Flood Risk & Drainage Requirements for Adur & Worthing

Adur District Council and Worthing Borough Council determine planning applications through a single shared service, but against two different Local Plans and, since April 2026, two different validation lists. Most sites near the coast, the tidal River Adur or the Teville Stream will need a flood risk assessment, a surface water drainage strategy built to West Sussex standards, or both, before either council will register the application as valid.

Unda prepares flood risk assessments across Adur and Worthing for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies (SuDS). Each of these is a separate report answering a separate question, and this page explains which of them Adur & Worthing will ask you for, which policies they will judge it against, and the technical standards the drainage reviewers apply.

Adur & Worthing's own drainage engineers review surface water proposals far below the size threshold most councils police: anything larger than two dwellings, and any application at all in an area at risk of flooding, is expected to show greenfield discharge rates, winter infiltration testing and a funded maintenance plan.

• Two planning authorities, one service. Adur District Council and Worthing Borough Council are separate local planning authorities that share officers, a policy team and a planning portal as Adur & Worthing Councils.
• Flagship policies. Policy DM20 of the Worthing Local Plan (2023), Policy 36 of the Adur Local Plan (2017) and Policy SH6 of the Shoreham Harbour Joint Area Action Plan (2019) carry the flood risk and drainage requirements.
• The drainage bar. Discharge is limited to the greenfield rate (Qbar), with at least 50% betterment on brownfield sites, a 2 l/s practical minimum, and storage designed for the 1 in 100 year storm plus 45% for climate change.
• Who reviews what. West Sussex County Council is the Lead Local Flood Authority and reviews major applications; the councils' in-house drainage engineers review everything smaller.
• The evidence base. A Level 1 Strategic Flood Risk Assessment (July 2024) covers both councils; a Level 2 SFRA for Adur followed in December 2025.
• Validation. Worthing has run its own validation requirements since 1 April 2026; Adur still uses the June 2020 joint list, with a replacement promised during 2026.

For a quote, or to talk a site anywhere in Adur or Worthing through first, call one of our experienced flood risk consultants on 01293 214444 or email enquiries@unda.co.uk.

Who decides flood risk and drainage for an Adur or Worthing application?

Adur District Council or Worthing Borough Council determines the planning application, West Sussex County Council advises on surface water drainage for major schemes as Lead Local Flood Authority, and the Environment Agency advises where a site sits in Flood Zone 2 or 3 or near a main river. On smaller schemes, the councils' own drainage engineers stand in for the county and apply the same standards.

That split confuses applicants everywhere, and it has a local twist. In most two-tier areas a minor application escapes technical drainage review altogether, because the LLFA is only a statutory consultee on major development. Not here. Adur & Worthing publish their own Supplementary Requirements for Surface Water Drainage Proposals (May 2022), adopt the West Sussex LLFA policy wholesale, and put schemes as small as three dwellings through it.

• Adur District Council / Worthing Borough Council. The local planning authorities. They validate, consult and decide, through the shared Adur & Worthing Councils service.
• West Sussex County Council. The Lead Local Flood Authority, a statutory consultee on surface water drainage for major applications (10+ dwellings, 1,000 m² of floorspace or sites of 1 hectare and above). It runs a charged flood risk pre-application advice service and will not discuss drainage proposals outside it.
• The councils' drainage engineers. Review surface water proposals on the applications the county never sees, against the councils' published May 2022 requirements. Thin drainage information tends to come back as a pre-commencement condition, or stops validation altogether.
• The Environment Agency. Covers Adur and Worthing from its Solent and South Downs area. It is consulted on more vulnerable development in Flood Zones 2 and 3 and regulates works on or within 8 metres of a main river, rising to 16 metres where the river is tidal. Read more on the EA's role in planning.
• Southern Water. The sewerage undertaker for the whole area. Connection to a public sewer needs its agreement, and both councils ask for a foul sewerage assessment on major schemes.
• No internal drainage board. The River Adur Internal Drainage District was abolished on 31 March 2017, so no IDB consenting regime applies; land drainage in the lower Adur valley now rests with riparian owners and the usual authorities.

Do you need a flood risk assessment or a drainage strategy here?

For Adur & Worthing planning, a flood risk assessment is required for any development in Flood Zone 2 or 3 — including householder extensions — for sites of 1 hectare or more in Flood Zone 1, and wherever the SFRA identifies surface water, groundwater or sewer risk. A drainage strategy is required on far smaller schemes than the national norm. The table below shows the triggers each council applies.

