Flood Risk & Drainage Requirements for Somerset Council

Somerset Council is one of England's newest unitary authorities, and that changes what a planning application here has to prove. Since 1 April 2023 a single council both determines your application as the local planning authority and signs off your surface water drainage as the Lead Local Flood Authority — while still judging flood risk against four different Local Plans inherited from the former districts. Getting a scheme through means answering the right authority, under the right policy, with the right flood risk assessment and drainage strategy.

We prepare the flood risk assessments and surface water drainage strategies that developments across Somerset need — for planning, property purchase, mortgage and insurance, and BREEAM — alongside sequential and exception tests, groundwater assessment and flood modelling. Whether the site sits on the tidal Parrett at Bridgwater, the surface-water-prone streets of Taunton and Yeovil, or the peat moors of the Levels, we deal directly with Somerset Council's drainage team, the Environment Agency's Wessex area and the Internal Drainage Boards on your behalf, and stay with the application through to a decision.

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

Somerset's real trap is not the Levels — it is that the same council writes the flood-risk rules under one of four legacy Local Plans and the drainage rules as the Lead Local Flood Authority, and a scheme has to satisfy both, to a local discharge standard that is tougher than national policy.

Flood risk and drainage for Somerset Council planning: at a glance

• One council, two roles. Somerset Council is a unitary authority, so it is both the local planning authority that decides your application and the Lead Local Flood Authority (LLFA) that reviews your surface water drainage. There is no separate county tier.
• Four Local Plans still apply. Until the Somerset Local Plan 2045 is adopted (expected 2029), flood and drainage policy depends on where the site sits — the Mendip, Sedgemoor, South Somerset or Somerset West & Taunton plan.
• The flagship flood policies are Mendip Policy DP23, Sedgemoor Policy D1, South Somerset Policy EQ1 and, in the Taunton and West Somerset areas, Taunton Deane Core Strategy Policy CP1 and West Somerset Policy CC2.
• A demanding discharge standard. Surface water runoff must be held to the greenfield rate across the 1-in-1, 1-in-30 and 1-in-100-year events, with a hard 2 litres per second per hectare cap in the River Tone catchment, and pumped SuDS are not accepted.
• Internal Drainage Boards and the Somerset Rivers Authority also shape drainage on and around the Levels, so a site draining into a board watercourse needs separate consent.

Who decides flood risk and drainage in Somerset?

Two questions decide who you answer to. Somerset Council decides the planning application and, as the Lead Local Flood Authority, reviews surface water drainage on major schemes. The Environment Agency leads on the main rivers and tidal flooding, and on the Levels the Internal Drainage Boards and the Somerset Rivers Authority add a layer no other English county carries in quite the same way.

Because Somerset is a unitary, the flood risk assessment and the drainage strategy are often read inside the same organisation — but by different teams applying different tests. Planning officers, arranged into area-based teams that still reflect the former districts, weigh the flood-risk case against the relevant Local Plan. The council's drainage team, as the LLFA, is a statutory consultee on surface water for major development and applies Somerset's own SuDS design standards. Our guides to what a local planning authority does and the role of the Lead Local Flood Authority explain how the two hats fit together.

Which Local Plan applies to your Somerset site?

This is the question that catches applicants out. Somerset Council inherited four district Local Plans when it formed in 2023, and until a single Somerset Local Plan replaces them, the flood and drainage policy your application is judged against depends entirely on which former district the site falls in. A scheme in Frome answers to a different policy from one in Bridgwater, Yeovil or Taunton.

The four plans still in force are the Mendip District Local Plan, the Sedgemoor Local Plan, the South Somerset Local Plan and the two plans of the former Somerset West & Taunton area (the Taunton Deane plans and the West Somerset Local Plan). A new Somerset Local Plan 2045 is being prepared under the government's plan-making system, with adoption expected in 2029 — so for now the district policies below remain the test. The council's own Somerset SuDS design standards then sit on top of all of them as the common drainage rulebook.

Somerset's Local Plan flood and drainage policies

Each inherited Local Plan carries its own flood-risk and water-management policy, and naming the right one is the difference between an assessment that reads as local and one a case officer sends back. The table sets out the flagship codes; the notes that follow explain what each requires and where it applies.

Policy DP23 and DP8 — the Mendip area (Frome, Shepton Mallet, Wells, Glastonbury, Street)

Policy DP23 of the Mendip Local Plan requires development to follow a risk-based, sequential approach to flooding and is specifically alert to the steep Mendip catchments that turn heavy rainfall into a fast flood peak. Alongside it, Policy DP8 requires development to have a neutral or positive impact on the water quality of rivers and groundwater, which is why a Mendip-area drainage strategy has to build in treatment as well as attenuation. Both were adopted in the Mendip Local Plan Part I in December 2014, with the Sites and Policies Part II adopted in December 2021.

