Flood Risk Assessment in Norfolk

A flood risk assessment in Norfolk starts with a county that drains in two directions. The Great Ouse, the Nar, the Wissey and the Little Ouse carry the west to the Wash at King's Lynn; the Wensum, the Yare, the Bure and the Waveney carry the rest through the Broads to the sea at Great Yarmouth. Our consultants write flood risk assessments in Norfolk for planning applications, house and land purchases, lenders and insurers, and prepare the sequential tests, exception tests and surface water drainage strategies that councils here ask for alongside them.

Norfolk County Council is the lead local flood authority for the whole county, while planning decisions are made by seven district councils and, inside the Broads, by the Broads Authority. So a site in Norwich, Thetford, Dereham, Attleborough, Downham Market, Cromer or Wells-next-the-Sea meets one county drainage standard and one of eight local plans. King's Lynn, Great Yarmouth and Sea Palling each have a page of their own, linked further down.

On the night of 31 January 1953 the North Sea surge killed 100 people in Norfolk. On 5 December 2013 a surge that the county council put at a 1 in 500 year event at Wells flooded 239 Norfolk properties, and nobody died.

Phone 01293 214444 or email enquiries@unda.co.uk with the address of the Norfolk site and a line on what is planned.

Is Norfolk below sea level? The two ways the county drains

Not the county as a whole, but some of its lowest ground is. The Broadland flood banks protect about 30,000 hectares of land that lies below sea level, and in the far west the fen villages around Downham Market and the Wiggenhalls sit behind the embanked tidal Great Ouse. Everywhere else, the catchment a site drains to decides its warning area and which regional committee funds the defences around it.

All of these warning areas belong to the Environment Agency's East Anglia area, so its planning advice on any Norfolk site comes from the same area team. To see whether the Wensum, the Yare or the Bure is high today, use our live river levels map, which reads the agency's gauges.

Checking a Norfolk postcode against the flood zones

The map below zooms to any Norfolk postcode and reports the river and sea flood zone, the surface water risk and the reservoir layer there; our flood risk map does the same anywhere in England. Anyone searching for a Norfolk flood map or the county's flood zones can start here. What it cannot show is a floor level, a pumped drain, a breach in a bank or the winter water table under a soakaway.

Flood Zone 1 says nothing about rain or groundwater, because surface water has its own map and groundwater has none on this layer. North Norfolk's SFRA also picks out 38 dry islands, patches of Flood Zone 1 ringed by Zones 2 and 3, where the danger is being cut off rather than flooded. Our guide to flood zones 1, 2 and 3 sets out what each zone means.

Which council decides a planning application in Norfolk?

The district or borough council decides it, or the Broads Authority inside the Broads executive area, and Norfolk County Council comments on the drainage of every major scheme. Because Norwich, Broadland and South Norfolk share one strategic plan, a flood risk assessment in Norfolk is tested against one of eight bodies of local policy. Each is backed by a Strategic Flood Risk Assessment, most of them from a joint 2017 study commissioned by six of the district councils and the Broads Authority.

In March 2026 the government chose three unitary councils to replace the county and district councils, then withdrew that decision on 7 September 2026 for a review. Until a new decision is made, the authorities above stay in place. National policy sits in chapter 18 of the August 2026 NPPF, which our NPPF flood risk guidance explains.

What Norfolk County Council asks of a drainage strategy

Since 15 April 2015 the county council has been statutory consultee on surface water for major development: ten or more homes, half a hectare where the number is unknown, 1,000 m² of floorspace or a site of a hectare or more. It asks applicants to read its Lead Local Flood Authority guidance for developers, updated in April 2025, before they submit, and the 2025 national standards for sustainable drainage now apply through policy F8 of the NPPF.

• Paid advice before an application. The county's pre-application service, at fees in force from 1 April 2026, starts at £99 for a desk study of the site and runs from £196 for 10 to 99 homes to £1,182 for more than 250 homes or 3 hectares, VAT included.
• Critical drainage catchments. Norwich's surface water management plan names catchments at Drayton, Catton Grove and Sewell, and Nelson and Town Close, and the city's policy DM5 expects a scheme in one to add no flood risk and to cut it where it can. The county published a wider critical drainage catchments report in 2026.
• Ordinary watercourses. Works that affect the flow in a ditch or stream need consent separate from planning: from the internal drainage board inside its district, otherwise from the county, which normally allows a culvert only to give access.
• Nutrients in the Wensum and the Broads. New homes draining to these protected catchments have to show nutrient neutrality, and a draft Norfolk Environmental Delivery Plan out to consultation until 27 October 2026 proposes a levy of £2,675 a home.

On the smaller sites that the county does not see, the district reads the drainage itself, using the same hierarchy of soakaway first, then watercourse, then sewer. Our note on why drainage strategies draw objections covers the reasons a Norfolk scheme is most often sent back.

