Flood Risk Assessment in Liverpool

A flood risk assessment in Liverpool is mostly about what happens below the street. The city drains through old combined sewers and culverted brooks, and all four flood investigations the council published in 2025 trace back to drains, sewers or a backed-up brook. On the waterfront the tidal Mersey still sets the flood levels, and in the north and east so do the River Alt and its brooks. Whether the job is a planning application, a house purchase, a mortgage or an insurance renewal, our consultants prepare flood risk assessments in Liverpool, alongside sequential and exception tests and surface water drainage strategies.

Here Liverpool means the city's built-up area as the Office for National Statistics maps it. That takes in the city centre and the docks, Everton, Anfield, Walton and Kirkdale to the north, Fazakerley, Croxteth and West Derby to the north-east, Wavertree, Childwall and Belle Vale to the east, and Toxteth, Aigburth, Mossley Hill, Woolton, Garston and Speke down the estuary. Bootle, Litherland, Huyton and Kirkby are separate built-up areas. The line crosses into Knowsley at Halewood, where Knowsley Council, not Liverpool, decides applications. The postcode districts we see most are L1, L3, L8 and L18.

About 84% of Liverpool's sewer network carries rainwater and sewage in the same pipes, and the Environment Agency counts 90,041 people and 37,517 homes in the city's surface water Flood Risk Area.

To discuss a Liverpool site with one of our flood risk consultants, ring 01293 214444 or write to enquiries@unda.co.uk.

Why Liverpool floods from its drains more than from the Mersey

Liverpool grew over a network of brooks that were piped and built over, and many of those culverts now run into the sewers. When a summer storm or two days of steady rain overloads the pipes, water comes up through gullies and manholes in streets that sit in Flood Zone 1 on the planning map. The Environment Agency's flood risk management plan material for the Liverpool and Sefton Flood Risk Area puts 17.68% of the 37,517 homes it counts at high risk from surface water, and the North West's Flood Hub counts 28,856 of the city's 223,004 properties at some risk of flooding.

The table draws on the council's new Level 1 SFRA, its Section 19 reports and the Environment Agency. A site a mile from the Mersey can still need an assessment, and the sewer records can matter more than the flood zone. Our guides to surface water flooding and planning and to foul, surface water and combined sewers cover the mechanics.

Look up a Liverpool postcode, from Fazakerley down to Speke

Treat the map below as a first flood risk map of Liverpool: enter a postcode to screen it against the Environment Agency's river, sea, surface water and reservoir data; our full flood risk map does the same for anywhere in England. The coral outline is the Liverpool built-up area, running from Fazakerley and Croxteth in the north to Speke and the airport by the estuary. Use it as a first screen only, because it cannot show which sewer serves a street, how deep a culvert runs under it or where the council's Section 19 reports place a problem.

Flooding in Liverpool since 2010: the dated record

Recent floods in Liverpool have come from short, heavy downpours and from long wet spells that leave the brooks and outfalls with nowhere to go. Each event below is recorded in the council's SFRA, its Section 19 reports or Environment Agency material, and four places were formally investigated under section 19 of the Flood and Water Management Act.

1. July 2010. A high-intensity storm flooded about 257 properties inside, among them 247 homes, around Deysbrook, East Prescot Road, Allerton Road, Wavertree and Aigburth.
2. September 2012. Surface water flooded homes on Egremont Lawn and Winster Drive in the east of the city, and Deysbrook Lane flooded again.
3. 5 December 2013. A storm surge driven by high winds and a high tide overtopped Canning Half Tide Dock on the waterfront (Canal & River Trust record).
4. June to December 2020. Dovecot, Mossley Hill and Garston flooded in June and August; in December West Derby and Deysbrook saw homes flooded inside.
5. May to August 2023. Queens Drive in Mossley Hill flooded five times where it runs in a cutting under Briardale Road and a railway bridge. On 26 August a car was fully submerged and two people died. On 23 July, after 65 mm of rain over two days, six homes on Egremont Lawn flooded from Winster Drive, and Camphill Road in Woolton flooded in May and July.
6. 9 July 2024. Deysbrook Lane in West Derby flooded once more, the latest of the ten events there that the council's investigation examined.
7. 2025. The Section 19 reports followed: Queens Drive and Deysbrook Lane in February, Winster Drive in May and Camphill Road in October.
8. 2026 to 2028. United Utilities plans a £30 million, 7 million litre storm water tank under Wavertree Park, with engineering works from 2026 and completion due in 2028.