Policy D1 — the Sedgemoor area (Bridgwater, Burnham-on-Sea, Highbridge, Cheddar)

Sedgemoor Policy D1, Flood Risk and Surface Water Management, sets a higher bar than most: development should provide an overall reduction in existing flood risk at the site, not merely avoid making it worse. On the tidal Parrett and across the Levels that is a demanding test, and it is why a Sedgemoor scheme benefits from a drainage strategy designed for betterment from the outset. The policy sits in the Sedgemoor Local Plan 2011–2032, adopted in February 2019.

Policy EQ1 — the South Somerset area (Yeovil, Chard, Crewkerne, Wincanton)

South Somerset Policy EQ1, Addressing Climate Change in South Somerset, requires development to account for the increased flood risk climate change brings and to integrate adequate sustainable drainage. It was adopted in the South Somerset Local Plan 2006–2028 in March 2015. On a Flood Zone 1 site here, the surface water and drainage half of the case is usually what a scheme turns on rather than a river.

Policies CP1 and CC2 — the Taunton and West Somerset areas

In the former Somerset West & Taunton area, flood risk is governed strategically by Taunton Deane Core Strategy Policy CP1 (Climate Change), adopted in 2012, with the detailed development-management requirements carried in the Site Allocations and Development Management Plan adopted in 2016. In the former West Somerset area, Policy CC2 of the West Somerset Local Plan to 2032 (adopted November 2016) manages coastal and fluvial flood risk, while land within Exmoor National Park is dealt with by the National Park Authority as a separate planning authority.

Does a Somerset application need a flood risk assessment or a drainage strategy?

Most Somerset applications in Flood Zones 2 and 3, all sites of a hectare or more, and every major development need a flood risk assessment, a surface water drainage strategy, or both. Somerset Council brought in a single Local Validation Checklist on 1 April 2025, so the documents an application must arrive with are now consistent across the county — and an application that is missing them is not registered.

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 at all, and where does the surface water go. Getting the scope right is what avoids the drainage objection our note on an LLFA objection to a planning application describes, and the validation refusal covered in why an application is invalidated for flood risk and drainage.

You can screen a site in a couple of minutes on our free flood risk map, and our guide to when you need a flood risk assessment walks through the triggers in full. The full list of documents a Somerset application must include is published on the council's information requirements for planning applications page.

Somerset's drainage and SuDS requirements as Lead Local Flood Authority

Somerset's drainage rules are where this authority is most demanding, and where most schemes come unstuck. As the Lead Local Flood Authority, the council applies its own Somerset SuDS design standards, which hold surface water runoff to the greenfield rate across every design event, impose a stricter cap in the River Tone catchment, and rule out pumped systems altogether. A drainage strategy built to these standards from day one is the surest route past a drainage objection.

The starting point is the SuDS hierarchy and the four pillars of SuDS: rainwater re-use first, then infiltration, then discharge to a watercourse, with a sewer connection only as a last resort. Somerset then layers its own numbers on top. Our surface water drainage strategy service builds the scheme to these figures, and where the ground may take water our free geology and ground conditions map, BRE 365 infiltration rate calculator and drainage calculators give an early read before a trial pit.

Two Somerset-specific points catch schemes out. Groundwater is the first: on the Levels and in the river valleys a high water table can defeat infiltration and rule out soakaways, so early evidence and, where needed, our groundwater flood risk assessment matter. The Internal Drainage Boards are the second: if a site lies in, or discharges into, an Axe Brue, Parrett or North Somerset Levels board district, byelaw consent from the Somerset Drainage Boards Consortium is needed alongside the planning application. The national picture behind the local rules is set out in the 2025 national SuDS standards, and the detailed figures are published in Somerset's own SuDS design standards.

Somerset's Strategic Flood Risk Assessment

A Strategic Flood Risk Assessment (SFRA) is the council's own map of where flooding constrains development, and it is the evidence the sequential test is argued against. Somerset currently relies on the SFRAs inherited from the former districts while a new county-wide SFRA is prepared for the emerging Somerset Local Plan 2045.

In practice that means a site in the Sedgemoor area is read against the Sedgemoor Level 1 and Level 2 SFRAs, the South Somerset and Taunton areas against the 2019 western SFRA, and the Mendip area against its 2020 assessment, until the new Somerset SFRA supersedes them. An SFRA does not replace a site-specific flood risk assessment — it sets the strategic context the assessment then tests at the site scale. Our explainer on what Strategic Flood Risk Assessments are sets out how they feed the sequential test and site allocations.

How national flood and drainage policy applies in Somerset

Somerset's local rules sit on top of national policy, not instead of it. The National Planning Policy Framework and its Planning Practice Guidance set the sequential, risk-based approach every English authority follows, and Somerset applies them through its Local Plans and validation list.

