Flood Risk Assessment in Weymouth

A flood risk assessment in Weymouth, Dorset, has to start with the sea. The town centre sits on low ground between Weymouth Bay and the harbour, where the River Wey reaches the sea by way of Radipole Lake, and a high tide can hold the river back while waves break against the Esplanade. We prepare flood risk assessments here for planning applications, house purchases, mortgages and insurance, together with sequential and exception tests and surface water drainage strategies, for sites from Melcombe Regis and the quays to Westham, Wyke Regis, Radipole and Broadwey.

On this page Weymouth means the built-up area the Office for National Statistics mapped in 2022: Melcombe Regis and the old town round the harbour, the Park District, Westham, Rodwell and Wyke Regis to the south, and Radipole, Southill, Nottington, Broadwey, Littlemoor and Preston inland, across the DT3 and DT4 postcode districts. Upwey, Chickerell and Portland lie just beyond that outline and are covered here as well. Dorset Council decides planning applications and is the lead local flood authority. The rest of the county has its own Dorset page, and every other place we write about is listed among the areas we cover.

Dorset Council's 2020 strategy for the harbour and seafront found that as many as 440 properties could flood from the sea in a 1 in 200 year event today, and more than 2,000 by 2120 as sea levels rise.

Email enquiries@unda.co.uk or call 01293 214444 with the address, and one of our flood risk consultants will tell you which reports a Weymouth site is likely to need.

When the tide is high and the Wey cannot drain

Weymouth can flood from the sea, the Wey, its smaller watercourses, heavy rain and the sewers. The worst events come when two or more of them coincide. The Dorset Coast Forum's household guide describes Melcombe Regis as bowl shaped, with parts of it below sea level, so water that gets in tends to stay. A high tide in the harbour can also stop the Wey draining out of Radipole Lake just as heavy rain is filling it. River and sea flooding then arrive together, in the lowest part of town.

The Environment Agency measures the Wey at Upwey, Broadwey and Weymouth and the sea at Portland, and our live river levels map shows those readings beside the warnings in force. The Weymouth gauge on the Wey has its own page too. This is Dorset's short Wey, which rises at Upwey, not the Surrey river of the same name. For how tide, surge and waves combine, see our explainer on tidal flooding and planning.

Look up a DT3 or DT4 postcode

The coral line on the map is Weymouth's 2022 built-up area from the Office for National Statistics. Radipole Lake and the Lodmoor reserve fall outside it, as do Upwey, Chickerell and Portland. Type a postcode to see its planning flood zone, its modelled risk from rivers, the sea and surface water, and any warning in force, or open our flood risk map for an address anywhere in England.

Much of the harbourside shows as Flood Zone 3 even with walls between it and the sea, because the planning flood zones are drawn as if the defences were not there. A protected street can therefore still need a full assessment, and our article on staying in a flood zone after new defences are built explains why. The assessment then shows how well the walls perform for a particular building, and for how long.

What the 2023 Level 2 study found on Weymouth's town centre sites

Dorset Council commissioned JBA Consulting to examine the town centre sites allocated in the 2015 Local Plan. The Weymouth Level 2 Strategic Flood Risk Assessment, dated June 2023 and published in February 2024, models the river, the sea and surface water to 2138. Any site assessment in the town centre will be checked against it.

The study concludes that most of these sites could pass the flood risk part of the exception test, though only with care. It looks for homes set above the design flood level with freeboard, or a refuge above the extreme flood level, a safe way in and out, a plan for warning and evacuating people if the walls are overtopped or breached, and no new building in Flood Zone 3b beyond essential infrastructure and water-compatible uses. The council and the Environment Agency are also updating the standing advice for the town centre, which is expected to tie finished floor levels to design flood levels. Our guide to strategic flood risk assessments explains how such studies are used.

Raising the harbour walls: the 2020 strategy to 2120

In October 2020 Dorset Council's cabinet approved the Weymouth Harbour and Esplanade Flood and Coastal Risk Management Strategy, a 100-year programme to replace and raise the walls round the harbour and improve the seafront defences. Its starting point is that the harbour walls are too low for the sea levels expected later this century, and some are near the end of their working life. One section would already be overtopped by today's 1 in 200 year tide.

• Properties at risk. Up to 440 properties in a 1 in 200 year sea flood today, and more than 2,000 by 2120 if nothing were done.
• Tide levels. The 1 in 200 year still-water level is put at 2.43 m above Ordnance Datum now and 3.74 m by 2120, a rise of 1.3 m under the most severe UK climate projection.
• The walls today. The harbour scheme the Environment Agency built in 2001 and 2002 has a crest of 2.30 m above Ordnance Datum, while the Esplanade defences stand between 3.0 m and 3.5 m.
• Erosion. Between the Pier Bandstand and Greenhill Groyne, the strategy puts erosion at 0.5 to 1.0 m a year should the defences fail.
• Cost and next steps. More than £115 million over 100 years. The scheme partnership is now preparing an outline business case for a first phase running to 2042.

The shoreline management plan has a hold the line policy for the town's frontage, so the defences are to be kept and raised rather than moved back. On this coast we prepare flood risk assessments that test tide levels, surge and overtopping over the life of the building, and due diligence for buyers, lenders and developers. A separate strategy for Portland and Wyke Regis is being drawn up, with public engagement held in March 2025.

Flood risk assessment in Weymouth: the policies an application is read against

Applications in Weymouth are decided against national policy, a local plan adopted in 2015 and a neighbourhood plan made in January 2026, read with two strategic flood risk assessments. The 2015 plan singles the town out, stating that "Weymouth Town Centre, the Park District and the Chiswell area of Portland are particularly vulnerable to flooding."

