Flood Risk Assessment in Stratford, London

A flood risk assessment in Stratford, London starts with the River Lea, which splits into the Bow Back Rivers along the west of the district on its way to the Thames at Bow Creek. Newham's Strategic Flood Risk Assessment puts more than a quarter of the Stratford and West Ham area in Flood Zone 3, behind river walls and engineered ground that keep a 1-in-100-year Lea flood largely in its channels. We prepare flood risk assessments in Stratford for planning applications, house purchases, mortgages and insurance, together with sequential and exception tests and surface water drainage strategies.

Here Stratford means three wards of the London Borough of Newham. The Stratford ward takes in the Broadway, Stratford Centre, the station, Carpenters, Sugar House Island and Pudding Mill. Stratford Olympic Park covers Stratford City, East Village and the Newham side of the Queen Elizabeth Olympic Park, and Maryland runs north and east to Stratford New Town. Together they hold most of the E15 postcode district and the Newham part of E20. Hackney Wick, which takes in the Hackney part of the Park, adjoins the outline to the west, while West Ham to the south-east and Leyton to the north lie outside it. This page covers the east London district; the Warwickshire market town has its own page on flood risk assessment in Stratford-upon-Avon.

Until Newham adopts its new Local Plan, a basement on the Olympic Park side of Stratford is judged against the old LLDC Local Plan, which permits none in Flood Zones 2 or 3. A few streets east, Newham's own 2018 policy applies instead.

Our flood risk consultants are on 01293 214444 and at enquiries@unda.co.uk; an E15 or E20 address and a line about the site is enough to start.

Which local plan applies to a Stratford site now the LLDC has gone?

Newham decides every application. The policies it applies depend on where the site is. The London Legacy Development Corporation planned the Olympic Park and the land around it until 1 December 2024, when its powers went back to Hackney, Newham, Tower Hamlets and Waltham Forest. In Newham the LLDC Local Plan 2020 to 2036 still forms part of the development plan for the former LLDC area. Newham's Local Plan 2018 governs the rest of Stratford and Maryland, and a new borough plan is waiting to replace both.

Which side of the old boundary a site falls on is a question for the LLDC policies map, and the council's LLDC page lists every LLDC document still in force. The new plan has passed examination, but the Newham Local Plan examination page gives no adoption date, and until Full Council adopts it the older policies remain the starting point. On adoption, the Inspector's report confirms, it supersedes the 2018 plan and the LLDC plan in their entirety. A draft replacement London Plan was consulted on from 16 July to 15 October 2026 and is not expected before 2028.

National policy is chapter 18 of the August 2026 NPPF, where F4 decides whether a Stratford scheme needs an assessment, F5 and F6 set the sequential and exception tests, and F8 brings in the 2025 National Standards for sustainable drainage. Newham also acts as Lead Local Flood Authority, which means its flood team reviews the drainage on the same applications its planners decide.

Is Stratford in a flood zone?

Partly. The planning map shows more of the district at risk than the defended modelling does. Appendix E of Newham's Level 1 Strategic Flood Risk Assessment places 40.5% of the Stratford and West Ham policy area in Flood Zone 2 and 27.3% in Flood Zone 3. Those zones are drawn as if the defences on the Lea and the Bow Back Rivers did not exist, and the same appendix finds no significant flooding there in a 1-in-100-year river flood with the defences in place.

• Higher ground to the north and east. Stratford New Town and Maryland lie outside Flood Zone 2 altogether, the SFRA notes, as does most of north and east Newham.
• Low land south of the High Street. In a 1-in-1,000-year river flood the modelling reaches the land between the Three Mills River and the Lea: Carpet Street, Sugar House Lane, Zinc Street and Hunt's Lane. Lea Junction, north of Carpenters Road, and ground west of Temple Mills Lane are also inside that extent.
• Functional floodplain only on the islands. Newham's Flood Zone 3b is confined to Channelsea Island, Island House in the Three Mills River and two pieces of open land on the banks of the Lea.
• Bigger extents in future. With climate change the Lea's flood extents widen either side of the DLR line through Stratford, and a 2100 breach of the Thames defences spreads further around Stratford and West Ham, according to the March 2025 Level 1 SFRA.

The flood zone decides which tests apply; the defended modelling and the breach levels decide what the building needs. Our guide to Flood Zones 1, 2 and 3 explains how they are drawn, and a second piece covers why defended land stays in a flood zone.

The Lea, the Bow Back Rivers and the lock that shut out the tide

Below Hackney Wick the Lea divides into the Bow Back Rivers, a web of channels the SFRA describes as heavily canalised and controlled by locks under the Canal & River Trust. Six channels matter to a site on the Stratford bank.

Three Mills Lock reshaped the southern channels. It opened on the Prescott Channel in June 2009 and cut a stretch of the Bow Back Rivers off from the tide, holding the water at about 2.3 m AOD where spring tides had reached 4.8 m AOD. The tide still runs up Bow Creek. The 2013 overtopping at Three Mills shows that the walls below the lock still matter.