Two of those rows do the most damage to unprepared applications. A single new dwelling in a surface-water-prone street still triggers a drainage strategy, and a completed West Sussex surface water proforma is a condition of validation on majors, not a nice-to-have. Our guide to invalidated planning applications covers the pattern, and when an FRA is required covers the national baseline. If you are unsure which zone your site sits in, check it on our free Flood Risk Map before you commit to a layout.

The Local Plan policies your application is judged against

Three adopted development plan documents carry the flood risk and drainage policies here: the Worthing Local Plan (adopted 28 March 2023), the Adur Local Plan (adopted 14 December 2017) and, for sites around the harbour, the Shoreham Harbour Joint Area Action Plan (adopted October 2019). Each contains a combined flood-and-drainage policy, so a weak drainage scheme can put a decision at risk even where flood risk itself is low.

Policy DM20 — Worthing's flood risk and drainage policy

Policy DM20 of the Worthing Local Plan (2023) requires a site-specific flood risk assessment for sites of 1 hectare or more in Flood Zone 1, for all new development in Flood Zones 2 and 3 including minor development and changes of use, and for land the SFRA flags for other sources of flooding. Its drainage limb is exacting: surface water schemes must use SuDS unless there is clear evidence they are inappropriate, limit discharge to the greenfield 1 year rate where possible for storms up to the 1 in 100 year event plus climate change, contain the 1 in 30 year storm plus climate change within the system, and follow the discharge hierarchy — infiltration first, then a watercourse, then a surface water sewer, with a combined sewer accepted only where Southern Water agrees there is no feasible alternative. Maintenance arrangements and funding must be settled before decision, not left to conditions.

Policy 36 — Adur's flood risk and drainage policy

Policy 36 of the Adur Local Plan (2017) requires a site-specific flood risk assessment for sites of 1 hectare and above in Flood Zone 1, all development or vulnerability-raising changes of use in Flood Zones 2 and 3, and development of any size where the SFRA identifies surface water, sewer or groundwater risk. It goes further than most district policies on drainage: every new development in Adur must include some form of SuDS or equivalent design measure, SuDS must be considered before any other form of disposal, and substantial storage is expected so that runoff falls below what left the site before development. Where on-site SuDS genuinely cannot work, the council can take contributions towards strategic drainage instead.

Policy SH6 — the harbour rules at Shoreham

Policy SH6 of the Shoreham Harbour Joint Area Action Plan (2019) applies fixed engineering numbers to regeneration sites along the harbour and the tidal Adur. Residential proposals must protect against a breach scenario with finished floor levels at 5.77 m AOD; where existing defences or ground levels sit below the 1 in 200 year tidal event for 2115, developers must deliver defences to 5.4 m AOD; and any works within 16 metres of the tidal river need Environment Agency consent before they start. Responsibility for delivering and maintaining those defences sits with the landowner. The Free Wharf scheme on the Western Harbour Arm shows what that means in practice: a £24m flood defence package was built before the homes.

One more thing worth knowing about the plans themselves. Adur's is the older of the two, and a replacement is in preparation — the councils' March 2025 timetable points to a draft plan consultation in late 2026 and adoption around 2028. Until then, Policy 36 and the 2017 plan remain the development plan for Adur, and applications are judged against them, not the emerging document. Neither council's area carries water neutrality restrictions: Adur and Worthing sit outside the Sussex North water supply zone, so the constraint that stalled housing in Horsham and Crawley never applied here.

What discharge rate do Adur & Worthing expect? The drainage standards in numbers

Surface water discharge from a development in Adur or Worthing is limited to the estimated mean greenfield runoff rate, Qbar, calculated on the positively drained area of the site rather than the whole red line. Brownfield sites get no free pass: if the greenfield rate is demonstrably unachievable, the councils expect discharge as close to it as possible, with at least 50% betterment on existing runoff. A practical minimum of 2 l/s applies so small orifices do not block.

Those figures come from the councils' Supplementary Requirements for Surface Water Drainage Proposals (May 2022), which adopt the West Sussex LLFA surface water policy and add the councils' own review standards on top. The design storms, the testing seasons and the documentation are all specified — which is good news for anyone who prepares drainage strategies properly, because it leaves little room for a reviewer to ask for more, and bad news for anyone hoping a soakaway assumption will slip through.

