Flood Risk Assessment in Molesey

A flood risk assessment in Molesey starts at a confluence. The River Mole and the Ember, the channel cut beside it for the Lower Mole flood scheme, pass either side of Island Barn Reservoir and reach the Thames opposite Hampton Court Palace, and the Dead River crosses West Molesey to join them. Our consultants write flood risk assessments in Molesey for planning applications, house purchases, lenders and insurers, and prepare sequential and exception tests and surface water drainage strategies from the same river evidence. Reports for sites in Molesey come from Unda Consulting Limited, a CIWEM Business Partner.

Here Molesey means East Molesey and West Molesey as the council's ward map draws them: the Molesey East and Molesey West wards, from Hurst Park and the Thames frontage at Molesey Lock to Bishop Fox Way and the Molesey Industrial Estate in the west. Island Barn Reservoir, Imber Court and the Esher Road end of KT8 sit just across the line in Thames Ditton ward, and the page covers them as well. Elmbridge Borough Council decides planning applications, Surrey County Council is the Lead Local Flood Authority, and the county-wide rules are on our flood risk assessment in Surrey page.

Elmbridge's 2024 Strategic Flood Risk Assessment puts 39% of East and West Molesey in Flood Zone 2 and 12% inside the modelled functional floodplain, an outline that crosses built-up streets such as Hurst Road and Molesey Road, where any redevelopment meets the borough's strictest flood rules.

For a KT8 address, ring our flood risk consultants on 01293 214444 or email enquiries@unda.co.uk.

Where Molesey's water comes from

Molesey is flat and low, between about 5 and 10 metres above sea level, with the Thames along its northern edge and the Mole system to the south and east. Elmbridge's Level 1 Strategic Flood Risk Assessment (AECOM, updated in 2024) profiles East and West Molesey source by source, and an assessment has to answer each one for the plot in question.

Which river sets the design flood level depends on where a plot sits. The SFRA explains that the Thames model overstates flooding from the Mole, so the Environment Agency agreed a split: along the Thames frontage and on the Mole downstream of the A309 Hampton Court Way, Thames-led floods apply; between Island Barn and Hampton Court Way, the floods driven by the Mole and Ember apply; and upstream of Island Barn, the Lower Mole model is used. Two houses a few hundred metres apart can therefore take their levels from different studies.

The rivers themselves have their own pages: the River Mole from its source near Rusper, and the River Thames through Surrey and London. Reservoir risk is rarer than either but covers more of Molesey than any river does, and our explainer on reservoir flooding and planning sets out how an assessment deals with it.

Screening an address in East or West Molesey

Enter a postcode in the map below to see the Environment Agency's river, surface water and reservoir data for that spot, or use our flood risk map for anywhere in England. The coral outline follows the two Molesey wards, so Island Barn Reservoir and Imber Court fall just outside it to the south-east. Across the Thames, Hampton Court Palace and the far bank lie in London.

Molesey's flood record, from 1968 to the winter of 2013/14

Molesey's modern flood history divides into before and after the Lower Mole scheme. The dates below come from Elmbridge's SFRA, the Environment Agency's scheme pages and Surrey County Council's Section 19 report for Elmbridge, published in October 2015 after the winter of 2013/14.

1. September 1968. After the wettest September on record, torrential rain on 14 and 15 September fell on saturated ground. The SFRA calls it the worst flood recorded in the Mole catchment, says it hit Esher and Molesey badly, and treats it there as roughly a 1 in 200 year event; up to 10,000 properties along the Mole flooded. Our article on the great flood of 1968 covers the wider event.
2. 1974 to 1991. Planning permission for the Lower Mole scheme was granted in 1974. The SFRA dates the works to between 1977 and 1991: an enlarged Mole, the new Ember channel, embankments beside Island Barn Reservoir and walls running to Hampton Court.
3. After 1991. The SFRA, citing the Environment Agency's 2009 Lower Mole study, records no out-of-bank flood on the Lower Mole or the Ember since the scheme was finished.
4. January 2003. One of the two largest recent floods on the lower Thames in the SFRA's list, with January and February 2014.
5. December 2013. On 13 December the Mole gauge near the Thames recorded its highest peak level for 16 years (the gauge holds 26 years of data). The Agency operated the scheme on 24 and 25 December, and Surrey's report records no property in its Esher and East Molesey area flooded from the Mole or the Thames that month.
6. January and February 2014. The Thames flooded one Molesey property in January and twelve in February. The Agency sent Thames warnings for Molesey to 1,736 registered owners in January and 1,770 in February, high flows eroded the scheme's banks (since repaired), and Elmbridge lists a Hurst Park flood forum among the groups formed afterwards.
7. January 2024. Storm Henk: the SFRA counts it among the smaller lower Thames floods, and Surrey's Section 19 investigation of the Thames that month lists no site in Molesey.

