Flood Risk Assessment in Maidenhead

A flood risk assessment in Maidenhead starts with a town the Thames floods less often than it used to. It still floods. Since 2002 the Jubilee River and the North Maidenhead Bund have kept high Thames flows out of the town centre. Even so, the council's flood study still marks parts of north Maidenhead as functional floodplain, and in September 2024 heavy rain got inside 40 homes across the town.

We prepare flood risk assessments in Maidenhead for planning applications, property purchases, mortgages and insurance, alongside sequential and exception tests and surface water drainage strategies. On this page Maidenhead means the built-up area the Office for National Statistics maps under that name: the town centre and riverside, Furze Platt, North Town, Boyn Hill and Cox Green, all in the SL6 postcode district. Cookham, Bray village and Holyport lie outside that outline, and they appear below where their rivers and defences affect the town.

Behind the 2002 bund, the strip of north Maidenhead between the Thames and Maidenhead Ditch is still treated by the council's flood study as functional floodplain, because groundwater and ponding keep flooding it.

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

What the Jubilee River changed in Maidenhead, and what it left

The Maidenhead, Windsor and Eton Flood Alleviation Scheme keeps the Thames out of most of the town in the floods it was built for. Its centrepiece, the 11.6 km Jubilee River, opened in 2002, and when the Thames runs high the Environment Agency opens weir gates at Taplow to send part of the flow down the channel, which rejoins the river at Datchet. The Environment Agency says the scheme reduces flood risk to about 3,000 properties in Maidenhead, Windsor, Eton and Cookham. Our article on how the Jubilee River works covers its route and operation.

• A bund as well as a channel. The scheme also built the North Maidenhead Bund, which the council's 2017 Level 1 flood study says defends the north of the town while the Jubilee River lowers flood levels through the centre.
• Defended does not mean dry. The same study finds that a relatively high susceptibility to flooding remains between the Thames and Maidenhead Ditch, from groundwater raised by the river and from rain ponding in low ground. It therefore highlights those areas as Flood Zone 3b, the functional floodplain.
• South Maidenhead and Bray Wick. A large share of the southern town centre and the land towards Bray is in Flood Zone 3a, and the study notes that the mapping already assumes the Jubilee River is running, and that it does not expect the number of properties at risk in a 1 in 100 flood to fall much.
• The bund does not change the zone. Flood zones leave raised defences such as the North Maidenhead Bund out of the picture, so land behind it keeps its Flood Zone 2 or 3 status even though the channel is counted. An assessment then deals with the residual flood risk of a larger flood or a defence failure.
• A record set in 2003. The first big test came in January 2003. The council's study says about 1,000 properties were protected, and the Thames gauge at Maidenhead reached its highest level on record, 3.87 m, on 4 January 2003.

Cookham did not miss out on the scheme. The 2002 works included the Cookham Bund and Cookham Flood Wall, and after Strande Lane flooded in 2003 the Environment Agency added a raised bund across Cookham Marsh and lowered the sill of Odney weir. The village still floods. Low ground surrounds it, so high water cuts it off. In January 2024 the council recorded 14 Cookham properties flooded inside and closed the Causeway.

Search a Maidenhead postcode for flood risk

Enter a Maidenhead postcode below to screen it against Environment Agency data for rivers, surface water and reservoirs, or use our full flood risk map for anywhere in England. The coral line marks the built-up area this page covers.

Rain, river gravels and the town channels: where water comes from in Maidenhead

The council's flood study puts chalk under Maidenhead, with Thames gravels over it along the floodplain, and that geology explains much of the local pattern. Groundwater moves through the gravels when the river is high, while the clay lenses over the chalk in north Maidenhead slow rain soaking in.

The sources overlap, and the council's September 2024 investigation found that flooding followed the modelled surface water flow routes almost exactly, and that a high Thames slows the outfalls that would normally carry rain away. Our guides to groundwater flooding and surface water flooding and planning set out how an assessment deals with each.