Two Thames Estuary 2100 policy units name Stratford. The Isle of Dogs and Lea Valley unit follows the tidal Lea up to Stratford and Hackney Wick, includes the Olympic Park and carries policy P5: further action to reduce flood risk, with defences raised by 2050. The Royal Docks unit, whose western boundary is the Lea, lists Stratford, West Ham and East Ham under policy P4, which aims to stop risk rising as the climate changes. Newham's draft plan expects the Thames walls upstream of the Barrier to rise by up to 0.5 m by 2050 and another 0.5 m by 2100; our article on the Thames Barrier looks at the barrier's own future.

Screen an E15 or E20 postcode before you buy or build

Enter a Stratford postcode below to check it against Environment Agency data for rivers and the sea, surface water and reservoirs, or open our full flood risk map for anywhere in England. The coral line follows the Stratford, Stratford Olympic Park and Maryland wards: Hackney Wick sits beyond its western edge and West Ham beyond the south-east. Expect the reservoir layer to show colour. The SFRA finds that a failure of the King George V or William Girling reservoir in Enfield would reach most of Stratford west of the A112, a very unlikely event that Newham's draft policy still asks some schemes to plan for.

Floods recorded in Stratford, from 1947 to Pudding Mill Lane

Stratford's written record is short: the Lee Flood Relief Channel was built after 1947, and the Olympic works reshaped the land west of the station. These dates come from Newham's flood studies and the Environment Agency's recorded flood outlines.

1. 6 March 1947. The Lea overtopped its banks at Stratford and West Ham, where there were no raised defences, according to the Environment Agency's recorded outline. Newham's flood strategy calls it the greatest flood on record on the Lea and Roding, falling mainly on western Newham around Stratford. Our article on the floods of 1947 covers the national picture.
2. 4 November 2013. High spring tides overtopped the riverbank on Bow Creek at Bow Lock and at Three Mills Lock, the only overtopping the Canal & River Trust has recorded in Newham.
3. September 2014. Newham's Section 19 flood investigation that month covered surface water and sewer flooding in Stratford, Forest Gate, Manor Park, West Ham and East Ham, including basement flats.
4. 6 May 2020. The Environment Agency logged river flooding on the Lea beside the East London Science School after the operational failure of a defence.
5. January 2021. Flooding on Warton Road, at the southern edge of the Greater Carpenter's District, from a source and cause the records leave unknown.
6. 25 July 2021. Torrential rain flooded Pudding Mill Lane DLR station, on the southern edge of the Park, on a day when nearly four hours of rain fell across much of London and Essex. Our piece on the Mayor's basement flash flood warning covers the advice for homes below ground.
7. 4 January 2024. Upstream, the Lea at the Lea Bridge gauge reached 6.52 m, its highest level on record, during Storm Henk; our River Lea page describes the sluice failure that flooded part of Hackney Wick that day.

Two Environment Agency warning areas show whether a flood warning is in force in Stratford today: Lower River Lee at Stratford covers the Lea at Stratford and Mill Meads, while Tidal Thames at Mill Meads and East Plaistow takes in the south Stratford marshes. The Lea Bridge gauge and the other stations on the river are on our live river levels map.

Sewers, reservoirs and groundwater: the risks behind the river walls

Rain and overloaded drains cause most of the flooding a Stratford building is likely to see. The national river maps show little of it. Newham's own records list 290 surface water, sewer and groundwater incidents across the borough since 2011.

• The least sewer capacity in London. Newham's drainage guidance for applicants quotes a Thames Water assessment that gave the borough the lowest sewer capacity of all 33 London boroughs, projected to run over capacity within 20 to 30 years. More than half of the network is old combined sewer, the SFRA adds.
• Critical Drainage Areas along the railways. Two of them run through Stratford: one follows the Great Eastern main line from Stratford towards Forest Gate, the other the Central line through Stratford station, where cuttings gather runoff from higher ground. A new basement inside one needs its own assessment of surface water and sewer flooding; our article on Critical Drainage Areas explains why.
• Abbey Mills and the Lee Tunnel. Just south of the outline, Abbey Mills pumping station had London's largest polluting sewer overflow until the 6.9 km Lee Tunnel to Beckton opened in January 2016 to capture it. The Tideway Tunnel now joins the same system.
• Reservoirs up the valley. A breach of the King George V or William Girling reservoir, or of the Walthamstow group, would send water down the Lea; the Level 2 SFRA places the whole Greater Carpenter's District inside the reservoir 'wet day' extent. Our guide to reservoir flooding sets out how planning treats that risk.
• Groundwater in pockets. The SFRA picks out Stratford, with North Woolwich and West Ham, as the parts of Newham with low to moderate groundwater emergence risk, and the Stratford Station allocation also sits in groundwater Source Protection Zones 1 to 3, which limits what can drain into the ground.
• Rain gardens on the Broadway. In 2018 Newham built 11 rain gardens on the Stratford gyratory, increasing the surface water held on site by 99.6% in a 1-in-30-year storm, the SFRA reports.

Our explainer on surface water flooding and planning covers what councils ask for when rain, not a river, is the main risk. The Flood Ready London partners set out their plan for the capital in the 2025 to 2030 London Surface Water Strategy.

