Flood Risk Assessment in Cambridge

A flood risk assessment in Cambridge has to deal with three different kinds of water. The River Cam spreads slowly across the commons, intense summer storms overload the drains in the city centre, and groundwater sits close to the surface in the chalk and gravels. We prepare these assessments for planning, property purchase, mortgage and insurance, alongside sequential and exception tests and surface water drainage strategies for sites across the City of Cambridge.

The city is its own planning area, handled by Greater Cambridge Shared Planning on behalf of Cambridge City Council, while Cambridgeshire County Council is the Lead Local Flood Authority. Its streets fall in the CB1 to CB5 postcode districts, which run from Chesterton and King's Hedges in the north to Trumpington and Cherry Hinton in the south.

Cambridge has no critical drainage areas, yet the county's surface water plan lists eleven wetspots inside the city, from King's Hedges and Arbury to Trumpington and the city centre.

To talk through a Cambridge site, ring one of our experienced flood risk consultants on 01293 214444. Reports for sites in Cambridge come from Unda Consulting Limited, a CIWEM Business Partner.

Is Cambridge at risk of flooding?

Yes, though rarely from one source alone. River flooding from the Cam and Bin Brook affects the commons and the streets beside them, and the Great Ouse catchment plan counts 646 properties in the city at a 1% annual chance of river flooding, rising to 942 by 2110. Away from the river, surface water flooding and overloaded sewers cause most of the recorded damage.

There is no Internal Drainage Board inside the city boundary, and no Section 19 flood investigation has been published for Cambridge itself.

Check a site anywhere in Cambridge

Type a postcode below to see the flood map for any address in Cambridge, screened against the Environment Agency's river, surface water and reservoir data, or open the full flood risk map for anywhere in England. It is a first look, not a substitute for an assessment of the site.

The Cam, its commons and the city's brooks

The Cam flows north through the city to join the Great Ouse, and when it floods it spreads slowly across Coe Fen, Sheep's Green, Jesus Green and Midsummer Common. On the Environment Agency's planning flood map those commons sit in Flood Zone 3, while the Market Square is in Flood Zone 1. Our River Cam page follows the river beyond the city.

Each of the smaller watercourses has a different owner, which matters when a site backs onto one. Bin Brook is a main river from Newnham, so the Environment Agency deals with it. Hobson's Brook (which becomes Vicar's Brook), Cherry Hinton Brook and Coldham's Brook are maintained by the City Council, and Cherry Hinton Brook and the Nine Wells stretch of Hobson's Brook are chalk streams.

The Environment Agency's warning areas name the streets most often affected:

• Cam at Grantchester and Chesterton. Grantchester Meadows, Newnham Road, Silver Street, Queens' Lane, Bridge Street and the riverside colleges.
• Cam at Chesterton and Fen Ditton. Chesterton Road, Victoria Road, Midsummer Common, Riverside, Logans Way, Lynfield Lane, Water Street and Fen Road.
• Bin Brook at Newnham. Barton Road, Gough Way, Penarth Place, Herschel Road, Sylvester Road and Grange Road.

River levels are recorded at Jesus Lock, Baits Bite, Byron's Pool and on Bin Brook. Our live river levels map shows these gauges alongside current warnings.

Groundwater, chalk and basements in Cambridge

Groundwater shapes many Cambridge schemes, and the reason is the ground itself. Cherry Hinton, Romsey and the hospital campus stand on chalk, a principal aquifer, while Chesterton, Arbury, King's Hedges and Newnham sit on river terrace sand and gravel over Gault clay. Both can hold water close to the surface.

The Level 2 SFRA asks for groundwater investigation on every major allocation in the city. At the Cambridge Biomedical Campus, 38% of the site shows potential for groundwater flooding below ground, and hospital basements have already proved vulnerable. For any scheme with a basement, lift pit or deep attenuation tank, groundwater belongs in the assessment from the start; our guide to groundwater flood risk in planning applications sets out what the county expects to see.

Infiltration needs the same care. The county requires a tested rate of at least 1×10⁻⁶ m/s, the base of any soakaway at least 1.2 m above the highest groundwater level, and it will not accept soakaways deeper than 2 m as the first choice. The geology and ground conditions checker gives a first view before anyone digs a trial pit.

When has Cambridge flooded?

Records of Cambridge flooding split into slow river floods and fast storms that overload the drains.

• March 1947. Snowmelt sent the Cam out of bank; the 1947 mark on the Trinity College Avenue bridge sits several inches above the October 2001 level.
• May 1978. Flooding on Barton Road and Newnham Terrace from Bin Brook and the Cam.
• 21–23 October 2001. About 3.5 inches of rain fell on 21 October. Coe Fen, Sheep's Green, Jesus Green and Midsummer Common went under water, with flooding on Logans Way, Water Lane, St Andrews Road and Lynfield Lane, and on Herschel Road, Gough Way and Grange Road from Bin Brook.
• February 2010. Groundwater flooding recorded on Coleridge Road and Mawson Road.
• 25 August 2012. A cloudburst flooded Sidney Street, the Market Square and Lion Yard; the ceiling of the Central Library collapsed and the Grand Arcade was evacuated.
• 8 February 2014. The Cam came out of bank at Silver Street and flooded The Anchor.
• 16 July 2015. A thunderstorm breached a basement at Addenbrooke's, which declared a major incident, and flooded a University server room.
• 14 September 2021. Heavy rain flooded the entrance and ticket hall at Cambridge station.
• January 2024. Storm Henk raised the Cam far enough to cut off the college boathouses.

