on residual flood risk sets out how a breach or overtopping scenario is characterised, and the parallel with the Somerset Levels shows how low-lying former wetlands behave under pressure.

Surface water and the drained marsh

Behind the coast, the Levels are kept workable by an artificial drainage system. Two embanked main rivers, the Pevensey Haven and the Wallers Haven, carry water off the marsh to the sea, supported by the Hurst Haven and a dense web of ditches the area calls “sewers”. Top-opening retention gates sit roughly 500 metres from the main outfalls, and because those outfalls are tide-locked for about half of every day, the channels and pumping stations have to store water until the tide drops far enough to discharge. When heavy rain coincides with a high tide, water has nowhere to go and ponds on the land.

• Named low spots. Areas repeatedly identified at risk include the Crumbles, Manxey, Horse Eye, the Hooe Levels, Mountney Bridge and Norman’s Bay.
• An engineered system. The Pevensey and Cuckmere Water Level Management Board actively maintains only the most critical ordinary watercourses, around a quarter of the total length, alongside pumping stations and water-level control structures.
• Gravity runs out at high tide. Tide-locked outfalls mean surface water is stored and pumped rather than draining freely, so undersized site drainage shows up quickly here.
• Surface water is now the widest risk in England. Since the 2025 Planning Practice Guidance update, surface water can trigger an assessment even on land that screens as Flood Zone 1.

Groundwater on low-lying ground

On ground this low, the water table is rarely far down. Groundwater appears on no national flood map, rises from below according to the geology, and can sit high enough to flood basements and break the assumptions behind soakaway drainage. It is assessed within the flood risk assessment rather than as a separate exercise, but on the Levels it deserves real attention: infiltration drainage routinely fails here, and a credible design needs a wet-season picture of the water table rather than a single dry-day reading. See our notes on groundwater flood risk and on infiltration testing.

A history of flooding in the Pevensey Levels

The Levels have been won from the sea, lost to it and won back many times over, and that long record is why the authorities here scrutinise development so closely. A flood risk assessment in the Pevensey Levels has to be evidence-led rather than generic, because the events below are exactly what a scheme now has to be designed around.

• 1287 — the great storm. The storms of 1287 reshaped this coast, destroying the ports of Old Winchelsea and battering the Sussex shore. The damage was severe enough that the first recorded Commissioners of Sewers for the Sussex Coast were appointed soon afterwards, the start of organised flood management on the Levels.
• Medieval reclamation and relapse. The reclaimed marsh was prized as some of the most valuable arable land in the county, but it could not be kept dry: by 1402 the whole area was under water again, a reminder that drainage here is a continuous effort, not a finished job.
• 1953 — the North Sea flood. The catastrophic east-coast surge of 1953 remains the benchmark coastal flood event and the reason modern tidal defences and warning systems exist.
• December 2013 — the Xaver surge. The storm surge of 5–6 December 2013 produced some of the highest still-water levels on record around the southern North Sea and English Channel coasts. The Environment Agency warned of the most serious tidal surge in 30 years and thousands were moved to safety, with the Pevensey Bay defences among those tested.
• Winter 2013–14. A run of storms through that winter brought repeated coastal flooding along the south coast, underlining how quickly a high tide, low pressure and strong winds combine here.

Planning and drainage policy for development in the Pevensey Levels

Development on or near the Levels has to satisfy several bodies at once, and getting their expectations right early is what keeps an application moving. Because almost all of the area sits in Flood Zone 3, most schemes trigger both the sequential, risk-based approach in national policy and the surface-water requirements of the lead local flood authority and the internal drainage board.

Who you must satisfy

The Levels straddle three planning authorities and sit within a nationally designated flood risk area, “Eastbourne and Pevensey Bay”, which covers around 45km². The strategic evidence has just been refreshed: the Eastbourne and South Wealden Level 1 Strategic Flood Risk Assessment was updated in 2025 and signed off by the Environment Agency and East Sussex County Council, the North Wealden Level 1 SFRA followed in January 2026, and Rother maintains its own Level 1 SFRA.

SuDS, drainage-board byelaws and discharge

Surface-water design on the Levels follows the drainage hierarchy, but the usual first step, infiltration, rarely works on this low, wet ground, so most schemes store water and release it at a controlled rate. Development must also have regard to the byelaws of the Pevensey and Cuckmere Water Level Management Board, and works that affect a watercourse on the marsh need the board’s consent. A scheme that increases flood risk elsewhere, or that leaves its occupants unsafe, will not be supported. A surface-water drainage strategy built around the four pillars of SuDS, with discharge rates and climate change allowances evidenced, is what an objection-free application needs. Where infiltration is proposed at all, it should be proven with BRE 365 testing rather than assumed, and riparian and watercourse responsibilities understood from the outset.