Maidenhead floods on record, from 1947 to 2024

Maidenhead's record shows the shift the scheme made: river floods fill the older entries, and since 2002 most of the damage inside the town has come from rain landing on it and from groundwater rising beneath it.

1. March 1947. Snowmelt on frozen ground followed the wettest March in Maidenhead since before 1860, according to the University of Reading's local record, and the Thames produced what was probably its worst flood of the century on this reach. Accounts of the event put the homes flooded in Maidenhead at more than 2,000; our article on the 1947 floods follows the wider story.
2. November 1974. Flooding in Maidenhead and Bray lasted three days after 101.6 mm of rain fell at Hurley in nine days; more than 500 properties in the area were affected, some of them cut off.
3. February 1990. The Thames burst its banks shortly before the flood alleviation scheme was approved, and Maidenhead was one of the hardest hit places.
4. 2002 and 2003. The Jubilee River opened. In its first big operation, in January 2003, the Thames gauge at Maidenhead set its record of 3.87 m, while about 128 houses downstream were affected, many of them at Ham Island and Wraysbury.
5. July 2007. Surface water flooded about 30 Maidenhead homes and closed Nicholson's Walk, while the scheme kept the river out.
6. Winter 2013–14. About 170 properties across the borough flooded inside, with Cookham, Eton and Windsor among the places badly hit, although the University of Reading's record notes that Maidenhead itself escaped relatively lightly, thanks to the Jubilee River.
7. January 2024. Storm Henk filled the Jubilee River to capacity by 8 January, when a flood warning went out for Windsor and Maidenhead, and inside the town the council recorded road and garden flooding on Maidenhead Court Road, which it put down to groundwater rising through the soakaways that drain the street.
8. 23 and 27 September 2024. In the Thames area's wettest month since 1871, rain flooded 40 Maidenhead homes inside, 14 of them in Boyn Hill; on the 23rd every reported home flooded between 2am and 4am. Camley Gardens residents said similar flooding had happened almost every year for a decade.

The Environment Agency issues its warning 'River Thames at Maidenhead to Windsor and Eton' for Maidenhead, Bray and Dorney, and runs a separate groundwater alert for East Maidenhead. The River Thames gauge at Maidenhead has a normal range up to 3.55 m, and the Maidenhead Ditch gauge at Raymill Road peaked at 1.47 m in December 2000. Both appear on our live river levels map with the Boulters Lock and Jubilee River gauges.

Policy NR1 and the Maidenhead Neighbourhood Plan: the flood tests for a site

The Royal Borough of Windsor and Maidenhead decides planning applications in the town and, as Lead Local Flood Authority, comments on the surface water drainage of major schemes. Its Borough Local Plan 2013–2033, adopted on 8 February 2022, sets the flood rules in Policy NR1, Managing Flood Risk and Waterways. The plan replaced the old Maidenhead Town Centre Area Action Plan.

• When an assessment is needed. NR1 asks for one in Flood Zones 2 and 3 and on sites of a hectare or more in Flood Zone 1; the supporting text adds every change of use in Zones 2 and 3.
• No sequential test on allocated sites. The sequential test applies to all development in areas at risk, except sites allocated in the plan or in a made neighbourhood plan that accord with it. In the functional floodplain only water-compatible uses and essential infrastructure are supported.
• The exception test still applies. Part 7 applies the exception test in line with national policy, including on allocated sites, and asks development to reduce flood risk overall where it can.
• What a scheme must not do. Development must not impede flood flows, take floodplain storage, put more people or property at risk, or worsen flooding on or off the site. It should add storage where possible, use SuDS, build in resistance and resilience, and show safe access and an evacuation plan where needed.
• An 8 m strip by watercourses. Part 9 keeps an undeveloped 8 m buffer on both banks of main rivers, including culverted ones, measured from the top of the bank; on ordinary watercourses the council applies it more flexibly.
• The waterways. Part 10 expects development to help improve and join up the waterways in Maidenhead, including completing the Maidenhead Waterway Project.

