Flood Risk Assessment in Enfield

A flood risk assessment in Enfield usually starts with a brook rather than the Lee. The Salmons, Pymmes and Turkey Brooks run from the higher ground of Enfield Chase and the western edge of the borough down to the Lee Valley and rise quickly in heavy rain, and the worst flood the council has recorded, on 30 October 2000, came from them and from rain on the streets. The reservoirs and the Lee itself add risk along the eastern side. Our consultants prepare flood risk assessments across the borough for planning applications, purchases, mortgages and insurance, as well as sequential and exception tests and surface water drainage strategies.

Enfield here means the whole London Borough of Enfield, the northernmost borough in London: Enfield Town, Edmonton and Edmonton Green, Southgate, Palmers Green, Winchmore Hill, Bush Hill Park and Grange Park, Ponders End, Enfield Highway, Enfield Wash, Enfield Lock and Brimsdown along the Lee, Cockfosters, Oakwood, Hadley Wood, Forty Hill and Crews Hill, and Meridian Water by the North Circular. The main postcode districts are EN1, EN2 and EN3 in the north and N9, N13, N14, N18 and N21 in the south. Tottenham, across the Haringey boundary, has a page of its own, and the borough sits within our London coverage.

On 30 October 2000 the Salmons Brook and the Turkey Brook reached levels their Environment Agency gauges at Edmonton Green and Albany Park have not matched since, and 192 properties flooded around Montagu Road in Edmonton.

Call one of our experienced flood risk consultants on 01293 214444 or email enquiries@unda.co.uk for a free, no-obligation quote, usually within 60 minutes.

30 October 2000 and the brook records: Enfield's flood history

Enfield's flood record is written mostly in summer storms and autumn brook floods, not in the Lee. The council's 2011 Preliminary Flood Risk Assessment lists more than a dozen recorded events since about 1970, and judged only one to have had significant harmful consequences: October 2000. The gauges on the brooks still carry the evidence, and they explain why a site two streets from a brook can need a full assessment.

1. 14 August 1975 and the summer of 1981. Storms flooded 36 sites over about 123 hectares across the borough in 1975, and on three days in July and August 1981 between 21 and 50 sites each time, mostly from surface water and, in August 1981, mainly in the south-west.
2. 12 October 1993, the Pymmes Brook. The gauge at Silver Street in Edmonton reached 1.452 m, still the highest it has recorded.
3. 30 October 2000, Edmonton and Turkey Street. Heavy rain sent the Salmons Brook out of bank, and 192 properties flooded in the Montagu Road area, which had long been exposed to the brook and the Saddlers Mill Stream. The Turkey Brook flooded at Turkey Street too. The Salmons Brook gauge at Edmonton Green peaked at 1.19 m at 4.30 am and the Turkey Brook at Albany Park at 1.394 m half an hour later; both remain the gauge records.
4. October 2001, groundwater. The Environment Agency recorded groundwater flooding at South Lodge Drive and along the A105 north of the North Circular.
5. 10 February 2009, The Chine. The Salmons Brook gauge at The Chine, N21, set its record of 2.418 m.
6. January 2021, the parks fill. On 14 and 28 January the Salmons, Cuffley and Turkey Brooks spilled into Cheyne Walk Open Space, Whitewebbs Park, Forty Hall and three golf courses. No homes were reported flooded, because the parks held the water as the storage areas were designed to.

The Environment Agency's answer to 2000 was the Salmons Brook scheme, opened in March 2016 at a cost of £15.3 million. It holds water back behind an embankment at Enfield Golf Course, World's End and Cheyne Walk, stores more at Montagu Recreation Ground and walls the brook beside Salmons Walk, protecting 1,393 properties (2,587 homes). For the 727 homes most at risk the yearly chance of flooding fell from 1 in 20 to 1 in 75. That is a real improvement, and it still leaves those streets with a chance of flooding every year.

Checking a site from Cockfosters to the Lee on the borough map

Type an Enfield postcode into the map to see the Environment Agency's river, surface water and reservoir layers at that point, or use our flood risk map for anywhere in England. The coral line follows the boundary of the London Borough of Enfield, from Hadley Wood and Cockfosters in the west to the reservoirs and the Lee Navigation in the east. The council holds its own, more detailed Flood Zone 3b mapping and the national layers ignore some of the brook storage, so read the result as a first screen.

Salmons, Pymmes, Turkey and the Lee: the borough's main rivers

Three brooks cross Enfield from west to east and drain to the Lee system on the borough's eastern edge, and the Environment Agency maps every one of them as a main river where it passes its gauges. The table sets out what each one does in the borough; current levels at every gauge named here are on our live river levels map.

Streams that are not main rivers, including many culverted ditches, are ordinary watercourses looked after by the council as lead local flood authority, and the difference matters for consents and setbacks (main rivers and ordinary watercourses explained). The Lee's own story, upstream through Hertford and Ware and down to Hackney Wick, is on our River Lea page. The Pymmes Brook's upper reaches are covered on our Barnet council page.

