Flood Risk Assessment in Chippenham

A flood risk assessment in Chippenham, Wiltshire, starts with the Bristol Avon, which runs south through the middle of the town between the High Street and Monkton Park. Smaller brooks feed it from the west: Ladyfield Brook, Pudding Brook and the partly culverted Hardenhuish Brook. Underneath, thin water-bearing limestone and sand can hold groundwater close to the surface. Clients with land or property in the town ask our consultants for flood risk assessments in Chippenham to support planning applications, house purchases, mortgages and insurance, and for sequential and exception tests and surface water drainage strategies.

On this page Chippenham means the built-up town that the Office for National Statistics maps: the centre and the station, Hardenhuish, Cepen Park and Frogwell to the west, Lowden and Rowden Hill to the south-west, the Monkton Park estate across the river and Pewsham to the south-east, covering the SN14 and SN15 postcode districts. Wiltshire Council decides planning applications here and is also the lead local flood authority.

On the evening of Sunday 24 November 2024, during Storm Bert, the Avon burst its banks and flooded Chippenham town centre to a greater extent than at any time since 1968, closing the High Street, the Town Hall and the Bridge Centre roundabout into the Tuesday.

Call 01293 214444 or email enquiries@unda.co.uk with a Chippenham address. We check it against the two Chippenham warning areas, the brook corridors and the council's groundwater study before we quote.

Is Chippenham in a flood zone? The Avon and the brooks that join it

Only a narrow band of the town is. The Environment Agency's Flood Zones 2 and 3 follow the Avon through the centre and along Monkton Park, and reach up the valleys of Ladyfield Brook and Pudding Brook on the south-western side. The rest of Chippenham sits on higher ground: levels rise from about 50 m above sea level in the Avon floodplain to around 120 m on the ridges either side, according to the council's 2011 surface water study.

The Environment Agency runs two warning areas in the town: one for riverside properties on the High Street, Borough Parade, River Parade, The Bridge, Rowden Hill and Bath Road, and one for properties set back from the river, from Avon Reach, Foghamshire and St Mary Street to the Monkton Park closes and Eastern Avenue. There is no public gauge in the town itself. Upstream, the Avon at Great Somerford is gauged at a level where property flooding becomes possible above 1.10 m, and it peaked at 2.43 m on 11 July 1968. To the east, the River Marden at Stanley reached its record 3.45 m on 20 July 2007. Readings from each gauge feed our live river levels map.

Searching an SN14 or SN15 address

Type a Chippenham postcode into the map to see the planning flood zones, the surface water extents and any warning in force at that point, or try our flood risk map for anywhere else in England. The coral line is the ONS built-up area, which leaves out some of the riverside meadows.

For more detail, Wiltshire Council publishes its strategic flood risk assessments: the countywide Level 1 study by JBA Consulting (November 2024), with appendices on groundwater emergence, recorded flooding and sewers, and an online data explorer. The older Chippenham surface water management plan of November 2011 still holds the most local analysis, street by street.

Storm Bert and the floods before it: Chippenham's record since 1894

The Environment Agency's recorded flood outlines for Chippenham go back more than 130 years, and almost every one records the Avon or one of its western brooks spilling over when its channel could carry no more.

1. 15 November 1894. The earliest Avon flood the Agency has mapped in the town; further outlines follow for 1925, May 1932 and June 1952.
2. 4 and 5 December 1960. The Avon and the Hardenhuish Brook both overtopped, leaving one of the largest recorded outlines inside today's built-up area.
3. December 1965, February 1967 and February 1974. Ladyfield Brook burst out of its channel on the south-western side of the town.
4. 10 July 1968. During the Great Flood, Ladyfield Brook spread across the Rowden side of the town, and upstream at Great Somerford the Avon reached the record level that still stands there.
5. 30 October 2000. The one groundwater flooding incident the Agency had logged for the town by 2011, on the Cornbrash and river terrace gravels near the Avon.
6. 2006 and 2007. Surface water and surcharged sewers flooded the High Street. Wessex Water enlarged the sewer and added an underground storage tank in 2006, and further works on New Road followed in January 2007.
7. April 2012 and winter 2013 to 2014. The Agency recorded the Avon overtopping defences in the Chippenham area, as well as a channel-capacity flood in November 2012.
8. 24 to 26 November 2024, Storm Bert. The river burst its banks on the Sunday evening. On the Monday nobody could reach the High Street, all three secondary schools shut and the Town Hall, museum, Neeld and Stanley Park sports ground closed. The Bridge Centre roundabout and Avenue La Flèche stayed shut until late on the Tuesday morning. Wiltshire Council called it the worst flooding in Chippenham and Melksham since the 1960s.

