Flood Risk Assessment in Somerset

Unda prepares compliant flood risk assessments and drainage strategies for commercial and residential development across Somerset, from the peat moors of the Levels to the tidal Parrett at Bridgwater and the surface-water hotspots of Taunton and Yeovil. A flood risk assessment in Somerset demonstrates to your local planning authority that a scheme will stay safe for its whole lifetime and will not increase flood risk anywhere else.

Few counties in England flood the way Somerset does. The Somerset Levels and Moors sit at or below the level of the rivers and tides meant to drain them, so the questions a planning officer asks here go beyond a desktop map. We assess every source that matters — river, tidal, surface water and groundwater — and deal directly with the Environment Agency and the relevant lead local flood authority on your behalf, guiding developers, planning consultants, architects and agents through to approval.

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

Flood risk assessment in Somerset at a glance

Somerset combines lowland river and tidal flooding on the Levels with surface-water risk in its towns, all under three separate lead local flood authorities. The headline points a developer needs to hold in mind:

• A floodplain by design. Much of the Levels and Moors lies at or below mean high-water spring tide, so the Parrett, Tone, Brue and Axe can only discharge at low tide — flooding here is natural, not an anomaly.
• 2026 was a major incident. Somerset recorded its second wettest January since records began in 1871, more than double the average rainfall, and a major incident was declared across the Levels and Moors.
• Three lead local flood authorities. Somerset Council, North Somerset Council and Bath & North East Somerset Council each run their own surface-water and drainage regime. The authority you deal with depends on where the site sits.
• Flood Zone 1 is not a free pass. Since the September 2025 Planning Practice Guidance update, surface-water risk can trigger an assessment even on a Flood Zone 1 site.

Check flood risk anywhere in Somerset

Somerset 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 to orient a site, not a substitute for a site-specific flood risk assessment.

Why is Somerset prone to flooding?

Somerset floods because much of it is a drained wetland. The Levels and Moors are a low-lying clay-and-peat basin where the land sits at or close to sea level, the gradients are minimal, and the main rivers can only discharge into Bridgwater Bay at low tide. Add one of the largest tidal ranges in the world in the Bristol Channel, intense rainfall on saturated upland catchments, and surface water in the built-up towns, and most sites here face more than one source of flooding at once.

Nearly all of central Somerset drains through the Parrett catchment. The River Parrett and the River Tone carry water off the Blackdown, Brendon and Quantock hills, while the Brue, the Axe and the Cary — the last running through the artificial King’s Sedgemoor Drain — drain the moors further north. Because the outfalls are tide-locked, the system leans on pumping stations, rhynes and clyces to move water when the rivers themselves are full. Knowing which watercourse drives the risk on a given site, and how the tide constrains it, is what a credible assessment has to pin down.

The Somerset Levels and Moors

The Levels (the coastal clay belt) and the Moors (the inland peat) were reclaimed over centuries and only stay dry through constant management. Glastonbury Tor and Athelney were islands in this wetland within recorded history, which tells you how readily the basin returns to water. For a developer this means a Somerset site can be technically in Flood Zone 3 yet show as lower risk on public maps because it sits behind defences — the planning flood map for planning deliberately ignores defences and shows the undefended floodplain.

Tidal and coastal flood risk

The Bristol Channel coast from Bridgwater Bay round to Weston-super-Mare and the Axe estuary carries serious tidal flood risk. Spring tides here can run more than 13–14 metres, among the highest on earth, and a storm surge on top of a high tide is the scenario the Bridgwater Tidal Barrier is being built to control. Tidal defences are designed to a 0.5% annual probability (1-in-200-year) standard rather than the 1% used for most rivers, which changes the design flood level your floor levels are measured against.

• Surface water is now the leading source. Across England, surface water affects more properties than rivers and the sea; in Somerset’s towns it is the risk most likely to catch out a Flood Zone 1 site. See our guide to surface-water flooding.
• Groundwater on the moors. Peat holds water like a sponge and the Mendip limestone can push water tables up without any river showing on a map — decisive for soakaways and basements. See groundwater flooding and what to submit on groundwater in planning applications.
• Defended does not mean safe. Pumps, banks and barriers reduce the chance of flooding, not the consequence if they are overtopped or fail — the residual risk a Somerset assessment has to characterise.

