Flood Risk & Drainage Requirements for West Oxfordshire District Council

West Oxfordshire District Council now asks for a flood risk assessment with every major planning application, whatever the flood zone. It also wants a surface water drainage strategy with any development in Flood Zone 2 or 3, minor schemes included. Those requirements sit in the council's validation checklists, revised on 20 July 2026, alongside Policy EH7 (Flood risk) of the West Oxfordshire Local Plan 2031, adopted on 27 September 2018. Oxfordshire County Council reviews the drainage on major schemes as the Lead Local Flood Authority, against standards it rewrote in June 2026.

This page explains what West Oxfordshire District Council (WODC), Oxfordshire County Council and the Environment Agency each require on flood risk and drainage, policy by policy, and what our reports contain to meet each requirement. The district takes in Witney, Carterton, Chipping Norton, Woodstock, Burford, Charlbury, Eynsham and the villages of the Windrush, Evenlode and upper Thames valleys. To talk through a site, call 01293 214444 or email enquiries@unda.co.uk.

West Oxfordshire, Oxfordshire County Council or the Environment Agency: who decides what?

West Oxfordshire is a two-tier area, so the planning decision and the drainage advice come from different councils. WODC registers the application against its own checklists and decides it against the Local Plan, any made neighbourhood plan and Chapter 18 of the NPPF. Oxfordshire County Council comments on surface water only for major development. The Environment Agency advises on fluvial flood risk in Flood Zones 2 and 3 and on work within 20 metres of a Main River.

That structure may change. On 16 July 2026 the government announced it was minded to replace the seven existing councils of Oxfordshire and West Berkshire with three unitary authorities from 1 April 2028, with most of West Oxfordshire going into a new Northern Oxfordshire Council. On 7 September 2026 it said it would review its reorganisation decisions across England, and Oxfordshire County Council reported the provisional decision paused. Until anything is confirmed, WODC stays the planning authority and the county the Lead Local Flood Authority. Our guide to local government reorganisation and flood risk planning covers what a change of council means for a live application, and our explainer on what a Lead Local Flood Authority does sets out the county's part.

Policy EH7 and the other West Oxfordshire flood and drainage policies

Four policies of the 2018 Local Plan bear on flood risk and drainage, and EH7 does most of the work. The Salt Cross Area Action Plan, adopted in February 2026, adds a stricter water policy for the garden village north of Eynsham. Five of the district's ten made neighbourhood plans have policies of their own on drainage or flood risk. Policy EH8 replaced the water policies of the 2006 Local Plan, including Policy NE7 (The Water Environment), when the 2031 plan was adopted in September 2018.

Requirements checked November 2026, against the adopted Local Plan 2031, the Salt Cross Area Action Plan, the made neighbourhood plans, the Regulation 19 draft Local Plan 2043, the July 2026 validation checklists and Oxfordshire County Council's June 2026 guidance.

Policy EH7 (Flood risk): what West Oxfordshire asks of every application

Policy EH7 manages flood risk through the sequential, risk-based approach, and it asks for a site-specific flood risk assessment on "all proposals of 1ha or more and for any proposal in Flood Zone 2 and 3 and Critical Drainage Areas". In the functional floodplain, "only water compatible uses and essential infrastructure will be allowed" (Local Plan 2031). The policy also requires every source of flooding to be addressed, sewer and surface water flooding included, with resilient and resistant measures and sustainable drainage whose long-term maintenance is secured.

Two expectations that applicants attribute to EH7 sit in its supporting text, not the policy. Paragraph 8.60 says development should not increase surface water runoff and should show betterment in rate and volume where possible, and paragraph 8.61 requires SuDS on all major development unless shown to be inappropriate. Officers apply both. Our flood risk assessments answer each bullet of EH7 in turn, with the sequential evidence in a separate report where the site needs one, and the drainage strategy shows the runoff comparison paragraph 8.60 asks for.

