Flood Risk Assessment in West Berkshire

West Berkshire is a single unitary council, which makes it one of the more straightforward authorities to submit to and one of the more demanding. The same organisation determines your planning application and, as the Lead Local Flood Authority, decides whether your drainage stands up. Unda prepares flood risk assessments and drainage strategies that satisfy both sides of West Berkshire Council in one go.

The requirements here are set by an up-to-date development plan. The West Berkshire Local Plan Review 2023–2041 was adopted in June 2025, and its Policy SP6 pulls flood risk and sustainable drainage into one test that every application in a flood-risk or critical-drainage location has to pass. We read your site against SP6, against the council’s 2022 Strategic Flood Risk Assessment and its SuDS guidance, and against the surface-water rules that apply across Newbury and Thatcham, then deal directly with the council and the Environment Agency on your behalf. Whether the report is needed for planning, a property purchase, a mortgage or insurance, BREEAM, or a standalone surface-water drainage strategy, the goal is the same: defensible evidence that gets a decision without a flood or drainage objection.

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

Because West Berkshire is both the planning authority and the Lead Local Flood Authority, one body signs off your flood risk and your drainage — and under Policy SP6 it applies the sequential test strictly across the district, holds new development to greenfield runoff rates, and caps redevelopment at half the existing runoff.

Flood risk and drainage for West Berkshire planning at a glance

• One authority for both jobs. West Berkshire Council is a unitary authority, so it is the local planning authority that decides the application and the Lead Local Flood Authority that assesses surface-water drainage. There is no separate county tier to satisfy.
• The plan is current. The West Berkshire Local Plan Review 2023–2041 was adopted in June 2025. Policy SP6 (flood risk and sustainable drainage) and Policy DM7 (water resources and waste water) are the flood and drainage backbone, and SP6 replaced the old Core Strategy Policy CS16.
• Redevelopment is expected to improve runoff. New development on greenfield land must restrict runoff to greenfield rates and volumes up to the 1-in-100-year event plus climate change; on previously developed sites the council will accept a maximum discharge of 50% of the existing 1-in-100-year runoff rate.
• Newbury and Thatcham are a special case. The Environment Agency designated them a nationally significant surface-water Flood Risk Area, so every development there — whatever its size — needs a Surface Water Drainage Strategy.
• It is a water-stressed district. Under Policy DM7 new homes must meet the tighter 110 litres per person per day water-efficiency standard, because West Berkshire sits in a seriously water-stressed catchment served by Thames Water.

Who decides flood risk and drainage in West Berkshire?

Two national bodies and one council set the rules for a West Berkshire site. The Environment Agency leads on the main rivers — the Kennet, the Lambourn, the Pang, the Enborne and the Thames along the northern boundary. West Berkshire Council leads on everything else: as the planning authority it determines the application, and as the Lead Local Flood Authority it is the statutory consultee for surface water and sustainable drainage.

Because West Berkshire has been a unitary authority since 1998, there is no county council in the middle. The council’s own drainage team responds to your drainage strategy, while the Environment Agency is consulted where a main river, the functional floodplain or its standing advice is engaged. Thames Water is the sewerage undertaker for the whole district and a consultee where a connection or capacity question arises. Understanding the role the Lead Local Flood Authority plays, and how it differs from the Environment Agency’s planning role, is the difference between a strategy that lands first time and one that draws an objection.

Does a West Berkshire application need a flood risk assessment or a drainage strategy?

Policy SP6 sets out exactly when a site-specific flood risk assessment is required in West Berkshire, and it goes further than a simple flood-zone test. You will need one for any development over one hectare even in Flood Zone 1, for anything in Flood Zone 2 or 3 or within the 1-in-100-year extent plus climate change, for smaller Flood Zone 1 sites that could flood from another source, and for any site in an area the council or the Environment Agency has flagged for critical drainage problems.

A drainage strategy answers a different question — where the surface water goes and how discharge is held within limits — and it is triggered separately. A flood risk assessment, a sequential or exception test and a surface-water drainage strategy are three distinct reports. They often travel together in a West Berkshire submission, but they answer three questions: is the site safe, should the development be here, and where does the water go. Getting the scope right is how you avoid a planning application being invalidated. Our guide to when a flood risk assessment is required sets out the national triggers, and the table below shows how West Berkshire applies them.

West Berkshire’s Local Plan flood and drainage policies

The adopted development plan for West Berkshire is the Local Plan Review 2023–2041, adopted in June 2025. Two policies carry the flood and drainage requirements an applicant has to satisfy: Policy SP6 on flood risk and sustainable drainage, and Policy DM7 on water resources and waste water. Naming them, quoting them and designing to them from the outset is what keeps a scheme moving.

