Flood Risk Assessment in Dorking

Dorking grew up in the gap between two hills, Box Hill and Leith Hill, where the Pipp Brook cuts its own valley between the North Downs and the Greensand Ridge before meeting the River Mole at Pixham, on the town's northern edge. That confluence, only a few hundred metres from the shops on the High Street, is why a flood risk assessment in Dorking has to read two watercourses working together rather than one river in isolation.

Unda prepares flood risk assessments in Dorking for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies (SuDS). A flood risk assessment asks whether a site is safe from flooding for its lifetime; a sequential or exception test asks whether the development should be on that site at all; a drainage strategy asks where the surface water goes once it leaves the roof and the car park. They often travel together in a planning submission, but they are different reports answering different questions.

On Christmas Eve 2013 the River Mole filled so fast that it could no longer take the extra flow arriving from the Pipp Brook, and the water backed up into the centre of Dorking within hours.

• Main watercourses. The River Mole, the Pipp Brook and Bent's Brook, a tributary of Tanner's Brook that joins the Mole upstream of the town.
• Dominant risk. Fluvial flooding from the Mole and the Pipp Brook, compounded by surface water; groundwater risk is low across most of Dorking but rises where the Pipp Brook meets the Mole in the north of the town.
• Local authorities. Mole Valley District Council as the local planning authority and Surrey County Council as the Lead Local Flood Authority, until both are replaced by a new East Surrey unitary council in April 2027.
• Flood zones. Dorking spans all three flood zones, with Zones 2 and 3 concentrated around the Mole, the Pipp Brook and the Pixham corridor.
• Planning policy. The Mole Valley Local Plan 2020–2039, adopted in October 2024, sets the current housing and flood policy framework for the district.

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

Check flood risk anywhere in Dorking

Before commissioning a full assessment, it helps to see how the Environment Agency's own data reads a specific postcode. Mole Valley, the district covering Dorking and Leatherhead, is outlined below in coral. Enter any postcode in or around Dorking to screen it against rivers and sea, surface water, reservoirs and the planning flood zones, with a climate change outlook to 2125 and live flood warnings.

Flood risk in Dorking: the River Mole, Pipp Brook and Bent's Brook

The River Mole runs from the east to the north of Dorking, a flashy river that rises quickly after rain falls over its Wealden catchment and crosses the North Downs a little further on through the steep-sided Mole Gap towards Leatherhead. At Pixham it is joined by the Pipp Brook, which drains the north-eastern slopes of Leith Hill and runs through the town centre itself before reaching the Mole, and separately by Bent's Brook, a tributary of Tanner's Brook that flows north-east through the south of the town before it too reaches the Mole upstream of Dorking. The Environment Agency's fluvial flood maps identify land near all three watercourses as being at risk, and the corresponding surface-water maps show a similar pattern wherever the ground drains towards them; in past events it has often been impossible to say where river flooding ends and surface-water flooding begins.

Not sure what your Dorking site needs? Start a quote and one of our experienced flood risk consultants will confirm which sources of flooding apply to your plot.

A history of flooding in Dorking

The worst flooding ever recorded on the River Mole struck in September 1968, when a storm now put at somewhere between a 1-in-100 and 1-in-200-year event dropped over 100mm of rain across the catchment in 24 hours and pushed the Lower Mole's discharge above 240 cumecs. Dorking sits well up the catchment from the worst-hit reaches around East Molesey and Thames Ditton, but the same storm system is still how flood risk across the whole Mole valley, Dorking included, has been read ever since.

The Christmas 2013 flood

The clearest recent example of how the Mole and the Pipp Brook interact came on 24 December 2013. The Environment Agency had initially forecast around 45mm of rain for the area; the Mole corridor received 75mm instead, and the river rose by roughly a foot an hour through the day. According to Surrey County Council's own flood investigation, some of the flooding was caused by the Mole reaching capacity and being unable to take the extra flow arriving from the Pipp Brook, and this pushed water into properties in the centre of Dorking. The Mole returned to normal levels around 12 hours after its peak, but not before Vincent Lane and Snowerhill Road had been closed, and the Environment Agency had issued a flood warning for the River Mole at Dorking and Mickleham at 04:47 that morning, covering 59 properties, of which the Agency recorded 9 as flooded. Further warnings followed on 17 January and 1 February 2014, though neither recorded any further flooded properties.

Across the wider Mole Valley district, that winter produced roughly 270 reported incidents of internal property flooding, 181 properties received council tax relief and 13 businesses received business rate relief, and the council opened rest centres in Dorking and Leatherhead on Christmas Eve itself. It remains the reference event against which the Environment Agency's flood maps, and any flood risk assessment in Dorking, continue to be read.

Planning and drainage policy for a flood risk assessment in Dorking

Mole Valley District Council is currently the local planning authority for Dorking, determining applications against the Mole Valley Local Plan 2020–2039, which was adopted in October 2024 with its flood risk and drainage policies brought into line with national policy shortly before adoption. Surrey County Council is the Lead Local Flood Authority, a statutory consultee on surface water drainage for major applications since April 2015, and the author of the Surrey Local Flood Risk Management Strategy. Mole Valley, Reigate & Banstead and Tandridge also share a joint Level 1 Strategic Flood Risk Assessment, first published in December 2017, which sits behind each council's Local Plan. Surrey County Council's own Section 19 flood investigation report into the winter 2013/14 floods remains the fullest public account of how the Mole and the Pipp Brook behaved together that Christmas.