Policy EH8 (Environmental protection) and Policy OS3 (Prudent use of natural resources): water quality and water use

Policy EH8 accepts development only where there is "no adverse impact on water bodies and groundwater resources, in terms of their quantity, quality and important ecological features". Its supporting text singles out the Source Protection Zone for Chipping Norton's public water supply, which matters for any soakaway on the limestone there. Policy OS3 asks every proposal to show consideration of "minimising risk of flooding" and "making use of appropriate sustainable drainage systems", and expects new homes to meet the optional standard of 110 litres per person per day. Our guide to groundwater Source Protection Zones explains how the zones limit infiltration.

Policy WIT2 (North Witney Strategic Development Area): runoff below greenfield and the Hailey Road Drain

Policy WIT2 allocates about 1,400 homes north of Witney and goes further than EH7 on runoff: criterion (l) asks for post-development rates "attenuated to achieve a reduction in greenfield run-off rates", which may include off-site solutions. Criterion (m) steers all development to Flood Zone 1 and asks for flood alleviation for the Hailey Road Drain where appropriate. The draft 2043 plan keeps WIT2 in force, so a reserved matters or condition submission on this site is still judged against it.

Salt Cross Area Action Plan Policy 10 (Water environment): building clear of the future floodplain

The Salt Cross Garden Village Area Action Plan, adopted on 25 February 2026, sets the strictest flood line in the district: "Built development will need to be located outside the 70% climate change fluvial flood extent" (Salt Cross AAP). Every major application there needs a detailed flood risk assessment with cumulative impacts and a look at flood betterment for Eynsham downstream. It also needs evidence of water sensitive design and an exemplar SuDS scheme, informed by infiltration testing, groundwater monitoring and greenfield rates for each sub-catchment. Where the county or the Environment Agency asks for it, the ordinary watercourses on the site must be modelled to define the flood zones, which is work our flood modelling service carries out.

Charlbury Policy NE8 (Flood Risk and Water Quality Management) and Eynsham Policy ENP2 (Design)

Charlbury's neighbourhood plan, made on 14 June 2021, says "Sustainable Urban Drainage Systems will be required for all developments and measures should be taken to reduce surface water run-off for greenfield sites" (Charlbury plan). That reaches a single house in the parish, well below the county's major-development threshold, and the policy does not support schemes that would harm water quality in the Evenlode catchment. In Eynsham, clause E of Policy ENP2 asks for sustainable drainage "in line with national guidelines", and the plan's supporting text points to flash flooding along the Chil Brook.

Chipping Norton Policy BD9 (Sustainable drainage systems) and Policy BD10 (Water supply and sewerage)

Chipping Norton's plan, made on 15 March 2016, expects developments of ten or more homes and major commercial schemes to "provide and incorporate sustainable drainage systems unless it is demonstrated that this would be inappropriate" (Policy BD9). Policy BD10 asks that foul water from all development connects to the foul sewer, because much of the town sits on a Principal Aquifer, and that developers show water and sewerage capacity on and off site (Chipping Norton plan).

Brize Norton Policy SD1 (Sustainable Development) and Milton-under-Wychwood Policy CH4 (Separation of Milton-under-Wychwood and Shipton-under-Wychwood)

Brize Norton's plan, made on 12 September 2025 after a referendum the day before, asks every proposal, in proportion to its scale, to "avoid increased the risk of flooding from either increased run off or from building within flood risk areas and take account of the predicted impact of climate change" (clause i of Policy SD1). In Milton-under-Wychwood, Policy CH4 is a landscape policy with a flood clause: development on land the Environment Agency identifies as high flood risk between the village and Shipton-under-Wychwood "will not be supported" (Milton-under-Wychwood plan). Cassington, Hailey, Shilton, South Leigh and Woodstock have made plans without a flood or drainage policy.

Local Plan 2043: proposed Policy CP5 at Regulation 19

A replacement plan is close to submission. The Regulation 19 consultation on the draft West Oxfordshire Local Plan 2043 ran from 26 August to 9 October 2026. The council's Local Development Scheme of July 2026 plans submission for examination in December 2026, with examination and adoption in 2027. Until it is adopted, EH7, EH8 and OS3 remain the policies an application is decided against.