Below King George V and William Girling: reservoir risk in the Lee Valley

Two large storage reservoirs sit on Enfield's eastern edge, and the Greater London Authority's 2026 Regional Flood Risk Assessment lists the King George V and William Girling reservoirs in Enfield as one of the two main reservoir risks in the capital. A failure is very unlikely, because large reservoirs are inspected under the Reservoirs Act, but the mapped consequences fall mainly on the east of the borough.

• How the risk is mapped. The Environment Agency's reservoir maps show the area that could flood if a dam failed, once with river levels normal and once with the rivers already in flood.
• What the borough's sites showed. The council's 2023 Level 2 Strategic Flood Risk Assessment found reservoir flooding across all scenarios, especially in the east, affecting 34 of its 110 tested sites in the dry-day case and 35 in the wet-day case.
• Why it matters to a scheme. Reservoir risk does not change the flood zone, but it shapes safe access, evacuation and the vulnerability of uses such as care homes, schools and basement flats.

A planning assessment for an eastern Enfield site should say how far the reservoir extent reaches, how deep and fast water would be, and where people would go. Our note on how reservoir flooding is assessed sets out the method.

Rain, sewers and gravel: the risks the flood zones leave out

Many Enfield properties at risk of flooding sit well outside the river flood zones. Modelling for the 2011 Preliminary Flood Risk Assessment put about 30,100 properties in the borough at risk of surface water flooding in a 1 in 30 storm and 39,000 in a 1 in 200 storm, which is why the council asks about drainage on every application.

• Surface water. The council's surface water management plan defined critical drainage areas, mainly in north-east Enfield, along the North Circular and around Enfield Town (what a critical drainage area means for an application).
• Sewers. Thames Water's records for the 2023 Level 2 assessment held 263 sewer flooding incidents across the postcodes of the tested sites, 108 of them inside buildings, with the largest number in N14 4 around Southgate.
• Groundwater. The Environment Agency logged 38 groundwater flooding records between July 2002 and March 2021 in ten of the borough's eleven postcode districts, every one except EN1 (how to check groundwater risk on a site).

Surface water is a London-wide problem: the 2025-30 London Surface Water Strategy chose the Lee Valley as one of its first two catchment partnerships (what the strategy means for planning). In Enfield the council is also slowing water upstream, with beavers released into a six-hectare enclosure at Forty Hall Farm in March 2022 and, for 2026/27, natural flood management on the Salmons Brook in Enfield Chase, a scheme at Bullsmoor Lane and new wetlands at Enfield Playing Fields.

CP28, the 2014 DMD and a plan at examination: what an Enfield application is judged by

Enfield is between plans. The policies in force are still the 2010 Core Strategy and the 2014 Development Management Document, with an area action plan for Meridian Water. The new Enfield Local Plan was submitted in August 2024; the Inspector wrote to the council after the hearings on 15 June 2026, and the council expects to consult on main modifications later in 2026. Until it is adopted, a well-made application answers both.

The Inspector's June 2026 letter is best known for its site decisions: Crews Hill and Chase Park stay in, while the Hadley Wood site and land east of junction 24 are to be deleted. Where a scheme leans on national policy in detail, our NPPF guidance covers chapter 18 in full.

A drainage strategy with every application: Enfield's SuDS and watercourse rules

Enfield sets a low threshold for drainage evidence. Its sustainable drainage page requires every planning application to include a drainage strategy, with a short pro-forma for householder work and a full one for everything else, and the policies set clear numbers for floors, setbacks and basements.

• Every application. A householder extension, a lawful development certificate or a householder prior approval uses the council's minor SuDS pro-forma; all other schemes use the full pro-forma and a strategy behind it.
• Runoff rates. Under the submitted plan, major schemes are expected to match greenfield rates for the 1 in 1 and 1 in 100 year storms with climate change, or Qbar where a single control is used, and smaller ones to get as close as they can.
• The first 5 mm. Source control across the site should capture the first 5 mm of rain, so roofs and hard surfaces need green roofs, permeable paving or rain gardens rather than a pipe to the sewer.
• Floor levels. Finished floors at least 300 mm above the 1% plus climate change river flood level, or 150 mm above the surface water level, with dry access or a very low hazard route out.
• Basements. Not permitted where there is river or surface water risk, and a groundwater assessment is needed for any basement (basement and cellar conversions in a flood zone).
• Brook-side land. A minimum 8 m setback from any watercourse, open or culverted, unless the bodies responsible for the watercourse agree a smaller distance.

Where the ground is clay, infiltration is limited, so any soakaway claim needs testing; our BRE 365 infiltration calculator shows how a test result becomes a design rate.

Meridian Water, Crews Hill and Chase Park: growth in the floodplain and the Green Belt

Enfield's largest sites face very different flood questions. Meridian Water lies in the Lee floodplain beside the Pymmes and Salmons Brooks, while Crews Hill and Chase Park are Green Belt land in the north and west of the borough. The 2023 Level 2 Strategic Flood Risk Assessment tested each as a broad location for the new Local Plan.

