Flood Risk Assessment in Cranleigh

Cranleigh sits on the flat Low Weald, drained by Cranleigh Waters and a web of small brooks rather than one large river, and that shapes how the village floods. Rain struggles to soak into the heavy clay and ponds on roads and low ground, Cranleigh Waters and its tributaries spread across the valley floor after prolonged rain, and a decade of new housing has put real pressure on the drains. A flood risk assessment in Cranleigh shows your planning authority that a development will stay safe from flooding for its whole lifetime, and that it will not push flood risk onto anyone else.

We prepare flood risk assessments in Cranleigh for planning, property purchase, mortgage and insurance, and BREEAM, alongside the sequential and exception tests and surface-water drainage strategies (SuDS) that a low-lying village on heavy Weald clay so often needs. We assess every source that matters on your site, then deal directly with the Environment Agency and with Surrey County Council as Lead Local Flood Authority, guiding architects, planning consultants, developers and landowners through to approval.

Most Cranleigh sites face more than one source of flooding at once — Cranleigh Waters, surface water shedding off the Weald clay, and a high winter water table — which is why a desktop map rarely satisfies a planning officer on its own.

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

Flood risk assessment in Cranleigh at a glance

• Surface water is the village's biggest flood problem. On heavy Weald clay, rain runs off rather than soaking in, so surface-water flooding and overwhelmed drains affect roads and low ground across Cranleigh.
• Cranleigh Waters is a main river. The brook and its tributaries place land along the valley in Flood Zones 2 and 3, and carry an Environment Agency flood alert and flood warning area through Cranleigh and Shamley Green.
• The village sits on low-permeability clay. Soakaways frequently fail here, so a drainage strategy usually has to store run-off and release it to a watercourse at a restricted rate rather than rely on infiltration.
• A large amount of new housing is being built. Waverley's Local Plan directs more than 1,700 new homes to Cranleigh, several on greenfield sites where flooding and drainage have been the central planning issues.
• Surrey County Council is your Lead Local Flood Authority. It is a statutory consultee on surface water drainage for major development, with its own SuDS guidance and a Surface Water Drainage Statement pro-forma; Waverley Borough Council determines the application.

Flood risk across Cranleigh: Cranleigh Waters, surface water and groundwater

Cranleigh faces three main sources of flooding, and on the flat Low Weald they often act together. Cranleigh Waters and its tributary brooks flood the valley floor; surface water cannot soak into the clay and runs off into roads and low ground; and groundwater rises in the wetter winters. Most sites in and around the village face more than one of these, which is why a desktop map rarely satisfies a planning officer on its own.

Cranleigh Waters rises in the rural land north of the village and runs north and west as a main river, picking up Littlemead Brook and Nanhurst Stream before forming the boundary between Wonersh and Bramley and joining the River Wey at Shalford. The disused Wey and Arun Canal closely parallels the brook for much of its length. Because the gradient is gentle, a prolonged spell of rain spreads water wide across the valley floor rather than passing quickly downstream. Working out which watercourse drives the risk on a given site, and how it behaves, is the heart of a credible fluvial flood risk assessment.

• Rivers (fluvial). Cranleigh Waters, Littlemead Brook and Nanhurst Stream place land along the valley in Flood Zones 2 and 3, from the rural north of the village down through Shamley Green, Bramley and Wonersh towards Shalford. Land in these zones almost always needs an assessment.
• Surface water (pluvial). Now the most widespread flood risk in England, and the dominant one in Cranleigh. Rain runs off the clay faster than the drains can take it, ponding on the High Street, Knowle Lane, the Common and low-lying roads. 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.
• Groundwater. Though the Weald clay holds water at the surface rather than in a deep aquifer, the higher Greensand ground to the north and a high winter water table can saturate low-lying land and below-ground structures. See groundwater flooding.
• Ordinary watercourses and sewers. Many Cranleigh sites sit beside a ditch, brook or culvert classed as an ordinary watercourse, which brings riparian responsibilities and, for works, consent from Surrey County Council rather than the Environment Agency.

Because these sources interact, a single national map is rarely enough on its own. Our notes on critical drainage areas and on the difference between the public flood-risk map and the Flood Map for Planning explain why a Flood Zone 1 site can still need assessment, and why the right starting point is the Environment Agency mapping read alongside the Waverley Strategic Flood Risk Assessment.