Policy SP6 — flood risk and sustainable drainage

Policy SP6 requires the sequential, risk-based approach to be applied strictly across West Berkshire, so development is steered to the lowest-risk land first and only permitted in a flood-risk area where the sequential test, and where necessary the exception test, are passed. In the functional floodplain (Flood Zone 3b) only water-compatible uses and essential infrastructure are supported. Where development is justified, SP6 requires it to be safe for its lifetime with an appropriate climate change allowance, to provide safe access and egress in the 1-in-100-year plus climate change event, and not to reduce floodplain storage. It also sets the district’s surface-water rules: greenfield runoff rates and volumes on undeveloped sites, a 50% reduction on previously developed sites, an undeveloped 10-metre buffer alongside main rivers, and SuDS in accordance with the council’s SuDS Supplementary Planning Document. This policy is the reason a West Berkshire assessment has to be evidence-led rather than generic.

Policy DM7 — water resources and waste water

Policy DM7 requires foul flows to be drained separately from surface water to a suitable point of connection, and it bars surface water from discharging to the foul sewer — a common cause of sewer flooding. Because West Berkshire lies in a seriously water-stressed area served by Thames Water, DM7 sets a tighter water-efficiency standard of 110 litres per person per day for new homes, with a BREEAM “excellent” water standard for larger non-residential schemes. It protects Source Protection Zones, where only certain types of SuDS are acceptable and must be agreed with the Environment Agency, and it allows the council to phase development where the treatment works at Chieveley, Hungerford or Newbury are near their capacity. For many sites the practical work is proving a clean foul connection and demonstrating that infiltration or discharge will not harm groundwater. Our note on water neutrality explains why the water-stress angle matters here.

West Berkshire’s SuDS and drainage requirements

Drainage is where most West Berkshire applications succeed or stall, because the council reviews surface water itself as the Lead Local Flood Authority. The discharge rules under Policy SP6 are specific: on undeveloped land, runoff must be held to greenfield rates and volumes for all events up to the 1-in-100-year storm plus climate change; on previously developed land, the council will accept a maximum discharge of 50% of the existing 1-in-100-year runoff rate. In both cases the aim is betterment, not a like-for-like continuation of the old runoff.

The design has to follow the drainage hierarchy set out in the council’s SuDS Supplementary Planning Document (adopted December 2018) and the CIRIA SuDS Manual (C753): reuse and store, then infiltrate, then discharge to a watercourse, with the surface-water sewer as a last resort. Infiltration has to be proven, not assumed — the chalk and clay-with-flints across the Berkshire Downs behave very differently, so BRE 365 infiltration testing is expected wherever soakaways are proposed. Where the ground will not infiltrate, the strategy has to attenuate and discharge at the restricted rate. Designing to the four pillars of SuDS — quantity, quality, amenity and biodiversity — is how you pre-empt an LLFA objection rather than answer one after the event.

• No surface water to the foul sewer. Policy DM7 requires foul and surface water to be drained separately — connecting surface water to the foul system is a standard reason for refusal and later sewer flooding.
• Prove the ground before you rely on it. The council expects infiltration to be evidenced by infiltration testing to BRE 365, not assumed from a desk study — screen the geology first with our free ground conditions and soakaway map.
• Newbury and Thatcham always need a strategy. Their nationally significant surface-water designation means a Surface Water Drainage Strategy accompanies every application, however small.
• Maintenance and adoption matter. The council wants to see who maintains the SuDS for the lifetime of the development, in line with how local planning authorities handle flood and SuDS.

The West Berkshire Strategic Flood Risk Assessment

West Berkshire Council published a Level 1 Strategic Flood Risk Assessment in November 2022, agreed with the Environment Agency, to support the Local Plan Review. It maps flood risk from every source across the district — fluvial, surface water, groundwater, sewers and reservoirs, now and with climate change — and it is the evidence base the council uses to apply the sequential test and to test allocation sites.

Two features of the SFRA shape individual applications. First, it carries a Cumulative Impact Assessment addendum that identifies river catchments sensitive to the combined effect of development; where a catchment is highly sensitive, every proposal there must be accompanied by a Surface Water Drainage Strategy. Second, it reflects the Environment Agency’s designation of Newbury and Thatcham as a nationally significant surface-water Flood Risk Area. Reading your site against the SFRA before you design is the quickest way to know whether the functional floodplain, a critical drainage area or the cumulative-impact rule applies. Our overview of what a Strategic Flood Risk Assessment does explains how it feeds a site-specific report, and you can screen the flood zones yourself on the Flood Map for Planning.

What must accompany a West Berkshire application to validate

An application to West Berkshire is validated against the council’s local list as well as the national requirements. On flood risk and drainage, the documents that most often decide whether an application is registered or returned are a proportionate flood risk assessment where Policy SP6 is triggered, and a drainage strategy or Surface Water Drainage Strategy where the site or its location demands one.

• A flood risk assessment that addresses every source SP6 lists — fluvial, surface water, groundwater, sewers and reservoirs — and applies the correct climate change allowances over the development’s lifetime.
• A drainage strategy that follows the SuDS hierarchy and holds discharge to greenfield rates, or to 50% of existing runoff on redevelopment, with infiltration evidenced where it is claimed.
• A Surface Water Drainage Strategy for any site in Newbury or Thatcham, or in a catchment the Cumulative Impact Assessment flags as highly sensitive, whatever the size.
• A sequential test where the site sits in Flood Zone 2 or 3, or covers a hectare or more, unless the allocation already covers it.
• The right level of detail. Reports have to be proportionate to the proposal — too little and it is returned, as our note on the drainage information needed for planning explains.