A new Dorset Council Local Plan is at an early stage. Its scoping consultation closed on 26 October 2026 and adoption is not expected before 2029, so the 2015 policies and the neighbourhood plan will govern Weymouth applications for some years. The council has said the new plan will review the town centre allocations, consider limiting the more vulnerable uses there and reserve land for flood defences.

Radipole Lake, Lodmoor and the Jordan

Not every Weymouth flood comes off the sea. The Wey rises at Upwey and runs through Broadwey and Nottington into Radipole Lake, which empties into the harbour through the sluices at Westham Bridge. East of the town, the watercourse through Lodmoor and the River Jordan at Preston carry water off the hills to Weymouth Bay. The Environment Agency's flood alert for Weymouth's rivers and streams covers the Wey, Preston Brook and the Jordan.

• July 1955. After the storm that set the UK rain-day record at Martinstown, Weymouth Museum records that Radipole Lake overflowed onto Radipole Park Drive, Commercial Road, the Park District, Marsh Road and the Westham coach park, and that homes at Preston and Sutton Poyntz flooded.
• 2012. Radipole Park Drive flooded again when the Wey burst its banks, as the household flood guide records.
• 2014. Repeated coastal storms brought significant flooding, which the 2023 Level 2 study cites alongside the floods of the 1950s and 1960s.
• Lodmoor and Overcombe. The 2023 model added flows from the watercourse crossing Lodmoor and from Preston Brook at Overcombe, and part of the Lodmoor allocation lies in Flood Zone 3b.

Sites in the Wey valley suburbs, from Broadwey down to Radipole, therefore need river and surface water evidence as much as tide levels. Upwey sits just above the mapped outline, but the same river and the same alert apply there.

Drainage when the outfall is under the tide

Getting rainwater off a Weymouth site is complicated by the tide. Outfalls to the harbour, the lake and the bay can stay shut for hours at high water, and in the Park District runoff from the roads drains into combined sewers run by Wessex Water. Managing surface water on the site therefore means storing it until it can leave, as well as limiting how fast it goes.

Infiltration has to be tested, and on low ground by the harbour and the lake, where the 2023 study notes past groundwater flooding, it may not work at all. Policy W34 of the neighbourhood plan looks for permeable surfaces and sustainable drainage in new building, alongside the national standards. Our BRE 365 infiltration rate calculator turns soakaway test results into an early design figure.

Reports for harbourside flats, Esplanade hotels and plots up the Wey valley

People commission flood and drainage work in Weymouth to build, buy, insure or lend against property. A flood risk assessment asks whether a site is safe, a sequential test asks whether it should be developed at all, and a drainage strategy asks where its rainwater goes.

• Applications to Dorset Council. Homes, conversions and hotel extensions in the harbour and seafront flood zones need a flood risk assessment for planning that answers Policy ENV5 and, beside the Wey or the Jordan, Policy W12.
• Tide, river and rain together. A flood risk assessment for a Weymouth site weighs harbour tide levels, wave overtopping, the Wey and surface water, then sets floor levels and a dry route out.
• Buying near the harbour or the Esplanade. Flats in Melcombe Regis and cottages round Hope Square sit inside the harbour and seafront warning areas, and a flood risk survey for property purchase explains what the risk means for one building before exchange.
• New homes in Flood Zone 3. Most of the town centre allocations are in Flood Zone 3, so new homes there need a sequential and exception test showing why the site was chosen and how it stays safe.
• Drainage evidence for the council. Larger schemes need a drainage strategy that works with outfalls the tide can close and sewers with little room to spare.
• Runoff in the Park District and Melcombe Regis. A surface water drainage strategy shows how new roofs and paving drain without adding to combined sewers or low-lying streets.
• Conditions on a consent. Where a consent comes with a drainage condition, discharge of drainage conditions supplies the calculations and details the council asks for before work starts.
• Buying land or commercial property. Quayside and town centre land in Flood Zone 3b, and a seafront where erosion would follow any failure of the defences, make flood risk due diligence worth doing before a purchase or a loan.
• Getting people out in time. With six Environment Agency warning areas round the harbour and the seafront, a flood warning and evacuation plan sets out who acts, when, and where occupants go if the walls are overtopped.
• Insuring a Weymouth home. Up to 440 properties face a 1 in 200 year sea flood today, and a flood risk assessment for insurance gives an insurer evidence about the actual building.
• Testing levels the maps cannot settle. The Wey is a main river through the town, and where a site lies outside the council's 2023 town centre model or a scheme reshapes the ground, flood modelling works out river and tide levels for that site.

Who to call when the harbour or the Wey rises

Call 999 straight away if anyone is caught or cut off by floodwater, and 105 if the power goes off. Floodline, on 0345 988 1188, gives warnings and advice day and night, and anyone living or working round the harbour or the seafront can sign up for flood warnings for the area that covers their street.

The household guide to flood risk in Weymouth, written by the Dorset Coast Forum with the council, the Environment Agency, Wessex Water and residents, explains how to prepare a home or business in Melcombe Regis and around the harbour.

Flood risk assessment in Weymouth: questions we are asked

Every report we write for a Weymouth site is checked and signed off by a senior consultant, the consultants who prepare them hold chartered status, and Unda Consulting Limited is a CIWEM Business Partner. Email enquiries@unda.co.uk or call 01293 214444 about a site anywhere from Wyke Regis to Preston. Along the coast to the west we also cover Bridport, and inland the county town of Dorchester.