The Maidenhead Neighbourhood Plan, made on 21 April 2026, adds two local policies for its seven wards. Policy BI-2 asks schemes in Flood Zones 2 and 3, and those over a hectare in Zone 1, to show there is enough drainage infrastructure to serve the site without the foul sewers surcharging, no surface water harm to land upstream, downstream or next door, and that no mechanical pumping is needed to prevent flooding in events up to 1 in 100. Policy SS-1b keeps at least 8 m of green space on either bank of the Waterway and asks adjoining development to contribute to its upkeep.

The evidence behind NR1 is the council's Strategic Flood Risk Assessment: a Level 1 study of June 2017 and a Level 2 study with sequential and exception testing of sites from April 2018. For floor levels it asks for at least 300 mm above the 1 in 100 flood level with climate change. Floodplain storage lost to a building is replaced level for level with 5% extra. Nationally, flood risk sits in chapter 18 of the NPPF, where policy F4 says when an assessment is needed, F5 and F6 set the sequential and exception tests and F8 expects drainage to meet the 2025 national standards for SuDS.

Allocated sites in Maidenhead and the flood requirements on each

The Borough Local Plan allocates sites in and around Maidenhead for more than 5,000 homes up to 2033, each with its own requirements in Appendix C. The neighbourhood plan records four tall apartment buildings at One Maidenhead and a further 1,150 town-centre flats approved. Because NR1 lifts the sequential test from allocations but not the exception test, several sites have flood conditions written into the plan itself.

Desborough and Spencer's Farm lie on the edge of the built-up area, Desborough planned around the Maidenhead Golf Course land south-west of the town. On York Road and Saint-Cloud Way the plan itself asks for the exception test and a safe way out. Bray Lake goes further: its requirement is betterment, so a scheme there has to leave flood risk on the site lower than it found it. A windfall site with no allocation has to pass the sequential test as well; our article on applying the sequential test after Mead explains how the area of search is set.

Surface water drainage in Maidenhead: what the council asks for

The council's SuDS major design guidance follows the 2025 national standards for sustainable drainage and adds a few rules of its own. The council comments as LLFA on major applications, while NR1 and, in its seven wards, the neighbourhood plan apply to schemes of every size.

• Rainwater reuse every time. The borough is classed as water stressed, so collecting rainwater for non-potable use is always required, usually alongside another outfall. Our article on rainwater harvesting in SuDS covers how the two combine.
• 2 l/s/ha from long-term storage. Flows from long-term storage must soak away or leave at no more than 2 l/s/ha. Nothing up to the 1 in 100 storm may leave the site uncontrolled.
• Storage above ground. The council prefers ponds, swales and other surface features. Crates or tanks need robust justification, and they must sit where they can be reached for maintenance, not in private back gardens.
• Infiltration on chalk and gravel. Infiltration tests are expected at application stage. Deep bore soakaways may suit parts of the borough, subject to Environment Agency approval, and contaminated land needs a risk assessment first.
• Drainage that works in a flood. In Flood Zone 3 the council's flood study asks for drainage that keeps working up to the 1 in 100 flood with climate change, with SuDS features placed outside Zone 3 where the site allows.

Our free ground conditions and soakaway map gives a first read of the geology under a Maidenhead site before trial pits are dug.

From extensions to basements: does your scheme need a flood risk assessment in Maidenhead?

An assessment is required for most building work in Flood Zones 2 and 3, for any site of a hectare or more, and for every change of use in Zones 2 and 3. Outside the river zones, surface water or groundwater shown on the planning map can also trigger one. The table sets out common Maidenhead schemes and what each usually needs.

Our guide to Flood Zone 3b explains what functional floodplain means for development. In north Maidenhead it matters behind the bund as well as in front of it, because the council's study draws 3b there.

