Flood Risk Assessment in the Pevensey Levels

A flood risk assessment in the Pevensey Levels deals with land that stays dry only because it is drained, pumped and defended. Between Eastbourne, Hailsham and Bexhill-on-Sea the protected grazing marsh alone covers 36 square kilometres, much of it only about 2 m above Ordnance Datum, criss-crossed by ditches that reach the sea through tide-locked outfalls. Our consultants write flood risk assessments in the Pevensey Levels for planning, for buyers and lenders and for insurance, and prepare sequential and exception tests and surface water drainage strategies on the same footing. Reports for sites in the Pevensey Levels come from Unda Consulting Limited, a CIWEM Business Partner.

The Levels, sometimes called the Pevensey Marshes, here mean five Wealden parishes that between them hold most of the marsh. They are Pevensey (the village and castle, not the seafront), Westham with Stone Cross, Hankham and Rickney, Wartling with Boreham Street, Herstmonceux with Manxey, and Hooe. Postcodes run BN24 in the south and west, BN27 around Herstmonceux and Wartling and TN33 at Hooe. The Levels also reach into Hailsham parish and into Rother at Barnhorn and Cooden, which our East Sussex page and Bexhill page cover.

On the Environment Agency's planning flood map, three quarters of the Pevensey Levels SSSI lies in Flood Zone 3 and nine tenths in Zone 2 or 3, and Wealden's 2026 flood study expects Flood Zone 3 to cover the whole marsh by 2125.

To talk through a site on the Levels, call one of our flood risk consultants on 01293 214444 or email enquiries@unda.co.uk.

Ditches, sluices and six pumps: how the marsh is kept workable

The marsh was won from a tidal estuary. Natural England's character profile for the Levels records inning from the 13th century onwards, mostly by religious houses, and pumps draining most of the marsh since the 1960s, which shrank the area that floods each winter. What keeps it workable now is a managed network: main rivers looked after by the Environment Agency, and smaller watercourses, sluices and pumping stations run by the Pevensey and Cuckmere Water Level Management Board through the Water Management Alliance.

In 2018 the board's district ran to 7,759 ha, with water from about 46,900 ha of Weald draining into it. The board's own modelling, reported in Wealden's flood study, found the tidal outfalls along the Pevensey coast already partly submerged, and climate change will make that worse. When rain falls heavily on a high tide, water backs up across the fields until the outfalls can run again.

Map of the Levels, from Stone Cross to Hooe

The coral outline marks the five parishes described above, with the Pevensey Bay seafront left out. Enter a postcode to screen it against Environment Agency data for rivers and the sea, surface water and reservoirs, or use our full flood risk map for anywhere in England. It gives a first reading, which a site-specific assessment then tests.

Flood Zone 3 across the farmland, and what changes by 2125

We overlaid the Environment Agency's Flood Map for Planning on Natural England's boundary for the Pevensey Levels SSSI on 26 October 2026. About 75% of the 3,603 ha site falls in Flood Zone 3 and almost 90% in Flood Zone 2 or 3, most of it mapped as at risk from rivers and the sea together. Pevensey village, Westham and Stone Cross stand mostly on slightly higher ground in Flood Zone 1, although the lower end of Pevensey's High Street dips into Zone 2. The map shows the land as if the defences were absent, which is why a field that has stayed dry for years can still sit in Zone 3. Our guide to flood zones in England explains the categories.

• The sea. The shingle barrier keeps the tide off the marsh. Breach modelling for an earlier Wealden SFRA showed most land between the shoreline and the A259 flooding if it failed, along with low land beside Pevensey Haven upstream of the A259, so an assessment in those areas needs a breach scenario. The defences themselves, and their history, are on our Pevensey Bay page.
• Rising sea level. The 2026 SFRA warns that with predicted sea level rise, high tides would overtop the present defence in a 1 in 200-year event and put Pevensey and Westham at risk, unless the defence is raised in step.
• Bigger river flows. The Levels fall in the Environment Agency's Cuckmere and Pevensey Levels management catchment, shared with the Cuckmere, where peak river flows for the 2080s are assumed to rise by 32% (central), 43% (higher central) or 76% (upper end).
• Heavier rain. For the same catchment, peak rainfall in a 1% annual chance storm is assumed to rise by 25% (central) and 45% (upper end) over 2061 to 2125, which sizes on-site storage.
• Flood Zone 3 by 2125. Under both higher sea level scenarios, Flood Zone 3a spreads across all of the Levels and onto the southern and western fringes of Hailsham, according to the SFRA.

Defences lower the chance of flooding without taking it away, so an assessment here deals with residual flood risk: depth and hazard if a bank or the beach fails, how quickly the water arrives, and whether people can get out. Our note on climate change allowances covers which figures apply to which development.

High groundwater, clay and soakaways that rarely work

Under the marsh, marine silts and clays sit over Low Weald mudstones, so rain soaks in slowly and the water table stays close to the surface for much of the year. The East Sussex flood strategy says infiltration is likely to be inappropriate across most of the Low Weald and coastal marshes, and on tidal and river floodplains it adds that groundwater can rise with the tide and swamp drainage systems.