The Section 19 investigations are worth reading before buying or developing on any of these streets. Our note on why some floods get a Section 19 report explains what they can and cannot tell you. The Environment Agency gauges Netherley Brook at Winster Drive and the Mersey at Liverpool, and our live river levels map shows those readings alongside any flood warnings in force.

The River Alt, Netherley Brook and the city's buried brooks

River flooding in Liverpool is concentrated in the north-east and east of the city, on the Alt and its brooks. The Alt and three of its tributaries are main rivers, looked after by the Environment Agency; Tue Brook and the smaller brooks are ordinary watercourses under the council. Many of them run in culverts for long stretches. The risk to a site can turn on a pipe nobody has looked inside for years.

• River Alt and Deys Brook, West Derby. The only place in the city the Environment Agency's asset records show as benefiting from defences, with embankments and engineered high ground. They did not stop the flooding. The Deysbrook Lane investigation found that when the Alt runs high it backs up into Hall Brook and the slow, culverted Deys Brook, while the combined sewer and the highway drains fill at the same time.
• Fazakerley, Hall and Sugar Brooks. With the Alt they account for most of the city's river flood zones, across Fazakerley, Croxteth and West Derby. The SFRA shows the extents along Fazakerley Brook, Deys Brook, Tue Brook and the Alt growing with climate change.
• Netherley Brook. It runs along the eastern edge past Belle Vale. In July 2023 its record level locked the outfall of the surface water sewer serving Winster Drive. The rain had nowhere to go.
• Tue Brook. An ordinary watercourse in the north of the city, where the city region's SFRA records past surface water flooding around Tuebrook. The Mersey Rivers Trust's £2.1 million River Alt programme plans to restore the Tue Brook wetlands at Fazakerley, alongside a wetland in Croxteth Country Park and leaky dams in Dam Wood.
• Opening culverts. At Alt Meadows in Croxteth, a straight 300 m stretch of the Alt that ran underground was opened up and given a meandering channel 870 m long. Local Plan policy R5 resists new culverting except to give access across a watercourse.

On a site near one of these brooks, the assessment has to establish who owns and maintains the watercourse or culvert and whether any consent is needed for works to it. Our guides to main rivers and ordinary watercourses and to culverts and who is responsible for them go into the detail.

The waterfront, the docks and a rising estuary

Tidal risk follows the estuary. Along Liverpool's western and southern edge the SFRA places Flood Zones 2 and 3 beside the Mersey Estuary, and the Environment Agency's climate change mapping shows the tidal extent growing most in Sandhills and through the city centre. For a site there, the question is the design tide level a century from now and how a building, its ground floor and its escape route sit against it.

The allowances in the SFRA for the North West put sea level rise between 2000 and 2125 at 1.01 m on the higher central estimate and 1.41 m on the upper end. An assessment tests both. Tide-locking matters too: when the estuary is high, drainage outfalls cannot discharge, and the SFRA lists that as a cause of flooding along Netherley Brook. The draft Local Plan 2043 allocates waterfront land for homes and workspace, including Ten Streets and the North Docks north of the centre and 800 homes on the former Garden Festival site by Otterspool. Our explainers on tidal flooding and on residual flood risk cover the principles.

Groundwater and reservoirs under the Liverpool flood map

Most of Liverpool sits on Triassic sandstone, a principal aquifer, under a cover of clay-rich till. Industry once pumped heavily from the sandstone; since that stopped the water table has recovered, and the British Geological Survey lists Liverpool among the UK cities where groundwater has rebounded. Local Plan policy R3 names flooding "due to, or exacerbated by, rising groundwater" as a reason to refuse a scheme that cannot deal with it.

• Where groundwater is closest to the surface. Fazakerley, Croxteth, Belle Vale and Netherley carry the highest emergence risk on the SFRA's groundwater map.
• Perched water. The council has confirmed a perched water table under Thingwall Allotments in Wavertree, which feeds overland flow after heavy rain.
• Basements and soakaways. The council's flood strategy records more reports of basement and garden flooding, partly from groundwater. That affects both below-ground rooms and whether a soakaway will drain.
• Reservoirs. Thirteen reservoirs could send water into the city if a dam failed, among them Sefton Park Lake and Kensington No.3. The modelled flood path runs through the city centre, Edge Hill, Croxteth and Childwall.

