Flood Risk Assessment in Littlehampton

Our consultants prepare comprehensive flood risk assessments and drainage strategies for residential and commercial sites across Littlehampton and the wider Arun valley. A flood risk assessment in Littlehampton shows your local planning authority, and the Environment Agency, that a development will stay safe from flooding for its whole lifetime without pushing risk onto neighbouring land. We prepare these reports for planning, for property purchase and mortgage lending, for insurance, and for BREEAM, alongside the sequential and exception tests and the surface-water drainage strategies that a Littlehampton scheme often needs.

Littlehampton is one of the more demanding places in West Sussex to get a flood risk case right. The town sits at the mouth of the River Arun, where tidal water, river flow and surface water all meet, so an assessment here has to read several sources of flooding together rather than treating the river in isolation. We know the Arun, the local defences and the way West Sussex County Council and Arun District Council assess development, and we translate that into a report that holds up first time.

Littlehampton is built around the tidal mouth of the River Arun, one of the fastest-flowing rivers in England, so flooding here is driven by the tide and storm surge as much as by rainfall — and an assessment that misses that interaction will not satisfy the Environment Agency.

To talk through a site, contact one of our experienced flood risk consultants on +44 (0) 1293 214444 or email enquiries@unda.co.uk. We reply to every quote request within 60 minutes.

Flood risk assessment in Littlehampton at a glance

The essentials a developer, buyer or agent in Littlehampton needs before commissioning work:

• Tidal town at the Arun mouth. The dominant flood sources are tidal and fluvial flooding from the River Arun, combined with surface water in the low-lying streets near the harbour and the seafront.
• Defended, but not risk-free. A £22 million Environment Agency scheme raised the tidal defences along the east bank between 2013 and 2015, yet the town still flooded in April 2024 when tidal water exceeded the existing defences.
• Two authorities set the rules. The Environment Agency leads on the tidal River Arun; West Sussex County Council is the Lead Local Flood Authority for surface water, groundwater and ordinary watercourses.
• Flood Zone 3 across much of the town. Large parts of Littlehampton fall within Flood Zones 2 and 3 on the Flood Map for Planning, so most development will need a site-specific flood risk assessment and, often, the Sequential Test.
• Climate change matters here. Arun District Council's 2026 Strategic Flood Risk Assessment carries climate projections to 2125, and a tidal town has to be shown safe against rising sea levels for its whole lifetime.

Check flood risk anywhere in Littlehampton

Littlehampton is outlined below. Screen any postcode in the town 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 Littlehampton: the tidal Arun, the sea and surface water

Tidal and fluvial flooding from the River Arun dominate flood risk in Littlehampton. The town grew up on both banks of the river where it meets the English Channel, so the same water body brings river flow from the South Downs catchment and tidal water and storm surge from the sea. Surface water adds a third source in the low-lying streets behind the harbour, and rising groundwater in the chalk and river-valley deposits can compound the picture. Most sites here face more than one source at once, which is exactly why a generic, single-source report tends to fail at the Environment Agency.

The Arun is a serious river. It runs about 60 kilometres from the Weald through a gap in the South Downs at Arundel before reaching the sea at Littlehampton, and it is tidal a remarkable 25 miles inland to Pallingham. At spring tides the range at Littlehampton is around 5.2 metres, and the river runs at four to six knots, which makes it one of the fastest-flowing rivers in England. That combination of a large tidal range, a fast current and a built-up estuary is what gives Littlehampton its flood character.

If you want a quick read on a specific address, our free flood risk map shows the Environment Agency layers by postcode, the live river levels map shows where the Arun is sitting right now against its normal range, and the geology and ground conditions checker gives an indicative view of whether infiltration drainage is likely to work on the local ground. None of these is a flood risk assessment, but they are a sensible starting point before you commission one.

A history of flooding in Littlehampton

Dated events are why the local authorities scrutinise development here so closely, and why a flood risk assessment in Littlehampton has to be evidence-led rather than generic. Each episode has shaped the defences and the policy a developer now has to design around.