The town council's account of those three days also noted that work would be needed in Monkton Park afterwards. No published investigation gives a count of Chippenham properties flooded in 2024, so a site near the river is judged on the warning areas, the recorded outlines and its own levels.

The radial gate and the Chippenham Avon Project

The level of the Avon through the centre is held by an ageing radial sluice gate. The Environment Agency says the gate is nearing the end of its life and that, if it failed to operate, flood risk to the town centre could rise sharply. The Chippenham Avon Project would replace it with two rock weirs and open up the riverside between the town centre, Monkton Park and Pewsham.

On 11 November 2025 Wiltshire Council's Cabinet raised its contribution from £1 million to £1.8 million, the 10% match needed to secure up to £16.2 million from Defra, with about £6 million more still being sought. The published timetable puts consultation on the final option in autumn 2026, a planning application in winter 2026 and construction from early 2028. Until then, an assessment beside the river takes the present gate and walls as they are, and asks what happens if the gate sticks.

Perched groundwater under the Cornbrash and the Kellaways sand

Chippenham's other hidden source is groundwater. The council's groundwater susceptibility study for the town (Scott Wilson, November 2011) found that thin, permeable beds sitting on clay can hold water tables close to the surface, and that buildings with cellars or basements are the ones most exposed.

• Cornbrash limestone, central and west Chippenham. A perched water table can rise after prolonged rain, after leaks from water pipes, or where new soakaways put more water into the ground.
• Kellaways sand, north-east of the centre. The same mechanism in a thin sand bed above the Kellaways clay.
• River terrace gravels by the Avon. The most susceptible ground of all: water levels in the gravel follow the river even while it stays in its banks.
• Barriers underground. Sheet piling and similar obstructions can hold groundwater back and raise its level behind them.

The study had no incident records later than October 2000, and it warned that one-off readings taken for a planning application cannot show the winter peak. Wiltshire's June 2024 drainage betterment strategy now asks for monitoring from November to May, a soakaway base at least 1 m above peak winter groundwater and an infiltration rate of about 1x10-6 m/s or better. Our soakaway and ground conditions checker gives a first view, and our article on groundwater monitoring for planning explains why the season matters to the programme.

When the Avon is high, the High Street drains back up

Surface water in Chippenham tends to be local and short-lived, and it gathers in a few places the 2011 plan picked out. Rain running down the High Street ponds at its lower, northern end beside the river, where the study found the gullies small and widely spaced. Once the Avon rises, the outfalls into it lock shut and the water has nowhere to go. At Langley Park the railway embankment holds back a flow path from the culverted Birds Marsh stream, and behind the flood bank south of Gleneagles Close water collects along Downham Mead and Eastern Avenue. Wessex Water runs the public sewers; our guide to sewer flooding explains who answers for water coming up through a drain.

What a flood risk assessment in Chippenham must satisfy under Core Policy 67 and the 2017 allocations

Chippenham applications are judged against the Wiltshire Core Strategy, the 2017 Chippenham Site Allocations Plan and the council's drainage standards, on top of national policy. The draft Wiltshire Local Plan to 2038 was withdrawn in May 2026, so none of its proposed Chippenham allocations carry weight.

The council's drainage officers also work through a SuDS validation checklist, and its householder flood risk form asks for an assessment where groundwater may be within 0.5 m of the surface. Our explainers on the 2025 National Standards for SuDS and on why a lead local flood authority objects show what has to be in place before an objection is lifted.

Rowden Park, Rawlings Green and the next Wiltshire plan

Growth in Chippenham sits mostly on the town's edges and on the river's floodplain margins, so drainage and the brook corridors shape the layouts.

