Flood Risk Assessment in Berkshire

A flood risk assessment in Berkshire is judged by whichever of six unitary councils covers the site, and each of them applies its own local plan, flood policy and Strategic Flood Risk Assessment. The water itself comes from the Thames and the Kennet, from chalk groundwater under the Downs and from storm runoff in the towns. Our consultants prepare these assessments anywhere in the county, for planning, property purchase or insurance, together with sequential and exception tests and surface water drainage strategies.

The Royal County of Berkshire (Berks on older addresses) has been run by six unitary councils since 1998, and this page covers all of them: West Berkshire, which takes in Newbury, Thatcham, Hungerford and the Downs; Reading; Wokingham; Bracknell Forest, with Bracknell itself, Sandhurst and Crowthorne; the Royal Borough of Windsor and Maidenhead; and Slough. Most addresses sit in the RG and SL postcode areas, and the larger Thames towns have pages of their own, listed further down.

Six councils decide planning applications and review drainage in Berkshire, each on its own patch and against its own local plan, adopted at dates from 2008 to 2025.

To talk through a Berkshire site, call 01293 214444 or email enquiries@unda.co.uk.

Six councils, six rule books: who reviews a site in Berkshire?

The council that covers the site does both jobs. Each Berkshire unitary is the local planning authority and the Lead Local Flood Authority for its area, so the body deciding the application is also the one commenting on its surface water drainage. The Environment Agency is consulted on main rivers and on Flood Zones 2 and 3. The plans those councils work from are years apart, which is why the table below matters before a report is scoped.

Two things follow for any site. The report has to answer the policy wording of the right council, and it has to draw on that council's SFRA, which may be older or newer than the national flood map. Our explainer on the Lead Local Flood Authority covers the general role, and our West Berkshire council guide goes through SP6 and the district's drainage rules in detail.

Screen a postcode anywhere from Hungerford to Colnbrook

The map below takes any Berkshire postcode and returns the Environment Agency's river, surface water and reservoir data for that spot; our full flood risk map does the same for the rest of England. Anyone after a Reading flood risk map, or the equivalent for Maidenhead or Newbury, can start here. Treat the result as a screening: it cannot see floor levels, the water table under a building or the policy wording a planning officer will apply.

For what is happening today, the Environment Agency lists every alert and warning in force on its Check for flooding page for Berkshire.

The Thames, the Kennet and the smaller rivers that shape Berkshire's flood zones

Most of the county's Flood Zone 2 and 3 land follows six river systems. The Thames runs along the northern edge from Reading down to Wraysbury; the Kennet crosses West Berkshire to join it at Reading; chalk streams drain the Downs; the Loddon and the Blackwater drain the south-east; and Slough's eastern edge sits on the Colne Brook. Where a site sits on that network decides which records its assessment draws on: the Thames gauges and Section 19 reports at Reading and Wraysbury, or the groundwater plans for the Lambourn and Pang valleys.

How the Jubilee River works, and whether it moves floodwater downstream to Datchet and Wraysbury, is set out in our article on the channel. Further down the river, the River Thames Scheme between Egham and Teddington lies outside Berkshire, though Windsor and Maidenhead's policy NR1 safeguards land for it and for a Datchet to Wraysbury channel. To see whether any of these rivers is rising before a site visit, open our live river levels map.

Is Berkshire at risk of groundwater flooding?

Yes, above all in the chalk west. After a wet winter the chalk beneath the Berkshire Downs fills until springs break out, the Lambourn and the Pang run high and low ground floods from below, sometimes for weeks. In the winter of 2013/14, West Berkshire Council recorded at least 181 homes and businesses flooded, and the Thames Valley Local Resilience Forum describes that winter's groundwater as unprecedented across its area.

• The Downs valleys. West Berkshire's groundwater record is why the council keeps separate flood management plans for the Lambourn and Pang valleys, and why groundwater flooding has to be assessed on its own terms there whatever the flood zone says.
• Chalk under north Wokingham. Wokingham's 2023 SFRA places white chalk and a principal aquifer under the north of the borough, with clay, silt and sand to the south and more sand around Barkham and Wokingham itself.
• Gravel along the rivers. The same SFRA maps alluvium and gravel along the Thames and the Loddon, where floodplain soils hold naturally high groundwater.
• What it changes on a site. Basements, floor levels and soakaways. Bracknell Forest asks for a back-up drainage route wherever infiltration is proposed without ground investigation, and our note on when infiltration testing is required explains the testing behind that.