• April 2024 — the major incident. In the early hours of 9 April 2024 the River Arun burst its banks and flooded Ferry Road and Rope Walk, with around 15 people evacuated to the Littlehampton Wave leisure centre and a caravan park inundated. West Sussex County Council's investigation found the main cause was tidal water exceeding the existing defences.
• November 2023 — Storm Ciarán. The Arun was reported as the highest it has ever been at Arundel, just upstream, as the storm drove water down the catchment and held it against a high tide — a reminder that what happens up the valley reaches the town.
• A defended but exposed coastline. Following the 2024 flooding, further works were carried out to reinforce ageing defences around Littlehampton harbour, underlining that the structures protecting the town need continual maintenance.

The River Arun and Littlehampton's tidal defences

Littlehampton is a defended town, but a defended town is not a risk-free one. Between 2013 and 2015 the Environment Agency, with Arun District Council, West Sussex County Council and Littlehampton Harbour Board, delivered a roughly £22 million tidal defence scheme on the Arun east bank that raised about 2.5 kilometres of defences, from Arun Parade near the river mouth through the town centre. The new walls were built to hold a 1-in-300-year storm surge and to allow for 100 years of predicted sea-level rise, protecting a large value of homes and businesses across the area.

Beyond that scheme, the Environment Agency's Lower Tidal River Arun strategy sets the long-term approach for managing flood risk along the river from Pallingham down to Littlehampton and Ford over the next 100 years, including maintaining and, in time, enhancing defences as the climate changes. For a developer, the key consequence is that the Environment Agency flood maps deliberately show the risk as if the defences were not there. That keeps the residual risk visible, which is why much of the town remains in Flood Zone 3 even behind good walls, and why a credible assessment has to test what happens if a defence is overtopped or breached.

Because the flood maps ignore the defences, a Littlehampton site can sit in Flood Zone 3 and still be developable — but only if the assessment models the residual breach and overtopping risk and shows the scheme stays safe for its lifetime.

Working out residual risk on a tidal site usually means hydraulic modelling and a clear-eyed look at finished floor levels, safe access and egress, and a flood warning and evacuation plan. Our note on residual flood risk explains the principle, and our flood modelling service derives the levels where the national mapping is too coarse to answer the question.

Planning policy and your flood authorities in Littlehampton

Two kinds of authority set the rules in Littlehampton. The Environment Agency leads on the tidal and main-river Arun and is the statutory consultee on higher-risk development. West Sussex County Council is the Lead Local Flood Authority, responsible for surface water, groundwater and ordinary watercourses, and the statutory consultee on surface-water drainage for major development. Arun District Council determines most applications and acts as the coastal erosion risk management authority.

Arun District Council published its Level 1 Strategic Flood Risk Assessment in March 2026, superseding the 2016 version and carrying climate-change data through to 2125. It assesses risk from fluvial, tidal, estuarial, groundwater, surface water and artificial-drainage sources, and it sits behind the Sequential Test that steers development to lower-risk land. The council also flags long-standing surface-water and drainage problems in the catchments of the Aldingbourne and Lidsey rifes, addressed through a Strategic Surface Water Management Study. On the drainage side, West Sussex County Council's Supplementary Requirements for Surface Water set the local standards a drainage strategy has to meet, and Arun tightened its drainage checklists in late 2025 so that assumed infiltration rates without test data no longer pass.

• Site-specific FRA. Normally required for development in Flood Zones 2 and 3, on sites of one hectare or more in Flood Zone 1, and wherever surface-water risk is mapped — which covers most of Littlehampton.
• Sequential and Exception Tests. A higher-risk Littlehampton site usually has to show, through the Sequential Test, that there is no reasonably available lower-risk site, before the application can proceed.
• Drainage to the local standard. Surface-water drainage must follow the SuDS hierarchy and the county's requirements, with infiltration evidenced by BRE 365 testing where it is relied on.
• Climate change over the lifetime. A tidal development must be shown safe against sea-level rise for its whole lifetime, usually taken as 100 years for housing.