The winter testing rule catches more programmes than any other line in that table. Infiltration testing to BRE 365 and groundwater monitoring both have to happen between October and March, so a scheme conceived in spring can lose most of a year if nobody plans the site investigation early. High water tables on the coastal plain rule infiltration out on many sites regardless — our free geology and ground conditions checker gives a first read on whether a soakaway is even plausible, and the BRE 365 infiltration rate calculator turns trial pit timings into a design rate. For sizing the rest of the scheme, our drainage calculators cover flow controls, attenuation and the climate change allowances.

On major applications, the West Sussex SuDS proforma must be completed and attached before the application will be validated, and the county's checklist asks for the topographical survey, the ground investigation, the exceedance drawings and the maintenance plan by name. Miss any of those gates — winter data, exceedance routing, funded maintenance — and the scheme is exposed to exactly the kind of consultee objection we cover in LLFA objections and how to resolve them.

The Strategic Flood Risk Assessment behind the decisions

Adur & Worthing's Level 1 Strategic Flood Risk Assessment, prepared by JBA Consulting and issued in July 2024, supersedes the 2020 version and is the evidence base both councils use to screen applications, apply the sequential test and shape allocations. A Level 2 SFRA for Adur followed in December 2025, with site-by-site assessments for the district's biggest allocations. Both sit on the councils' flood risk evidence base page.

Two features of the 2024 SFRA matter for individual applications. First, its functional floodplain: Flood Zone 3b is defined at the 1 in 30 year event with defences taken into account, and where no detailed model exists the SFRA maps a precautionary Zone 3b based on Flood Zone 3a — leaving it to your site-specific FRA to establish the true extent. Wave overtopping is included, so 3b locally runs wider than 3a along parts of the coast. Second, its climate change layers: surface water mapping carries uplifts of 40% and 45% on peak rainfall, the same allowances the drainage standards apply to design storms. Our guide to climate change allowances explains how these feed an FRA, and the Yatton judgment shows how much weight sequential and exception test evidence now carries at appeal.

Validation: two lists, one portal

Since 1 April 2026 Worthing has run its own validation requirements document, written around the 2023 Local Plan; Adur still works to the joint list last updated in June 2020, with a new Adur document promised during 2026. Both councils receive applications through the same portal, which is exactly why applicants miss the split — the portal looks identical either side of the district boundary, but the paperwork demanded differs.

• Worthing, from April 2026. Requirement 19 sets the FRA triggers, requirement 38 the SuDS information: a site plan, the SuDS design with calculations and a maintenance management plan, following the national standards, CIRIA C753 and West Sussex guidance. Where infiltration is proposed inside groundwater Source Protection Zone 1, a hydrogeological risk assessment is required too.
• Adur, current list (June 2020). Item 8 sets the FRA triggers, item 23 the drainage strategy triggers, and item 9 requires a foul sewerage assessment on major schemes. The list warns that insufficient drainage information is likely to mean pre-commencement conditions.
• The common failure. "Flood Risk Assessment" appears by name among Worthing's published common invalidation reasons. An application is not valid until it meets both national and local requirements, so a missing FRA or drainage strategy stops the clock before an officer ever reads the scheme.

The full lists sit on the councils' submit-an-application pages. If a validation letter has already landed, our note on what drainage information planning permission needs explains what each missing document actually is.

How national policy applies in Adur and Worthing

The National Planning Policy Framework and its planning practice guidance set the baseline the local policies build on: development directed away from flood risk by the sequential test, an FRA proportionate to the risk, and safety for the development's lifetime with climate change allowed for. Since the 2025 guidance update, surface water counts in the sequential test as well as rivers and the sea — a real constraint on a coastal plain where surface water, not the sea, is the dominant hazard. Flood zones come from the national Flood Map for Planning, and where the map disagrees with reality, a site-specific assessment can demonstrate the difference; our note on why the long-term flood risk map cannot support an application explains which dataset counts. For the framework itself, see our NPPF flood risk guidance.

Flood risk on the ground, briefly

The requirements above exist because of how this coastal strip floods. Three main rivers cross it — the tidal River Adur, the Teville Stream and the Ferring Rife — and all three tide-lock in their lower reaches, so heavy rain at high water has nowhere to drain. The recorded flood years the SFRA lists (1980, 2000, 2007, 2012 and winter 2013/14) are mostly surface water stories, and the June 2012 event put water into properties across west and central Worthing.

