Flood Risk Assessment in Liverpool

Unda prepares flood risk assessments and surface water drainage strategies for residential and commercial sites across Liverpool. A flood risk assessment in Liverpool shows the city council and the Environment Agency that a development will stay safe from flooding for its whole lifetime, and that it will not push flood risk onto neighbouring land.

Liverpool is one of the most surface-water-exposed cities in England. Dense Victorian streets, large areas of hard standing and a web of culverted brooks mean heavy rain, rather than the tidal Mersey, is what floods most of the city. The waterfront and the docks add tidal risk, the upper River Alt drains the north and east of the city, and rising groundwater over the Sherwood Sandstone shapes basement and city-centre schemes. We assess every source that matters on your site, then deal directly with the Environment Agency and Liverpool City Council as the lead local flood authority on your behalf, guiding developers, planning consultants, architects, homebuyers and businesses through to a decision.

We prepare flood risk assessments in Liverpool for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface water drainage strategies. A flood risk assessment, a sequential or exception test and a drainage strategy are three different reports. They often travel together in a planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go.

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

Liverpool is one of the largest surface water Flood Risk Areas in England: around 90,000 people and more than 37,500 homes sit where surface water can flood, so even a Flood Zone 1 site in the city often needs its surface water risk assessed.

Flood risk assessment in Liverpool at a glance

• Surface water is the dominant risk. Liverpool is one of the country's highest-ranked cities for surface water flooding, the legacy of dense Victorian development, extensive hard standing and a drainage network that struggles in intense rainfall.
• Liverpool City Council is your lead local flood authority. The council manages surface water, groundwater and ordinary watercourses, while the Environment Agency leads on the tidal Mersey and the sea and United Utilities runs the public sewers.
• The waterfront carries tidal risk. The Mersey runs the full length of the city's docks, so waterfront and dock-regeneration sites bring tidal levels, sea-level rise and finished floor levels into the assessment.
• Hidden rivers and rising groundwater. Much of the River Alt and the city's older brooks run in culverts, and groundwater has risen over the Sherwood Sandstone beneath central Liverpool as historic industrial abstraction has declined.
• Flood Zone 1 is not a free pass. Since the 2025 Planning Practice Guidance update, surface water risk can trigger an assessment even on a Flood Zone 1 site in Liverpool.

Check flood risk anywhere in Liverpool

Liverpool is outlined below. Screen any postcode in the city 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 Liverpool: surface water, the Mersey and the city's hidden rivers

Surface water is the leading flood risk across Liverpool. Heavy rainfall overwhelms old, undersized drains in the densely built streets of the city centre, Kirkdale, Everton and Toxteth, and a large share of the city's watercourses run in culverts that surcharge when they fill. The tidal Mersey adds risk along the waterfront and the docks, the upper River Alt drains the north and east, and groundwater rises from the Sherwood Sandstone beneath the centre. Most sites here face more than one source at once, which is why a desktop map rarely satisfies a planning officer on its own.

Because the city is so heavily urbanised, its flood risk is now dominated by surface water rather than rivers. That does not mean the river and the sea can be ignored: the tidal Mersey shapes risk along the whole western edge of the city, while the Alt and the city's culverted brooks matter inland. A credible assessment has to identify which source actually drives the risk on your site. You can screen any location against the live Environment Agency data on GOV.UK Check for Flooding or through our own flood risk map.

Surface water: the dominant risk

Liverpool sits within one of the surface water Flood Risk Areas designated as nationally significant. Around 90,000 people and more than 37,500 homes in the Liverpool area are in places where surface water flooding can occur, the result of dense Victorian development, large areas of hard standing and a drainage network that struggles in intense rainfall. This is why a pluvial (surface water) assessment and a sound drainage strategy matter so much on Liverpool sites, even those that map as low fluvial risk. Liverpool City Council is reviewing the city's culverts to identify those that could pose a flood risk to property or critical infrastructure, a reminder that much of the local risk is hidden underground.

