Flood Risk Assessment in Suffolk

Our team at Unda prepares comprehensive, compliant flood risk assessments and drainage strategies for commercial and residential sites right across Suffolk. A flood risk assessment in Suffolk shows your local planning authority and the Environment Agency that a development will stay safe from flooding for its whole lifetime, and that it will not increase flood risk anywhere else.

Suffolk is a low-lying, water-shaped county, and its flooding is unusually varied. We assess every source that matters here: tidal and coastal flooding along the North Sea coast and the Orwell, Stour, Deben, Alde–Ore, Blyth and Waveney estuaries; river flooding from the Gipping and the western rivers; surface water that overwhelms drains in Ipswich, Lowestoft and the market towns; and groundwater rising through the chalk of the west. We then deal directly with the Environment Agency and Suffolk County Council as Lead Local Flood Authority 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 Suffolk at a glance

• Every source on one coast. Tidal, coastal, fluvial, surface water and groundwater flooding all occur across Suffolk — often on the same estuary-side scheme.
• More than 14,900 properties at risk. Suffolk's flood risk work records over 14,900 properties at risk of flooding across the county, the majority of them on the coast.
• One county council, five planning authorities. Suffolk County Council is the Lead Local Flood Authority; Ipswich, East Suffolk, West Suffolk, Babergh and Mid Suffolk are the local planning authorities you submit to.
• Flood Zone 1 is not a free pass. Surface water risk, a Critical Drainage Area or a site of one hectare or more can each trigger an assessment even in Flood Zone 1.

Check flood risk anywhere in Suffolk

Suffolk 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 Suffolk: coast, rivers and surface water

Suffolk faces five sources of flooding. Tidal and coastal flooding from the North Sea and the estuaries is the dominant risk and the one with the most severe history; surface water and ordinary watercourses cause the most frequent, scattered flooding inland; fluvial flooding follows the main rivers; and groundwater rises through the chalk in the west. Most coastal and estuary sites carry more than one source at once.

Suffolk's main rivers nearly all end in tidal estuaries, which is what makes its flood risk distinctive. The Gipping rises above Stowmarket and flows south-east into Ipswich, where it becomes the tidal Orwell and reaches the sea at Felixstowe. The Stour forms the Essex border and shares the Orwell–Stour estuary system. The Deben, Alde–Ore and Blyth each terminate in tidal estuaries along the coast, while the Waveney drains the north of the county through the Broads. In the west, the Lark, Little Ouse and Black Bourn flow the other way, towards the Fens and the Great Ouse. Because so much of the county is low-lying, high tides can hold back river flows and stop them draining — an effect known as tide-locking that raises levels well inland of the open coast.

Which source dominates decides what your report must prove. Our guides explain each in turn: tidal and sea flooding, surface water flooding and groundwater flooding, plus the difference between main rivers and ordinary watercourses. The starting point for any site is the Flood Map for Planning and which of Flood Zones 1, 2 or 3 the land sits in.

A history of flooding in Suffolk

Suffolk's flood record is dominated by North Sea storm surges. The catastrophic 1953 flood and the December 2013 surge both struck the same coast and estuaries, and both shape the tidal levels your assessment has to design against today. Dated, real events — not generic warnings — are the evidence the Environment Agency expects a credible report to engage with.

• 31 January – 1 February 1953. The great North Sea flood overwhelmed the Suffolk coast; contemporary accounts record that not a single estuary or valley in the county was left unaffected. Around 41 people died at Felixstowe when flood walls on the Orwell estuary collapsed, and roughly 400 properties flooded in Lowestoft.
• 5–6 December 2013. A storm surge produced the highest still-water levels on record at several east-coast tide gauges. Around 230 properties flooded across Suffolk and Lowestoft town centre was inundated, a stark modern reminder that the 1953 coastline is still exposed.
• Repeated surface water flooding. Heavy rainfall regularly floods properties and roads in and around Ipswich and the market towns, the everyday risk behind Suffolk's surface water management work.

This history is why a defended site can still sit in a high flood zone, and why residual flood risk — what happens if a defence is overtopped or fails — has to be assessed over the whole life of a development, including rising sea levels.

Flood defences and major development in Suffolk

The county is investing heavily in defences and is under real pressure to build, much of it on or near the water. The two facts pull against each other, and a flood risk assessment is where they are reconciled site by site.

The clearest example is the Ipswich Tidal Flood Barrier, opened in February 2019. With around 1,100 metres of new and refurbished flood walls and a series of gates on the Orwell, it reduces tidal flood risk to about 1,608 homes and 422 businesses, and is designed for the 1 in 300 year tidal event with climate-change allowance to 2118. That protection is exactly what has unlocked regeneration on the Ipswich Waterfront — but because the Flood Map for Planning is drawn as though defences are absent, those same sites often remain in Flood Zone 3 and still need a site-specific assessment.