Neither groundwater nor reservoir failure appears on the main planning flood zones, so a city-centre basement or a scheme in Croxteth needs them looked at separately. See our guides to groundwater flooding, perched groundwater and reservoir flooding.

Policy R3 now, draft CN5 next: the plan a Liverpool application meets

Liverpool City Council is both the planning authority and the Lead Local Flood Authority for the city, so one council looks at the flood risk and the drainage, with the Environment Agency advising on the Mersey and the main rivers. The policies in force are in the Liverpool Local Plan 2013 to 2033, adopted on 26 January 2022.

• Policy R3, Flood Risk and Water Management. Development follows the sequential approach and, where needed, the exception test. Where one is needed, a flood risk assessment shows the scheme will not increase risk on site or elsewhere, and permission is withheld where a site faces unacceptable risk from any source, would add to flooding, block maintenance access to a watercourse or harm tidal and river defences.
• R3 on drainage. Sustainable drainage wherever reasonably practicable, considered at the earliest stage on major schemes, and proof of enough wastewater capacity.
• Policy R4, Coastal Protection. No development that raises tidal flood risk or impairs the estuary's ability to act as a natural defence.
• Policy R5, watercourses and culverts. No new culverting or diversion except for access, no harm from extra runoff, and the Canal & River Trust consulted next to its waterways.

The Liverpool Local Plan 2043 will replace it. Its proposed submission version was out for comment from 10 August to 30 September 2026 and now goes forward to examination. Draft policy CN5 keeps R3's tests and adds to them: climate change over the lifetime of the development in the sequential test, floodplain storage replaced level for level and volume for volume, residual risk managed through safe access, flood warnings and emergency plans, and property flood resilience never accepted on its own as a reason to build in a flood risk area.

The evidence has moved on too. The 2022 plan relied on a 2017 SFRA; the plan now in preparation is backed by a new Level 1 SFRA prepared by JBA Consulting (final draft, July 2026) and a Level 2 SFRA for individual allocations, both on the council's Local Plan evidence page. The city region's own SFRA of November 2023 is broader and says it does not replace the council's. Our guide to SFRAs explains how they are used.

National policy sits above both plans in chapter 18 of the August 2026 NPPF: policy F4 sets which sites need an assessment, F5 and F6 hold the sequential and exception tests, and F8 expects drainage to meet the 2025 National Standards for sustainable drainage. Our summary of the August 2026 changes and our explainer on the two tests go further.

What Liverpool's flood authority expects of the drainage

Because the city's sewers are mostly combined, the council looks hard at where new surface water goes. A brownfield site that already drains to a combined sewer is expected to send less to it, not the same. Its guidance for developers, summarised in the 2026 SFRA, sets the numbers below, and the full document is available from the Lead Local Flood Authority.

In practice a brownfield site in Kensington or Edge Hill will normally need a sewer survey to prove its existing connection before any reduction can be claimed. A soakaway counts only once infiltration tests show that it drains, which in the clay-rich till covering much of the city it often will not, while the sands around Sandhills, Belle Vale and the airport take water far more readily. Our BRE 365 infiltration calculator and drainage calculators give a first estimate, and our note on why drainage strategies draw LLFA objections covers the common gaps.

From dockside flats to Flood Zone 1 infill: when a flood risk assessment in Liverpool is needed

Nationally an assessment goes with any development in Flood Zone 2 or 3, any site of 1 ha or more in Flood Zone 1, Flood Zone 1 land shown at risk of surface water or of future river or sea flooding, and a change to a more vulnerable use where another source could reach it. In Liverpool the last two triggers apply far more often than the river ones. Architects and planning consultants preparing Liverpool City Council applications can check a site against them with us before the drawings are fixed.

