Flood Risk Assessment in Esher

Flood risk assessment in Esher: the essentials

Esher is one of the few Surrey towns sitting inside two separate Environment Agency flood warning areas at once: the River Mole at Esher and East Molesey flood warning area, and the River Rythe from Oxshott to Thames Ditton. A flood risk assessment in Esher has to read both rivers alongside the surface water that closed the A3 through the Hook Underpass three times in a single day in August 2021, and the groundwater that moves through the gravels beneath the town. We prepare flood risk assessments in Esher for planning, for a property purchase or mortgage, for insurance and for BREEAM, alongside sequential and exception tests and surface-water drainage strategies, dealing directly with the Environment Agency and Surrey County Council on your behalf.

Esher is protected to a 1-in-200-year standard by the Lower Mole Flood Alleviation Scheme, yet a 1968 storm still put an estimated 8,000 of the former Esher Urban District's 20,000 buildings under water. Defended is not the same as risk-free.

• Two rivers, one town. Esher is named in both the River Mole at Esher and East Molesey flood warning area and the River Rythe from Oxshott to Thames Ditton flood alert.
• Defended, not risk-free. The Lower Mole Flood Alleviation Scheme protects Esher to a standard equivalent to a 1-in-200-year (0.5% annual) flood.
• A real flood history. Esher has flooded in 1968, in 2000 and again over the winter of 2013/14, plus twice in 2021 from surface water alone.
• Flood Zone 2 reaches Esher. Elmbridge's Level 1 Strategic Flood Risk Assessment (April 2024) places Esher within the roughly 11% of the borough mapped as Flood Zone 2.
• Two authorities to satisfy. Surrey County Council is the Lead Local Flood Authority; Elmbridge Borough Council applies flood policy through Core Strategy Policy CS26 and its Flood Risk SPD.
• Every situation, one team. Planning, property purchase, mortgage, insurance, BREEAM, sequential and exception tests, and drainage strategies, all prepared in-house.

Check flood risk anywhere in Esher

Elmbridge, the borough that contains Esher, is outlined below. Screen any postcode 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, useful for an early read on a site or a property, not a substitute for a site-specific flood risk assessment.

Alongside this checker, our Flood Risk Map and Live River Levels Map track conditions on the Mole and the Rythe in real time, and our Geology & Ground Conditions checker gives an early read on soakaway potential. Scoping a drainage strategy? Our Drainage Calculators and BRE 365 Infiltration Rate Calculator help size a scheme before detailed design begins.

Flood risk in Esher: the Mole, the Rythe and surface water

Esher's flood risk comes from more than one direction, and a credible assessment has to read them together rather than in isolation. The River Mole runs to the west of the town and gives Esher its own named flood warning area; the River Rythe rises near Oxshott and is separately named in an Environment Agency flood alert covering Esher, Thames Ditton and Oxshott. Surface water behaves independently of either river: it is what closed the A3 through the Hook Underpass three times in one day in August 2021. Groundwater rises through the river-terrace gravels beneath the town on its own timescale, sometimes persisting for weeks after rain has stopped.

The Level 1 Strategic Flood Risk Assessment that Elmbridge Borough Council updated in April 2024 puts this in borough-wide context: roughly 2% of Elmbridge sits in Flood Zone 3a and around 11% in Flood Zone 2, a band that takes in Esher alongside Claygate, Hinchley Wood and Thames Ditton. None of that tells you what a specific plot needs. For that, the flood zone has to be read against surface water mapping, ground levels and, where relevant, the Council's own Section 19 flood investigation findings for the area.

Esher's rivers connect it to the flood risk picture in neighbouring towns: to Cobham and Oxshott upstream on the Mole and the Rythe, to Thames Ditton and Molesey where the Rythe and the Mole reach the Thames, and to Walton-on-Thames and Weybridge further along the river. We prepare flood risk assessments across Surrey as a whole, with the same local knowledge applied wherever your site sits.

