Flood Risk Assessment in Leatherhead

A flood risk assessment in Leatherhead starts with the River Mole, which runs north past the town's western edge, between Leatherhead and Fetcham, on its way from the North Downs to the Thames. On Christmas Eve 2013 it rose fast enough to put homes on both banks under water. We prepare flood risk assessments in Leatherhead for planning applications to Mole Valley District Council, for buyers, lenders and insurers, and alongside them sequential and exception tests and surface water drainage strategies.

In this guide Leatherhead means the town as the Office for National Statistics maps it: the town centre, the riverside streets on the Leatherhead bank such as Thorncroft Drive and Minchin Close, and the housing east to the Ashtead boundary. Fetcham, across the Mole, and Great Bookham beyond it share the KT22 and KT23 postcodes, the same river and the same council, and so does Ashtead, which drains to the Mole along the Rye Brook; all three are covered here. Mole Valley District Council decides planning applications, Surrey County Council is the Lead Local Flood Authority, and our page on flood risk assessment in Surrey covers the rest of the county.

On 24 December 2013 the Mole reached 3.74 m at the Leatherhead gauge, its highest level since the gauge opened in 1986, and the Environment Agency counted 41 flooded properties in its Leatherhead and Fetcham warning area.

Anyone weighing up an address in Leatherhead, Fetcham, Bookham or Ashtead can speak to our flood risk consultants on 01293 214444 or write to enquiries@unda.co.uk.

Christmas Eve 2013 and the Mole's record at Leatherhead

The Environment Agency lists significant floods in Leatherhead and Fetcham in 1947, 1960, 1968, 1974, 1990, 2000 and 2008 before the winter of 2013/14, and Surrey County Council's Section 19 investigation for Mole Valley, published in October 2015, records how the last of those unfolded. The dates below come from those two sources and from the town's regeneration programme.

1. September 1968. The 2017 Strategic Flood Risk Assessment records this flood as widespread across Mole Valley, Reigate and Banstead and Tandridge, part of the September 1968 flood across the South East.
2. December 2000. Flooding along the length of the Mole, made worse by blocked culverts, surface water and sewers, after a wet autumn that had already flooded Crawley and Gatwick upstream.
3. 24 December 2013, 08:09. The Environment Agency issued a flood warning for the River Mole at Leatherhead and Fetcham to 281 registered properties. Its later count found 41 of them flooded.
4. 24 December 2013, 14:10. The warning became a severe flood warning, meaning danger to life, sent to 269 properties, and Mole Valley opened a rest centre in Leatherhead that evening. Waterway Road was closed during the flooding, and Surrey Fire and Rescue had to move out of its flooded Leatherhead offices.
5. January and February 2014. Four more warnings went out for the same area, on 2, 6 and 17 January and 1 February, each to around 300 properties; the Agency counted no further flooded properties.
6. December 2019. A temporary flood barrier plan for Minchin Close and Emlyn Lane, on the Leatherhead bank, was put into use for the first time.
7. March 2020. Work began on an Environment Agency property resilience scheme for homes in Leatherhead and Fetcham (described in the next section).

Peak flows on the Mole in December 2013 were too high for the Dorking and Leatherhead gauges to measure, so the Section 19 report could only estimate the event: about a 1 in 50 year flood from the flows that were recorded, and more likely between 1 in 60 and 1 in 90 years at both towns. Across the Mole valley the river rose about a foot an hour and fell back within roughly ten hours. Readings from the Leatherhead gauge and the rest of the river can be followed on our live river levels map, and our guide to why some floods get a Section 19 investigation explains how these reports are triggered.

Reading the Leatherhead gauge before you build or buy

The Environment Agency's River Mole level at Leatherhead gauge publishes the levels at which it expects trouble. They give a simple test of how exposed a riverside plot has been, and an assessment uses them alongside the modelled flood levels.

Homes near the river can sign up to the River Mole at Leatherhead and Fetcham warning area, and the Agency notes that flooding may not repeat at the same levels because of schemes put in place since. The Leatherhead and Fetcham scheme protects individual houses rather than the river corridor. After assessing 20 options with Surrey County Council, Mole Valley and Thames Water, the Agency chose property flood resilience: 170 homes in Leatherhead and Fetcham were found eligible, the owners of 85 agreed the work, and Be Flood Ready, a CIWEM initiative, reports that 70 were fitted and audited. The Flood Map for Planning shows river risk without defences in any case, so the flood zones are unchanged and our explainer on residual flood risk covers what remains.

