Flood Risk Assessment in Erith

Any flood risk assessment in Erith has to begin with the river wall. The town faces the tidal Thames on its south bank in the London Borough of Bexley, and its riverside, from Erith Pier east to the Crayford Marshes, lies in Flood Zone 3 behind defences built to a 1-in-1,000 standard. Our consultants prepare flood risk assessments in Erith for planning applications, property purchases, mortgages and insurance, along with sequential and exception tests and surface water drainage strategies.

On this page Erith means two Bexley wards. The Erith ward takes in the town centre, Erith station, Riverside Gardens and the pier, with the streets south to Bexley Road and Queens Road. Slade Green & Northend runs east through Northend and Slade Green to the industrial riverside off Manor Road and the Crayford Marshes, as far as the Darent. All of it lies in the DA8 postcode district. Belvedere and the Erith Marshes lie west of the outline and Northumberland Heath to the south-west; the same council, Local Plan and flood evidence cover them.

Bexley's own flood study puts the water level from a breach of the river wall at 5.71 m AOD on the Erith Riverside housing site today, and 6.56 m AOD by 2115, with a hazard it rates a danger to everyone.

Our flood risk consultants can talk through an Erith site on 01293 214444 or by email at enquiries@unda.co.uk.

Erith Pier, two defence plans and the breach case

Erith Pier marks a join in the Environment Agency's long-term plan for the Thames. Upstream of it, the Thamesmead policy unit of Thames Estuary 2100 runs to the Woolwich Ferry; downstream, the Dartford and Erith policy unit runs from the pier to Greenhithe. Both carry policy P4, which means further action to keep pace with climate and land use change, and both expect the owners of the walls to adapt and raise them by 2040.

• Defended, but low. Bexley's Local Plan puts the land in its Thamesmead policy unit, which reaches Erith Pier, typically two to three metres below high water on spring tides. The walls give a 1-in-1,000 standard of protection. Beside the Western Gateway, the council's own guidance records their crest at 7.12 m AOD.
• Flood Zone 3 all the same. The Flood Map for Planning is drawn as if the walls were not there, so the riverside stays in Flood Zone 3. An assessment answers the residual flood risk of a breach or overtopping instead.
• A breach is tested everywhere. Bexley's 2020 flood study uses the Environment Agency's 2018 Thames Estuary Breach Assessment, which opens 20 m gaps in hard defences and 50 m gaps in soft ones along the whole estuary. Over the low marsh embayments the modelled water is consistently more than 2 m deep.
• Site levels come later. That model was built to map risk across the borough. It was not built to give levels for one site, and the SFRA expects a riverside scheme in Erith to carry out a breach assessment of its own.
• A 16 m strip and a wider margin. Buildings keep at least 16 m back from the landward edge of the tidal defences, and under policy DP32 schemes within 100 m of them have to leave room for the walls to be raised and rebuilt in line with TE2100.

Slade Green has a second risk. The flood study names areas of Slade Green, with Thamesmead and Belvedere, as at particular risk if the defences fail, and Bexley's 2021 site study adds that Slade Green could be flooded by a reservoir breach. Our explainer on tidal flooding and planning sets out how surge, breach and overtopping differ.

Check a postcode from Erith Pier to Slade Green

Enter an Erith or Slade Green postcode below to screen 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 Erith and Slade Green & Northend wards; Belvedere lies beyond its western edge and Northumberland Heath beyond its south-western one. The flood zone it shows takes no account of the river wall. Postcode tools that count the defences rate most of Erith as very low risk, which is why one street can look safe on one map and sit in Flood Zone 3 on another.

Surface water, sewers and the tide-locked Crayford Marshes

Away from the wall, rain causes more of the flooding. Bexley's 2021 Level 2 study finds Erith's surface water risk mostly along roads and drains, and a very high localised risk in Slade Green. It places the whole town inside a critical drainage area except the land south of Bexley Road and Queens Road, and every Erith allocation it assessed lies wholly within one.

On the marshes the sources meet. Rain reaching the Crayford Marshes ditches waits behind a flap valve whenever the tide is up, so storage on a site there is sized for a closed outfall as well as for the storm. Our guide to critical drainage areas explains why Bexley asks for a site-specific assessment inside one, even in Flood Zone 1.

Floods and turning points on the Erith riverside since 1953

The Environment Agency holds one recorded Thames flood in Bexley: the North Sea surge of 1953. Planning in Bexley now works from modelled breaches rather than from that one night, and the dates below show the steps in between.