Proposed Policy CP5 (Water Environment), Regulation 19 draft

Appendix 4 of the Regulation 19 draft lists EH7 as superseded by proposed Policy CP5 (Water Environment) once the plan is adopted. The draft CP5 asks for all sources of flooding to be managed in line with national policy, through a sequential, risk-based approach that allows for climate change. Development would have to be safe for its lifetime and reduce flood risk where possible, with SuDS and, where appropriate, natural flood management. The draft CP5 also tightens water use for new homes to "no more than 100 litres per person per day", against 110 in OS3, and draft CP5 clause 6 commits the council to Grampian-style conditions where water supply or foul capacity is lacking. Major proposals would also need a Sustainability Statement showing how the draft CP5 is met.

The July 2026 validation checklists: when West Oxfordshire asks for each report

WODC's validation checklists were revised as Rev 1 on 20 July 2026, and the full planning permission checklist sets the flood and drainage items most applicants need. It asks for a flood risk assessment in Flood Zone 2 or 3, minor development and changes of use included, on all major applications, and on Flood Zone 1 land with critical drainage problems notified by the Environment Agency. A surface water drainage strategy is needed for every major application and for development in Flood Zones 2 or 3, minor development included. Check a site's flood zone on our flood risk map before reading across the table.

Two items reach beyond the national triggers: an assessment on every major application even in Flood Zone 1 below one hectare, and a drainage strategy on a minor scheme in Flood Zone 2 or 3, which the county will not review because it comments on major development only. The supporting information page also offers an old Environment Agency surface water pro-forma that quotes 20% and 30% climate change allowances; we work to the current allowances instead. Missing flood or drainage evidence is a common reason for the council to declare an application invalid, and our guide lists the usual gaps.

How Oxfordshire County Council judges drainage on a West Oxfordshire site

Oxfordshire County Council assesses major schemes against the National Standards for sustainable drainage published in June 2025, read with its own Local Standards & Guidance for Major Development with Surface Water Drainage, version 2.0 of June 2026. The county's Flood Toolkit page says the January 2022 version would stay available until October 2026 and then be archived, so the QBAR-or-2-litres-per-hectare and blanket brownfield reduction figures still quoted online do not appear in version 2.0. Our summary of the 2025 National Standards explains the national framework.

• The 50% AEP rate. Where the capacity of the receiving watercourse or sewer is in any doubt, discharge is held to the 50% AEP (1 in 2 year) greenfield runoff rate; on previously developed land the relaxation can be no greater than five times that rate.
• Rates and volumes, four storms. Post-development rates and volumes must not exceed pre-development for the 100% AEP, Qbar or Qmed, 3.3% AEP and 1% AEP events, with greenfield values applied pro rata to the developable area.
• Climate change. The upper end peak rainfall allowance for the development's design life; the central allowance is accepted where the design life is under 100 years.
• Calculation settings. FEH22 rainfall, Cv of 1 for roofs and paving, MADD and pipe storage set to zero, storms from 15 minutes to 10,080 minutes, and 10% added to impermeable areas within residential curtilages for urban creep (flats excluded).
• Infiltration proved. Infiltration tests repeated three times with the lowest rate used, groundwater monitored to at least 1 m below the base of any infiltration feature, and half the storage emptied within 24 hours for events up to 3.3% AEP.
• Where water may go. Rainwater reuse first, then the ground, a surface water body, a surface water sewer and a combined sewer last; foul sewers and highway drains are not acceptable for new surface water, and deep-bore soakaways only by exception.
• Everyday rain. The first 5 mm of rainfall should produce no runoff from the site, and an exceedance plan must show how flows beyond the system's capacity are kept out of buildings.