Screen a Leatherhead, Fetcham or KT22 postcode

Enter a postcode below to see the Environment Agency's river, surface water and reservoir data for it; our flood risk map gives the same screening for any address in England. The coral outline is the ONS built-up area of Leatherhead, which follows the town to the Leatherhead bank of the Mole. Fetcham Grove, Mill Lane and the rest of Fetcham lie across the river and outside the line, as does Waterway Road, so check those addresses by postcode.

Chalk, clay and the Rye Brook: what floods Leatherhead

Leatherhead sits where the Mole leaves the chalk of the North Downs. The Section 19 report describes chalk under the south of the town and clay under the north, with a narrow band of Thanet sand between them, and that change of ground brings groundwater into play alongside the river and surface water. The December 2017 Level 1 SFRA that JBA prepared for Mole Valley, Reigate and Banstead and Tandridge records many properties in Flood Zone 3 where the Mole passes through, with flood outlines mapped in Fetcham and the west of Leatherhead.

Groundwater also shapes drainage. The SFRA names a groundwater Source Protection Zone centred on Leatherhead, which protects a drinking water supply, and it asks for a hydrogeological risk assessment before infiltration SuDS take anything but clean roof water inside an inner zone. So a soakaway on Leatherhead chalk has to be tested before it is relied on. Our guides to source protection zones, checking groundwater at a site and BRE 365 infiltration testing cover the steps, and the ground conditions and soakaway map gives a first reading of the geology. The River Mole page follows the river from Gatwick to the Thames.

What Mole Valley's INF3 and the 2017 SFRA ask of a flood risk assessment in Leatherhead

Mole Valley decides applications against the Mole Valley Local Plan 2020-2039, adopted on 15 October 2024. Its flood policy, INF3 Flood Risk, applies the sequential test to flooding from any source, then the exception test where needed, and expects a site-specific assessment. It avoids development entirely in Flood Zone 3b, except essential infrastructure that passes the exception test, and asks for mitigation designed in from the start with an allowance for climate change. Its drainage clause sets runoff at greenfield rates from every greenfield site and from brownfield sites in Areas of Critical Drainage, and as close to greenfield as feasible elsewhere. Policy S3 on the town centre plans a Riverside Park that reduces the risk of flooding in Leatherhead and Fetcham.

The SFRA's treatment of Zone 3b matters on the Mole. Where the Environment Agency's model gives a 1 in 20 year outline, that is the functional floodplain; where it does not, the whole of Zone 3a is treated as functional floodplain until a site assessment shows otherwise with the Agency's agreement, and our explainer on Flood Zone 3b sets out what that rules out. The SFRA also expects an assessment for any development in Flood Zones 2 and 3, including householder extensions and changes of use, and says temporary or demountable barriers are not acceptable protection for new development.

On drainage, Surrey County Council comments on smaller schemes too where they sit inside the 1 in 100 year surface water extent or beside a watercourse, and it signs off the drainage for major ones. Both councils change on 1 April 2027, when Mole Valley and Surrey County Council's local functions pass to the new East Surrey Council; until then they work as before, and our article on local government reorganisation explains what a planning applicant should expect.

From a Fetcham extension to Bull Hill: when a flood risk assessment in Leatherhead is needed

Proposals in Leatherhead range from extensions, replacement houses and conversions to regeneration in the town centre. The table sets out the usual position for each; the flood zone of the plot, its surface water risk and whether it falls in the SFRA's functional floodplain decide the detail.

The largest current proposal is the Swan Centre and Bull Hill regeneration, for which the Leret Partnership, a joint venture between Mole Valley District Council and Kier, submitted a planning application in November 2025 covering 480 homes and more than 10,000 m² of offices. At the other end of the table, our guides to building an extension in a flood zone and to sewer flooding cover what a householder in KT22 is likely to be asked for.

Fetcham, Bookham and Ashtead: one river, three different problems

The villages around Leatherhead share its council and its river, but each floods in its own way, so an assessment there starts from a different set of records.