A history of flooding in Cranleigh

Ground that has flooded once tends to flood again, so a robust assessment treats Cranleigh's recorded flood history as evidence rather than background colour. The dated events below are why the Environment Agency and the council scrutinise development around Cranleigh Waters and on the clay so closely, and why a flood risk assessment in Cranleigh has to be evidence-led rather than generic.

• November 2000. Prolonged autumn rain produced the highest level on record at the Cranleigh Waters gauge at Flash Bridge, near Alfold, a benchmark event for the brook through the village.
• Winter 2013-14. The wettest UK winter in records going back to 1766 brought the highest recorded level on Cranleigh Waters at Bramley, on 24 December 2013, with low-lying land and roads flooded along the valley and through the surrounding villages.
• Recurrent surface-water flooding. Away from the brook, intense rain repeatedly overwhelms drains and ponds on roads and low ground across the village; Surrey County Council, as Lead Local Flood Authority, records surface water as a major part of Cranleigh's flood problem.
• Development-era drainage concerns. As large housing sites have come forward over the last decade, flooding and surface-water drainage have been raised repeatedly by the Environment Agency, the parish council and residents, keeping the village's flood history at the centre of local planning.

The pattern that runs through all of it is persistent, systemic risk on a flat clay valley floor rather than a string of isolated extreme events.

Building on the Weald clay: why surface water and drainage lead in Cranleigh

Cranleigh sits on the heavy clay and siltstone of the Low Weald, with higher Greensand ground rising to the north. For drainage that geology is decisive: water does not readily soak into clay, so most of the rain that falls on a new development has to be managed at the surface rather than allowed to disappear into the ground. It is the single biggest reason surface water dominates flooding in the village and why drainage so often decides a Cranleigh application.

On low-permeability clay, soakaways frequently fail an infiltration test, so a Cranleigh drainage strategy usually has to store run-off and release it to a watercourse at a tightly restricted rate.

That makes the order of the surface-water hierarchy, and the evidence behind it, central to any scheme here. Infiltration is tested first, normally to BRE 365; where the clay fails it, as it often does, the designer moves down to a discharge to a watercourse, then a surface water sewer, with each step justified by evidence. You can get an early read on whether infiltration is even worth pursuing with our ground conditions and soakaway checker before committing to a trial pit.

• Test infiltration early. A failed infiltration test on clay is normal and is accepted as evidence, but only if it is done; assuming a rate without testing is a common reason an LLFA objects to a drainage strategy.
• Attenuate and restrict. Where soakaways will not work, the scheme stores the climate-change-adjusted run-off and releases it slowly, as close to the greenfield rate as possible, usually to Cranleigh Waters, Littlemead Brook or an ordinary watercourse.
• Mind the four pillars. Surrey expects schemes to deliver water quantity, water quality, amenity and biodiversity together, in line with the four pillars of SuDS and the 2025 national standards, not just hydraulics.
• Permeable paving has limits here. On clay a permeable or tanked paving system can still help by storing and releasing water at a restricted rate, but it cannot be assumed to infiltrate.

Check flood risk anywhere in Cranleigh

Cranleigh and its built-up area are outlined below. Screen any postcode in or around the village against Environment Agency data for rivers and sea, surface water and the planning flood zones, with a climate outlook to 2125. It is an indicative first pass, not a substitute for a site-specific flood risk assessment.

Do you need a flood risk assessment in Cranleigh?

You need a flood risk assessment for most development in Cranleigh within Flood Zones 2 or 3, for sites of one hectare or more in Flood Zone 1, and increasingly for smaller Flood Zone 1 sites where the Flood Map for Planning shows surface water risk or the Waverley Strategic Flood Risk Assessment flags a critical drainage area. Because surface water is so widespread on the clay, many sites that look low-risk on the river map still need an assessment or a drainage strategy. If you are unsure, send us the address and we will tell you quickly.

The detail expected scales with the application. An outline scheme needs to show the principle is sound, a full application needs design and calculations, and discharge of a condition needs full technical compliance. Our guide to whether you can do your own assessment explains where that line falls.