• Tidal risk is concentrated in Adur. Shoreham and East Lancing sit behind the £45m Shoreham Adur Tidal Walls, completed in February 2019: 7.2 km of defences protecting over 2,300 homes to a 1 in 300 year standard including 50 years of sea level rise. Development behind them must still assess breach and overtopping, because residual risk never falls to zero and the SFRA expects finished floors set above the modelled defended levels.
• Surface water dominates Worthing. The borough is flat, drains to the sea by gravity and locks against the tide twice a day. A site can sit in Flood Zone 1 and still fail validation without a drainage strategy — the reason surface water and planning is the constraint to plan around here.
• Groundwater rises from the chalk. The SFRA's groundwater mapping picks out Durrington, Goring, East Worthing, Sompting and Lancing as the most vulnerable areas. High groundwater breaks soakaway assumptions and adds a monitoring season to programmes; see groundwater flood risk in planning applications for what reviewers expect.
• The pressure is upward. Adur's largest allocations — New Monks Farm and the harbour wharf sites — sit in or beside tidal Flood Zone 3, and Worthing's roughly 4,600 planned homes are overwhelmingly brownfield schemes on the same constrained plain, so flood risk and drainage evidence is decision-critical on nearly every major application either council determines.

This page covers what the councils require. For the full picture of how Worthing itself floods — the Teville Stream's culverted route through the town centre, the flood history, the postcode-level risk — see our flood risk assessment in Worthing page, and for the county-wide setting, West Sussex.

How Unda helps with Adur & Worthing's requirements

Unda has prepared more than 5,000 flood risk assessments and drainage strategies across England and Wales since 2014, and we know the West Sussex regime well — the Qbar calculations the drainage engineers check, the winter testing windows, the proforma the county wants attached, and the defended-but-residual tidal picture behind the Adur walls. A Senior Flood Risk Consultant signs off every report, and our flood risk consultants stay involved after submission to answer consultee queries.

1. We scope the site against both regimes. The right validation list, the right Local Plan policy, the SFRA layers, and whether the county or the councils' engineers will review the drainage.
2. We plan the evidence early. If infiltration is plausible, winter BRE 365 testing and groundwater monitoring go in the programme before they can cost you a year.
3. We prepare the reports the reviewers expect. An FRA, a drainage strategy, a sequential test — whichever the site needs, each to the councils' published standards, with the proforma completed on majors.
4. We defend the application. If the LLFA or the drainage engineers raise questions, we answer them and keep the determination moving.

Flood risk and drainage services for every situation here

A flood risk assessment, a sequential or exception test and a drainage strategy are three different reports. They often travel together in a submission to Adur & Worthing, but they answer different questions: is the site safe, should the development be here, and where does the surface water go. Whatever brought you to this page, we prepare all of them, alongside assessments for transactions and certification.

• Flood risk assessment for planning. The site-specific FRA an Adur or Worthing application needs under Policy DM20 or Policy 36.
• Surface water drainage strategy (SuDS). Designed to the Qbar discharge limits and design storms in the table above, with the maintenance plan the councils insist on.
• Sequential and exception tests. The locational case for a site at risk, using the councils' own July 2024 sequential test methodology and SFRA layers.
• Discharge of drainage conditions. The detailed design stage, including the verification evidence the councils condition on major schemes.
• Preliminary drainage design. An early read on discharge rates and storage volumes before the layout is fixed.
• Flood risk survey for property purchase. An independent homebuyer assessment when a conveyancing search flags risk in Shoreham, Lancing or Worthing.
• Flood risk assessment for insurance. Property-specific evidence when an insurer or broker queries the mapped risk.
• BREEAM flood risk assessment. Structured for Pol 03 credits — worth noting where JAAP Policy SH1 asks for BREEAM 'Excellent' at the harbour.
• Groundwater flood risk assessment. The dedicated groundwater work within an FRA where the chalk water table drives the risk, as it does across much of Worthing and Lancing.
• Flood modelling. 1D and 2D hydraulic modelling to establish levels where national mapping is not enough — including breach scenarios behind the Adur tidal walls.

Who to contact at the authorities

• Adur & Worthing Councils. Applications, validation queries and the councils' drainage engineers, via the shared planning portal and the planning pages. A charged pre-application advice service has applied since January 2025.
• West Sussex County Council (LLFA). Surface water drainage on majors, and the county's charged pre-application advice for flood risk and drainage scope.
• Environment Agency. Main river consents and flood risk advice; check live warnings at GOV.UK's check for flooding service or call Floodline on 0345 988 1188.
• Southern Water. Sewer capacity, connection agreements and the foul sewerage assessments both councils request on major schemes — see southernwater.co.uk.

Adur & Worthing flood risk and drainage: common questions