• Fetcham. Across the Mole from the town, Fetcham was one of the most affected places in the middle Mole catchment in 2013; the Environment Agency put the number of flooded homes there at about 75 on 24 December. The Section 19 report describes flooding there from the river, surface water and the foul sewer acting together, notes significant surface water flow routes through its streets, and finds potential for groundwater to reach the surface near the river.
• Great Bookham. Bookham has no main river, but in 2013/14 Mole Valley reported serious problems there with springs and surface water; Lower Road was closed, and Surrey County Council planned new soakaways on Dorking Road and studied wider conveyance and storage options. The KT23 3 postcode sector carries 17 sewer flooding records.
• Ashtead. The Rye Brook drains Ashtead to the Mole. Part of it is a main river, and a restoration on Ashtead Common carried out in 2006 by the City of London, Natural England, the Environment Agency and the Ashtead Residents Association brought back its bends and added ponds that fill in floods, with a low embankment protecting nearby houses. KT21 2 has 20 sewer flooding records.

Upstream the Mole comes through Dorking, and its headwaters rise around Crawley; downstream it passes Cobham and Esher on its way to the Thames. Each has its own page.

The reports Leatherhead and Fetcham sites call for

We work for homeowners, buyers, landlords, developers and businesses across Leatherhead and its villages. A replacement house on the Fetcham bank may need three of these reports in one submission; a loft conversion near Leatherhead station may need none.

• Every source together. A flood risk assessment for a Leatherhead site weighs the Mole, the Rye Brook, surface water running off the chalk slopes, groundwater and the sewers on one plot.
• Applications to Mole Valley. Extensions, rebuilds and conversions need a flood risk assessment for planning written to Policy INF3 and the 2017 SFRA's functional floodplain.
• Buying near the river. Homes on both banks flooded in December 2013, so a flood risk survey for property purchase is worth having before exchange.
• New homes in Zones 2 and 3. A replacement house or extra flat counts as new housing in policy terms, so Mole Valley expects a sequential and exception test report with the assessment.
• Reuse and soakaways. Surrey always asks for rainwater reuse and the Source Protection Zone limits infiltration, so a drainage strategy for Leatherhead starts there.
• Holding runoff back. A surface water drainage strategy shows discharge held to Surrey's 1 in 2 year rate, with 10% allowed for urban creep.
• After permission. Surrey's standard drainage condition asks for infiltration results, calculations and a maintenance plan, and our discharge of drainage conditions service prepares them for Mole Valley.
• When the gauge cannot tell. The Leatherhead and Dorking gauges could not measure the 2013 peak, so flood modelling sets design levels where the national mapping is too coarse for a riverside plot.
• Water under the chalk. Groundwater can rise near the Mole, so a groundwater flood risk assessment answers basement and soakaway questions the flood maps cannot.
• Cover after 2013. Owners in the Leatherhead and Fetcham warning area, where 41 properties flooded, use a flood risk assessment for insurance to show insurers the actual risk to the building.
• Foul water in KT22. Leatherhead's KT22 7 sector has more sewer flooding records than anywhere else in Mole Valley, so a foul drainage strategy checks capacity before new homes connect.
• Warnings and closed roads. With Waterway Road shut in 2013 and a severe warning issued for the area, a flood warning and evacuation plan sets out how residents leave in time.
• Town centre offices. Office and leisure space proposed at Bull Hill and the Swan Centre seeking BREEAM credits needs a BREEAM flood risk assessment.
• Keeping services running. Surrey Fire and Rescue's Leatherhead offices flooded in the winter of 2013/14, and a business continuity flood risk assessment helps an occupier plan for the next event.

Leatherhead's flood contacts, from Floodline to the Surrey Local Resilience Forum

Ring 999 if floodwater puts anyone in danger, and 105 to report a power cut. The table lists who manages each kind of flooding in Leatherhead and how to reach them.

Surrey's Local Flood Risk Management Strategy, refreshed in 2025, sets out how these bodies share the work. The Leatherhead and Fetcham Flood Action Group spoke for residents when the Agency consulted on its options for the town, and the Agency's long-term flood risk service shows the risk to any address.

Questions we are asked about Leatherhead sites

Every report we issue for a Leatherhead, Fetcham, Bookham or Ashtead address is checked and signed off by a senior consultant. Our flood risk consultants are chartered, and Unda Consulting Limited is a CIWEM Business Partner. Call 01293 214444 or email enquiries@unda.co.uk with the site address to start.