A history of flooding in Somerset

Somerset’s flood record is why its authorities scrutinise development so closely, and why a flood risk assessment in Somerset has to be evidence-led rather than generic. Each major event reshaped local policy and the defences a developer now designs around.

• 1607 — the Bristol Channel flood. On 30 January 1607 a surge, possibly a tsunami, drove far inland across the Levels, drowning an estimated 2,000 people in Somerset, Devon and Wales and inundating around 200 square miles. Markers on church walls still record the height.
• 1968 — the July floods. A summer deluge on 10 July 1968 overwhelmed Taunton and the wider West Country, a benchmark surface-water event still referenced locally. We cover it in remembering the great flood of 1968.
• 2013–14 — the winter the Levels drowned. Around 600 homes flooded and roughly 17,000 acres of the Moors lay under water for weeks; Muchelney, Thorney and Moorland were cut off, some reachable only by boat. The response triggered an 8km dredge of the Parrett and Tone and a 20 Year Flood Action Plan.
• 2026 — a major incident again. Somerset had its second wettest January since 1871; at Storm Chandra’s peak the Somerset Rivers Authority recorded 1.2 million cubic metres of water an hour moving down the Tone and Parrett. Around 100 properties flooded internally while defences and pumping protected a further 2,860.

In June 2026 the government awarded Somerset a one-off £50 million flood fund for a two-year programme — welcome money, but at an early stage, and no investment removes flood risk from a development site.

Do you need a flood risk assessment in Somerset?

You will normally need a flood risk assessment in Somerset if your site is in Flood Zone 2 or 3, is one hectare or larger in Flood Zone 1, or sits in an area at risk from surface water, groundwater or other sources — and increasingly even on smaller Flood Zone 1 sites where the local surface-water mapping shows a risk. Given how much of the county is tidal or low-lying, a large share of Somerset development triggers one.

Two kinds of authority set the rules. The Environment Agency leads on the main rivers, the Parrett and Tone tidal reaches and the coast. A lead local flood authority leads on surface water, groundwater and ordinary watercourses — and Somerset has three of them. Our overview of who manages flood risk in England explains how the pieces fit together.

Who is the Lead Local Flood Authority for Somerset?

It depends where the site is. Local government reorganisation merged Somerset County Council and the former district councils into a single unitary Somerset Council on 1 April 2023, so most of the county now has one lead local flood authority. North Somerset and Bath & North East Somerset remain separate unitary authorities, each its own LLFA, statutory consultee on surface-water drainage for major development.

On the Levels, a third layer applies. Large parts of the Moors fall within internal drainage board districts run by the Somerset Drainage Boards Consortium (the Parrett and Axe Brue boards), which maintain the rhynes and pumping stations and issue ordinary watercourse consents in their areas. We explain why internal drainage boards matter for planning.

The flood zones, the sequential and exception tests and the September 2025 PPG update together decide what your report must prove. On a constrained Somerset floodplain site the sequential test is frequently where an application is won or lost — the recent North Somerset case at Yatton turned on exactly that, and we cover what the Yatton appeal means for developers.

Drainage strategies and SuDS in Somerset

Most major Somerset schemes need a drainage strategy alongside the flood risk assessment, and on the Levels that strategy has to work with a tide-locked, pumped system rather than against it. The lead local flood authority will judge it against national policy, the 2025 National Standards for SuDS and the CIRIA SuDS Manual, and an unresolved drainage objection will usually stop the application being determined.

Infiltration is the first option in the drainage hierarchy, but on Somerset’s clay and peat with high water tables it frequently fails, so a credible strategy tests it early and keeps a discharge route ready. Where a site abuts a rhyne or ordinary watercourse, expect questions on riparian maintenance and consent.

• Design for all four pillars. Quantity, quality, amenity and biodiversity — LLFAs increasingly expect schemes to address all four pillars of SuDS, not just hydraulics.
• Discharge where the system can take it. On the Moors, discharge rates and volumes have to respect a pumped catchment with limited headroom; betterment on previously developed sites is often expected.
• Watercourses carry duties. A ditch or rhyne on your boundary brings riparian responsibilities, and works usually need ordinary watercourse consent from the LLFA or the internal drainage board.
• Get it in early. A weak strategy is the most common reason for an LLFA objection; sites in a critical drainage area face tighter requirements still.

Flood defences and residual risk in Somerset

Somerset is one of the most heavily managed flood landscapes in the country, and the defences are central to how a planning case is argued. The point a Somerset assessment must confront is that defences reduce the probability of flooding but never remove it — which is why defended sites stay inside the flood zones on Environment Agency maps.

