Flood Risk Assessment in Ely, Cambridgeshire

A flood risk assessment in Ely, Cambridgeshire, starts from an unusual shape: a city on a fen island. The cathedral and most of the streets stand on a hill that reaches about 26 m above Ordnance Datum, while the River Great Ouse runs along its eastern foot and drained fen surrounds it. For Ely sites we prepare flood risk assessments, sequential and exception tests and surface water drainage strategies, whether the need is a planning application, a purchase, a mortgage or an insurance renewal.

This page covers the City of Ely as the Office for National Statistics maps its built-up area, from the Princess of Wales Hospital in the north to the station and Waterside in the south, in the CB6 and CB7 postcode districts. It also covers the low ground that sites at the city's edge depend on: Stuntney and its causeway across the river, Chettisham beyond the northern estates, and Queen Adelaide and Prickwillow out on the pumped fen of the old Isle of Ely. Ely in Cardiff is a different place, with its own river and Welsh planning rules.

East Cambridgeshire's flood evidence says Ely itself is unlikely to flood from its river because it stands on high ground. Yet the Environment Agency's warning area for the Great Ouse at Ely names Waterside, Ship Lane, Annesdale, Station Road and Angel Drove. What a site needs depends on which part of the slope it occupies.

To talk through an Ely site with one of our flood risk consultants, call 01293 214444 or email enquiries@unda.co.uk. Reports for sites in Ely, Cambridgeshire come from Unda Consulting Limited, a CIWEM Business Partner.

A hill above the fen: where flood risk reaches Ely

In Ely, height decides most flood questions. The district's 2017 Strategic Flood Risk Assessment (SFRA) records that the flood zones show no main-river flooding to the town and that, given its position, Ely is unlikely to flood from rivers. The lower ground at the edges is where that changes:

• The hilltop. The island is capped by glacial sand, gravel and till over Jurassic clay. Around the cathedral, the Market Place and the older streets, an application deals with surface water and drainage rather than the river.
• Waterside and the riverside. The Great Ouse passes the eastern edge of the city below Waterside, Ship Lane, Annesdale and The Dock, where the old town meets the river on its lowest ground.
• The station, Angel Drove and Stuntney Causeway. South of the centre the land falls to the railway, the A142 and business parks built on former fen. The warning area takes in these roads too, and they are the main routes out of the city to the south and east.
• The pumped fen. Across the river and below the south-eastern and northern fringes, land is kept dry by drainage boards whose pumps lift water into the Ely Ouse. Their districts run right up to the edge of the built-up area.

The Flood Map for Planning shows the Fens as if their banks and pumps were not there, a point the county's flood risk management strategy spells out. A site at the foot of the hill can be well protected in practice and still sit in Flood Zone 3, and our article on why a defended site stays in a flood zone explains why the assessment still has to show safe floors, access and the effect of a bank failing.

Check an Ely address, from the Princess of Wales Hospital to the station

Enter a postcode in the map below to screen an address in Ely for river, surface water and reservoir flooding from Environment Agency data, or open our flood risk map to see the flood zones across East Cambridgeshire. A screening tells you whether a site sits on the island or below it; it does not replace an assessment of the site itself.

The Ely gauge and the streets in its warning area

The Environment Agency measures the river for the city at its Ely station, with the Soham Lode gauge upstream. Its scale shows how little headroom the riverside has: low land can flood while the river is still inside its everyday band. Readings for this and nearby gauges are on our live river levels map.

The River Great Ouse at Ely flood warning area lists St Thomas Place, Bartholomews Walk, The Dock, Station Road, Angel Drove, Stuntney Causeway, Bridge Road, Waterside, Annesdale and Ship Lane. Around it sits the wider Ely Ouse flood alert area for the Great Ouse and the Cambridgeshire Lodes. A warning area does not fix the flood zone of a particular house, but it does mean the Environment Agency expects flooding on those streets when the river is high, and lenders, insurers and the council will ask about it.

Banks, sluices and pumps: what holds the water back around Ely

At Ely the Great Ouse is not tidal. The SFRA describes the Ely Ouse, the river's old course, as a fluvial channel that becomes tidal only below Denver Sluice, on its way to The Wash at King's Lynn. Embankments line both sides of the Ely Ouse and Ten Mile River, and the SFRA grades their condition from poor to very good, with many banks rated fair overall but very poor at their weakest point.