• Ports and Freeport East. Felixstowe is the UK's largest container port, and Freeport East development sites such as Gateway 14 near Stowmarket are bringing forward large commercial schemes, many on low-lying or estuary-edge land.
• Sizewell C and the energy coast. Major energy infrastructure on the East Suffolk coast brings intense scrutiny of coastal flood risk, drainage and climate resilience.
• Lowestoft and the coastal towns. Lowestoft's flood risk management scheme and the wider regeneration around the Gull Wing crossing sit alongside ongoing tidal risk to the town centre.
• The Shoreline Management Plan. Along parts of the coast the agreed policy is "no active intervention" — for example at Covehithe, north of Southwold — so some land will not be defended in the long term, which a robust assessment has to reflect.

On most Suffolk schemes the question is not whether flood risk exists, but whether your report proves the development is safe and the drainage will not make things worse.

Planning policy and your Lead Local Flood Authority in Suffolk

A flood risk assessment in Suffolk has to satisfy three layers at once: national policy in the NPPF and its Planning Practice Guidance, the Environment Agency on main-river and tidal risk, and Suffolk County Council as Lead Local Flood Authority on surface water and ordinary watercourses. Get all three aligned and an objection has nowhere to land.

Suffolk County Council is the Lead Local Flood Authority for the whole county, and a statutory consultee on surface water drainage for major development under the planning regulations. Its Suffolk Local Flood Risk Management Strategy (updated February 2023) and its Suffolk SuDS Guide set the local rules, while each district holds its own Strategic Flood Risk Assessment — Ipswich, East Suffolk, West Suffolk, and Babergh and Mid Suffolk — that defines flood zones and local policy for your site. Where a site borders a drained area, the East Suffolk Internal Drainage Board rather than the county council consents works on its watercourses.

Do you need a flood risk assessment in Suffolk?

For planning, a site-specific assessment is required under national policy in the circumstances below. The Environment Agency and the LLFA both feed into the decision.

If the answer is yes, the report must show safe floor and access levels, mitigation the regulators will accept, and, where policy requires, the Sequential and Exception Tests and the right flood risk vulnerability classification. Our overview of planning for flood risk under the NPPF sets out the framework, and a conveyancing flood report is not the same thing as a planning-grade assessment.

Suffolk's SuDS and drainage requirements

The county expects sustainable drainage on development that affects runoff, designed to the county's standards from the first sketch. The 2023 Suffolk SuDS Guide moved firmly away from underground storage towards open, above-ground systems that deliver all four pillars of SuDS — water quantity, water quality, biodiversity and amenity — and the joint Suffolk SuDS Palette with Anglian Water steers designs that suit the local landscape.

• Discharge rate. Suffolk County Council's preferred approach is to restrict discharge to the greenfield QBAR rate, with full justification needed for any alternative.
• Greenfield runoff. The county's preferred method for calculating greenfield runoff is the FEH methodology, attenuating runoff to pre-development rates and volumes up to and including the 1% (1 in 100 year) event plus climate change.
• Drainage hierarchy. Infiltration first, then discharge to a watercourse, then the sewer as a last resort — the order set out in the building regulations and enforced by the LLFA and Anglian Water together.
• Ordinary watercourses. Works affecting an ordinary watercourse need Ordinary Watercourse Consent from the county council, or from the Internal Drainage Board in its area.

A surface water drainage strategy built around this hierarchy from the outset is the surest way to avoid a drainage objection. Where infiltration is proposed on the chalk or sands of west Suffolk, survey work and infiltration testing carry the design.

How Unda helps with flood risk assessment in Suffolk

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

A flood risk assessment in Suffolk from Unda weighs every credible source — the tidal estuaries and open coast, the Gipping and the western rivers, surface water, groundwater in the chalk, and any ordinary watercourse on the boundary — compares modelled flood levels against your proposed floor levels, sets safe access and egress, and recommends mitigation the regulators will accept. Where a coastal or estuary site needs it, we set out compensatory flood storage level for level, and we keep the drainage strategy consistent with the flood case so the two arguments reinforce each other. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report.

Our flood risk services for Suffolk

• Flood risk assessment for planning. Site-specific reports that satisfy the Environment Agency and your Suffolk planning authority.
• Groundwater flood risk assessment. A defensible design water table for chalk, Breckland and basement sites, not a guess.
• Surface water drainage strategy and SuDS. Designed to Suffolk County Council's 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.
• How a flood risk assessment is done. What a robust report contains and how the process runs.

Home buyers and businesses come to us too. A flood risk question can affect mortgage lending and house prices, and knowing whether you need a planning-grade assessment or something lighter saves time and money. Our note on what a flood risk assessment costs explains what drives the fee.

Suffolk flood resources and contacts

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

• Check for flooding in Suffolk. Environment Agency live warnings, river levels and maps at check-for-flooding.service.gov.uk.
• Suffolk County Council development and flood risk. The LLFA's guidance for developers at suffolk.gov.uk.
• Suffolk Local Flood Risk Management Strategy. The county's strategy and flood management duties via Suffolk County Council.
• East Suffolk Internal Drainage Board. Consents and drainage in the IDB area via the Water Management Alliance.
• Developer drainage standards. Surface water and sewer connection guidance from Anglian Water.
• Live river levels. Whether the Gipping, Waveney or the estuaries are running high right now via our live river levels map.

For flooding from blocked or burst sewers, contact Anglian Water. For broader context, our notes on the groundwater flood risk maps and on the EA's NaFRA2 risk data are a useful starting point.

Flood risk assessment in Suffolk: frequently asked questions