The Lower Mole Flood Alleviation Scheme, and the risk that remains

Esher is a defended town. The Lower Mole Flood Alleviation Scheme, more than three kilometres of earth flood banks, protects Esher alongside Molesey, Hersham and Walton to a standard equivalent to a 1-in-200-year, or 0.5% annual, chance of flooding. That is a high standard of protection by UK river-defence norms, and it explains why Esher was not evacuated street by street in the way some undefended Mole-valley towns were during the storms of the last sixty years.

A defended standard is a probability, not a guarantee. The scheme's own banks suffered erosion during the winter 2013/14 floods and needed repair by the Environment Agency afterwards, and a 1-in-200-year standard still leaves a residual chance of the defence being overtopped or of flooding arriving from a source the bank was never built to stop, such as surface water or a rising water table. That residual risk, and how a development manages it if the defence is ever exceeded, is exactly what a flood risk assessment in Esher has to demonstrate; see our note on residual flood risk for how this is assessed; it does not disappear because a site sits behind a flood bank.

A history of flooding in Esher

Esher's flood record is well documented, and the detail matters more than the headline: three fluvial events over almost sixty years, and two more recent events driven by surface water alone.

Read together, the record shows a town that floods from more than one direction and on more than one timescale: a defended river that can still be overwhelmed by an exceptional event, and drains that flood on their own with no river anywhere near their limit.

Planning policy and your flood authorities in Esher

Two authorities sit behind any flood risk assessment in Esher, and it helps to know which does what. Surrey County Council is the Lead Local Flood Authority, responsible under the Flood and Water Management Act 2010 for surface water, groundwater and ordinary watercourse flood risk, and for investigating significant local flooding. Elmbridge Borough Council is the local planning authority, and applies flood policy through the development plan and through planning conditions.

• Core Strategy Policy CS26 (Flooding). Elmbridge's central flood policy, requiring development to be located, designed and laid out so it stays safe without increasing flood risk elsewhere. Read more in Elmbridge's flood risk planning policy.
• The Flood Risk Supplementary Planning Document. Adopted to help applicants prepare flood risk assessments that satisfy CS26, including a small-scale development template for extensions and householder schemes.
• A SuDS hierarchy with no off-site trading. The SPD requires each development to offset its own increase in surface water runoff on-site: attenuation cannot simply be traded elsewhere in the catchment.
• The 2024 Strategic Flood Risk Assessments. Elmbridge's Level 1 SFRA (borough-wide overview of every flood source) and Level 2 SFRA (site-specific detail) were both updated in April 2024 by AECOM, replacing earlier 2015/2019 versions.
• The NPPF's risk-based approach. National policy steers development to the lowest-probability flood areas first and, since the September 2025 update, applies that approach to surface water and groundwater as well as rivers and the sea. See our NPPF guidance and advice and our explainer on the NPPF's approach.

Elmbridge's own evidence base gives a sense of scale: its Strategic Flood Risk Assessment records more than 12,500 properties across the borough at risk of flooding from one source or another, which is why the Council takes a precautionary line even on minor development in areas the SFRA flags. Even a small extension can still be asked to compensate for any floodplain storage it removes.

Development and flood risk assessment in Esher

Esher's live development context ranges from a major leisure and residential scheme to the routine extensions typical of a high-value Surrey town. Sandown Park Racecourse is the subject of a hybrid planning application covering an outline hotel of up to 150 bedrooms, a family and community zone, and residential development of up to 318 units, the kind of scheme where flood risk, drainage and the Sequential Test all have to be worked through together at the outline stage. Elmbridge's emerging Local Plan, running to 2037, is separately weighing Green Belt-adjacent development options near Sandown Park and at Moore Place Golf Club, alongside the steady flow of smaller applications along Esher High Street and the surrounding residential streets.

• Large mixed-use sites. Schemes on the scale of the Sandown Park proposals typically need a full flood risk assessment, a Sequential Test and a surface-water drainage strategy as a package, not a single document.
• High-value residential extensions. Even a modest extension can trigger Elmbridge's small-scale development FRA template where the site sits in Flood Zone 2 or 3, or where the Flood Map for Planning shows surface water risk.
• Basements and lower-ground development. Increasingly common on constrained Esher plots, and one of the site features that most changes how groundwater and flood resilience are assessed.
• High-street and town-centre schemes. Conversions and small commercial redevelopments need the same Core Strategy Policy CS26 compliance as any other Esher application.