Protected-site constraints: SSSI, Ramsar and SAC

The Pevensey Levels are among the most important wetlands in southern Britain, and the designations bite hard on development. The SSSI covers roughly 3,600 hectares and is also a Ramsar site, a Special Area of Conservation and a National Nature Reserve. The ditch network is the reason: it supports around 68% of all British aquatic plant species along with nationally rare invertebrates, including the endangered shining ram’s-horn snail, as well as water voles and the fen raft spider. The Habitats Regulations therefore apply to schemes that could affect the site, and drainage design has to protect water quality and levels in the ditches, not just move water off a plot. One quirk matters for site boundaries: the SSSI notification only protected land below 5 metres above Ordnance Datum, which puts particular pressure on proposals around the edges of the designated area.

What a flood risk assessment in the Pevensey Levels has to show

On a defended floodplain like this, a report that only quotes the flood-zone label will not satisfy the Environment Agency or the lead local flood authority. The assessment has to demonstrate that the site is safe for its whole lifetime, allowing for climate change, and that it does not push risk onto its neighbours.

• Every source screened. Tidal and coastal, fluvial, surface water, groundwater, sewers and reservoirs, then a clear view of which ones actually drive the risk on the site.
• Residual risk modelled. A breach or overtopping scenario characterised by depth, velocity, hazard, speed of onset and duration, usually through hydraulic flood modelling, over the development’s lifetime.
• Levels that work. Finished floor levels set with freeboard above the design flood level, referenced to Ordnance Datum, with resilient construction or floodable voids where they are justified.
• Safe access and escape. A route in and out that stays usable, plus flood warning and evacuation planning where the marsh can be cut off.
• Drainage that respects the marsh. A strategy that keeps discharge within agreed limits and honours the drainage board’s byelaws and the ditch ecology.

A flood risk assessment, a sequential or exception test and a drainage strategy are three different reports. They often travel together in a planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go. We make clear from the start which ones a Pevensey Levels site actually needs.

How Unda helps with flood risk in the Pevensey Levels

We are experts on the Pevensey Levels and the way flood risk works here, not a generic template with the place name swapped in. We read the Environment Agency and drainage-board data for the specific site, model flood behaviour where the maps are not enough, and design proportionate mitigation that the regulators accept. We stay involved past the report to answer objections, and a Senior Flood Risk Consultant signs off every project. Unda has completed more than 5,000 flood risk assessments since 2014 and is rated 5.0 on Google.

You can read more about how our flood risk consultants work, see our wider coverage across East Sussex and Sussex, or learn about Unda.

Flood risk assessments for every situation in the Pevensey Levels

Whatever the reason you need one, we prepare it for sites on and around the Levels. Each report is built to the question it has to answer and to the bodies that will review it.

• Flood risk assessment for planning. The site-specific report that supports a planning application under the NPPF and its Planning Practice Guidance. See flood risk assessment for planning.
• Flood risk survey for property purchase. An independent, property-specific survey for buyers and their advisers during conveyancing. See flood risk survey for property purchase.
• Flood risk report for insurance. Property-level evidence for brokers and underwriters where premiums rise or cover is restricted. See flood risk assessment for insurance, and how flood risk affects house prices.
• Flood risk assessment for BREEAM. Structured around BREEAM Pol 03 for schemes targeting certification. See flood risk assessment for BREEAM.
• Sequential and exception tests. The locational justification a Flood Zone 3 site usually needs. See sequential and exception tests and the Yatton judgment.
• Drainage strategy and SuDS. Surface-water design that meets policy and the drainage board’s requirements, with discharge of drainage conditions and preliminary drainage design as the scheme develops.

Working out a site for yourself first? Our free tools give a useful starting read: the Flood Risk Map, the Live River Levels Map, the Geology & Ground Conditions checker, our drainage calculators and the BRE 365 infiltration rate calculator.

Local flood risk management and emergency contacts for the Pevensey Levels

If you need to report flooding, check live conditions or prepare for a tidal warning, the contacts below are the right first ports of call. In an emergency where there is a danger to life, always call 999.

• Flood warnings. Sign up for Environment Agency flood warnings and check the current picture on the GOV.UK flood service for Pevensey; Floodline is 0345 988 1188.
• Lead local flood authority. East Sussex County Council leads on surface water, groundwater and ordinary watercourses, and works with the drainage board. See its flooding and drainage-board pages.
• Internal drainage board. The Pevensey and Cuckmere Water Level Management Board manages water levels across the marsh.
• The defences. The coast is managed through the Pevensey Bay to Eastbourne Coastal Management Scheme.
• Live river and tide levels. Use Unda’s Live River Levels Map for current readings near a postcode.

Frequently asked questions about flood risk assessment in the Pevensey Levels