• Meridian Water. The broad location failed both the sequential and exception tests in the Level 2 assessment because of its large areas of Flood Zones 2 and 3, so each phase depends on site-level modelling, the infrastructure works and Policy EL8. The allocation rose to about 7,400 homes during the 2025 hearings.
• Crews Hill. Rated 'may pass': river risk is localised along the brooks that cross it, so a scheme passes if a flood risk assessment shows the homes sit outside it. The Inspector kept the 5,500-home allocation in June 2026.
• Chase Park. Passed the sequential test, with surface water, groundwater and reservoir risk to manage instead. The Inspector kept its 3,700 homes and asked for the Trent Park extension to be delivered alongside.
• A proposed new town. In March 2026 the Government named Crews Hill and Chase Park as one of seven proposed new town locations, at up to 21,000 homes. Final locations are due before the end of 2026, so nothing is settled yet.
• Industrial land. The borough holds the second largest stock of industrial space in London, much of it in the Lee Valley at Brimsdown, Ponders End and the Meridian hinterland, and the plan's evidence calls for 304,000 square metres more.

For an owner or promoter on any of these sites, the useful work comes before the layout is fixed: where the brook corridors and storage must stay open, what the reservoir and groundwater layers mean for access and basements, and which parts of the land can carry homes.

From a Palmers Green extension to a Brimsdown warehouse: when you need a flood risk assessment in Enfield

Whether a flood risk assessment in Enfield is needed depends on the flood zone, the size of the site, the use and, in this borough, the drainage forms. The table covers the cases we see most often across the borough.

If a site sits within 8 m of a brook or over a culvert, the layout is often the first thing to check, because the setback and access strip can decide what fits before any flood level is set.

Reports for sites along the Enfield brooks and the Lee Valley

Each report answers a different question: whether a site is safe, whether it should be built on at all, and where its rainwater goes. These are the ones Enfield sites ask for.

• Brook, reservoir and sewer together. A flood risk assessment for an Enfield site weighs the nearest brook, the Lee, the reservoir extent, surface water and groundwater in one report.
• Applications under CP28 and DMD 60. The council expects a flood risk assessment for planning in Flood Zones 2 and 3, on sites over a hectare and on Meridian Water land under EL8.
• Buying near the Salmons Brook. The 2016 scheme left the most exposed Edmonton homes with a 1 in 75 yearly chance of flooding, so a flood risk survey for property purchase checks a home in Edmonton or Bush Hill Park before exchange.
• Sites in Flood Zones 2 and 3. Housing on brook-side or Lee Valley land needs a sequential and exception test, and at Meridian Water the council runs it at masterplanning stage.
• A strategy with every application. Because Enfield asks for drainage evidence on every scheme, a drainage strategy is part of the submission from a single house upwards.
• The first 5 mm and the London hierarchy. A surface water drainage strategy shows how a scheme captures the first 5 mm and meets the London hierarchy on clay.
• Pre-commencement conditions. Where consent arrives with a drainage condition, we prepare the evidence for the discharge of drainage conditions the council's flood team will check.
• Storage areas and culverts. The brooks run through flood storage at Enfield Golf Course and Montagu Recreation Ground and the council holds its own Flood Zone 3b data, so flood modelling can set levels for a site beside the Salmons, Pymmes or Turkey Brook.
• Basements and allocated sites. The Level 2 assessment asks for a groundwater flood risk assessment on many allocated sites and for any basement, where 38 groundwater flooding records since 2002 show the risk is real.
• Warning areas on the brooks and the Lee. Homes, schools or care uses in the Turkey, Salmons, Pymmes Brook or Lower Lee warning areas may need a flood warning and evacuation plan for the people who will use them.
• Land at Crews Hill and Chase Park. Before an option or an offer, a flood risk feasibility study tests which parts of a Green Belt or brook-side parcel can take homes once the corridors and storage are kept open.
• Industrial deals in the Lee Valley. Before buying or lending on a unit at Brimsdown, Ponders End or the Meridian hinterland, flood risk due diligence sets out the flood zone, the reservoir extent and the drainage limits.
• New logistics and office space. With 304,000 square metres of industrial floorspace planned, schemes seeking BREEAM credits need a BREEAM flood risk assessment for the Pol 03 issue.

Agency, council, Thames Water or the Canal & River Trust: who deals with flooding in Enfield

Responsibility in Enfield is split by source. The Environment Agency deals with the main brooks and the Lee, the council with surface water, groundwater and the smaller streams, Thames Water with the sewers, and the Canal & River Trust with the Lee Navigation.

To check a home's long-term risk from rivers, surface water and reservoirs, the government's long term flood risk service gives the official result by address. Our page on Middlesex, the historic county Enfield belonged to, and our Haringey council page cover the neighbouring ground; other places are listed among the areas we cover.

Questions from Enfield, Edmonton and Southgate

Every Unda Consulting Limited report on an Enfield site is signed off by a senior consultant, and the firm is a CIWEM Business Partner. To talk through a site anywhere in the borough, call one of our chartered flood risk consultants on 01293 214444 or email enquiries@unda.co.uk.