The NPPF steers development towards lower-risk land and, where a higher-risk site is involved, brings in the sequential and exception tests. The September 2025 update to the Planning Practice Guidance extended the sequential test to all flood sources, so surface water alone can now trigger it even in Flood Zone 1. National climate change allowances must be applied over the development's lifetime — generally 100 years for housing — which sets finished floor levels, freeboard and how much attenuation a drainage scheme needs, as our guide to climate change allowances for planning explains. Where the details of what an application must show are involved, our NPPF flood risk guidance and our note on the drainage information needed for planning permission set out the requirements in full.

Flood risk across Somerset

Few counties in England flood the way Somerset does, and the risk changes completely across the county. The tidal Parrett threatens Bridgwater, surface water overwhelms drains in Taunton and Yeovil, and the peat moors of the Levels flood slowly and for weeks when the embanked rivers spill and the drainage tide-locks against the Severn Estuary. For the full physical picture, see our flood risk in Somerset area guide.

• The Levels and Moors. A low basin drained by the Parrett, Tone, Brue, Axe and Yeo, where water is moved by gravity and pumps and can sit for weeks. The 2013–14 Somerset Levels floods put hundreds of properties under water and cut off villages for weeks.
• Bridgwater and the tidal Parrett. The most exposed town, where the Bridgwater Tidal Barrier is being built to protect thousands of homes and businesses against tidal and river flooding, expected to be operational later this decade.
• Taunton and the River Tone. River and surface water risk together, managed by the Taunton flood alleviation scheme — and the reason for the strict 2 litres per second per hectare discharge cap in the Tone catchment.
• Recent events. A major incident was declared across the Levels and Moors in January 2026 after the county's second-wettest January on record, and in June 2026 the government announced a £50 million fund to strengthen Somerset's flood resilience.

How Unda helps with Somerset applications

We are experts on how Somerset Council decides flood risk and drainage, and on how its consultees behave in practice. We act as the accurate translation between your scheme and the requirements set by the council, the Environment Agency and the Internal Drainage Boards, so the flood risk assessment and the drainage strategy tell one consistent story.

On Somerset schemes we have taken outline applications through to an Environment Agency no-objection by restricting discharge into a main river to the greenfield runoff rate, and we know the council's drainage team will scrutinise how surface water from access roads is held on site up to the exceedance event, how gullies intercept flow, and how attenuation under a carriageway affects road adoption. That is the level of detail a Somerset drainage strategy is read at. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report; a surface water drainage strategy sits alongside the flood risk assessment as a separate report so a drainage objection has nowhere to land.

Flood risk and drainage services for every situation in Somerset

A flood risk assessment, a sequential or exception test and a drainage strategy answer different questions, and the right report depends on why you need it. We prepare each of these across Somerset, for planning and beyond.

Flood risk assessments

• Flood risk assessment for planning. The core report, site-specific and prepared to satisfy the relevant Somerset Local Plan, the Environment Agency and national policy.
• Homebuyer and property-purchase survey. For conveyancing, where a search has flagged Levels, tidal or surface water risk and you need the actual building assessed, not a broad map.
• Flood risk assessment for insurance. Property-specific evidence for brokers and underwriters where premiums have risen or cover has been restricted.
• Flood risk assessment for BREEAM. Structured around BREEAM Pol 03, which is credit-driven rather than safety-driven, so a planning FRA alone rarely satisfies it.
• Groundwater flood risk. A defensible design water table for Levels and river-valley sites and any basement or soakaway — assessed within the FRA, or as a standalone hydrogeological report.

Sequential and exception tests

The sequential and exception tests are a separate, locational report about whether a development should be in a higher-risk part of Somerset at all. The sequential test defines an area of search, identifies reasonably available lower-risk sites and justifies the proposed one; the exception test is the second gate where development still needs to proceed.

Drainage strategy and SuDS

• Sustainable drainage strategy (SuDS). Surface-water engineering that calculates existing versus proposed runoff and holds discharge within Somerset's greenfield and Tone-catchment limits.
• Preliminary drainage design. The early, outline read that flags infiltration and groundwater issues before they affect layout and land value.
• Discharge of drainage conditions. The detailed stage to discharge a pre-commencement or pre-occupation drainage condition.
• Flood modelling. 1D and 2D hydraulic modelling that feeds the assessment or drainage design where the national maps are not enough — often the case along the Parrett and Tone.

You can watch the Parrett, Tone and the county's other rivers on our live river levels map, and every report is overseen by a chartered flood risk consultant who stays involved past the report to answer objections. Our guide to flood risk assessment cost explains how a fixed fee is scoped.

Somerset flood risk and drainage: frequently asked questions