Two gauges show what the rivers are doing now: the Thames at Molesey Lock and the Mole at Esher, upstream of the scheme. Both appear with every other gauge in the area on our live river levels map, and the Agency issues warnings for two areas that cover Molesey: the River Thames at East and West Molesey, which names Hurst Park, Buckingham Avenue and the Royal Mews area, and the River Mole at Esher and East Molesey.

What the Lower Mole scheme protects, and the risk it leaves

Most homes on the Mole side of Molesey rely on the Lower Mole Flood Alleviation Scheme. The Environment Agency says it protects around 1,300 homes and businesses. Its enlarged channels carry high flows, and its sluice gates hold river levels steady in normal conditions and are opened in a flood to pass water to the Thames as fast as possible.

The 1,300 figure comes from the Agency's current modelling. If the gates at Viaduct Sluice failed to open today, water would leave the river on its eastern side near the railway and run north, flooding property between Esher and Thames Ditton. Older papers give larger numbers, about 3,000 in the Agency's earlier correspondence and 10,000 in Surrey's 2015 Section 19 report, and they measure different things, so an assessment quotes the source it relies on.

The scheme is ageing. It is reaching the end of its design life, with decisions due on six main sluice structures. From 15 August to 6 November 2024 the Agency consulted on four refurbishment options. Of 203 responses, 63% put first the option that keeps gates at Island Barn and Viaduct and holds today's water levels. All four options keep protection at a 1 in 100 standard allowing for climate change, the costs exceed the government grant available, and the Agency's pages give no construction timetable.

None of that removes the need for an assessment. The Flood Map for Planning draws flood zones as if the defences were absent, updated climate change allowances are not yet available for the Lower Mole, and the Thames side of Molesey has no formal raised defence: the Agency's asset records show only high ground along the river there. That last point matters on Hurst Road. A Molesey assessment therefore tests residual flood risk, meaning what happens if a gate sticks or a wall is overtopped, and explains to buyers why a site stays in a flood zone after defences are built.

Hurst Road to Bishop Fox Way: building in Molesey's functional floodplain

Elmbridge draws the functional floodplain, Flood Zone 3b, in Molesey from three outlines: the 1 in 30 year Thames flood, the 1 in 75 year Lower Mole flood and the 1 in 50 year Dead River flood. Together they cover 0.7 km2, 12% of the SFRA's Molesey area, and they run through housing. Building footprints that keep water out are not themselves treated as Zone 3b, but the SFRA lists the Molesey streets where the outline crosses development: Monks Avenue, Knights Close, Ivydene and The Dene; Molesey Avenue and Armfield Close; Walton Road, Central Avenue, Dunstable Road and Minster Gardens; Molesey Road, Pool Road, Brokenhurst, Nydene and Bishop Fox Way; the A3050, Hampton Court Crescent and The Riverside; and Graburn Way, Hurst Road, Riverbank and Feltham Avenue.

• No higher vulnerability. A redevelopment must not raise the site's vulnerability class, and a change of use or conversion to a more vulnerable use should not be permitted.
• A net cut in flood risk. Every scheme must reduce flood risk overall and leave storage and flow routes untouched, for example by keeping or shrinking the footprint and raising floor levels.
• No more people at risk. Conversions and rebuilds that add dwellings are to be avoided.
• No basements. New basements, basement extensions and basement conversions to a more vulnerable use should not be permitted.
• Storage replaced level for level. Any lost floodplain volume is replaced at the same level, in 100 mm or 200 mm slices up to the 1 in 100 year flood with climate change, on land the applicant owns nearby. Voids under floors do not count.

Smaller works on these streets must still avoid any effect on storage or flow routes, which in practice means raised floors and, where possible, level-for-level compensatory storage. Hurst Park has extra protection. Core Strategy Policy CS26 lists it, with Desborough Island, as undeveloped floodplain to be kept from any use that is not flood-compatible. Our guide to Flood Zone 3b explains the national rules behind all of this.

Policy for a flood risk assessment in Molesey: CS26 and the withdrawn Local Plan

Applications in Molesey are still decided under the Core Strategy that Elmbridge adopted in 2011. The Elmbridge Local Plan 2037, submitted in August 2023, was withdrawn by Full Council on 26 February 2025, and work on a new Local Plan has begun, so nothing in it carries weight yet. On 1 April 2027 Elmbridge joins East Surrey Council, which will take over planning and the Lead Local Flood Authority role from the borough and the county.