• Winter monitoring. East Sussex County Council asks for groundwater levels monitored over a six-month winter period, preferably October to March, where infiltration or below-ground storage is proposed. Our article on groundwater monitoring for planning explains the timing problem this creates.
• Storage that empties. On the coastal and river floodplains the strategy wants attenuation to be half empty within 24 hours of a storm, so the next one has room.
• Tanks built to float. Underground storage has to resist uplift and groundwater leaking in, as well as hold the rain.
• Testing before relying on it. Where a sandy pocket makes infiltration plausible, BRE 365 testing has to prove it; the ground conditions checker gives a first indication of the geology.

Wealden's proposed drainage policy makes a further point: a site that cannot infiltrate still has to reduce the volume of runoff it sends off site.

How the marsh has flooded, been drained and been protected

None of the county council's published flood investigations covers the Levels, because floods here mostly reach fields, lanes and outlying houses. The record is kept instead in drainage works, rankings and designations.

1. 13th century onwards. Religious houses begin inning the tidal marsh behind the shingle, the start of continuous reclamation recorded in Natural England's profile.
2. 1960s. Pumps take over the drainage of most of the marsh, and winter flooding retreats to a smaller area.
3. 2 February 1999. The Levels are designated a Ramsar wetland of international importance, covering 3,578 ha.
4. 2016. East Sussex County Council's flood strategy ranks the Pevensey and Westham ward ninth of 101 wards for overall flood risk, and fourth among settlements and wards for properties at risk in a 1 in 100 surface water event. Herstmonceux ward comes 99th. From that autumn the Pevensey and Cuckmere Water Level Management Board serves the drainage district.
5. 11 February 2016. The Pevensey Levels become a Special Area of Conservation (3,585 ha) for the little whirlpool ram's-horn snail, which survives in the ditches of drained grazing marsh.
6. 2011 to 2021. Southern Water's sewer flooding records show Herstmonceux and Hailsham with the most incidents anywhere in Wealden, according to the 2026 SFRA.
7. 2025 to 2026. The board installs five new tilting weirs, starts replacing culverts and embankments east of Hailsham and at Hankham Gut, and rebuilds the Drockmill pumping station north of Polegate and Stone Cross.

The Environment Agency's tidal warning area for the Levels covers the Crumbles, East Langney Levels, Mountney Bridge, Pevensey, Manxey, Horse Eye and the Hooe Levels; its current status is published online. For levels on the Havens and at the coast, our live river levels map shows the nearest gauges, including the sea level gauge at Pevensey and the stations on the Weald streams that feed the Havens.

Wealden, Rother and the county: the policies a scheme on the Levels meets

The five parishes on our map are all in Wealden District, so Wealden decides applications there and East Sussex County Council, as the lead local flood authority, comments on drainage for major schemes. The Rother side of the marsh at Barnhorn and Cooden answers to Rother's plan. Both councils are replacing their plans, and both new plans single out the Pevensey Levels.

National policy sits in chapter 18 of the NPPF, where policy F4 sets when a site-specific assessment is needed, F5 and F6 the sequential and exception tests, and F8 the expectation that development follows the 2025 National Standards for sustainable drainage. The county's 2016 to 2026 flood strategy is due to be replaced: consultation on a draft for 2027 to 2037 closed on 18 October 2026. Wealden's evidence comes from the Level 1 SFRA of March 2026, and the county's requirements are on its guidance for developers.

The drainage board's consent and the wetland designations

Two things set the Levels apart from ordinary Flood Zone 3 land: an internal drainage board whose byelaws reach every ditch, and a protected wetland that receives whatever a site discharges.

• The 9 m strip. Byelaw 10 bars buildings, roads, fences, planting and level changes within 9 m of board watercourses and structures without consent. Layouts that ignore it are redrawn later.
• Consent for new flow. Any increase in the rate or volume of water entering the board's system, treated foul effluent included, needs land drainage consent under byelaw 3, and the board seeks attenuated discharges to protect its pumps. Consent can carry a surface water development contribution. Our guide to internal drainage boards explains how consent and planning interact.
• Three protected layers. The SSSI covers 3,603 ha, the Ramsar site 3,578 ha and the Special Area of Conservation 3,585 ha. A scheme that could change water levels or quality in the ditches has to be screened under the Habitats Regulations, and assessed in full where a significant effect cannot be ruled out, before the council can approve it.
• Treatment before discharge. Both councils' new plans ask for three stages of SuDS treatment for runoff reaching the Levels, which shapes the drainage layout from the outline stage onwards.

One of our own jobs shows how these rules combine. On a former mill site in East Sussex, the only outfall for 24 new homes was a private ditch feeding the Pevensey Levels SSSI and Ramsar site. The drainage conditions were discharged once the Environment Agency had issued a permit and the board had granted land drainage consent. The project summary sets out the approach.

