Flood Risk Assessment in Grimsby

A flood risk assessment in Grimsby starts with the Humber. Most of the town sits in a shallow dish of low ground behind the dock walls and the estuary sea wall. On almost every site, the tide and what happens if a defence fails decide the design. Inland, the River Freshney and the New Cut Drain threaten the western estates, and heavy summer storms back up sewers that in places are more than a century old. We prepare flood risk assessments in Grimsby for planning applications, house and commercial purchases, mortgages and insurance, along with sequential and exception tests and surface water drainage strategies.

Grimsby is taken here as the ONS built-up area: the town centre, the docks and Pyewipe, the East Marsh and West Marsh, the Willows, Wybers Wood, Great Coates and Little Coates on the Freshney side, and Scartho, Nunsthorpe, Weelsby and Old Clee to the south and east, across the DN31, DN32, DN33 and DN34 postcode districts and the DN37 streets around Great Coates. Cleethorpes, the seaside town next door, is a separate built-up area. It shares the council, the Humber frontage and the flood evidence, so a Cleethorpes site is assessed the same way. Grimsby is in the ceremonial county covered by our Lincolnshire page, but North East Lincolnshire Council is a unitary authority. It is both the planning authority and the lead local flood authority here; Lincolnshire County Council has no say on a Grimsby site's drainage.

In December 2013 the tide gauge at Immingham, just up the estuary, recorded a high water up to 0.7 metres above its 1953 level. No homes in the borough flooded. The council's flood strategy records why: the wind was blowing offshore, and had it blown onshore the sea would have stood higher and lives could have been at risk.

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

A town in a shallow dish behind the Humber walls

The joint strategic flood risk assessment for North and North East Lincolnshire, published in June 2022, describes the ground most of Grimsby is built on as "in effect a shallow dish". The dock estate forms its northern rim, generally above 4.5 metres above Ordnance Datum, with one stretch of about 200 metres nearer 4 metres. Inside the Royal Dock and the Fish Dock, water is normally held no higher than about 3.5 and 3.2 metres. Any site in the bowl behind that rim depends on the walls and gates around it.

• The dock walls. Associated British Ports maintains the sheet-piled walls, concrete revetments and lock gates of the Royal and Fish Docks, with an external flood gate on each lock. A scheme finished in 2015 raised the defences round the town to protect against a tide with about a 1 in 200 chance in any year.
• The estuary wall to Immingham. West of the docks the Environment Agency maintains the concrete sea wall towards Stallingborough and Immingham. Its £29 million Stallingborough scheme, which protects about 2,400 properties, has placed 90,000 tonnes of rock armour along 3 kilometres of that frontage. The same scheme is improving the outfalls of the Oldfleet Drain and the New Cut Drain near Grimsby.
• The wall to Cleethorpes. East of the docks a concrete sea wall, also the Agency's, runs to the Cleethorpes promenade. It was built in the late 1970s to replace the wall destroyed by the 1976 tidal surges.
• Breach as well as overtopping. The Environment Agency's breach study models 30 failure points on this coast, one of them a failed dock gate at Grimsby, for present-day and 2115 sea levels. Its depth and hazard maps for Grimsby and Cleethorpes sit with the SFRA, and a site in the dish is judged against them as well as against the flood zones.

The shoreline plan for this coast is to hold the line. The Humber 2100+ partnership of the Environment Agency and 11 councils is now working out how tidal risk round the estuary will be managed for the next century. For a site, the question is residual flood risk. A Grimsby assessment has to show floor levels, access and refuge that still work if a wall is overtopped or breached. The council's draft plan adds a rule for land fronting the estuary wall between the two ports, set out in the policy section below.

Screen a Grimsby address from Great Coates to Weelsby

Type a postcode into the map to see the Environment Agency's flood zones, surface water and reservoir data, warning areas and climate outlook for that spot. For anywhere else, use our full flood risk map. The coral line follows the ONS outline of Grimsby: it takes in the docks, Pyewipe and the Freshney estates, and stops at the edge of Cleethorpes, Humberston, Waltham, Laceby and Healing. The result is a first look. It cannot see floor levels, and it shows the flood zones as if the walls were not there.

The Freshney, the New Cut Drain and the town's tidal outfalls

Grimsby's own watercourses all end at the Humber, and several can only empty when the tide is low enough or when a pumping station runs. The council's 2015 strategy lists Laceby Beck, with the Freshney below it, and the New Cut Drain among the borough's highest-risk watercourses for flooding inside buildings.