The county does not offer pre-application advice on minor development of one to nine homes; for larger schemes the service is charged and targets a response within 21 working days. Works to an ordinary watercourse need consent from WODC itself, which holds that power for the district (watercourses and ditches); our guide to ordinary watercourse consent covers the process. Before trial pits are dug, our ground conditions map and BRE 365 infiltration rate calculator show whether soakage is worth testing, and our guide to BRE 365 infiltration testing explains the test. If a county drainage objection has already been lodged, our note on responding to an LLFA objection sets out the route back.

West Oxfordshire's 2025 Level 1 and 2026 Level 2 SFRAs

Two documents now make up the council's flood evidence. The Level 1 Strategic Flood Risk Assessment by Wallingford HydroSolutions is version 2.0, issued on 7 July 2025 and still marked draft; the Level 2 SFRA, version 1.0 of 17 April 2026, is also a draft and was prepared for the Local Plan 2043. The 2016 update, the 2015 North Witney Level 2 study and the 2009 assessment shared with Cherwell still appear in search results, but they are no longer the current evidence. Our explainer on Strategic Flood Risk Assessments covers how councils use them.

• Functional floodplain. The 2025 Level 1 SFRA follows national guidance: Flood Zone 3b is land with a 3.3% or greater annual probability of flooding, with defences working, or land designed to flood.
• Groundwater. Floodplain soils along the Thames and the Windrush have naturally high groundwater and are rated high risk; shallow lime-rich soils under parts of Carterton, Witney, Burford, Charlbury, Woodstock and Chipping Norton are rated moderate.
• Sewer flooding. Thames Water supplied 184 historic sewer flooding records for the district, with the OX18 area around Carterton, Burford and Bampton the most affected.
• Climate change. Table 3 of the Level 1 SFRA sets peak rainfall allowances for the district, with a 40% upper end allowance for the 1% AEP event in the 2070s epoch.
• Level 2 sites. The 2026 study covers candidate sites from the draft plan, among them Land south of Witney, a 107.9 ha site crossed by the Colwell Brook, and Welch Way in Witney.

The SFRA's own triggers match the validation checklist closely: Flood Zone 2 or 3, minor development and changes of use included; sites over one hectare in Flood Zone 1; and smaller Flood Zone 1 sites changing to a more vulnerable use where other sources could affect them. Where the national maps are coarse on an ordinary watercourse, we check the SFRA layers and, if needed, the model data before fixing floor levels.

Sewage capacity and Grampian conditions in West Oxfordshire

Foul drainage is a live constraint here. The council's sewerage capacity page says most of the district's 20 sewage treatment works are already operating at or beyond capacity. It lists developments in Brize Norton, Carterton, Chipping Norton and elsewhere with Grampian conditions, which allow homes to be built but not occupied until the network is upgraded. The July 2026 checklist asks every major application for a mains sewage capacity assessment, including confirmation that the network "will not cause or increase local sewer flooding or unplanned discharges of untreated effluent". A foul drainage strategy that records Thames Water's response, and keeps surface water out of the foul network, answers both the checklist and EH7's concern with sewer flooding.

How Chapter 18 of the August 2026 NPPF applies alongside EH7

National policy now sits in Chapter 18 of the NPPF, published in the August 2026 Framework. Policy F4 sets when a site-specific assessment is needed, including Flood Zone 1 land identified in an SFRA or the Flood Map for Planning as at risk from any source; F5 sets the sequential test, capped at the anticipated catchment of the development and with exemptions for householder work, most changes of use, sites where no built development falls on land at risk, and sites at risk from surface water only where occupiers stay safe; F6 sets the exception test in Flood Zones 2, 3a and 3b; F7 sets the safety tests; and F8 asks for SuDS designed to the National Standards. The Planning Practice Guidance on flood risk, last updated on 17 September 2025, explains how they work.

EH7 was written in 2018 against an earlier Framework, so where its sequential test wording differs from F5, the newer national exemptions are a material consideration that officers weigh with the development plan. Our guides to the sequential and exception tests and to the August 2026 NPPF changes go into the detail.