Stratford's allocated sites and what Newham's 2025 flood study found

Most of Stratford's large sites are allocated in neighbourhood N8, Stratford and Maryland, of the new Newham Local Plan, and the council's Level 2 SFRA site tables, issued in March 2025, tested each one. Every Stratford allocation in the table below needs the exception test.

The references come from the plan as submitted. They may change with the main modifications. On Pudding Mill the defended Lea model shows no flooding in any modelled event, so what drives the exception test is the undefended zone, the breach and the rain. For each site the study asks for an assessment that tests the 2100 breach, shows safe access in a 1-in-100-year storm with climate change, and starts with early talks with the council and the Environment Agency. Our guide to residual flood risk explains how breach evidence is used, and a separate article sets out what an SFRA is for.

When is a flood risk assessment in Stratford, London needed?

For most new building on the western, riverside half of the district, and less often in Maryland. Newham's 2020 drainage guidance asks for one with surface water details on sites in Flood Zones 2 and 3 over 250 m², on any site of a hectare or more, and anywhere in a Critical Drainage Area.

Where housing is proposed in Flood Zone 2 or 3 outside an allocation, LLDC policy S.10 and Newham policy SC3 both expect the sequential test to be passed before the site-specific case is heard.

Reports we prepare for sites from Maryland to Pudding Mill

The report a site needs depends on how close it sits to the Lea and who is asking. A flood risk assessment asks whether the site is safe, a sequential test asks whether it should be there at all, and a drainage strategy shows where the rain goes. Our consultants are chartered, a senior consultant signs off each report, and Unda is a CIWEM Business Partner.

• Homes beside the Bow Back Rivers. New flats at Pudding Mill, Sugar House Island or Carpenters need a flood risk assessment for planning that answers policy S.10 or SC3 and the 2025 breach modelling.
• Every source on one plot. A flood risk assessment for a Stratford site weighs the Lea and a Thames breach against overloaded sewers, the Enfield reservoirs and pockets of shallow groundwater.
• Before exchange in E15 or E20. Buyers of East Village flats or Maryland terraces turn to a flood risk survey for property purchase when a lender or a search raises the Lea.
• Housing in Flood Zone 3. Unallocated housing on the riverside half of Stratford faces the sequential and exception test, and the Level 2 SFRA found the exception test necessary on every Stratford allocation it assessed.
• Rain on London's tightest sewers. Newham expects greenfield runoff from major schemes, and our drainage strategy work shows the council how a scheme reaches it.
• Soakaways or storage. With Source Protection Zones under the station and moderate groundwater in places, a surface water drainage strategy here tests infiltration before falling back on attenuation and a controlled outfall.
• After consent. When Newham attaches a drainage condition to a permission, we prepare what is needed for the discharge of drainage conditions.
• Lea levels the national maps miss. The Environment Agency regards its 2014 Lea model as out of date and the SFRA asks developers to run their own, which is where flood modelling comes in.
• A way out when access floods. Pudding Mill loses vehicle access in the 2100 breach case, and the SFRA asks for evacuation planning where a reservoir failure could threaten life, set out in a flood warning and evacuation plan.
• Water in the ground under the town centre. The Level 2 SFRA finds moderate groundwater risk across part of the Stratford Central allocation, so a groundwater flood risk assessment suits basements and deep foundations there.
• Cover for a home behind the walls. Ground-floor homes in Flood Zone 3 near the Lea draw insurer questions, and a flood risk assessment for insurance sets out what the building itself is exposed to, defences included.
• Buying land at Pudding Mill or Carpenters. Allocations that need the exception test carry flood constraints into a land price, and flood risk due diligence brings them out before contracts.
• Shops, offices and the interchange. Westfield, the International Quarter and the station interchange depend on rail links that can flood, as Pudding Mill Lane station did in July 2021, and a business continuity flood assessment plans for the next storm.
• Connecting to a stretched network. More than half of Newham's sewers are old combined sewers, the SFRA notes, so a foul drainage strategy is worth settling with Thames Water before a large scheme is fixed.
• New workspace. Employment space planned at Stratford Town Centre West and Stratford Waterfront South can earn BREEAM Pol 03 credits with a BREEAM flood risk assessment.

Who deals with flooding in Stratford, and how to reach them

Dial 999 if floodwater puts anyone in danger, and 105 to report a power cut. Otherwise, responsibility in Stratford is shared between the bodies below.

Next door to the west, Hackney Wick shares the Olympic Park and the Isle of Dogs and Lea Valley policy unit, which reaches the Thames at the Isle of Dogs. Upstream on the same river is Tottenham, and Barking lies at the eastern end of the Royal Docks unit on the Roding. The river itself has a River Lea page, the estuary below Bow Creek is on our River Thames page, and every place we cover is listed on our areas page.

Stratford flooding: questions from buyers, owners and developers

Unda Consulting Limited works on sites across Stratford, Maryland and the Olympic Park, preparing flood risk assessments, sequential and exception tests and drainage strategies for owners, buyers and developers. Call 01293 214444 or email enquiries@unda.co.uk with the address and what you have in mind.