Flood Risk Assessment in Waverley Borough Council

Waverley Borough Council decides planning applications across Farnham, Godalming, Haslemere, Cranleigh, Bramley and the villages between them, but it shares the job with Surrey County Council, which steps in as the Lead Local Flood Authority the moment surface water and drainage are involved. A flood risk assessment and a drainage strategy are separate documents that answer different questions, and Waverley's own validation list asks for both far more often than national policy alone requires. We prepare both for developers, architects and planning consultants working across the borough, and for the property purchase, mortgage, insurance and BREEAM situations that turn on the same evidence.

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

Waverley's own validation list goes further than national policy. A surface water drainage strategy or SuDS proforma is required "for all scales of development where surface water will be created or affected," not only the major schemes national guidance targets, so even a modest Waverley application can stall on drainage evidence nobody thought to prepare.

Flood risk and drainage for Waverley Borough Council planning, at a glance

• Two authorities, two jobs. Waverley Borough Council decides the application; Surrey County Council is the Lead Local Flood Authority for surface water, groundwater and ordinary watercourses.
• Flood risk policy: CC4. Adopted Local Plan Part 1 (February 2018) Policy CC4, Flood Risk Management, sets the flood zone and drainage tests; Policy CC1, Climate Change, cross-refers to it.
• Drainage is checked locally, not just at national thresholds. Waverley's validation list requires a surface water drainage strategy or SuDS proforma for development of any scale where surface water is created or affected.
• Discharge basis: greenfield. Surrey County Council expects post-development runoff to match the greenfield QBar or Q1 rate, tested against the 1-in-30 and 1-in-100-year (plus climate change) storms.
• The evidence base: two SFRAs. A Level 1 Strategic Flood Risk Assessment (updated November 2018) and a Level 2 SFRA (2016) underpin the Local Plan and the Sequential Test.

Who decides flood risk and drainage for a Waverley planning application

Waverley Borough Council is the Local Planning Authority for the whole borough, so it issues the decision notice and applies its own Local Plan policies. But once a proposal touches surface water, groundwater or an ordinary watercourse, Surrey County Council takes over as the statutory consultee, reviewing the drainage strategy and telling Waverley whether it is acceptable. Waverley is very unlikely to grant permission for a major scheme against a live Surrey County Council drainage objection, so satisfying both bodies from the outset matters more than satisfying either one well.

• Waverley Borough Council is the Local Planning Authority, deciding the application against its Local Plan and the National Planning Policy Framework.
• Surrey County Council is the Lead Local Flood Authority, the statutory consultee for surface water drainage, SuDS design and discharge rates on major applications.
• The Environment Agency advises on the borough's main rivers, principally the River Wey and Cranleigh Waters, and on climate change allowances.
• No Internal Drainage Board covers any part of Surrey, so there is no third consenting regime to factor in.
• Thames Water is the sewerage undertaker across the borough, relevant wherever a drainage strategy proposes a public sewer connection.

This two-tier split catches out applicants more than almost anything else. A drainage strategy addressed only to Waverley, without the technical detail Surrey County Council's SuDS planning advice sets out, is one of the most common reasons a Waverley drainage submission comes back for more information. Our guide to what a Lead Local Flood Authority actually does explains the split in more detail.

Does a Waverley planning application need a flood risk assessment or a drainage strategy?

Most applications in Waverley need one or both. A flood risk assessment is triggered by the site's flood zone and size; a drainage strategy or SuDS proforma is triggered separately, and Waverley's own validation list sets a lower local bar than the national default. Treating the two as the same test is one of the easiest ways to have an application invalidated before it is even registered. See our note on what gets a planning application invalidated for flood risk and drainage.

These triggers come from Waverley's own validation checklist, alongside the national tests in the NPPF and its Planning Practice Guidance. If you are unsure which apply to your site, send us the address and we will tell you free of charge.

Waverley's SuDS and drainage requirements, set by Surrey County Council

Surrey County Council expects a Waverley drainage strategy to hold post-development surface water runoff to the site's greenfield rate, tested against both the 1-in-30-year and the climate-change-adjusted 1-in-100-year storm, with an allowance for urban creep that scales with the density of the scheme. Infiltration is the first choice in the drainage hierarchy, and Surrey County Council wants it proved with a Building Research Establishment (BRE) Digest 365 soakage test, not assumed.

• Discharge rate. Post-development runoff should match the greenfield QBar or Q1 rural rate for the site, calculated for its own catchment rather than a borough-wide figure.
• Storm events tested. Hydraulic calculations must show the scheme manages the 1-in-30-year event with no flooding on site outside designed areas, and the 1-in-100-year event plus a climate change allowance with no flooding on or off site.
• Urban creep allowance. Surrey County Council scales the allowance with density: 10% below 25 dwellings per hectare, falling to 2% above 50 dwellings per hectare, and 0% for flats and apartments.
• Infiltration testing. Where a soakaway is proposed, Surrey County Council expects BRE Digest 365 testing with at least a 1-metre unsaturated zone above the seasonal high groundwater level, not an assumed rate.
• The SuDS proforma. Waverley's validation list requires a completed surface water drainage strategy or SuDS proforma for development of any scale, following the Surrey-wide pro-forma format Surrey County Council uses across the county.
• Non-major development. For schemes of 1–9 dwellings or under 1 hectare, Surrey County Council typically only comments where the site sits within the mapped 1% annual-probability surface water extent, adjoins a watercourse, or Waverley specifically asks it to, and applies a simpler discharge test based on the 1-in-2-year event.

