Flood Risk Assessment in Norfolk

Our team at Unda use years of experience to prepare comprehensive flood risk assessments and drainage strategies for commercial and residential sites right across Norfolk. A flood risk assessment in Norfolk shows your local planning authority that a development will stay safe from flooding for its whole lifetime, without pushing flood risk onto anyone else.

Norfolk is a low-lying, water-shaped county, and its flooding comes from every direction: the North Sea and the tidal estuaries on the coast, the Wensum, Yare, Bure, Waveney and Nar inland, the surface water that overwhelms drains in Norwich, King's Lynn and the market towns, and the chalk groundwater beneath the west of the county. We prepare flood risk assessments in Norfolk for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies (SuDS). We then deal directly with the Environment Agency and Norfolk County Council on your behalf, guiding architects, planning consultants, developers and landowners through to approval.

If you need a quote or want to talk a site through, contact one of our experienced flood risk consultants on 01293 214444.

Flood risk assessment in Norfolk at a glance

• Every source in one county. Tidal, coastal, river, surface water and groundwater flooding all occur across Norfolk, often on the same scheme.
• Around 37,000 properties in Norfolk are at risk of surface water flooding in a 1-in-200-year rainfall event, making it the 10th most at-risk authority of 149 assessed in England.
• One Lead Local Flood Authority. Norfolk County Council leads on surface water, groundwater and ordinary watercourses; the Environment Agency leads on the main rivers and the sea. We work with both.
• Flood Zone 1 is not a free pass. Since the 2025 PPG update, surface water risk can trigger an assessment even on a Flood Zone 1 site.

Check flood risk anywhere in Norfolk

Norfolk is outlined below. Screen any postcode in the county against Environment Agency data for rivers and sea, surface water and the planning flood zones, with a climate outlook to 2125. It is an indicative first pass, not a substitute for a site-specific assessment.

Flood risk in Norfolk: coast, rivers and surface water

Norfolk faces almost every type of flooding there is. The North Sea and the tidal estuaries bring saltwater risk to the coast and the eastern Broads; the Wensum, Yare, Bure, Waveney and Nar bring river flooding inland; surface water now threatens the built-up centres of Norwich, King's Lynn, Great Yarmouth and the market towns; and chalk groundwater rises beneath the west of the county. Most sites here face more than one source at once, which is why a desktop map rarely satisfies a planning officer on its own.

Norfolk drains through several river systems that mostly move slowly across very flat ground. The Wensum, Bure, Ant and Yare flow east through the Broads to the sea at Great Yarmouth; the Waveney runs along the Suffolk border; and the Nar and the fenland streams drain west to the Great Ouse and the Wash. Because the gradients are gentle and much of the land sits at or below high-tide level, water leaves slowly, and a tidal lock or a sustained wet spell can hold flood levels up for days. Understanding which watercourse drives the risk on a given site, and how it behaves, is the heart of a credible river flood risk assessment.

• Tidal and coastal. The 1953 and 2013 surges show the North Sea is Norfolk's most dangerous flood source. The coast from Hunstanton round to Great Yarmouth, the Broads and the tidal reaches of the Yare and Bure are all exposed to surge and sea-level rise. See our guide to tidal and sea flooding.
• Rivers (fluvial). The Wensum, Yare, Bure, Waveney and Nar flood low-lying land along their corridors. Land in Flood Zones 2 and 3 along these rivers almost always needs an FRA.
• Surface water (pluvial). Now the most widespread flood risk in England, and the source that puts around 37,000 Norfolk properties at risk. Intense rain overwhelms drains in Norwich, King's Lynn, Thetford and the market towns. Since the 2025 PPG update, surface water on the Flood Map for Planning can trigger an assessment even on a Flood Zone 1 site.
• Groundwater. The Chalk beneath west and central Norfolk can raise water tables that flood low-lying ground and basements without ever showing on a river map. Critical for any soakaway or below-ground level. See groundwater flooding.

The Broads are the textbook case for why a single map is never enough: a shallow, low-lying network of rivers and lakes at the meeting point of river flow and North Sea tide, where fluvial, tidal and surface water risk all act on the same ground and the land is kept dry only by continuous pumped drainage. A scheme there has to reconcile all of them. Our wider notes on the sources of flood risk and on surface water and planning set out how these sources interact.

A history of flooding in Norfolk

These dated events are why local authorities here scrutinise development so closely, and why a flood risk assessment in Norfolk has to be evidence-led rather than generic. Each one reshaped local policy and the flood defences a developer now has to design around.