1. 31 January to 1 February 1953. The surge flooded large parts of Abbey Wood and Belvedere and the western side of Slade Green, according to Bexley's 2021 Level 2 SFRA. Aerial photographs dated 3 February show the British Insulated Callender's Cables works at Erith under water. The wider disaster is told in our piece on the 1953 North Sea flood.
2. 1968. The Cray and the Shuttle flooded, the event the SFRA records for the borough's main rivers; the upper Cray flooded again in 1977.
3. 1982. The Thames Barrier came into use upstream, near Woolwich. Erith lies downstream of it, so its own frontage still depends on the walls along the estuary.
4. 2018. The Environment Agency's Thames Estuary Breach Assessment modelled breaches along the whole tidal river below the Barrier. Bexley's flood studies are built on it.
5. 2020 to 2023. Bexley published its Level 1 SFRA in November 2020 and its Level 2 SFRA in March 2021, then adopted the Local Plan they support on 26 April 2023.
6. 2030 and 2040. Under TE2100, councils are to plan the riverside by 2030 and defence owners to adapt and raise the walls by 2040. The Thamesmead unit, which ends at Erith Pier, has no riverside strategy yet.

Two Environment Agency warning areas meet at Erith High Street East. Tidal Thames from Dartford Creek to Erith High Street East covers Slade Green and the Darent Industrial Estate, and Tidal Thames from Erith High Street East to Woolwich Arsenal runs west across the Erith Marshes. The River Thames gauge at Erith Deep Wharf has a statutory defence level of 6.90 m and a highest recorded level of 5.04 m; it sits with the Cray gauge at Crayford on our live river levels map.

Building in Erith town centre: what the Level 2 SFRA found on each site

The Local Plan allocates five sites in and around Erith town centre for at least 1,430 homes between them. Bexley's 2021 Level 2 SFRA assessed each site before the plan was adopted, so an application on any of them starts from a published assessment of its flood zone, its breach level and whether the exception test applies.

For Erith Riverside the SFRA asks for living accommodation above the 2115 breach level, site access on the south-western boundary where the residual risk is lowest, the 16 m gap from the defences and, at the Environment Agency's suggestion, 40 m kept clear for future raising. Older figures for the western side of the town sit in the Erith Western Gateway SPD, adopted in 2012 and factually updated in June 2026: bedrooms above a predicted flood level of 6.7 m AOD and refuge at or above 7 m AOD.

Beyond the allocations, Erith Quarry, the last housing site carried over from the old Unitary Development Plan, is being built out under outline permission 14/02155/OUTM. The wider Bexley Riverside Opportunity Area, which takes in Erith, Belvedere, Slade Green and Crayford, has London Plan capacity for 6,000 homes.

Policies DP32 and DP33: the tests Bexley applies in Erith

The London Borough of Bexley is both the local planning authority and the Lead Local Flood Authority, so one council decides an Erith application and comments on its drainage, while the Environment Agency advises on the tidal Thames and the walls. The local tests are in the Bexley Local Plan, adopted on 26 April 2023. Policy DP32, Flood risk management, asks for the following.

• Location first. New development in Flood Zone 2 or 3a has to fall inside a Sustainable Development Location or a designated industrial area. Erith town centre is one of those locations, which the plan treats as having passed the sequential test; the exception test still applies where national policy requires it.
• An assessment on more sites. A site-specific flood risk assessment, including a drainage impact assessment, is required for every proposal in Flood Zones 2 and 3 and for every site of 0.25 ha or more in any zone.
• Floor levels. In the tidal flood zones, habitable rooms are set at the predicted 1-in-200 level; beside rivers, 300 mm above the 1-in-100 level with climate change. A note on metres above Ordnance Datum shows how to read those levels against a survey.
• Refuge and evacuation. Space occupied below the predicted flood level needs a detailed evacuation plan and internal safe refuge above the design flood level. Staying in the building is accepted only in exceptional cases.

Policy DP33, Sustainable drainage systems, applies to every development, including those that take hard surfacing away. Each has to manage surface water through SuDS and reach greenfield runoff rates for storms up to 1 in 100 years plus 40% for climate change, with permeable paving for hardstanding and water reuse built in. Sites of 0.25 ha or more submit a drainage strategy with a maintenance plan, and major schemes add the London SuDS proforma.

The evidence behind both policies is the Level 1 SFRA of November 2020 and the Level 2 SFRA of March 2021, both prepared by Wood. The Erith and Slade Green map appendix that often comes up in searches belongs to an earlier Level 2 study, with maps dated 2010 and 2011; the council re-uploaded it in 2020, and it warns that its modelling may have been superseded. Our guide explains what an SFRA is for, and Bexley's Local Flood Risk Management Strategy was last reviewed in March 2017.