• Rowden Park, South West Chippenham. About 171 hectares under Policy CH1, with around 100 hectares set aside as a riverside country park; the plan leaves the Pudding Brook corridor and the Holywell stream unbuilt and puts flood mapping of them ahead of detailed layouts.
• Rawlings Green. About 50 hectares north-east of the station under Policy CH2, sloping down to the Avon, with a 10-hectare country park on its lower edge and off-site improvements to the drainage network required.
• Land south of Stanley Lane. An outline scheme for up to 150 homes, on land wholly in Flood Zone 1, went to the strategic planning committee on 23 January 2025. The drainage officers raised no objection, on condition that a full surface water strategy is approved before work starts, covering exceedance routes and a check that a surcharged outfall would not flood property, as the committee report sets out.
• A new local plan. Wiltshire Council gave notice on 30 June 2026 that it was starting a new plan. Its published timetable has consultation on proposed content in April and May 2027, submission in October 2028 and the plan considered for adoption on 30 April 2029.

Which report a Chippenham site needs

Each one is scoped to the address and the reason it is wanted: how near it is to the Avon or a brook, what lies under it, which sewer it drains to, and what the council, a lender or an insurer has asked for.

• Applications to Wiltshire Council. New homes or commercial floorspace in Flood Zone 2 or 3 beside the Avon, Ladyfield Brook or Pudding Brook, or any site of a hectare or more, needs a flood risk assessment for planning that answers Core Policy 67 and, on the allocated sites, the Site Allocations Plan.
• Four sources at one address. In Chippenham a flood risk assessment has to weigh the river, the brooks in their culverts, groundwater perched in the Cornbrash and the surface water drains, because the town's recorded floods have come from each of them.
• Buying in the warning areas. A house on River Parade, Foghamshire or one of the Monkton Park closes sits inside an Environment Agency warning area, and a flood risk survey for property purchase looks at that building, its floor level and its cellar before exchange.
• Windfall plots near the river. Town-centre infill in Flood Zone 2 or 3 that the 2017 plan did not allocate has to show, through the sequential and exception test, why no lower-risk site in the town would do.
• Evidence for the drainage officers. Wiltshire Council expects a drainage strategy that meets its June 2024 betterment rules on greenfield and brownfield land alike.
• Where the runoff goes. A surface water drainage strategy sets the discharge rate, the storage and the outfall, and on Cornbrash or Kellaways sand it shows a soakaway will still work in a wet winter.
• Once permission is granted. Pre-commencement drainage conditions like those set on the Stanley Lane scheme are cleared through the discharge of drainage conditions, with the calculations and exceedance routes the officers ask for.
• Cellars and basements. The council's 2011 study found perched water tables in the Cornbrash under central and west Chippenham and in the Kellaways sand to the north-east, so a groundwater flood risk assessment suits a scheme with anything below ground.
• A managed river. The Avon through the centre is held by a radial gate due for replacement, and the Hardenhuish Brook runs in culvert to it, so some sites need flood modelling to set floor levels that national mapping cannot.
• Two warning areas over the centre. Flats, care uses and businesses along the High Street, Bath Road or Avon Reach may need a flood warning and evacuation plan that ties occupants to the Agency's Chippenham warnings.
• After Storm Bert. Households near the river renewing cover after November 2024 can give an underwriter an insurance flood risk assessment for the individual property.
• Town-centre trade. Shops and venues on and around the High Street closed while Storm Bert's floodwater stood in the centre, and a business continuity flood risk assessment helps an occupier plan for the next high river.

Malmesbury upstream, Bath downstream, and the villages outside the outline

Kington Langley and Langley Burrell to the north, Derry Hill and Stanley to the east and Lacock to the south all lie beyond the coral line, with Corsham and Calne a few miles off; Wiltshire Council's policies apply in each of them, and our Wiltshire page covers the county as a whole.

The same river reaches Chippenham from Malmesbury, where its two headwaters meet, and leaves through Melksham and Bradford on Avon for Bath. Swindon, along the M4, drains to the Thames and has its own council. The full list of towns and counties sits on our areas page.

Avon, brook, sewer or road: reporting a Chippenham flood

Who answers depends on the source: the Environment Agency for the Avon and the main-river brooks, Wiltshire Council for roads, groundwater and ordinary watercourses, and Wessex Water for the public sewers. If floodwater puts anyone at risk, ring 999 before anything else.

Before you commission a flood risk assessment in Chippenham

Whether the site is a terrace in Foghamshire, a plot in Cepen Park or a unit at Methuen Park, call 01293 214444 or email enquiries@unda.co.uk. Unda Consulting Limited is a CIWEM Business Partner, our consultants are chartered, and a senior consultant reviews and signs off every report before it goes to Wiltshire Council.