• Bridgwater Tidal Barrier. A £249 million barrier on the Parrett at Bridgwater, in construction with Kier, will give a 0.5% (1-in-200-year) standard of protection to around 12,800 homes and businesses against tidal surge.
• The 20 Year Flood Action Plan. Drawn up after 2013–14 and overseen by the Somerset Rivers Authority, it combined dredging, pumping, banks and natural flood management across the Parrett and Tone catchments.
• Pumping and dredging. The Levels depend on permanent and mobile pumping and on maintained channel capacity; the 2014 response dredged 8km of the Parrett and Tone at a cost of around £6 million.
• Why your site is still in a flood zone. Maps show the undefended floodplain, so a defended Somerset site can sit in Flood Zone 3 yet rarely flood — we explain why that happens.

For development behind defences, the assessment has to characterise a breach or overtopping scenario — depth, velocity, hazard, onset and time to safety — and may need raised floor levels with freeboard, safe access and egress, and compensatory flood storage so displaced water is not pushed onto a neighbour.

Development and flood risk assessment in Somerset

Somerset’s development is as varied as its flooding, and the kind of site you bring forward shapes the scope you need. The right scope is the difference between a clean approval and a drainage or flood objection that holds an application up for months.

• Growth around the towns. Housing and employment land at Taunton, Bridgwater (with the Hinkley Point C supply chain) and Yeovil regularly pushes against Flood Zone 2 and 3 and the functional floodplain, which puts the sequential test front and centre.
• Rural and agricultural conversions. Barn conversions and farm diversification on the Levels almost always sit near a watercourse or in a flood zone, needing safe access and finished floor levels set against a credible design flood level.
• Coastal and estuary sites. Schemes at Burnham, Highbridge and along the Axe must reckon with the 1-in-200-year tidal standard and surge, not just river levels.
• Previously developed land. Town-centre and brownfield redevelopment brings surface-water betterment and SuDS retrofit into play, even where the river risk is low.

Climate change is not optional here. A Somerset assessment must apply the Environment Agency’s allowances for higher river flows, rainfall and sea levels over the development’s lifetime — generally 100 years for housing — which sets floor levels, freeboard and the attenuation a drainage scheme needs.

How Unda helps with flood risk assessment in Somerset

We act as the accurate translation layer between your scheme and the requirements set by the Environment Agency, the relevant Somerset lead local flood authority and national planning policy. We are experts on the county’s flooding and its tide-locked drainage, not a generic report mill, and a senior consultant signs off every report.

A flood risk assessment in Somerset from Unda assesses every credible source — the Parrett and Tone, the tidal coast, surface water, groundwater on the peat and any rhyne or 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 the council needs it, the drainage strategy sits alongside the assessment so the two cases stay consistent and an objection has nowhere to land. We are a CIWEM Business Partner with chartered members.

Our flood risk services for Somerset

• Flood risk assessment for planning. Site-specific reports that satisfy the Environment Agency and your Somerset LPA.
• Flood risk assessments and drainage. The full service, from desk study to drainage strategy and sequential-test support.
• Honest scoping and cost. We will tell you what you do and do not need; see what a flood risk assessment costs and why expertise matters.
• Other areas we cover. See the rest of the locations in our areas we cover.

Somerset flood resources and contacts

These authoritative sources are useful background for a Somerset site, though none replaces a site-specific assessment. Flood risk is also increasingly a property issue, not only a planning one — it can affect value, insurance and lending, as we cover in does flood risk affect house prices.

• Somerset Council — Lead Local Flood Authority. Local flood risk, SFRA and reporting: somerset.gov.uk.
• Somerset Rivers Authority. The 20 Year Flood Action Plan and the SRA Strategy 2024–34: somersetriversauthority.org.uk.
• Bridgwater Tidal Barrier Scheme. The Parrett tidal barrier and associated works: somerset.gov.uk.
• Somerset SuDS. Local sustainable drainage guidance for developers: somerset-suds.co.uk.
• GOV.UK — Somerset Levels and Moors. The Environment Agency programme for reducing flood risk on the Levels: gov.uk.
• Check for flooding. The Environment Agency’s live warnings and long-term risk service: check-for-flooding.service.gov.uk.

Flood risk assessment in Somerset: frequently asked questions