The waterfront and the tidal Mersey

The Mersey runs the length of Liverpool's docks, from Seaforth in the north to the Garston shore in the south, and the waterfront is where the city's tidal risk concentrates. Schemes along the historic docks and at Liverpool Waters, a 60-hectare regeneration of the northern docks, sit close to a tidal river that is rising. Coastal and estuary sites bring sea-level rise into the assessment, so they often need flood modelling and careful attention to rising sea levels and tidal flooding. The proposed Mersey Tidal Power scheme is designed to deliver long-term flood protection alongside clean energy, but until it exists, every waterfront scheme has to make its own case on finished floor levels, safe access and residual risk.

The River Alt and Liverpool's culverted brooks

The River Alt rises at Hag Plantation in Huyton and flows through Croxteth Park and West Derby before leaving the city to the north, fed by tributaries including Fazakerley Brook. More than five miles of the Alt runs underground in culverts, and where the river was buried and built over, surface water and misconnected drainage add to the load it carries. A short section at Croxteth was opened back to daylight in 2014 to improve water quality and create green space, but most of the system stays hidden. On sites near these watercourses it is essential to understand both the fluvial flood risk and whether an ordinary watercourse on or near the boundary, open or culverted, changes the picture.

Groundwater and the Sherwood Sandstone

Central Liverpool sits on the Sherwood Sandstone, one of the most important aquifers in the country. The city's heavy industry once drew large volumes of water from it, with abstraction peaking in the 1970s. As that industry declined, groundwater levels beneath central Liverpool recovered by several metres, and abstraction by Network Rail to keep the Loop line tunnels dry is part of what now holds the level in check. For a developer this matters because groundwater rises from below, appears on no national flood map, and can break the assumptions behind a basement or a soakaway. A groundwater flood risk assessment and an early read of the ground conditions for a soakaway are often decisive on city-centre and basement schemes here. You can read more on how groundwater flooding works and why it is so often missed.

A history of flooding in Liverpool

Liverpool's flood record is largely a record of surface water and the slow story of its groundwater. Intense rainfall has repeatedly overwhelmed the city's drains, the Leeds & Liverpool Canal has burst in the north of the city, and groundwater has crept back up beneath the centre over decades. These are the kinds of events a planning officer expects an assessment to engage with, not gloss over.

• Early 1990s — Leeds & Liverpool Canal. A breach of the canal in the north of the city flooded more than 200 properties, a reminder that a raised, man-made watercourse carries its own residual risk.
• 1970s onwards — rising groundwater. As industrial abstraction from the Sherwood Sandstone fell away after its 1970s peak, groundwater beneath central Liverpool rose by several metres, bringing basement and below-ground risk into focus.
• January 2021 — Storm Christoph. The storm brought widespread surface water flooding across the Liverpool city region, with surface water and ordinary watercourses behind the majority of the flooding recorded.
• Repeated summer downpours. Short, intense storms regularly flash-flood streets and underpasses across the city as the drainage network is overtopped, the everyday face of Liverpool's surface water risk.

Do you need a flood risk assessment in Liverpool?

You will normally need a flood risk assessment for development in Liverpool that falls in Flood Zones 2 or 3, on sites of one hectare or more in Flood Zone 1, and increasingly on smaller Flood Zone 1 sites where the Flood Map for Planning shows surface water risk. With surface water the dominant local risk, that last trigger catches a growing number of Liverpool applications.

The flood risk assessment for planning is the report most Liverpool applications turn on, prepared to satisfy the NPPF and its Planning Practice Guidance. Knowing which flood zone a site sits in on the Flood Map for Planning is the starting point, but the map is only the first screen. The cost and scope then depend on the sources in play, as our guide to the cost of a flood risk assessment explains.

Planning policy and your lead local flood authority in Liverpool

In Liverpool you deal with one lead local flood authority, not several: Liverpool City Council is responsible for surface water, groundwater and ordinary watercourses across the whole city, while the Environment Agency leads on the tidal Mersey and the sea, and United Utilities runs the public sewers. That single point of contact is one way a city page differs from the wider Merseyside picture, where five boroughs each act as their own authority.

For planning, the council's flood risk and surface water policy sits in Policy R3 (Flood Risk and Water Management) of the adopted Liverpool Local Plan 2013–2033, which requires development to be supported by an appropriate flood risk assessment and to incorporate sustainable drainage where practicable. The strategic evidence sits in the council's Local Flood Risk Management Strategy and in the Liverpool City Region Strategic Flood Risk Assessment, with the council currently updating its own SFRA for the next Local Plan. A lead local flood authority is a statutory consultee on surface water drainage for major development, so a drainage strategy that follows the local discharge hierarchy from the start is the surest way to avoid an objection. Proportionate sustainable drainage is now expected on schemes of all sizes that affect drainage.