• Local Plan. The Mole Valley Local Plan 2020–2039 sets an annual housing target of 336 homes and identifies Dorking town centre for large-scale, housing-led redevelopment.
• Surface water drainage. Major planning applications must include a Surface Water Drainage Statement, and national SuDS standards published by Defra in June 2025 apply to greenfield and brownfield schemes alike.
• Strategic evidence. The joint Level 1 Strategic Flood Risk Assessment for Mole Valley, Reigate & Banstead and Tandridge underpins each authority's flood policy and Local Plan allocations.
• Statutory consultee. Surrey County Council reviews surface water drainage design for qualifying developments before permission is granted.

Local government reorganisation and what it means for a Dorking application

Surrey's council structure is changing. Mole Valley District Council, Surrey County Council and the county's other district and borough councils are being replaced by two new unitary authorities, and Mole Valley will become part of the East Surrey unitary council, alongside Elmbridge, Epsom & Ewell, Reigate & Banstead and Tandridge, from 1 April 2027. A shadow East Surrey authority first met in May 2026 to prepare for the handover. Until that date, Mole Valley District Council and Surrey County Council continue to determine applications and administer flood risk as they do now, and Unda tracks which authority is live at the time a report is submitted so an assessment is addressed to the right body.

Development and flood risk assessment in Dorking

Dorking's development pattern is shaped by geography as much as by policy. The town is hemmed in by the North Downs, the Greensand Ridge and the surrounding Surrey Hills National Landscape, so new housing tends to be directed into the town centre rather than onto the greenfield edges. The Local Plan's flagship schemes sit close to the Pipp Brook and the Mole rather than away from them. The refurbishment of Pippbrook House, and redevelopment proposals around the Foundry Museum and the Church Street workshops, are among the projects earmarked for the town centre, in the same corridor where the Mole and the Pipp Brook meet.

• Town centre redevelopment. Housing-led schemes around Pippbrook House, the Foundry Museum and Church Street sit within or close to Flood Zones 2 and 3.
• Conversion and infill. Limited greenfield land within the built-up area pushes many schemes towards conversion, infill and higher-density development on constrained sites.
• Surrey Hills setting. The surrounding National Landscape designation limits outward expansion, reinforcing the town centre's role in meeting the district's housing target.

Whatever the scale of the scheme, the questions are the same: is the site safe from the Mole, the Pipp Brook, Bent's Brook or surface water; does it push flood risk onto a neighbour; and does its drainage design satisfy Surrey County Council as Lead Local Flood Authority.

How Unda helps with flood risk assessment in Dorking

Unda has prepared flood risk assessments and drainage strategies across the River Mole catchment, from Dorking and Leatherhead down through Cobham, Weybridge and Thames Ditton to where the Mole meets the Thames, so the way this river behaves through a town centre is familiar ground rather than a new problem each time. A Senior Flood Risk Consultant signs off every report, and we deal directly with the Environment Agency and Surrey County Council on a client's behalf.

Read more about Unda's flood risk consultants or the team behind every report.

Flood risk assessments for every situation in Dorking

A flood risk assessment in Dorking is commissioned for more than one reason, and Unda prepares the right version of the report for each.

• Planning. A flood risk assessment for planning, submitted alongside a planning application and assessed against the NPPF and the Mole Valley Local Plan.
• Property purchase. A flood risk survey for homebuyers, going beyond a standard conveyancing search when a property near the Mole or the Pipp Brook is flagged as at risk.
• Insurance. A flood risk assessment for insurance purposes, providing property-specific evidence for brokers and underwriters.
• BREEAM. A flood risk assessment for BREEAM, structured around the Pol 03 flood and surface water credit.
• Sequential and Exception Tests. A Sequential or Exception Test report, prepared alongside an FRA where a Dorking site falls in Flood Zone 2 or 3.
• Drainage strategy and SuDS. A surface-water drainage strategy that satisfies Surrey County Council as Lead Local Flood Authority, with discharge of drainage conditions and preliminary drainage design available where a scheme needs them.
• Groundwater and modelling. Where the ground near the Pipp Brook/Mole confluence raises groundwater questions, or standard mapping is not detailed enough for a site beside the Mole, groundwater assessment and flood modelling are carried out within the wider FRA.

Free screening tools can help before a full assessment is commissioned: the Flood Risk Map, the Live River Levels Map for the Mole's gauge network, the Geology & Ground Conditions Checker for soakaway feasibility, and the Drainage Calculators and BRE 365 Infiltration Rate Calculator for sizing a scheme. Background reading on the wider policy picture is available in Unda's guide to the Environment Agency's May 2026 Flood Map for Planning update and its explainer on the Sequential and Exception Test following the Yatton judgment.

Local flood risk management and emergency contacts in Dorking

Dorking sits within a well-mapped network of flood risk bodies, and knowing which one to contact matters as much in an emergency as it does at planning stage.

Surrey is represented on the Thames Regional Flood and Coastal Committee, which oversees strategic flood and coastal investment across the wider catchment, and anyone in Dorking can sign up for free flood warnings directly from the Environment Agency. The Agency's own check for flooding service for Dorking and the River Mole level gauge at Dorking both give live, official readings, drawn from the same data as Unda's checker above.

Flood risk assessment in Dorking: frequently asked questions

The questions below come up most often when we talk to developers, homebuyers and agents about a Dorking site.