What our consultants prepare for Maidenhead sites, from the riverside to Cox Green

A buyer in Boyn Hill, a householder by the river and the developer of a town-centre allocation each need a different report. Our consultants are chartered. Every report is signed off by a senior consultant before it is issued, and Unda is a CIWEM Business Partner.

• Riverside and town-centre applications. Schemes in Flood Zones 2 and 3, or on sites over a hectare, need a flood risk assessment for planning that answers Policy NR1 and the council's flood study.
• River, rain and gravel together. A flood risk assessment for a Maidenhead site weighs the Thames and the bund against surface water flow routes, groundwater in the gravels and the town channels.
• Before exchange. Where a search flags the riverside zones or a Boyn Hill or Furze Platt flow route, a flood risk survey for property purchase looks at the building itself rather than the postcode.
• Unallocated and allocated sites. Windfall homes in Flood Zones 2 and 3 need the sequential and exception test; allocations such as York Road and Saint-Cloud Way still need the exception test.
• SuDS on every scheme. NR1 asks every scheme to use SuDS to restrict runoff, so even a small Maidenhead site needs drainage strategy evidence of some kind.
• Rainwater reuse and 2 l/s/ha. A surface water drainage strategy for a major scheme shows rainwater reuse, the 2 l/s/ha limit on long-term storage and, on Desborough, greenfield runoff rates.
• After permission. Where a Maidenhead permission comes with a drainage condition, discharge of drainage conditions supplies the detail, calculations and maintenance plan the council asks for.
• High water in the gravels. East Maidenhead has its own groundwater alert area and several allocations must address groundwater, so a groundwater flood risk assessment matters for basements and soakaways.
• Levels the national map cannot give. The flood study warns that the Thames model above Windsor is unreliable for floodplain hazard, so riverside schemes may need site-specific flood modelling.
• A route out. NR1 and the allocation requirements ask for safe access and evacuation on sites in Zones 2 and 3, which a flood warning and evacuation plan sets out against the Maidenhead warning areas.
• Sewer capacity. West Street and Saint-Cloud Way must provide waste water infrastructure, and the neighbourhood plan rules out foul surcharge, so a foul drainage strategy may be needed.
• Cover after a flood. With 40 homes flooded inside in September 2024, a flood risk assessment for insurance gives an insurer the picture for one house.
• Testing land early. With Desborough, Spencer's Farm and Bray Lake allocated, a flood risk feasibility study shows whether a layout can meet the exception test before an offer is made.
• Buying commercial land. Town-centre redevelopment sites and riverside land in Zones 2 and 3 need flood risk due diligence before a purchase or loan.
• Offices and workplaces. New commercial space in the town centre, at St Cloud Gate and on the Triangle site can use a BREEAM flood risk assessment for the Pol 03 credits.
• Staying open. A High Street business and a Bath Road business closed after the September 2024 rain, and a business continuity flood risk assessment plans for the next storm.

Reporting flooding and getting warnings in Maidenhead

If floodwater threatens anyone in Maidenhead, call 999; for a power cut during a flood, call 105. For everything else, the organisations below each look after part of the picture.

The council publishes its flood investigations, including the September 2024 Maidenhead report and the January 2024 Thames report; our explainer on Section 19 investigations covers when they happen. Across the river, Taplow holds the Jubilee River's weir gates; upstream sits Marlow, and downstream Windsor and Eton and Datchet, where the channel rejoins the Thames. Our River Thames page covers the whole river, the Berkshire page the county, and the full list of areas every other place we cover.

Maidenhead flooding and planning: questions clients ask

Unda Consulting Limited prepares flood risk assessments, sequential and exception tests and drainage strategies for homes, businesses and development land across Maidenhead, from the riverside to Furze Platt and Cox Green. To discuss a Maidenhead site, call 01293 214444 or email enquiries@unda.co.uk.