How Unda helps with flood risk assessment in Esher

Knowing that Esher sits inside two separate Environment Agency warning areas, behind a named defence scheme, and inside an SFRA that already flags the borough's flood exposure is only useful if it is applied correctly to your site. Our flood risk consultants read the Mole and Rythe designations, the Lower Mole scheme's standard of protection, Elmbridge's Core Strategy Policy CS26 and the April 2024 SFRAs together, and translate them into a report Surrey County Council, Elmbridge Borough Council and the Environment Agency will accept.

Call 01293 214444 or email enquiries@unda.co.uk to talk through what your Esher site or property needs.

Flood risk assessments for every situation in Esher

A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go.

• Flood risk assessments. Prepared for planning, for a property purchase or mortgage, for insurance, and for BREEAM, each read against the audience it serves.
• Sequential and exception tests. The locational check that sits alongside a flood risk assessment where national policy asks whether a lower-risk site is reasonably available. See how the tests work and the Yatton judgment for how finely the balance can turn.
• Surface-water drainage strategies. SuDS design for new development, plus discharge of drainage planning conditions and preliminary drainage design at the earlier feasibility stage.
• Groundwater and flood modelling. Where a site's risk includes groundwater or needs hydraulic modelling to establish accurate flood levels, that analysis is built into the flood risk assessment itself rather than treated as a separate report.

Whatever brought you to a flood risk assessment in Esher, whether a planning condition, a lender's question, a search result flagging risk, or a BREEAM credit, contact one of our experienced flood risk consultants and we will tell you plainly what your site or property needs.

For background, see how flood zones explained are defined, the the four pillars of SuDS every drainage strategy has to satisfy, and BRE365 infiltration testing and soakaway design for a site relying on a soakaway. The climate change allowances for planning apply to every assessment we prepare in Esher, and the same evidence explains why flood risk and mortgage lending has tightened, why what is Flood Re matters for insuring a property here, and why does flood risk affect house prices long before any water reaches the door. We also cover flood risk assessment for BREEAM, explained, how surface water flooding and planning interact, the different the types of flooding explained a site can face, riparian ownership rights and responsibilities for anyone with a watercourse on their land, and how groundwater flood risk in planning applications is assessed alongside every other source.

Local flood risk management and emergency contacts in Esher

Several bodies share responsibility for flood risk around Esher, each with a different job.

• Surrey County Council: Lead Local Flood Authority. Handles surface water, groundwater and ordinary watercourse flood risk, and investigates significant flooding under Section 19 of the Flood and Water Management Act 2010. See Surrey County Council's flooding advice.
• Environment Agency. Manages the Mole and the Rythe as main rivers, issues flood warnings and alerts, and maintains the Flood Map for Planning.
• Thames Regional Flood and Coastal Committee. Oversees flood and coastal erosion risk management funding and strategy across the wider Thames catchment, including Surrey. Details: GOV.UK.
• Surrey Prepared and the Local Resilience Forum. Surrey's multi-agency emergency planning network, which also supports local flood action groups through its Flood Action Group Forum.
• Thames Water. The sewerage undertaker for Esher, responsible for flood risk from the public sewer network. Report a problem via Thames Water's sewer flooding pages.
• Floodline. Call 0345 988 1188 for live flood warning information, or sign up for free flood warnings for the Mole or the Rythe.
• In an emergency. Call 999 if flooding is a danger to life, or 105 to report a power cut caused by flooding.

Flood risk assessment in Esher: frequently asked questions

Talk to a flood risk consultant about your Esher site

Whether you need a flood risk assessment in Esher for a planning application, a property purchase, a mortgage, insurance or a BREEAM rating, our flood risk consultants can tell you exactly what your site needs. Explore our full range of flood risk assessments, or see how we cover other areas across the country.