Cranleigh's housing growth and flood risk

Cranleigh has seen some of the largest house-building in Waverley. The adopted Local Plan directs more than 1,700 new homes to the village over the plan period, much of it on greenfield land south and east of the centre around Knowle Lane and Alfold Road. On flat clay beside Littlemead Brook and Cranleigh Waters, that scale of development makes flood risk and surface-water drainage the issues that most often decide whether a scheme is approved, delayed or refused.

The largest sites have been closely fought on exactly these grounds. Parts of the strategic land south of the High Street fall within Flood Zones 2 and 3, the Environment Agency has objected to development on flood-risk grounds, and the surface-water strategy for the early phases relied on discharging run-off at a restricted rate to Littlemead Brook. The sequential test evidence prepared for one major site underlined how flood-constrained the village's growth land is.

For anyone bringing a site forward in or around Cranleigh, the lesson is that the flood risk and drainage case has to be right at the point of submission. Since the April 2026 appeal changes placed more weight on first-time submissions, a weak or missing assessment is far harder to repair later. Where higher-risk land is unavoidable, the Sequential and Exception Tests and the right residual risk case have to be argued from the start.

Climate change is not optional here: a Cranleigh assessment must apply the Environment Agency's allowances for higher river flows and heavier rainfall over the development's lifetime, generally 100 years for housing, which sets floor levels, freeboard and how much attenuation a drainage scheme needs.

Planning policy and your authorities: Waverley Borough Council and Surrey County Council

Two kinds of authority set the rules in Cranleigh. The Environment Agency leads on Cranleigh Waters as a main river. Surrey County Council is the Lead Local Flood Authority, leading on surface water, groundwater and ordinary watercourses, and acting as a statutory consultee on surface water drainage for major development. Waverley Borough Council is the planning authority that determines the application.

Waverley Borough Council, the SFRA and the Cranleigh Neighbourhood Plan

Waverley Borough Council holds the local Strategic Flood Risk Assessment, which maps flood risk from rivers, surface water, groundwater and sewers across the borough in more detail than the national maps, and the adopted Local Plan carries the borough's flood risk policy. Cranleigh also has its own Cranleigh Neighbourhood Plan, which responds directly to the village's flood history by expecting new homes to be flood resilient and designed to minimise surface-water run-off and sewer flooding. Your assessment must satisfy this local framework alongside national policy, the NPPF and its Planning Practice Guidance.

Surrey County Council as your Lead Local Flood Authority

For major development, Surrey County Council is a statutory consultee, and its advice on surface water drainage is a material consideration the borough must take into account. An LLFA objection usually stops the application being determined until it is resolved, so getting the drainage strategy right first time is the surest way to keep a Cranleigh scheme moving.

• The Surrey SuDS pro-forma. The Surface Water Drainage Statement pro-forma is completed for major applications and records how a scheme follows the drainage hierarchy and the national SuDS standards.
• Greenfield runoff rates. Surrey expects discharge as close to greenfield as possible, with the proposed 1-in-100-year-plus-climate-change rate no greater than the existing 1-in-100 rate, which matters on every greenfield Cranleigh site.
• The drainage hierarchy. Infiltration first, then a watercourse, then a surface water sewer, then a combined sewer, with each step down justified by evidence such as BRE 365 infiltration testing.
• Pre-application advice. Surrey County Council offers a chargeable pre-application SuDS service and takes SuDS queries at SuDS@surreycc.gov.uk; early engagement reduces time at the formal consultation stage.

What your flood risk assessment in Cranleigh must show

• Risk assessed from every credible source, using the Flood Map for Planning and the Waverley Strategic Flood Risk Assessment.
• An appropriate location, tested against the Sequential Test where policy requires it.
• Safe for its lifetime, once Environment Agency climate change allowances are applied, generally 100 years for housing.
• No increase in flood risk elsewhere, with attenuation to greenfield rates and, where needed, compensatory storage.
• Residual risk managed, with safe access, egress and finished floor levels, the area where many clay-valley applications are won or lost.

Flood risk assessments for every situation in Cranleigh

Whatever brings you to a flood risk assessment in Cranleigh, there is a report scoped for it. A flood risk assessment, a sequential or exception test and a drainage strategy are three different reports: one asks whether the site is safe, one asks whether the development should be in that location, and one asks where the surface water goes. They often travel together in a planning submission, and we will tell you which ones your situation needs.