Windrush, Evenlode and the Thames: flood risk across West Oxfordshire

The district drains to the Thames, which follows its southern boundary past Kelmscott, Radcot and Northmoor, through two large tributaries: the Windrush through Burford and Witney, and the Evenlode through Charlbury towards Cassington. In July 2007 around 1,631 homes and 72 businesses flooded across West Oxfordshire (council summary), roughly 240 properties of them in Witney. Our Witney page covers the Windrush and Bridge Street in detail, our Oxfordshire page sets the district in its county, and our River Thames page follows the main river downstream.

Surface water and groundwater add to the river risk: the 2025 SFRA records surface water incidents in Witney and Middle Barton in 2020, and parts of Eynsham, Standlake and Bampton sit on freely draining soils with a mobile water table. Places such as Carterton, Chipping Norton, Woodstock, Burford, Charlbury and Eynsham have no area page of their own yet, so this page and the SFRA are the starting points there. River levels on the Windrush, Evenlode and Thames can be followed on our live river levels map, and other councils' requirements are listed in our local authority guides.

Reports for a planning application to West Oxfordshire District Council

A flood risk assessment, a sequential or exception test and a drainage strategy are three separate reports that answer three separate questions: is the site safe, should the development be here, and where does the surface water go. In West Oxfordshire the checklists can ask for the drainage strategy even where the county will never see it, so each is scoped against the council's own trigger.

• Every major scheme. The July 2026 checklist asks for an assessment on all major applications, in any zone, so we prepare a flood risk assessment that also answers each bullet of EH7.
• Flood Zone 2 or 3. EH7 and the checklist need site-specific evidence here, minor schemes and householder extensions included: a flood risk assessment for planning.
• Buying in the valleys. Before exchange on a property near the Windrush, the Evenlode or the Thames, a flood risk survey for property purchase looks at the building itself.
• Testing the location. EH7 applies the sequential test and, where needed, the exception test, within the F5 catchment limit: our sequential and exception test report sets out the search.
• Drainage for the council. Paragraph 8.61 of the Local Plan and Policy NE8 in Charlbury ask for SuDS, so every scheme benefits from a drainage strategy scaled to its size.
• The county's rules. For a major scheme, a surface water drainage strategy written to the June 2026 Oxfordshire standards and the 2025 National Standards.
• After permission. Where a West Oxfordshire decision notice carries a drainage condition, we prepare the evidence for the discharge of drainage conditions.
• National policy. Chapter 18 sits behind every decision here, and our NPPF guidance explains how F4 to F8 apply to a site.
• Sewage capacity. Most treatment works are at or beyond capacity and majors need a capacity assessment, so a foul drainage strategy records Thames Water's position.
• Groundwater. High groundwater on the Thames and Windrush floodplains, the Chipping Norton Source Protection Zone and Salt Cross Policy 10's monitoring call for a groundwater flood risk assessment within the FRA.
• Modelled extents. Salt Cross Policy 10 asks for the 70% climate change extent and, where required, modelled ordinary watercourses: flood modelling provides them.
• Large allocations. Candidate sites in the 2026 Level 2 SFRA, such as Land south of Witney on the Colwell Brook, suit an early feasibility study before a layout is fixed.
• Thames floodplain villages. The SFRA places Kelmscott, Radcot, Chimney, Moreton and Northmoor mostly or entirely in Flood Zones 2 and 3, and F7 asks for safe access as part of an agreed emergency plan: a flood warning and evacuation plan sets it out.
• Homes that have flooded. With about 1,631 homes flooded in 2007, owners facing higher premiums can use a flood risk assessment for insurance.

West Oxfordshire flood and drainage questions, answered

Our experienced flood risk consultants are chartered and prepare flood risk assessments, sequential tests and drainage strategies to the requirements on this page. Reports for applications to West Oxfordshire District Council come from Unda Consulting Limited, a CIWEM Business Partner. Call 01293 214444 or email enquiries@unda.co.uk for a no-obligation, free quote.