When the SFRA modelled breaches of those banks in a 1 in 100 year flood, the water reached parts of Littleport, Ely and Prickwillow as well as wide areas of open fen. That is residual flood risk, and an assessment for a riverside or fen-edge site in Ely sets out how deep the water would be and how fast it would arrive if a bank failed. Away from the river, three boards of the Ely Group of Internal Drainage Boards manage the fen at the city's edge:

The SFRA takes the general standard of protection in these districts as a 1 in 20 annual chance on farmland and 1 in 100 in developed areas. A new discharge into a board drain needs the board's consent on top of planning permission; our guide to internal drainage boards and planning covers that process, and our reading of the Fens 2100+ evidence looks at what the Environment Agency expects for this land in the longer term.

Ely's flood record, from 1795 to the 2003 peak

The county council has published no flood investigation report for Ely, and the SFRA's settlement table records no historic flood events for the city itself. The record on the river around it goes back further:

1. 1795. The SFRA's table of documented floods records 25,000 acres under water between Denver and Ely on the Great Ouse.
2. March 1947. In the snowmelt flood of that spring, an aerial photograph caught the Great Ouse in flood at Middle Fen Bank, Ely, looking across the fen east of the city.
3. January 2003. The Ely gauge peaked at 1.39 m on 4 January 2003, still its highest reading. Across the Great Ouse catchment that winter, the SFRA records river, surface water and groundwater flooding at 196 properties, with road and rail disrupted.

Our River Great Ouse page follows the 2003 flood upstream to Earith, where the gauge also set its record that week.

Surface water on the hill, and the flow route from Lynn Road

On the island, the risk an assessment usually turns on is rain that cannot get away quickly enough. Cambridgeshire County Council identified Ely as one of its highest-priority surface water wet spots, and a detailed Surface Water Management Plan for the city, prepared by Hyder Consulting in 2012, modelled it and picked out three priority wet spots. The SFRA summarises what the surface water mapping shows:

• North-west Ely. Water runs along roads and small drains and ponds in gardens, most notably in the north-west of the city, from storms with a 1 in 30 annual chance upwards.
• Lynn Road to the A10. In the same 1 in 30 year storm, a flow route runs west from Lynn Road through the college and school grounds, reaching homes and roads east of the A10.
• Roads in and out. Most of the main roads into and out of Ely are at risk in a 1 in 1,000 year event.
• Groundwater. Ely sits in the lower bands of the groundwater susceptibility map the SFRA uses, with less than half of each grid square marked as susceptible.

Soakaways need testing before anyone relies on them. The Local Plan notes that the southern half of the district suits infiltration while the north will generally depend on storage and controlled discharge, and Ely lies between the two. The county's surface water planning guidance asks for a tested rate of at least 1 × 10⁻⁶ m/s and 1.2 m between the base of an infiltration feature and the groundwater; our page on soakaways and ground conditions explains the testing.

What will East Cambridgeshire ask of a flood risk assessment in Ely?

East Cambridgeshire District Council decides planning applications in Ely. Cambridgeshire County Council, as lead local flood authority, reviews the drainage of major schemes; our page on the county council's flood and drainage role sets out how it works. The plan in force is the East Cambridgeshire Local Plan 2015 (as amended 2023), which runs to 2031; the council paused work on a replacement in February 2025.

Modelled Zone 3 matters in Ely. ENV 8 treats land the SFRA's own modelling puts in the high-risk zone in the same way as the Environment Agency's Flood Zone 3, so a site can need an assessment where the national map alone would not suggest one. Where new homes are proposed in Flood Zone 2 or 3, the sequential test comes before anything else.