• 1953 — the North Sea flood. The worst peacetime disaster on the English east coast. At King's Lynn around a fifth of the town flooded, 1,800 people were evacuated and 15 died; at Great Yarmouth 10 people were killed and around 3,500 homes were ruined. The marshes from Hunstanton to the Broads were inundated.
• 1978 — the January surge. A second major North Sea surge again flooded the coast and the tidal towns, prompting further investment in the King's Lynn and Great Yarmouth tidal defences.
• 2007 — summer surface water. The nationwide deluges that triggered the Pitt Review flooded towns across Norfolk from surface water and overwhelmed drainage, feeding directly into the Flood and Water Management Act 2010 and the lead local flood authority system that governs drainage today.
• 2013 — the 5 December tidal surge. The most serious North Sea surge since 1953 overtopped and outflanked defences; Wells-next-the-Sea and Blakeney were badly hit and more than 1,000 homes and businesses flooded along the Norfolk coast, though improved defences kept levels below 1953.
• 2023 — Storm Babet. Sustained October rain caused surface water flooding around Attleborough and Diss, record-high groundwater, and flooding on the chalk-stream River Burn that affected Burnham Market and the Creakes, with foul water surcharging through manholes.

A pattern runs through all of it: ground that flooded once tends to flood again. A robust assessment treats this recorded history as evidence, not background colour.

The Broads, the fens and Internal Drainage Boards

Much of Norfolk stays dry only because it is actively drained. Large parts of the Broads, the Yare and Waveney valleys and the west Norfolk fens sit within Internal Drainage Districts, where water levels are managed by pumps, sluices and maintained channels rather than by gravity. That changes what a development has to prove.

Internal Drainage Boards (IDBs) are the bodies responsible for managing water levels in these low-lying areas. In Norfolk the Broads (2006) IDB, the Norfolk Rivers IDB, the King's Lynn IDB and the Waveney, Lower Yare and Lothingland IDB — all members of the Water Management Alliance — manage the ordinary watercourses and pumped systems across much of the county. If your site sits within an IDB district, works in or near a board-maintained watercourse usually need the board's consent, and your drainage strategy has to respect the district's discharge limits.

• Consent for watercourse works. Works affecting an ordinary watercourse in an IDB district need the board's consent; elsewhere it is Norfolk County Council's ordinary watercourse consent. Works on a main river need an Environment Agency permit — see our note on riparian ownership.
• Tighter discharge limits. Pumped catchments have finite capacity, so IDBs often expect surface water restricted to low discharge rates, with attenuation sized accordingly under the 2025 national SuDS standards.
• Critical drainage areas. Parts of Norfolk are identified as having heightened surface water sensitivity, which can require a drainage strategy even in Flood Zone 1 — see critical drainage areas.
• Riparian duties. Owning land next to a dyke or drain brings maintenance responsibilities that affect both flood risk and what you can build.

Planning policy and your Lead Local Flood Authority in Norfolk

Two kinds of authority set the rules. The Environment Agency leads on the main rivers and the sea. Norfolk County Council is the Lead Local Flood Authority (LLFA), leading on surface water, groundwater and ordinary watercourses and acting as statutory consultee on surface water drainage for major development.

Unlike counties that have been split into several unitary authorities, Norfolk has a single LLFA — Norfolk County Council — covering all seven districts. Planning applications are determined by the relevant district or city council (Norwich, South Norfolk, Broadland, Breckland, North Norfolk, Great Yarmouth, or King's Lynn and West Norfolk), while the county council reviews surface water drainage and the role the LLFA plays as statutory consultee. Our overview of who manages flood risk in England explains how the pieces fit together.

Your assessment and drainage strategy must satisfy national policy — the NPPF and its Planning Practice Guidance — and the local framework: Norfolk County Council's Local Flood Risk Management Strategy, the district Strategic Flood Risk Assessment and adopted Local Plan flood policies, such as Norwich's policy DM5 on flood resilience and the Greater Norwich Local Plan's drainage requirements. Where a higher-risk site is involved, the Sequential and Exception Tests apply, and the right vulnerability classification has to be argued. On drainage, the 2025 national SuDS standards and the four pillars of SuDS shape what the LLFA will accept.

What your flood risk assessment in Norfolk must show

• Risk assessed from every credible source, using the Flood Map for Planning and local data.
• An appropriate location, tested against the Sequential Test where policy requires it.
• Safe for its lifetime, once the climate change allowances are applied.
• No increase in flood risk elsewhere, with attenuation and, where needed, compensatory storage.
• Residual risk managed, with safe access, egress and finished floor levels. Get one of these wrong and the application stalls, as our note on LLFA drainage objections shows.