Flash flooding in Norfolk: what the county's investigations record

Norfolk County Council investigates a flood whenever a single property floods inside, which is lower than the five-home threshold many lead local flood authorities use. Its reports therefore record small summer storms that would go uninvestigated elsewhere. Since 2014 they show a pattern: intense rain over Norwich, Dereham, Watton and Attleborough, with Section 19 reports following almost every year.

1. May to October 2014. Over 550 flood reports reached the county, about 270 of them from properties flooded inside, with the worst around Norwich, Ormesby St Margaret and Hemsby, and Outwell and Upwell.
2. Summer 2016. More than 250 properties flooded, Dereham among them on 23 June.
3. 23 to 25 June 2017. Storms tracked from Diss to Cromer; 193 of the 450 reports were confirmed as internal flooding, mostly in Watton, Saham Toney, Shipdham, Dereham and the edge of Norwich.
4. 23 and 24 December 2020. More than 180 homes flooded in an arc from Martham through South Norfolk to Watton. Over the whole of 2020, more than 350 properties in 120 settlements were affected, and the Norfolk Strategic Flooding Alliance was set up in February 2021.
5. October 2023. During Storm Babet about 130 homes flooded in Attleborough, where the county found that a temporary construction road across the Besthorpe Stream had held water back for around 300 metres.
6. 2024 and 2025. Further county-wide investigations cover winter 2023 to 2024, January to March 2024, May to October 2024, winter 2024 to 2025 and central and east Norfolk in summer 2025.

Our explainers on surface water flooding and Section 19 flood investigations cover how these reports are used, and the Attleborough case is told in full in construction stage flood risk.

The Norfolk coast, from the Wash to Hopton-on-Sea

Coastal sites in Norfolk face the tide and, on the cliffs, erosion. Three shoreline management plans cover the county: SMP4, The Wash, SMP5 from Hunstanton to Kelling Hard and SMP6 from Kelling Hard to Lowestoft. A flood risk assessment for a coastal site tests the tide level, the defence in front of it and what happens if that defence is overtopped or breached.

• 31 January 1953. The surge killed 100 people in Norfolk, seven of them at Sea Palling, and flooded the coast from King's Lynn to Great Yarmouth; our account of the 1953 North Sea flood follows it down the coast.
• 5 December 2013. The most serious surge in over 60 years flooded 239 properties in Norfolk, with significant flooding at Wells, Blakeney, King's Lynn, Cley and Salthouse. Homes were destroyed at Walcott, and at Hemsby houses on the dunes fell into the sea.
• Defences and sand. Hard defences protect Sheringham, Cromer, Overstrand and Mundesley and long stretches between Happisburgh and Winterton Ness, and sand placed in September 2019 is expected to protect Bacton and Walcott for 15 to 20 years.
• Coastal change. North Norfolk's Coastal Change Management Area covers land the shoreline plans show at risk of erosion within 100 years. Policy CC5 requires a coastal erosion vulnerability assessment with any application there, a separate report from a flood risk assessment.

For background, see our guides to shoreline management plans, sea level rise and coastal flooding and the lack of any compensation for coastal erosion.

Do the Norfolk Broads flood? Banks, pumps and a separate planning authority

Yes, and the risk is mostly tidal. Over 20 years from May 2001 the Environment Agency's Broadland Flood Alleviation Project upgraded more than 240 km of flood banks and set 36 km further back, for about £140 million, giving better protection to 1,700 properties. Those banks reduce the chance of a breach, but high tides can still hold back the rivers as they try to drain to the sea.

• A planning authority of its own. Inside the Broads executive area, the Broads Authority decides applications under policy DM5 of its 2019 plan and its Flood Risk SPD, not the district council around it.
• Drained marshes. Water levels on the grazing marshes are held by the Broads Internal Drainage Board and its pumps, and the board's consent is needed for works that affect its drains.
• Riverside plots. Sites along the tidal Yare and Bure sit in Environment Agency warning areas, and a flood risk assessment there sets floor levels, refuge and the route out against a breached bank as well as an overtopped one.

Where the drains belong to a board, our explainer on internal drainage boards sets out what consent and discharge limits mean for a scheme, and our page on residual flood risk explains why a defended site still needs testing.

Norwich, Thetford and the inland towns

Inland, rain falling faster than the drains can carry it is the main threat. The county's first assessment, in 2011, put about 37,000 Norfolk properties at risk in a rainstorm with a 1 in 200 chance each year, the tenth highest of 149 authorities. When the county reviewed its surface water risk in 2017, the Norwich urban area was the only part of Norfolk it judged serious enough to report as a national Flood Risk Area, and Great Yarmouth, Thetford and Attleborough together carried less than a third of Norwich's total.