Surrey County Council objects most often for the same handful of reasons wherever it sits as LLFA: a scheme defaulting straight to sewer discharge without ruling out infiltration first, missing or assumed infiltration test data, runoff calculations that omit the climate change allowance, or no plan for what happens when a storm exceeds the design event. Our note on resolving an LLFA objection sets out how to answer each one, and our BRE365 infiltration testing guide explains what a defensible soakage test looks like.

Waverley's Local Plan flood and drainage policies

Waverley's flood and drainage requirements sit in adopted Local Plan Part 1: Strategic Policies and Sites (February 2018, covering the period to 2032). Policy CC4 carries the operative flood risk and drainage tests; Policy CC1 sets the wider climate change duty and cross-refers to it. Local Plan Part 2 (adopted March 2023) adds no separate flood or drainage policy of its own, so CC4 remains the reference point across the borough, alongside Policy DM1's general duty to avoid an increase in flood risk.

Policy CC4: what Waverley's flood risk policy actually requires

Policy CC4 requires development to be safely located, designed and laid out against the flood zones the Council's Level 2 Strategic Flood Risk Assessment defines, with permission only granted in at-risk locations where the Sequential and Exception Tests have been passed, the development sits in the lowest appropriate flood risk location available, and it will not constrain the floodplain's natural function. The same policy carries the borough's drainage test: no increase in the volume or rate of surface water leaving the site, and no off-site property or highway flooding up to the 1-in-100-year storm plus a climate change allowance.

Policy CC1: how Waverley's climate change policy ties in

Policy CC1 sets Waverley's overarching climate change duty and explicitly directs flood risk back to Policy CC4, while separately expecting green infrastructure and sustainable drainage to help absorb heat and reduce surface water runoff. In practice, a scheme's flood risk assessment and its drainage strategy get read together against CC1 as much as against CC4 on its own.

Waverley is also consulting on a new Local Plan (Issues and Options, late 2025) to guide development beyond the current plan period; at Issues and Options stage it has not reached examination and carries no adopted flood or drainage policy of its own yet, so CC4 and CC1 remain the tests that apply now. Read the current Local Plan Part 1 and Local Plan Part 2 in full.

Waverley's Strategic Flood Risk Assessment

Waverley's evidence base runs on two linked studies. The Level 1 Strategic Flood Risk Assessment, originally produced in July 2015 and updated by AECOM in November 2018, screens flood risk across the whole borough from every source. The Level 2 SFRA, produced in 2016, goes further on the sites the Level 1 study flags as higher risk, defining the functional floodplain (Flood Zone 3b) using the 1-in-20 annual probability (5% chance) river event. That is the same extent as Flood Zone 3a on the published Flood Map for Planning, since Waverley does not map 3b separately.

• Used for the Sequential Test. Both SFRAs feed Waverley's application of the Sequential Test to Local Plan allocations and to individual planning applications.
• No separately mapped Critical Drainage Area. Neither SFRA identifies a formally designated Critical Drainage Area in Waverley, though Surrey County Council can still request extra drainage evidence on a site-specific basis.
• Read alongside the Flood Map for Planning. The SFRA adds surface water, groundwater and functional floodplain detail the national Flood Map for Planning does not show on its own.

What Waverley's validation list requires before an application is registered

Waverley's validation checklist, approved in November 2022, sets out exactly what must accompany an application for it to be registered at all. Missing any of it means the application is invalidated before the determination clock even starts, as our guide on planning applications invalidated for flood risk and drainage explains.

• A site-specific flood risk assessment is required wherever the site is in Flood Zone 2 or 3 (including minor development and changes of use), on any site over 1 hectare, and on smaller Flood Zone 1 sites affected by another source such as surface water.
• A sustainable drainage statement is required nationally for major applications (10 or more dwellings, 1,000m² of floor space, or a 1-hectare site), and a completed Flood Matrix is required for householder and other minor extensions in Flood Zone 2 or 3.
• A surface water drainage strategy or SuDS proforma is Waverley's own local addition: required for development of any scale where surface water will be created or affected, not only the major schemes national policy targets.

That local SuDS proforma requirement is the detail applicants miss most often on a Waverley application that looks too small to need drainage evidence. Submitting it up front, rather than leaving it to a condition, is the surest way to avoid the delay our guide on what drainage information planning permission actually needs describes.