Sewer flooding is rising. Across Greater Cambridge, Anglian Water recorded 306 external sewer flooding incidents in 2023 and 367 in 2024.

What Cambridge planning policy asks of a flood risk assessment

The adopted plan is the Cambridge Local Plan 2018, and two of its policies drive most drainage conditions in the city. Policy 31 covers integrated water management and Policy 32 covers flood risk. Both apply to every development, small or large. The county's guidance then adds its own figures for major schemes.

The evidence behind these decisions is the Greater Cambridge Level 1 Strategic Flood Risk Assessment of October 2025 and its Level 2 companion for the strategic sites. The Cambridgeshire Flood and Water SPD and the county's Surface Water Planning Guidance set out how the LLFA reviews drainage on major applications. National policy is in chapter 18 of the NPPF, which covers flood risk, read with the Planning Practice Guidance.

A replacement plan is well advanced. The Proposed Submission Greater Cambridge Local Plan was consulted on from 3 August to 25 September 2026 and is due to be submitted by the end of 2026. Its draft policy CC/FM keeps the 300 mm floor level and the limiting discharge, and would bar highly or more vulnerable uses in basements or ground-floor-only homes in Flood Zone 3 with climate change. Policy CC/IW asks for wastewater capacity to be in place before occupation.

Where Cambridge is growing, and what it means for drainage

Each of the city's growth areas has its own drainage constraint.

• North East Cambridge. Consent to move the sewage treatment works was granted in April 2025, but government funding was withdrawn that August and Anglian Water says the move will not go ahead. The draft plan now treats the area as a special policy area with the works staying. The land is in Flood Zone 1, but the First Public Drain that crosses it has never been modelled.
• Cambridge Biomedical Campus. All of it is in Flood Zone 1, yet surface water mapping shows depths of 600 to 900 mm around Addenbrooke's, and the groundwater findings above apply to any new laboratory with a basement.
• Cambridge East. The draft plan expects around 8,000 homes on the airport land from 2032, subject to water supply infrastructure being in place.
• Wastewater capacity. Anglian Water has objected to schemes over treatment capacity at the Cambridge works, and the councils now attach conditions that must be met before occupation.

Water supply is a separate constraint. Cambridge Water draws almost all its supply from groundwater and brought in a hosepipe ban on 17 July 2026, so new non-residential buildings face demanding water efficiency targets under the BREEAM water credits as well as the flood and drainage rules.

Reports for Cambridge sites, from riverside homes to laboratories

Each of these reports answers a different question about a Cambridge site, from a riverside house sale to a new laboratory:

• Any site in the city. A flood risk assessment tests river, surface water, groundwater and sewer risk on the plot itself, instead of leaning on the city-wide map.
• Planning applications. Greater Cambridge Shared Planning expects a flood risk assessment for planning in Flood Zones 2 and 3, on sites of a hectare or more, and on Zone 1 sites shown at risk from surface water.
• Buying near the river. Houses on Logans Way, Water Street or Gough Way sit inside Environment Agency warning areas, and a flood risk survey for property purchase explains what that means before exchange.
• Sites in Zone 2 or 3. The sequential and exception test is weighed against the Greater Cambridge sequential test evidence updated in 2026.
• New buildings of any size. Policies 31 and 32 reach small schemes too, so most applications need a drainage strategy showing the 5 mm interception and the discharge limit.
• Major schemes. The county reviews a surface water drainage strategy against its February 2026 guidance, including the 3 l/s/ha brownfield figure.
• After consent. Conditions on city schemes often ask for infiltration results, groundwater monitoring and maintenance plans, which is where discharge of drainage conditions comes in.
• Insurance. With 646 properties at a 1% annual chance of river flooding, a flood risk assessment for insurance gives an underwriter the levels and flow routes for the building itself.
• Laboratories and offices. Policy 28 asks new non-residential buildings for BREEAM Excellent and full water credits, and a flood risk assessment for BREEAM covers the flood risk credit.
• Commercial transactions. Plots on the Cambridge Biomedical Campus and around Cambridge Science Park carry groundwater and surface water constraints that a due diligence flood risk assessment brings out before purchase.
• Hospitals, data rooms and basements. The 2015 storm at Addenbrooke's showed what one flooded basement can stop, which is the subject of a business continuity flood risk assessment.
• Sewage capacity. Treatment capacity at the Cambridge works is a live planning issue, so larger schemes often need a foul drainage strategy.
• Chalk and gravel sites. Basements and soakaways in Cherry Hinton, Trumpington or Chesterton may need a groundwater flood risk assessment with monitoring.
• Brook-side sites. The Vicar's Brook and Cherry Hinton Brook models predate current climate change allowances, so some sites need fresh flood modelling.

For the county as a whole, see our page on flood risk assessment in Cambridgeshire and the Cambridgeshire County Council requirements, or browse every area we cover.

Who manages flood risk in Cambridge

In Cambridge the river, the brooks and the drains each answer to a different body, so the first call depends on where the water is coming from.

The county's Flood Risk Management Strategy 2021 to 2027 sets out how these bodies share the work. Our explainer on the Lead Local Flood Authority covers what the county does and does not handle.

What people ask us about Cambridge sites

Our chartered consultants know the city's rivers, brooks and drainage policies well. Call 01293 214444 or email enquiries@unda.co.uk to talk through a site in Cambridge.