Above the borough plan sits the London Plan 2021, whose policies SI 12 on flood risk management and SI 13 on sustainable drainage stay in force until a replacement is adopted; the draft replacement closed for consultation on 15 October 2026, with adoption expected in early 2028. National policy is chapter 18 of the NPPF published in August 2026. F4 decides whether an Erith scheme needs an assessment at all, F5 and F6 are the sequential and exception tests, and F8 asks every development to meet the 2025 National Standards for sustainable drainage.

From Pier Road to the marshes: when a flood risk assessment in Erith is required

Under DP32 one is needed for any site in Flood Zone 2 or 3 and for any site of 0.25 ha or more, a lower threshold than the national one hectare. Inside a critical drainage area, the Level 2 SFRA asks for one on smaller sites too. The table shows how common Erith and Slade Green schemes fall.

Housing on a windfall site in the town centre still has to pass the sequential test and, where national policy requires it, the exception test, as the Level 1 SFRA sets out for sites the plan did not allocate.

What our consultants prepare for the riverside, the town centre and Slade Green

A flat buyer near the pier and the developer of a town-centre allocation need different reports, and the Crayford Marshes raise questions the town centre never does. Our consultants are chartered. Every report is signed off by a senior consultant before it is issued. Unda is a CIWEM Business Partner.

• Riverside and town-centre applications. Schemes behind the wall or in the critical drainage area need a flood risk assessment for planning that answers policy DP32 and the Level 2 SFRA.
• The tide, the rain and the marsh together. A flood risk assessment weighs the breach case against surface water, sewer flooding and, in Slade Green, the reservoir risk.
• Before exchange on a riverside flat or a Slade Green house. Lenders ask about the Flood Zone 3 riverside and Slade Green's surface water, and a flood risk survey for property purchase answers them for one building.
• Homes in Flood Zone 2 or 3. Windfall housing on the riverside, and the three riverside allocations, need the sequential and exception test.
• SuDS on every scheme. DP33 asks every development to use SuDS, so even a small Erith scheme needs drainage strategy evidence of some kind.
• Greenfield rates and tide-locked outfalls. A surface water drainage strategy holds runoff to greenfield rates up to the 1-in-100 storm plus 40%, and near the marshes allows for an outfall shut by the tide.
• After the permission. Where an Erith permission comes with a drainage condition attached, discharge of drainage conditions supplies the detail and maintenance plan the council asks for.
• Breach levels for one site. The 2018 breach model behind the SFRA was not built to give levels for single sites, so a riverside scheme may need site-specific flood modelling to set its floor levels.
• Refuge and a way out. DP32 asks for a detailed evacuation plan and internal refuge wherever people occupy space below the flood level, which a flood warning and evacuation plan sets out against the two Erith warning areas.
• Cover in the defended floodplain. About 13,000 properties in Bexley, 12% of the borough, are in areas at flood risk, mostly from the tide; a flood risk assessment for insurance gives an insurer the picture for one home.
• Workspace and industrial units. New commercial buildings in Erith's industrial areas, from Fraser Road to Manor Road, can use a BREEAM flood risk assessment for the Pol 03 credits.
• Buying land on the marshes. Industrial land on the Crayford Marshes and off Manor Road sits in Flood Zone 3 with tide-locked drainage, and flood risk due diligence sets that out before a purchase.
• Keeping a business open. The SFRA records frequent flooding on the Darent Industrial Estate from saturated ground, reed growth and blocked ditches; a business continuity flood risk assessment plans around it.
• Testing a site before an offer. With five town-centre allocations and the Bexley Riverside Opportunity Area, a flood risk feasibility study shows early whether a layout can meet DP32.

Warnings, sewers and the council: who to call about flooding in Erith

In Erith, ring 999 if floodwater is putting someone at risk and 105 if the power goes off. Other flood questions go to one of the organisations below.

Upstream, Thamesmead shares the Thamesmead TE2100 unit as far as Erith Pier, and Woolwich lies beyond it beside the Thames Barrier. Downstream, Dartford shares the Dartford and Erith unit across the Darent. The estuary as a whole is covered on our River Thames page and the valley upstream of Dartford Creek on our River Darent page; for other places, see the full list of areas.

Erith flooding and planning: what clients ask us

Unda Consulting Limited works on sites across Erith and Slade Green, from riverside blocks to single plots, preparing flood risk assessments, sequential and exception tests and drainage strategies for homes, businesses and development land. To discuss a site in Erith, Northend or Slade Green, call 01293 214444 or email enquiries@unda.co.uk.