Development and flood risk assessment in Norfolk

Norfolk's development is as varied as its landscape, and the kind of site you bring forward shapes the assessment you need. The right scope is the difference between a clean approval and a drainage objection that holds an application up for months.

• Coastal and estuary development. King's Lynn, Great Yarmouth and the north Norfolk coast bring tidal modelling, sea-level rise and, on parts of the coast, erosion into the picture — see sea-level rise and coastal flooding.
• Broads-edge and riverside sites. Schemes near the Bure, Yare or Wensum often sit in Flood Zones 2 and 3, needing finished floor levels, safe access and egress and often compensatory flood storage.
• Norwich and urban infill. Regeneration and infill in Norwich, Thetford and the market towns frequently turn on surface water and the capacity of the existing drainage network.
• Rural and agricultural schemes. Conversions and new builds across Breckland, mid-Norfolk and the fens often turn on ordinary watercourses, IDB drainage and groundwater rather than a main river, and on the right drainage information for planning.

Climate change is not optional here. A Norfolk assessment must apply the Environment Agency's allowances for higher river flows, rainfall and sea levels over the development's lifetime — generally 100 years for housing — which sets floor levels, freeboard and how much attenuation a drainage scheme needs.

Home buyers and businesses come to us too. A flood risk question can affect mortgage lending and house prices, and a conveyancing search is not the same thing as a planning-grade assessment. Knowing which you actually need saves time and money, and our guide on doing your own assessment explains where the line falls.

How Unda helps with flood risk assessment in Norfolk

We act as the accurate translation layer between your scheme and the requirements set by the Environment Agency, Norfolk County Council as LLFA and national planning policy. We are experts on the county's flooding, not a generic report mill.

A flood risk assessment in Norfolk from Unda assesses every credible source — the Wensum, Yare, Bure or the tidal coast, down to surface water, groundwater, sewers and any ordinary watercourse or IDB drain on the boundary — compares modelled flood levels against your proposed floor levels, sets safe access and egress, and recommends mitigation the regulators will accept. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report. Where the council needs it, the drainage strategy sits alongside the assessment so the two cases stay consistent and an objection has nowhere to land.

Flood risk assessments and related reports for every situation in Norfolk

• Flood risk assessment for planning. Site-specific reports that satisfy the Environment Agency and your Norfolk district council.
• Flood risk survey for property purchase. Independent, property-specific advice for buyers and their advisers.
• Flood risk assessment for insurance. Property-level evidence for brokers and underwriters.
• Flood risk assessment for BREEAM. Structured around Pol 03 for certification.
• Groundwater flood risk assessment. A defensible design water table for chalk and fenland sites, not a guess.
• Surface water drainage strategy and SuDS. Designed to the LLFA's and IDBs' standards from the first sketch.
• Sequential and Exception Test reports. Prepared alongside the assessment where policy requires them.
• Chartered flood risk consultants. Specialists who stay involved past the report to answer objections.

Norfolk flood resources and contacts

The most reliable Norfolk flood information comes from the lead authorities. For an immediate threat to life during a flood, always call 999.

• Check for flooding. Environment Agency live warnings, river levels and maps at check-for-flooding.service.gov.uk, or sign up to Floodline on 0345 988 1188.
• Report a flood in Norfolk. Norfolk County Council's flood team and the Norfolk flooding hotline (0344 800 8013) at norfolk.gov.uk.
• Norfolk Local Flood Risk Management Strategy. The LLFA's strategy and developer guidance at Norfolk County Council.
• Internal Drainage Boards. Mapping and consents for the Norfolk IDBs via the Water Management Alliance.
• Anglian (Eastern) Regional Flood and Coastal Committee. Regional investment and priorities via the Anglian (Eastern) RFCC.
• Emergency planning. Flood preparation and response from the Norfolk Resilience Forum; call 105 for power cuts.
• Live river levels. Whether the Wensum, Yare or Bure are running high right now via our live river levels map, or screen a postcode on our flood risk map.

For flooding from blocked or burst sewers, contact Anglian Water. Planning to infiltrate surface water on a chalk or sandy site? Check the ground first with our geology and soakaway checker and BRE 365 infiltration calculator. For broader policy context, our notes on the Environment Agency's planning role and on flood zones 1, 2 and 3 are a good starting point.

Flood risk assessment in Norfolk: frequently asked questions