Where policy requires it, a sequential and exception test is prepared alongside the assessment to justify the location, and detailed drainage work to discharge a drainage condition follows once permission is granted. Designing to the 2025 national SuDS standards and the four pillars of SuDS from the outset keeps the council on side. A site in a critical drainage area can attract this scrutiny even in Flood Zone 1.

Development and flood risk assessment in Liverpool

Liverpool is a regeneration city, and the kind of site you bring forward shapes the assessment you need. Getting the scope right is the difference between a clean approval and a surface water or drainage objection that holds an application up for months.

• Waterfront and dock regeneration. Schemes along the historic docks and at Liverpool Waters sit close to the tidal Mersey, needing finished floor levels, safe access and egress, and sometimes compensatory flood storage.
• City-centre and basement schemes. Dense sites over the Sherwood Sandstone bring surface water and groundwater into play, so a defensible design water table matters rather than a guess.
• Inner-city infill and conversions. High-density residential and student schemes on small footprints turn on surface water and a workable drainage strategy where space for SuDS is tight.
• Employment and logistics land. Large impermeable sites around the port and in north Liverpool turn on surface water and the right drainage information for planning.

Climate change is not optional here. A Liverpool assessment must apply the Environment Agency's allowances for higher rainfall, river flows 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. Where mapping is not enough to define the risk, flood modelling fills the gap, and on defended or low-lying waterfront sites the residual risk is often where the case is won or lost.

Homebuyers and businesses come to us too. A flood question can affect mortgage lending and house prices, and a conveyancing search is not the same thing as a planning-grade report. Knowing which you actually need saves time and money.

How Unda helps with flood risk assessment in Liverpool

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

A flood risk assessment in Liverpool from Unda assesses every credible source — the tidal Mersey and the waterfront, the Alt and the city's culverted brooks, surface water, groundwater from the Sherwood Sandstone 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. 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 for every situation in Liverpool

• Flood risk assessment for planning. Site-specific reports that satisfy the Environment Agency and Liverpool City Council.
• Flood risk survey for property purchase. An independent, property-specific answer for buyers, lenders and their advisers.
• Flood risk assessment for insurance. Property-level evidence for brokers and underwriters where cover or premiums are in question.
• Flood risk assessment for BREEAM. Structured around Pol 03 so credits are not lost at assessment stage.
• Sequential and exception test reports. Locational justification prepared where policy requires it.
• Surface water drainage strategy and SuDS. Designed to the council's standards from the first sketch, with preliminary drainage design available at outline stage.
• Groundwater flood risk assessment. A defensible design water table for basement and city-centre sites on the sandstone.
• Chartered flood risk consultants. Specialists who stay involved past the report to answer objections.

Liverpool flood resources and contacts

The most reliable Liverpool flood information comes from the lead authorities. For an immediate threat to life during a flood, always call 999; for power cuts, call 105.

• Check for flooding in Liverpool. Environment Agency live warnings, river levels and maps at check-for-flooding.service.gov.uk.
• Floodline. Advice and flood-warning sign-up on 0345 988 1188.
• Report flooding to the council. Liverpool City Council takes reports of surface water, groundwater and ordinary watercourse flooding through its local flood risk management team.
• Strategic Flood Risk Assessment. The Liverpool City Region SFRA sets the strategic flood risk picture for planning.
• Regional context. Merseyside flood and coastal information from The Flood Hub, which serves the North West.
• Live river levels. Whether the Alt or other rivers are running high right now via our live river levels map.

For flooding from blocked or burst sewers, contact United Utilities. For broader policy context, our notes on the Environment Agency's planning role and on the sources of flood risk are a good starting point, and our free BRE 365 infiltration rate calculator and drainage calculators help with an early drainage read.

Flood risk assessment in Liverpool: frequently asked questions

Talk to an experienced flood risk consultant about your Liverpool site

We have prepared flood risk assessments and drainage strategies across Liverpool, from the waterfront and the city centre to Croxteth, Speke and the northern docks. Get a free, no-obligation quote and a consultant will call you back within 60 minutes.