Development in Littlehampton and what it means for your assessment

Littlehampton sees a steady mix of development that almost always touches flood risk: regeneration and infill around the harbour and town centre, residential schemes within the built-up area, conversions and changes of use near the seafront, and commercial and marine-related sites along the river. Because so much of this land sits in Flood Zones 2 and 3 behind tidal defences, the recurring challenge is not whether flood risk exists but how to demonstrate the scheme is safe despite it.

In practice that means getting finished floor levels right against the design tidal level plus freeboard, planning safe access and egress that works when the surrounding area floods, and showing that displaced floodwater is compensated rather than pushed onto neighbours. On a constrained estuary site, techniques such as raised floor levels, flood-resilient construction or, occasionally, floodable voids come into play. The Environment Agency and West Sussex County Council both expect this to be settled early, before a layout is fixed, which is where preliminary advice saves time and money later.

How Unda helps with flood risk assessment in Littlehampton

We are experts on Littlehampton and the Arun, not a faceless template. Our consultants have prepared flood risk assessments and drainage strategies across West Sussex and the South Coast, and we know how the tidal Arun behaves, how the local defences are designed and how West Sussex County Council and Arun District Council assess what comes in. A Senior Flood Risk Consultant oversees and signs off every report, and we stay involved past submission to answer the Environment Agency's and the council's questions rather than handing over a document and disappearing.

Whether you are a developer, a planning consultant, an architect, a homebuyer or an agent, you can talk a Littlehampton site through with a consultant who already understands the area. See how our flood risk consultants work, read more about Unda, or explore our wider coverage of West Sussex and Sussex, including neighbouring Worthing and Chichester.

Flood risk assessments for every situation in Littlehampton

People come to us for a flood risk assessment in Littlehampton for many reasons, and we prepare the right report for each. It helps to keep three things separate: a flood risk assessment, a sequential or exception test, and a drainage strategy are three distinct 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. Groundwater and flood modelling are not separate reports: groundwater is a source every assessment considers, and modelling is a technique that feeds one.

• Flood risk assessment for planning. The site-specific report that satisfies the NPPF and shows your development is safe for its lifetime without increasing risk elsewhere.
• Flood risk survey for property purchase. An independent, property-specific survey for buyers and their advisers, going beyond the conveyancing search to assess the actual building.
• Flood risk assessment for insurance. Property-level evidence for brokers and underwriters where cover has been restricted, declined or priced on flood risk.
• Flood risk assessment for BREEAM. Structured around BREEAM Pol 03 so a scheme keeps its flood and surface-water credits.
• Sequential and exception tests. The locational justification that a higher-risk site is the most appropriate available, prepared alongside the assessment.
• Groundwater flood risk. A defensible design groundwater level, tested against floor levels, basements and infiltration drainage.
• Flood modelling. 1D and 2D hydraulic modelling for tidal and river sites where national mapping does not reflect how the Arun behaves on the ground.
• Surface-water drainage strategy (SuDS). A scheme that manages runoff to the local standard, following the four pillars of SuDS and the drainage hierarchy.
• Discharge of drainage conditions. The detailed design that discharges a pre-commencement or pre-occupation drainage condition on a permission.
• Preliminary drainage design. An early read on infiltration and runoff before they affect your site layout and land value.

Local flood risk management and emergency contacts in Littlehampton

If you need to report flooding, sign up for warnings or understand who is responsible for what, these are the bodies that manage flood risk in and around Littlehampton. In a flood emergency that threatens life, always call 999.

For planning decisions, the statutory dataset is the Environment Agency's Flood Map for Planning, which now carries surface-water climate-change extents alongside the river and sea flood zones. The Environment Agency's wider role as statutory consultee is explained in our guide to the Environment Agency and planning.

Frequently asked questions about flood risk assessment in Littlehampton