Thetford also lies where the Thet joins the Little Ouse, inside an Environment Agency warning area, and Dereham and Watton recur in the county's storm reports. Under clay, as at Poringland south of Norwich, a high or perched water table can stop a soakaway working, while in the north many streams are chalk-fed. A soakaway is only proposed once our ground conditions and soakaway checker and BRE 365 infiltration testing show the ground will take the water. Our explainer on groundwater flooding sets out how it is assessed.

Thresholds for a flood risk assessment in Norfolk, scheme by scheme

Policy F4 of the NPPF sets the national floor: any development in Flood Zone 2 or 3, a site in Flood Zone 1 that covers a hectare or more, or land that the flood map or the SFRA shows at risk from some other source. North Norfolk, King's Lynn and West Norfolk and Norwich each add a local rule, and the county's drainage review starts at ten homes.

Our guide to the sequential and exception tests explains how the area of search is set and when the exception test follows.

Our reports for Norfolk sites, from the Wash to Breydon Water

The report a Norfolk site needs follows from what floods it and who reads the result: a case officer, a lender or an insurer. Unda is a CIWEM Business Partner, the consultants who write these reports are chartered, and each is checked and signed by a senior consultant before issue. Across the county we prepare:

• Tide, river and storm together. On low Norfolk ground a spring tide, a main river, a pumped drain and a summer storm may all threaten one plot, so our flood risk assessment considers each source and how they combine.
• Applying for permission. Whether it is a Norwich conversion or a Breckland allocation, a flood risk assessment for planning is written to the district's own flood policy, to chapter 18 of the NPPF and, inside the Broads, to policy DM5.
• Before exchange. Searches and lenders pick out coastal, Broads and fen-edge houses, and a flood risk survey for property purchase tells the buyer what that warning means for the house itself.
• Alternative sites. Homes proposed in Zone 2 or 3 have to be justified against sites at lower risk, and our sequential and exception test report defines the search area within the right Norfolk district before comparing each candidate.
• Where the water goes. With eight planning authorities and one county reading drainage evidence in Norfolk, each drainage strategy is pitched at the rules of the authority deciding it.
• Ten homes and over. A surface water drainage strategy follows the county's April 2025 guidance and the 2025 national standards, and in Norwich shows no added risk to a critical drainage catchment.
• Conditions on a permission. Where a Norfolk consent comes with drainage conditions, we prepare the details needed for the discharge of drainage conditions and respond to the county's comments on them.
• Insuring a flooded home. With 239 Norfolk properties flooded by the 2013 surge and more than 350 affected by rain in 2020, a flood risk assessment for insurance gives an insurer evidence on the property itself.
• Coastal land and buildings. On a coast where homes were lost at Hemsby and Walcott in 2013, flood risk due diligence tells a buyer or lender what the tide and the defences mean for a site before contracts are signed.
• Off-mains and nutrient sites. Rural plots without a sewer, and new homes draining to the Wensum and the Broads where nutrient neutrality applies, need a foul drainage strategy that the council and Natural England can accept.
• Chalk and perched water. From the chalk streams of north Norfolk to perched water tables on the clay south of Norwich, a groundwater flood risk assessment finds the winter level before a soakaway or basement is relied on.
• Main rivers and tidal banks. Sites beside the tidal Great Ouse, the Yare or the Bure can need flood modelling to test a bank breach or a level the Environment Agency has not mapped.
• Homes in high-risk areas. North Norfolk's plan expects a flood warning and evacuation plan to accompany the assessment where getting in and out of a site in a flood is in doubt.

Coastal sites are covered by flood risk assessments and due diligence; the erosion assessment that North Norfolk's policy CC5 asks for is a separate specialist report.

Town, river and neighbouring pages for Norfolk

Three Norfolk places have pages of their own that go further into their rivers, defences and council policies:

• On the Wash. King's Lynn, where the tidal Great Ouse meets the Wash, and the River Great Ouse along its whole course.
• The east coast. Great Yarmouth at the mouth of the Yare and Bure, and Sea Palling behind its dunes and offshore reefs.
• Next door. Lowestoft and Suffolk to the south, Cambridgeshire across the fens and Lincolnshire on the far side of the Wash.
• The fens. Our article on the limits of Fens 2100+ covers the long-term plan for the fenland that reaches into west Norfolk.

Reporting a flood in Norfolk, and who to call

Ring 999 where water threatens life, and 105 for a power cut. For everything else, the source of the water tells you which of the bodies below to contact.

Before you commission: questions from Norfolk sites

From Hunstanton to Hopton-on-Sea, our consultants take on flood risk, sequential test and drainage work across Norfolk. Ring 01293 214444 or email enquiries@unda.co.uk to talk a site through.