North Ely, the Station Gateway and the riverside: where Ely is growing

Most of Ely's new homes are going in north of the city, on higher ground in Flood Zone 1, where the drainage rather than the river sets the conditions. The allocations and recent permissions are these:

• North Ely, Policy ELY 1. About 210 ha between the A10, the railway and Chettisham, allocated for up to 3,000 homes. The SFRA's screening placed the whole of it in Flood Zone 1, with small areas at surface water risk, and the planned country park includes ditches, swales, reed beds and ponds as part of the drainage.
• Highflyer Farm, phase 3. Reserved matters for 536 homes were approved on 10 June 2026. The drainage sends water through swales and basins to a watercourse at 3.5 l/s/ha; the lead local flood authority, the Environment Agency and the drainage boards did not object, the boards subject to byelaw consent, and Anglian Water confirmed Ely water recycling centre can take the foul flows.
• Highflyer Farm North. An outline application for up to 1,607 homes on 85 ha, the last part of the North Ely allocation, was reported in July 2026.
• Station Gateway, Policy ELY 7. About 12.3 ha around the station, with the Great Ouse on its eastern side, allocated for mixed use and at least 800 jobs. The policy asks each scheme to show that any flood risk can be adequately mitigated, and Station Road runs through the river's warning area.
• Ely Riverside, Policy ELY 13. The plan protects the riverside and supports new tourist, community and leisure uses there, so proposals in this area sit close to the river and its flood zones.
• Lancaster Way, Policy ELY 11. About 40.4 ha of employment land west of the city, outside the built-up area mapped here, where large roofs and service yards make surface water storage the main drainage question.

Many of the small watercourses on and near these sites are ordinary watercourses or board drains, so a new outfall or culvert needs consent from the county council or the board; our guide to ordinary watercourse consent explains when.

Matching an Ely proposal to the right flood report

As a guide, for the proposals that come up most often in and around the city:

Our page on the flood evidence a planning application needs sets out what goes to the council, and our guide to extending a home in a flood zone explains when standing advice is enough.

Flood and drainage reports for sites on and around the Ely island

A flat on Ship Lane, a phase at Highflyer Farm and a unit off Angel Drove each need different evidence. Each report is written by our chartered consultants and signed off by a senior consultant before it goes out.

• Riverside and station applications. Homes and commercial schemes in the Ely Ouse flood zones need a flood risk assessment for planning that answers ENV 8 and the Environment Agency.
• River, banks, rain and ground together. A flood risk assessment for an Ely site weighs the Great Ouse, a breach of its banks, surface water, groundwater and the boards' drains in one report.
• Buying below the hill. Before exchange on a house in the warning area, a flood risk survey for property purchase shows the buyer and the lender the risk to that address.
• Homes proposed in the flood zones. Where new homes are planned in Flood Zone 2 or 3 by the river, the sequential and exception test has to be passed before the council weighs the rest of the evidence.
• Drainage for major schemes. The county reviews every major Ely application against its February 2026 guidance, and a drainage strategy shows how the site meets it.
• Runoff where soakaways fail. On clay or where the tests come back slow, a surface water drainage strategy sizes the storage and the controlled flow to a board drain or watercourse.
• Conditions after permission. At North Ely and on other approved schemes, discharge of drainage conditions supplies the detail the outline conditions held back.
• Sites by the Ely Ouse banks. Where national mapping cannot show what a breach of the Ely Ouse embankments would do to a particular site, flood modelling gives depths and arrival times.
• Homes and businesses in the warning area. For new homes or premises on Station Road, Waterside or Angel Drove, a flood warning and evacuation plan shows how people leave before water reaches the roads out.
• Land at Highflyer Farm North or Lancaster Way. Before an offer on land on the northern or western edge of Ely, a flood risk feasibility study tests how much can be built and where its water can go.
• Riverside homes and cover. For a house on Annesdale or Ship Lane, a flood risk assessment for insurance gives the insurer evidence about that one building.

Ely's flood contacts: river, rain, drains and sewers

In an emergency where life is at risk, dial 999; power cuts go to 105. For anything else, these are the bodies responsible in and around the city:

Our Cambridgeshire page covers the county as a whole, including Fen towns such as Wisbech. Upstream, the Great Ouse passes St Neots and Huntingdon, while the River Cam flows north through Cambridge to join it south of Ely. All our area pages are listed in one place.

Questions from Ely buyers, builders and landlords

To discuss a riverside flat, a fen-edge unit or a North Ely plot, call 01293 214444 or email enquiries@unda.co.uk.