Windsor and Maidenhead adds a twist. As Lead Local Flood Authority, the Royal Borough says it is not a statutory consultee on groundwater, yet it still expects an applicant to deal with groundwater's effect on surface water management. Where monitoring is needed it runs through a wet season, which our guide to groundwater monitoring for planning puts into a programme.

Berkshire's recorded floods, 2002 to 2024

Berkshire flooding comes in three forms: slow Thames floods, chalk groundwater that lingers, and short summer storms that overwhelm town drains. Every figure below comes from a council investigation, the Environment Agency or the Local Resilience Forum, and the Section 19 reports behind them name the parishes affected.

1. 2002. The Jubilee River opened as the main element of the Maidenhead, Windsor and Eton flood alleviation scheme (Environment Agency).
2. 20 July 2007. A storm over the hills north of Thatcham sent runoff through the town; West Berkshire's Thatcham Surface Water Management Plan gives an initial estimate of about 1,100 houses flooded. Wokingham recorded at least 80 properties flooded inside and 120 outside the same month, with 58 roads under water.
3. Winter 2013/14. The wettest winter in the UK since records began in 1766, according to the Thames Valley Local Resilience Forum. West Berkshire counted at least 181 homes and businesses flooded; Windsor and Maidenhead's later investigation confirms about 170 properties flooded inside between December 2013 and February 2014.
4. January 2024. Storm Henk fell on saturated ground. Reading recorded 24 properties flooded (21 homes and three commercial) and a major incident was declared on 5 January; Windsor and Maidenhead recorded 271 properties affected, 94 of them inside, mostly in Hurley, Bisham, Cookham, Datchet, Wraysbury and Old Windsor.
5. Winter 2024. West Berkshire's latest Section 19 investigation reports about 210 properties affected, roughly 77 of them flooded internally.

Anyone searching for the Thatcham floods of 2007 or the map of what flooded will find West Berkshire's investigations on its flood reports page, and the Royal Borough's Storm Henk report breaks the 2024 figures down parish by parish.

Flood Zone 1 in Slough and Wokingham is not the end of the question

In the eastern towns the rivers matter less than the rain. Slough's preliminary assessment estimated 8,758 homes at risk of surface water flooding, and its 2017 review identified the town as a Flood Risk Area under the Flood Risk Regulations. Wokingham's SFRA records surface water floods around Wokingham, Winnersh and Three Mile Cross in 2008. A site can be in Flood Zone 1 and still be caught.

Councils deal with that in different ways. Slough's developer guidance asks for an assessment in Flood Zone 1 where there is a known local surface water, sewer or groundwater problem, and West Berkshire's SP6 asks for one wherever a smaller Zone 1 plot could flood from another source or lies in a critical drainage area. Our guides to surface water flooding and planning and to critical drainage areas set out the national position those local rules build on.

Which sites need a flood risk assessment in Berkshire: the national triggers and six sets of local ones

Anything in Flood Zone 2 or 3 does, and so does a site of a hectare or more in Flood Zone 1. Chapter 18 of the NPPF sets those national triggers in policy F4, with F5 and F6 governing the sequential and exception tests and F8 requiring development to follow the 2025 National Standards for sustainable drainage. Berkshire's councils then add triggers of their own.

The flood zones come from the Environment Agency's Flood Map for Planning, and national guidance is in the Planning Practice Guidance on flood risk. How the September 2025 changes reshaped the search for alternative sites is covered in our note on the PPG sequential test update.

What Berkshire's councils ask to see on drainage

Every council in the county expects the drainage hierarchy to be worked through in order, but each writes the details differently, and the details decide whether an application is validated and whether the drainage officer objects. The points below come from each council's own policy or guidance.

• West Berkshire. SP6 holds undeveloped sites to greenfield runoff rates and volumes up to the 1 in 100 year storm plus climate change, and previously developed sites to greenfield where achievable, otherwise to no more than half the existing 1 in 100 year rate, with SuDS designed to the council's supplementary planning document.
• Slough. A drainage strategy for every major scheme, submitted as its own document at validation; discharge goes to the ground, then a water body, then a surface water sewer and only then a combined sewer, and cost alone is not accepted as a reason to skip a step.
• Bracknell Forest. The January 2026 guidance asks for a sustainable drainage strategy with every major application and proportionate measures on minor ones, such as water butts, permeable paving, planters or green roofs.
• Wokingham. CC10 and the council's SuDS Strategy of April 2016 apply. The 2023 SFRA describes mostly loamy, moderately permeable soils, crossed by a slowly permeable clay band from south-west to north-east.
• Windsor and Maidenhead. Major-scheme drainage is reviewed against the Royal Borough's design guidance for major developments, which is built on the 2025 National Standards.
• Reading. EN18 covers both the flood risk tests and the sustainable drainage requirement; the partial update's main modifications propose narrowing its drainage wording to major schemes, so check which version applies on the decision date.