The Environment Agency gauge on Laceby Beck at the River Freshney Grimsby station normally reads between 0.19 and 0.78 metres. Above that, low-lying land can flood; the highest reading so far is 1.20 metres, on 3 January 2024. The Agency names seven warning areas after Grimsby itself, from tidal flooding in low-lying areas of the town to the New Cut Drain at Wybers Wood and the Willows. Our live river levels map follows the gauges across the area as a storm or a high tide comes in.

Grimsby floods on record, from the 1976 surge to the 2014 storms

Tide, river and sewers have each flooded Grimsby within living memory. These are the events the council and the Environment Agency cite, with the figures they give.

1. 1976. Tidal surges destroyed the sea wall between Grimsby Dock and the Cleethorpes promenade; the concrete wall that stands there now replaced it later in the decade.
2. June 2007. The Freshney overtopped its defences on the Willows Estate and, with surface water from the drains on top, 186 properties flooded inside. More than 630 properties flooded across the borough that summer, and the 2013 washland scheme followed.
3. 5 December 2013. A North Sea surge produced the highest tide on this coast for 60 years. Seafront businesses and the Port of Immingham flooded; according to the council, no homes in the borough did. A study of the 1953 and 2013 events found the 2013 high water at Immingham up to 0.7 metres above 1953's.
4. 20 July and 8 and 10 August 2014. Thunderstorms on three days overwhelmed the sewers, two of them with rainfall intensities that have about a 1 in 50 chance in any year. The council's flood investigation recorded 16 properties flooded inside on St Nicholas Drive, six businesses in Freshney Place, and homes on Lawrence Street, Henry Street and Ainslie Street flooded inside, some of them twice.
5. 2016 to 2020. The Humber flood risk management plan lists widespread flooding in Grimsby in June 2016, August 2017, August 2019, November 2019 and August 2020; in August 2017 at least four properties in the town flooded inside.
6. 3 January 2024. The Freshney gauge recorded its highest level, 1.20 metres.

A tide-locked outfall during a storm can bring river, sewer and sea water onto the same street, so a Grimsby report deals with all three at once. Our explainer on how storm surges form sets the 1953 and 2013 North Sea surges side by side.

Chalk springs, buried culverts and combined sewers under Grimsby

Below the estuary clay lies chalk holding water under pressure, and the oldest parts of the town drain to sewers that carry rain and foul water in the same pipe. Both matter for floor levels, basements and how a new building gets rid of its rainwater.

The council has begun a surface water study to build the business case for work across the Pyewipe catchment. A Greater Lincolnshire groundwater project plans a new wetland in Grimsby to manage spring flooding to homes. For a submission, our guides to groundwater flood risk in planning applications and to foul, surface water and combined sewers set out what each condition means, and the ground conditions checker gives a first view of whether a soakaway is worth testing where clay lies over the chalk.

Which flood rules will a Grimsby planning application be judged against?

North East Lincolnshire Council decides planning applications and answers for surface water as lead local flood authority, with the Environment Agency advising on the Humber and the main rivers. Its adopted plan is under review. Councillors voted on 24 September 2026 not to proceed with the new plan; the Minister issued a direction the next day, and the Pre-Submission Draft Local Plan went out for consultation from 30 September to 12 November 2026.

Much of the urban area lies in the high-risk flood zone, so the sequential test comes up on many Grimsby sites. The council's guidance keeps the search for alternatives within regeneration areas, drawn from the most deprived fifth of neighbourhoods. That keeps central Grimsby developable in policy terms. The exception test and a safe design still have to be proved. Our explainer on the sequential and exception tests covers the national method, and an assessment to support the application answers Policy 33 and, once adopted, Policy 8.

Grimsby West, Scartho Top and the brownfield streets

The draft plan sets North East Lincolnshire a target of 11,178 homes from 2025 to 2043, and the largest sites sit on the edges of Grimsby.

• Grimsby West (SH1). A 166-hectare urban extension west of Wybers Wood and the Willows that "straddles the River Freshney". The draft plan gives it 2,650 homes in the plan period and 3,337 in total, a Freshney country park and a link road from the A46 to the A1136. In September 2025 a council scrutiny panel recommended that its masterplan not be accepted without more flood risk detail, with one councillor citing floods on the Willows in 1979 and 2007.
• Scartho Top and the southern edge. Scartho Top had 450 homes left to build at April 2025; across Scartho the long-standing sewer limits mean surface water is held back before it reaches the public system.
• Brownfield and regeneration land. West Marsh Renaissance off Macaulay Lane and the town centre plots are previously developed land in the low-lying urban area, where tidal residual risk, sewer capacity and the sequential test meet.
• The docks and Pyewipe. Port and industrial schemes near the Humber need floor levels set against the 1 in 200 tide with climate change, safe access during a surge and, beside the estuary wall, the 15-metre buffer.