How national flood and drainage policy applies in West Berkshire

West Berkshire’s local policies sit on top of the national framework, and both have to be satisfied. The National Planning Policy Framework and its Planning Practice Guidance set the sequential and exception tests, the flood-zone approach and the expectation of sustainable drainage on major development; Policy SP6 then applies them strictly and adds the district’s own discharge rules.

In practice that means a West Berkshire assessment has to argue the correct flood zone and vulnerability classification, apply the NPPF sequential approach, and account for residual risk behind any defence. Since the 2025 Planning Practice Guidance update, surface water on the Flood Map for Planning can trigger an assessment even on a Flood Zone 1 site, which matters across the low-lying, surface-water-prone parts of the district. On drainage, the national SuDS standards and the CIRIA guidance shape what the council will accept, and the Environment Agency’s standing advice governs many of the smaller applications.

Local flood risk in West Berkshire’s area

West Berkshire is shaped by chalk and river valleys, and that geology drives the flood risk. The Kennet threads west to east through Newbury, Thatcham and Theale; the Lambourn and the Pang are chalk streams that rise and fall with groundwater; and the Thames runs along the northern edge past Pangbourne, Purley and Streatley. Surface water and groundwater matter here as much as the rivers.

The defining event is the flash flooding of July 2007, when intense rainfall over the hills north of Thatcham surged down through the town and overwhelmed culverted streams and surface-water sewers, flooding well over a thousand properties in Thatcham alone and inundating parts of Newbury. It is the reason the Thatcham flood alleviation scheme was built and the reason the town’s surface-water rules are now so firm. Groundwater flooding from the chalk followed again in the winter of 2013–14. For the full picture of the rivers, the chalk and the flood history across the county, see our flood risk assessment in Berkshire page; for a single site, we read the groundwater and critical drainage picture alongside the river maps.

How Unda helps with flood risk and drainage in West Berkshire

We act as the accurate translation layer between your scheme and what West Berkshire Council requires as both planning authority and Lead Local Flood Authority. We know Policy SP6 and DM7, the 2022 SFRA, the SuDS SPD and the Newbury and Thatcham surface-water regime, and we design to them from the first sketch rather than reworking a scheme after an objection.

A West Berkshire report from Unda assesses every credible source of flooding, compares modelled levels against your proposed floor levels, sets safe access and egress, and proposes drainage that holds discharge to the council’s greenfield or 50% rule. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report and stays involved to answer the council’s comments. Where the application needs a drainage strategy alongside the flood risk assessment, we prepare both so the two cases stay consistent and an objection has nowhere to land.

Flood risk and drainage services for every situation in West Berkshire’s area

A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports that answer different questions. We prepare all three for West Berkshire sites, alongside the right form of assessment for buyers, lenders and BREEAM, so whatever the reason for the report, the evidence stands up to the council and the Environment Agency.

Flood risk assessments

• Flood risk assessment for planning. The core report, site-specific and prepared to satisfy Policy SP6, the NPPF and West Berkshire Council, with groundwater and any modelling assessed within it.
• Homebuyer and property-purchase survey. For conveyancing, where a search has flagged Kennet-valley, Thames 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 report alone rarely satisfies it.
• Groundwater flood risk. A defensible design water table for chalk and river-valley sites and any basement — assessed as a source within the flood risk assessment, or as a standalone hydrogeological study on complex sites.

Sequential and Exception Tests

The Sequential and Exception Tests are a separate, locational report about whether a development should be in a higher-risk location at all. West Berkshire applies the sequential test strictly under Policy SP6, so on a Flood Zone 2 or 3 site the test usually has to be argued unless an allocation already covers it. A clean site-specific assessment showing the development is not actually at risk can remove the need at application stage.

Drainage strategy and SuDS

• Sustainable drainage strategy (SuDS). Surface-water engineering that calculates existing versus proposed runoff and proposes SuDS to hold discharge to greenfield rates, or 50% of existing runoff on redevelopment.
• Preliminary drainage design. The early, outline read that flags infiltration issues in the chalk and clay before they affect layout and land value.
• Discharge of drainage conditions. The detailed stage to discharge a pre-commencement or pre-occupation drainage condition set by the council.
• Flood modelling. 1D and 2D hydraulic modelling — a technique that feeds the assessment, sequential test or drainage design where the national mapping is not enough.

Early in a drainage strategy it helps to know whether the ground will take water: our free BRE 365 infiltration rate calculator and drainage calculators give an indicative read before a trial pit, you can screen a postcode on our flood risk map, and every report is overseen by a chartered flood risk consultant who stays involved past the report to answer the council’s comments.

West Berkshire flood risk and drainage: frequently asked questions