• Flats and offices on the waterfront. Tidal Flood Zone 3 near the docks: a full assessment with sea level rise, floor levels and a safe route out, plus the sequential test for new homes.
• Basements and lower ground floors. Groundwater and reservoir risk in the city centre, Fazakerley, Croxteth and Belle Vale, and sewer surcharge almost anywhere.
• Homes near the brooks. Plots by the Alt, the Deys, Fazakerley or Netherley Brooks: river risk, culvert blockage and outfalls that can lock.
• Conversions to flats or student rooms. Turning offices, shops or warehouses into homes is a change to a more vulnerable use, and needs an assessment wherever surface water or another source reaches the building.
• Infill in Flood Zone 1. Small sites on a surface water flow path or low spot, such as streets in Wavertree, Mossley Hill or West Derby.
• Large allocations. Sites over 1 ha, such as the Garden Festival land, need an assessment whatever the flood zone.

Our reports for Liverpool sites, from Sandhills to Speke

A flood risk assessment asks whether a site is safe, the sequential test asks whether it should be developed at all, and a drainage strategy asks where the water goes; in Liverpool they often travel together. A senior consultant checks and signs off each report we issue for a Liverpool site; our consultants are chartered, and Unda is a CIWEM Business Partner.

• Sites served by old sewers. A flood risk assessment for a Liverpool site looks at surface water, the combined sewer, any culverted brook and groundwater, as well as the river and tide.
• Applications to Liverpool City Council. A flood risk assessment for planning answers policy R3 now and is written so it still stands when draft CN5 takes over.
• Buying in Mossley Hill, West Derby or by the docks. A search can flag the street without saying whether the house itself has flooded. A flood risk survey for property purchase looks at that building before you exchange.
• New homes in the tidal or brook flood zones. Housing in Flood Zone 2 or 3 needs the sequential and exception test, with an area of search the council can check.
• Schemes that add hard surfaces. With combined sewers under most streets, the council expects a drainage strategy that shows where the rain will go.
• Keeping water out of the combined sewer. A surface water drainage strategy works down the discharge hierarchy, holds greenfield rates or a brownfield reduction, and keeps the 1 in 100 plus 40% storm on site.
• After permission is granted. Where a Liverpool consent comes with a drainage condition, our discharge of drainage conditions work supplies the calculations, drawings and maintenance plan the council asks for.
• Basements on the sandstone. Policy R3 names rising groundwater, and the SFRA maps emergence risk in Fazakerley, Croxteth, Belle Vale and Netherley, so a groundwater assessment belongs with below-ground schemes there.
• Sewer capacity. Policy R3 asks for proof of wastewater capacity, and with 84% of the network combined a foul drainage strategy shows how sewage will reach a public sewer without adding to surcharge.
• Brooks, culverts and the tide. Where a site depends on how the Alt backs up the Deys Brook culvert, or on estuary extents the SFRA notes were interpolated rather than modelled, flood modelling gives site levels.
• Residual risk on the waterfront and by the brooks. Four Environment Agency warning areas cover the city and draft CN5 asks for warnings and emergency plans, which a flood warning and evacuation plan sets out.
• Homes with a flooding history. After the 2010, 2012, 2020 and 2023 floods, an insurance flood risk assessment gives an underwriter evidence about the building rather than the postcode.
• Land deals on the docks. Buyers and lenders on waterfront and former industrial land in tidal Flood Zone 3 use flood risk due diligence before they commit.
• Commercial schemes in Ten Streets and the North Docks. Employment-led space in the draft plan's waterfront allocations often targets BREEAM, and a BREEAM flood risk assessment covers the Pol 03 credits.
• Land before allocation. The draft plan seeks at least 33,750 new homes by 2043, and a flood feasibility study tests a site's flood constraints before a promoter puts it forward.

Flood warnings, reporting and who answers in Liverpool

If floodwater puts anyone at risk, call 999; for a power cut, call 105. Beyond that, the right contact depends on the source: the council for drains, culverts and the brooks, United Utilities for the sewers, and the Environment Agency for the Mersey, the Alt and flood warnings in Liverpool.

For the five boroughs together, including Bootle, Huyton, Kirkby and the Sefton and Wirral coasts, see our page on flood risk assessment in Merseyside. Upstream, the Mersey's own flood picture is on our Warrington page, and other towns and cities are listed under the places we cover.

Liverpool flood risk questions from buyers, builders and architects

Unda Consulting Limited prepares flood risk assessments, sequential and exception tests and drainage strategies for sites across Liverpool, from the docks and Toxteth to Croxteth, Garston and Speke. Call 01293 214444 or email enquiries@unda.co.uk to talk a site through.