How national flood and drainage policy applies in Waverley

Waverley applies the National Planning Policy Framework's risk-based approach on top of its own Local Plan tests. Every application must show flood risk has been assessed from every relevant source, that development is directed to the lowest-risk appropriate location through the Sequential Test, that it will remain safe for its lifetime once climate change is factored in, and that it does not increase flood risk elsewhere, the same tests our NPPF flood risk guidance sets out nationally. Where a higher-risk site cannot pass the Sequential Test alone, the Exception Test applies, and our Sequential and Exception Test service covers both in detail.

On drainage, national policy and the 2025 national standards for sustainable drainage systems set the hierarchy Surrey County Council applies locally: infiltrate first, then a watercourse, then a surface water sewer, with a combined sewer as the last resort. The evidence expected scales with the size and risk of the scheme.

Flood risk across Waverley's area

Waverley's flood risk is dominated by the River Wey, whose North and South arms converge at Tilford, and by its largest tributary, Cranleigh Waters, alongside smaller watercourses including the River Lox, Hascombe Stream and Littlemead Brook. Surface water compounds the risk in several of the borough's towns, particularly where clay geology slows natural drainage. Waverley is entirely inland, so there is no tidal flood risk anywhere in the borough.

• Winter 2013/14 brought extensive flooding from the Wey, Cranleigh Waters and Hascombe Stream, with record river levels recorded at Tilford. It is the event behind Surrey County Council's Section 19 flood investigation into the borough.
• September 1968 brought a county-wide flood event that affected parts of Waverley, still referenced as the historic benchmark for the area.
• Godalming and Cranleigh each have their own detailed local flood risk profile on our site. See flood risk assessment in Godalming and flood risk assessment in Cranleigh for the river-by-river detail behind this borough-wide picture.

Waverley is also under real pressure to grow. Its five-year housing land supply stood at just 2.68 years in its January 2025 position statement, falling to 1.4 years against the increased government housing target confirmed in December 2025.

That growth pressure is already testing how strictly flood and drainage policy is applied at appeal: at Old Park Lane, Farnham, an inspector allowed up to 83 homes in June 2025 after Surrey County Council, as LLFA, accepted the scheme's drainage strategy and an exceedance-flow diversion corridor, with conditions requiring a detailed SuDS scheme, its verification and its long-term maintenance.

It is a useful marker of what a Waverley scheme has to get right on drainage to succeed, even as the borough comes under pressure to release more sites for the housing numbers government has set it.

How Unda helps with flood risk and drainage for Waverley planning

We read Waverley's Local Plan and Surrey County Council's drainage requirements together, rather than treating the flood risk assessment and the drainage strategy as two separate hurdles, because Policy CC4 and the borough's own SuDS proforma requirement are answered most efficiently as one coordinated case. We have prepared flood risk assessments and drainage strategies for towns across Waverley's area, including Godalming and Cranleigh, and elsewhere in Surrey County Council's catchment, so we know how Surrey County Council reviews a scheme before it reaches Waverley's planning committee.

Every report is signed off by a senior, CIWEM-qualified flood risk consultant, and we stay involved after submission to answer any Surrey County Council or Waverley query before it becomes an objection.

Flood risk and drainage services for every situation in Waverley's area

A flood risk assessment, a Sequential or Exception Test and a drainage strategy are three distinct reports. They often travel together in a Waverley planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go. We prepare all three, alongside the right form of assessment for buyers, lenders and BREEAM.

Flood risk assessments

• Flood risk assessment for planning. The core report prepared to satisfy the NPPF, Waverley's Policy CC4 and the Environment Agency. Groundwater and, where needed, flood modelling are assessed within it.
• Homebuyer and property-purchase survey. For conveyancing, where a search flags Wey or surface water risk on a Waverley property and you need the building itself assessed.
• 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 groundwater level for Wey valley sites and any basement, assessed within the FRA or as a standalone hydrogeological assessment on complex sites.

Sequential and Exception Tests

The Sequential and Exception Tests are a separate, locational report about whether development should be in a higher-risk part of Waverley at all. The Sequential Test defines an area of search, identifies reasonably available lower-risk sites and justifies the proposed site against Policy CC4; 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 proposes SuDS to hold discharge to Surrey County Council's greenfield standard.
• Preliminary drainage design. The early, outline read that flags infiltration 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 Waverley has attached to permission.
• Flood modelling. 1D and 2D hydraulic modelling that feeds the assessment, Sequential Test or drainage design where national mapping is not detailed enough for a Wey-side site.

Early in a drainage strategy it helps to know whether the ground will take water: our free geology and ground conditions map and BRE 365 infiltration rate calculator give an indicative read before a trial pit, and the drainage calculators help size the scheme. You can screen a Waverley postcode on our flood risk map, or check the Wey's current level 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.

Waverley flood and drainage contacts

For an immediate threat to life during a flood, always call 999; for a power cut during flooding, call 105. Check current conditions and sign up for warnings at check-for-flooding.service.gov.uk or gov.uk.

Flood risk and drainage for Waverley Borough Council planning: frequently asked questions