The householder guide matters on the Victorian streets of East Molesey and the 1960s estates of West Molesey alike. Elmbridge says the Environment Agency's table for minor extensions under standing advice does not give enough detail. It wants six steps: risk from every source with climate change, the extension's effect on flood water, mitigation, resistance and resilience with floors no lower than the existing house, a personal flood plan with an escape route, and drainage for the extra runoff. A thin report can be refused, because the council does not ask for more information during determination. Our note on extending a house in a flood zone covers the national side.

Soakaways are the weak point. The SFRA finds very significant constraints on widespread infiltration across the north and centre of Molesey, where the gravels carry groundwater near the surface, and room for bespoke infiltration only in the east and south. Surrey expects BRE 365 tests with the application, so our geology and soakaway map gives a quick first read before anyone digs a trial pit.

Molesey proposals and the assessments they trigger

Applications in Molesey run from house extensions, rebuilds and conversions to industrial and trade units on the two employment estates. The table gives the starting position for each; the plot's own flood zone, any Zone 3b outline and the surface water map decide the rest.

The two estates are Elmbridge's strategic employment land in Molesey. The Dead River runs along the southern edge of the Molesey Industrial Estate, and Imber Court sits just over the ward line towards Island Barn. A rebuild in Zone 2 or 3 counts as a new dwelling, which is why our guide to rebuilding a house in a flood zone applies to many Molesey plots, and the rules for basements and cellars in a flood zone apply on the gravels even outside Zone 3b.

Reports for Molesey homes, estates and riverside plots

Homeowners, buyers, landlords, developers and businesses in Molesey commission these reports. A riverside rebuild may need three at once; a West Molesey extension may need just one.

• One report, every source. A flood risk assessment for a Molesey plot weighs the Thames, the Mole and Ember, the Dead River, surface water, groundwater, sewers and the reservoirs together.
• Applications to Elmbridge. A flood risk assessment for planning answers Policy CS26, the householder guide and the SFRA's Zone 3b rules for the street concerned.
• Buying a house in KT8. With twelve Molesey homes flooded by the Thames in February 2014, home buyers can commission a flood risk survey for property purchase before exchange.
• Rebuilds and new homes. A replacement dwelling in Zone 2 or 3 needs a sequential and exception test alongside the assessment.
• Water reuse and the gravels. Surrey always asks for rainwater collection, and infiltration is tightly limited in north and central Molesey, so the drainage strategy starts there.
• Runoff from the site. A surface water drainage strategy holds discharge to Surrey's 1 in 2 year rate, and to greenfield rates in Zones 2 and 3 under CS26.
• Clearing conditions. Pre-commencement drainage conditions on an Elmbridge permission are handled through our discharge of drainage conditions service.
• Which model sets the level. Between Island Barn and Hampton Court Way the Agency's Thames and Mole models disagree, so flood modelling settles the design level for a plot.
• Getting out before the water. Elmbridge's Molesey rest centre is itself in Flood Zone 2, and the Zone 3b streets carry the SFRA's call for timely evacuation, so a flood warning and evacuation plan shows how occupants leave in time.
• Below ground on Kempton Park Gravel. Where the SFRA finds groundwater can rise to the surface in north and central Molesey, a groundwater flood risk assessment tests a cellar or lower floor before it is drawn.
• Insurance after February 2014. Owners in the Thames warning area around Hurst Park and the riverside can use a flood risk assessment for insurance to show insurers the risk at their own address.
• New industrial floor space. Units on the Molesey Industrial Estate or at Imber Court seeking BREEAM credits need a BREEAM flood risk assessment that covers the Dead River and the reservoir extent.
• Buying estate land. Strategic employment land beside the Dead River calls for due diligence before a purchase or a loan.
• Keeping a firm trading. Firms on the Molesey Industrial Estate, where the Dead River's modelled flooding spreads further once climate change is added, use a business continuity flood risk assessment to plan for closure and recovery.

Who to contact about flooding in East or West Molesey

Call 999 if floodwater puts anyone in danger, and 105 for a power cut caused by flooding. For everything else, the table shows which body deals with which water.

Elmbridge's primary rest centre for the area is the Molesey Centre, which the SFRA itself places in Flood Zone 2, so whether it opens depends on the flood. Across the Thames, the far bank belongs to Richmond and Kingston: our pages on flood risk assessment in Richmond upon Thames and the Royal Borough of Kingston upon Thames cover that side, and neighbouring Elmbridge towns have their own pages for Thames Ditton, Esher and Walton-on-Thames.

Flood risk assessment in Molesey: what owners and applicants ask

Every Molesey report is signed off by a senior consultant before it leaves us. The people writing them are chartered, and Unda Consulting Limited is a Business Partner of CIWEM. Call 01293 214444 or email enquiries@unda.co.uk with the address and plans.