Building at the edge of the marsh: Westham, Stone Cross, Herstmonceux and Hooe

Little is built on the open marsh itself. Most applications come from the higher ground around it, where Eastbourne, Stone Cross and Hailsham are growing towards the Levels and every new roof drains into them. The appeal decision on land east of Golden Jubilee Way at Westham, issued on 13 October 2026, shows what gets argued. Wealden had refused up to 250 homes over residual tidal risk; the inspector allowed them once the Environment Agency had withdrawn its objection, with floors at least 300 mm above the design flood level, a flood management plan before occupation and runoff held to the greenfield rate. A possible route to the SAC through backflow into the Langney Sewer meant drainage controls had to be secured by condition as well.

• Estates on the Stone Cross and Westham edge. Housing that drains to the Levels needs the breach question answered, the three treatment stages designed in, and a discharge the board will accept.
• Farmsteads, barns and stables. Conversions out on the marsh, around Rickney, Manxey and the Hooe Levels, sit in Flood Zone 3 and often off the sewer network, so safe access, raised floors and a foul outfall all need solving together.
• Village infill in Pevensey and Westham. Plots near the castle are mostly in Zone 1 or 2, but Pevensey lies inside the Environment Agency's tidal warning area, and lenders and insurers ask about that as well as the zone.
• Herstmonceux and Boreham Street. Higher ridge-top villages where surface water and sewer capacity matter more than the sea; Southern Water's drainage plan flags treatment permit pressure at Windmill Hill, Herstmonceux, and at Hooe by 2050.

Our Eastbourne page covers Langney and Sovereign Harbour on the western edge of the Levels, and the Hastings page the coast beyond Bexhill.

Does a site need a flood risk assessment in the Pevensey Levels?

Most do. The table sets out common schemes on and around the marsh and what the planning authority is likely to ask for.

Where a site sits in Flood Zone 2 or 3 the sequential test normally comes first, and around the Levels it often turns on whether drier land at Hailsham, Polegate or Stone Cross is reasonably available. A flood risk assessment, a sequential test and a drainage strategy answer three separate questions: whether the site is safe, whether it should be here at all, and where its water goes.

Reports we prepare for land on and around the Levels

Which reports a site needs depends on where it sits: out on the marsh, in the villages at its edge, or up on the Herstmonceux ridge.

• Tide, ditch and water table together. A flood risk assessment on the Levels weighs a breach of the shingle against tide-locked outfalls, pumped ditches and groundwater on the same plot.
• Applications to Wealden or Rother. Barn conversions on the marsh and estates on its edge need a flood risk assessment for planning that deals with residual risk and the board's role.
• Before exchange in Pevensey or Westham. A house inside the tidal warning area raises questions from lenders, and a flood risk survey for property purchase answers them for that one building.
• New homes in Flood Zone 3. Most of the marsh is Flood Zone 3, so housing there usually needs a sequential and exception test against drier land at Hailsham or Polegate.
• Water that has to leave by a ditch. With soakaways rarely viable, a drainage strategy shows the outfall, the storage and the board's agreement before anything is built.
• Three treatment stages. Runoff reaching the Ramsar ditches needs a surface water drainage strategy that meets the treatment and discharge rules in proposed CC8 and ENV3.
• Conditions on Levels consents. Wealden and appeal inspectors attach detailed SuDS, maintenance and construction runoff conditions, and discharge of drainage conditions clears them with the county council and the board.
• Water table at the surface. Clay under the marsh at Pevensey, Westham and Rickney and a tide-linked water table make a groundwater flood risk assessment worth having wherever basements, tanks or soakaways are planned.
• Breach and overtopping on the Havens. Wealden's SFRA asks for a breach assessment on low land between the coast, the A259 and Pevensey Haven, and hydraulic flood modelling supplies depths and hazard where national mapping stops.
• Roads that flood before houses do. Inside the tidal warning area at Pevensey, Manxey and the Hooe Levels, a flood warning and evacuation plan sets out how occupants leave before lanes across the marsh go under.
• Off the sewer network. Farmsteads at Rickney, Hankham and Wartling often need a package treatment plant discharging to a board ditch, and a foul drainage strategy covers the permit and consent that come with it.
• Village homes in Flood Zone 3. Pevensey village lies inside the Environment Agency's tidal warning area, and a flood risk report for insurance gives insurers evidence specific to the property.
• Land promoted on the urban edge. Buyers and promoters of farmland near Stone Cross and Westham use flood risk due diligence to price breach risk and drainage constraints before committing.

Who manages water on the Pevensey Levels, and who to call

Responsibility is split by source of water. Ring 999 if anyone on the marsh is in danger from floodwater.

For live readings at Pevensey and across the county, the Environment Agency's check for flooding service lists warnings in force, and our list of areas we cover links to every other Sussex page.

Questions about flood risk and planning on the Levels

You can also call 01293 214444 or email enquiries@unda.co.uk. Our chartered consultants prepare each report, and a senior consultant checks and signs it before it leaves us.