• Flood risk assessment for planning. The site-specific report submitted with a planning application; see flood risk assessment for planning and our NPPF guidance.
• Flood risk survey for property purchase. An independent, property-specific view for buyers and their advisers, set out on our homebuyer flood risk survey page.
• Flood risk assessment for insurance. Property-level evidence for insurers and brokers; see the insurance flood risk assessment.
• Flood risk assessment for BREEAM. Structured to support Pol 03 credits on new-build schemes from the outset; see FRA for BREEAM.
• Sequential and Exception Tests. The policy tests that direct development to lower-risk land, prepared alongside the assessment; see sequential and exception test reports.
• Surface water drainage strategy and SuDS. A separate drainage report, designed to Surrey's standards; see sustainable drainage strategy and design, with preliminary drainage design for outline schemes and discharge of drainage conditions after permission.
• Groundwater flood risk assessment. A defensible design water table where it matters, assessed within the wider FRA; see groundwater flood risk assessment.
• Flood modelling. Hydraulic modelling of Cranleigh Waters where national mapping does not reflect local conditions; see flood modelling services.

How Unda helps with flood risk assessment in Cranleigh

We act as the accurate translation layer between your scheme and the requirements set by the Environment Agency, Surrey County Council as Lead Local Flood Authority, Waverley Borough Council and national planning policy. We are experts on how Cranleigh floods, not a generic report mill, and we stay involved past the report to answer objections. A flood risk assessment in Cranleigh from Unda assesses every credible source, from Cranleigh Waters down to surface water, groundwater and any ordinary watercourse on the boundary, compares modelled flood levels against your proposed floor levels, sets safe access and egress, and recommends mitigation the regulators will accept. Where the council needs it, a surface-water drainage strategy sits alongside the assessment as a separate report so the two cases stay consistent and an objection has nowhere to land. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report.

Our flood risk services for Cranleigh

• Flood risk assessment for planning. Site-specific reports that satisfy the Environment Agency and Waverley Borough Council; see flood risk assessment for planning.
• Surface water drainage strategy and SuDS. Designed to Surrey County Council's standards and pro-forma from the first sketch, for clay sites where infiltration usually fails.
• Groundwater flood risk assessment. A defensible design water table for low-lying and below-ground space, not a guess.
• Sequential and Exception Test reports. Prepared alongside the assessment where policy requires them.
• Flood modelling. Hydraulic modelling of Cranleigh Waters where national mapping does not reflect local conditions.
• Chartered flood risk consultants. Specialists who sign their advice; read more about Unda and our wider flood risk assessment services.

Home buyers and businesses come to us too: a flood-risk question can affect house prices and insurance, and a conveyancing search is not the same thing as a planning-grade assessment. For the wider county picture, see our flood risk assessment in Surrey page, and for the nearest towns on the River Wey, our flood risk assessment in Godalming and flood risk assessment in Guildford pages.

Cranleigh flood resources and contacts

The most reliable Cranleigh flood information comes from the lead authorities. For an immediate threat to life during a flood, always call 999.

• Check for flooding. Environment Agency live warnings, river levels and maps, including the Cranleigh Waters flood alert area, the Cranleigh Waters near Cranleigh and Shamley Green flood warning area, and the national check for flooding service.
• Surrey County Council flooding and SuDS. The county's SuDS planning guidance and its Local Flood Risk Management Strategy.
• Waverley Borough Council and the Neighbourhood Plan. The council's Strategic Flood Risk Assessment and adopted Local Plan flood policy, and the Cranleigh Neighbourhood Plan.
• Catchment data. The Environment Agency's Cranleigh Waters water body record sets out its classification and the pressures on it.
• Floodline. Call 0345 988 1188 for recorded flood information and to sign up for free flood warnings; call 105 for power cuts during flooding.
• Live levels and screening tools. See whether Cranleigh Waters is running high right now on our live river levels map, take a first-pass postcode screen on our flood risk map, and size a soakaway with our drainage calculators and BRE 365 infiltration rate calculator.

For flooding from blocked or burst sewers, contact Thames Water as the local sewerage undertaker.

Flood risk assessment in Cranleigh: frequently asked questions