What the 2025 standards require of every scheme is explained in our guide to the National Standards for sustainable drainage, and the most common reasons a strategy is rejected are in our article on an LLFA objection.

What we prepare for sites from the Downs to the Thames at Wraysbury

A barn conversion in a chalk valley, a warehouse in Slough and a house purchase beside the Thames each need a different report. A senior consultant signs off each one; our consultants are chartered, and Unda is a CIWEM Business Partner. Across the county we prepare:

• Applications to any of the six councils. A scheme in Flood Zone 2 or 3, on a hectare or more, or on a smaller West Berkshire plot exposed to another source needs a flood risk assessment for planning.
• River, chalk and drains on one plot. Along the Kennet and the Lambourn a flood risk assessment often has to weigh the river, rising groundwater and runoff off the Downs together.
• Buying where a search raises a flag. When a conveyancing search marks a Berkshire home at risk, a flood risk survey for property purchase looks at the building and its levels rather than the postcode.
• New homes on the Thames floodplain. Away from allocated sites, housing in Zone 2 or 3 in Windsor and Maidenhead or West Berkshire faces the sequential and exception test on top of the site's own assessment.
• Runoff limits that change at the boundary. West Berkshire's greenfield-or-half rule and Slough's separate document at validation are two of the local requirements a drainage strategy here has to meet.
• Chalk or clay. On the chalk a surface water drainage strategy has to show the water table sits low enough for soakaways; on the clay, silt and sand further east it usually needs storage and a restricted outfall.
• After the permission. A pre-commencement drainage condition from any of the six councils is cleared with evidence we prepare for the discharge of drainage conditions.
• Renewal after Storm Henk. With 271 properties affected in Windsor and Maidenhead and about 210 in West Berkshire in 2024, a flood risk assessment for insurance gives an underwriter evidence about the building itself.
• The chalk valleys. In the Lambourn and Pang valleys, where at least 181 West Berkshire properties flooded in 2013/14, a groundwater flood risk assessment sets a design water table for floors, basements and soakaways.
• Main-river sites. Beside the Thames, the Kennet or the Loddon, where national mapping is too coarse for a single plot, flood modelling produces the levels a floor and an escape route are judged against.
• Getting out safely. NR1 asks for evacuation plans where appropriate and SP6 for safe access in extreme floods, which on the Thames floodplain often means a flood warning and evacuation plan alongside the assessment.
• Strategic land. On large sites such as the Loddon Valley Garden Village proposed in Wokingham's Local Plan Update, a flood risk feasibility study maps the flood and drainage constraints before a layout is drawn.
• Sewer capacity. Thames Water runs the sewers across Berkshire, and where a treatment works or the local network is near its limit a foul drainage strategy shows how the scheme's wastewater will be handled.
• National policy behind the local plans. Where an officer cites chapter 18 directly, our NPPF flood risk guidance sets out how policies F4 to F8 apply to the site.

Town pages across Berkshire and the neighbouring Thames towns

Six Berkshire places, and three just across the Thames, have pages of their own with more local detail:

• Reading. Reading, where the Kennet meets the Thames and sandbags went out to Lower Caversham and Southcote in January 2024.
• Maidenhead. Maidenhead, at the head of the Jubilee River.
• Windsor and Eton. Windsor and Eton, on either bank of the Thames below the castle.
• The reach below Windsor. Datchet, Old Windsor and Wraysbury, the villages below the Jubilee River's outfall.
• Across the river. On the Buckinghamshire and Oxfordshire banks, Taplow, Marlow and Henley-on-Thames share the same reach of the Thames.
• Over the Hampshire border. Sites south of the Blackwater are covered by our flood risk assessments in Hampshire.

Who to call about flooding in Berkshire

Call 999 if a flood puts anyone's life at risk, and 105 if the power goes off. Beyond that, who to ring depends on where the water is coming from and which of the six councils covers the address.

What people ask before a Berkshire site goes in

From the Lambourn valley to the Colne Brook, Unda Consulting Limited prepares flood risk assessments, sequential and exception tests and drainage strategies for Berkshire sites. Call 01293 214444 or email enquiries@unda.co.uk to discuss yours.