Each of these sites also has to allow for climate change. The council's draft strategy expects mean sea level on the Humber to rise by between 1.15 and 1.55 metres by 2125. It expects peak rainfall in the Louth, Grimsby and Ancholme catchment to rise by 20 to 40 per cent by the 2050s, which is the figure a drainage strategy sizes its storage against.

From a Scartho extension to a dockside warehouse: when a flood risk assessment in Grimsby is needed

Whether a report is needed depends on the flood zone, the size of the site and what is being built.

The flood zone is read from the Environment Agency's Flood Map for Planning, which shows the land as if the walls were not there. The floor level, though, comes from the SFRA breach depths for that spot and the tide level with climate change, not from the zone alone.

Reports we write for dockside, Freshney and spring-line sites in Grimsby

The three main reports answer different questions. A flood risk assessment asks whether the site is safe, the sequential test whether the development should go there at all, and a drainage strategy where the rainwater goes. A Grimsby scheme often needs all three, and the rows below show why.

• Tide, river and sewers on one site. A flood risk assessment for a Grimsby site weighs the Humber and a possible breach, the Freshney or the New Cut Drain, storm water in old sewers and spring water from the chalk together.
• Applications in the dish and the Freshney valley. Homes and commercial buildings behind the dock walls or beside the Freshney need a flood risk assessment for planning that answers Policy 33 now and Draft Strategic Policy 8 once it is adopted.
• Before exchange in the Willows or the East Marsh. Searches often flag Grimsby addresses in Flood Zone 3. A flood risk survey for property purchase looks at the house itself, its floor level and any recorded flooding.
• Housing on the tidal flood zones. Most of the urban area is in the high-risk zone. New homes there need a sequential and exception test: the search for alternative sites stays inside the council's regeneration areas, and homes in Flood Zone 3 must also pass the exception test.
• Sewers up to a century old. Combined sewers under the older streets flooded homes in the 2014 storms, and a drainage strategy shows how a scheme keeps its rainwater out of them.
• Runoff to a tide-locked outfall. A surface water drainage strategy for a Grimsby site sizes storage for outfalls that cannot discharge at high tide and keeps rainwater out of the combined system, as Policy 34 asks.
• Conditions on an approval. Where North East Lincolnshire Council has granted permission subject to drainage conditions, we prepare the details for the discharge of drainage conditions.
• Breach and river levels. Where the breach maps or the Freshney's flood levels are too coarse for a site, flood modelling sets depths and floor levels more precisely.
• Seven named warning areas. Sites inside the Environment Agency's Grimsby tidal and New Cut Drain warning areas often need a flood warning and evacuation plan.
• Chalk springs. On the spring line towards Convamore Road, or wherever the clay over the chalk is thin, a groundwater flood risk assessment looks at basements and foundations.
• Combined and surcharging sewers. In Scartho, Yarborough and the other areas the council names for sewer surcharge, a foul drainage strategy shows a new connection will not add to it.
• Homes with a flood record. After the Willows flooding in 2007 and the 2014 storms, owners renewing cover can use a flood risk assessment for insurance to show the insurer the real risk to the building.
• Port and industrial transactions. Buyers and lenders on dock and Pyewipe land use a due diligence flood risk assessment to price tidal exposure before a deal completes.
• Businesses that have flooded before. Freshney Place shops flooded in 2014 and seafront businesses in the December 2013 surge. A business continuity flood risk assessment plans how premises keep trading through the next event.
• New commercial buildings. Offices, warehouses and port buildings at Pyewipe and the docks that seek certification need a BREEAM flood risk assessment for the Pol 03 credits.

Grimsby flood contacts, from Town Hall Square to the drainage board

Responsibility for flooding in Grimsby is split by source, and the council asks residents to report to whichever body owns the water.

Sign up for free flood warnings by phone, text or email. In 2023 the Environment Agency reported that 46 per cent of the borough's 75,634 properties sit inside its flood warning areas. Its leaflet campaign that year went to seven Grimsby wards: East Marsh, West Marsh, Sidney Sussex, Park, Heneage, Yarborough and Freshney. Our guide to why drainage boards matter for planning covers consent near a board's drain.

Questions about Grimsby sites, flooding and planning

For a house in the Willows, a plot at Scartho or a warehouse at Pyewipe, ring 01293 214444 or email enquiries@unda.co.uk, and one of the consultants at Unda Consulting Limited will talk the site through with you. Scunthorpe, further up the Humber, and Hull on the north bank have pages of their own.