Flood Risk Assessment in the Isle of Wight

Any flood risk assessment in the Isle of Wight has to begin with the sea. The tide runs up the Medina past Cowes and East Cowes to Newport, and it washes the sea walls at Ryde, Seaview and Sandown Bay. Behind those frontages the Island's short rivers, the town brooks and the combined sewers can flood the same streets in a single night of rain, which is what happened in October 2023.

Our consultants prepare flood risk assessments for Island planning applications, for buyers, mortgage lenders and insurers, and write the sequential and exception tests and surface water drainage strategies that often go with them. Each one is checked against the Island Planning Strategy adopted in September 2026, the council's 2024 sustainable drainage rules and the Environment Agency's evidence for the Solent and the Island's rivers.

In Storms Babet and Ciaran, in October and November 2023, at least 317 homes and businesses on the Isle of Wight flooded internally, and in Ryde the rain gauge recorded a storm rated between a 1 in 144 and a 1 in 190 year event.

To talk through a site anywhere from Yarmouth to Bembridge, call one of our consultants on 01293 214444 or email enquiries@unda.co.uk.

Tides, estuaries and the Undercliff: where the Island's risk begins

The sea is the main source of flood risk on the Isle of Wight, and it makes river flooding worse wherever it holds a river back at high tide. The Island covers about 380 square kilometres and most of its main rivers flow north into the Solent, so the estuaries at Cowes, Wootton Creek, Newtown and Yarmouth carry the tide well inland. When a high tide shuts a gravity outfall, rainwater backs up behind it until the tide drops.

• Tide-locking. The council's Local Flood Risk Management Strategy lists the outfalls of Monktonmead Brook in Ryde, the Eastern Yar at Bembridge Harbour and Gurnard Luck, where closed tidal flaps raised river levels by about 300 mm in 2000.
• Record tides. Ryde's highest recorded tide, 3.06 m above Ordnance Datum, came on 14 February 2014, during the wettest winter in southern England for 250 years.
• Shoreline policy. The Isle of Wight Shoreline Management Plan, adopted by the council in 2011, sets a policy for each stretch of coast, and the 2016 West Wight strategy covers the shore from East Cowes round to Freshwater; both can be read on the national shoreline plan explorer.
• Coastal Change Management Areas. Stretches of eroding coast are mapped as Coastal Change Management Areas, where Policy EV16 restricts development to uses that need a coastal location and does not support new homes.
• The Undercliff and the Cowes slopes. Policy EV19 covers the Ventnor Undercliff from Bonchurch to Blackgang and parts of the slopes between Cowes and Gurnard, where landslip risk rules out new soakaways and surface water has to go to a sealed system or a watercourse.

Coastal sites on the Island are where we prepare flood risk assessments and flood risk due diligence, using the Environment Agency's sea level rise allowances for the full life of the building. Our explainers on shoreline management plans and on planning for sea level rise beyond 2100 cover the background.

Looking up an Island postcode on the map

Enter any IoW postcode, from PO30 to PO41, below to see the Environment Agency's flood zones, surface water and reservoir layers at that point, or open our full flood risk map for the same data at a larger scale. The coral line is the Isle of Wight Council area, which is the whole Island.

Flood Zones 2 and 3 show river and sea flooding as if no defence existed, so land behind the Ryde, Seaview or Yaverland walls can still be in Flood Zone 3. Surface water and groundwater are mapped separately. The council's 2019 Strategic Flood Risk Assessment adds tidal extents for 2045, 2080 and 2115, and our guide to flood zones in England explains how to read each zone.

The Medina, the two Yars and the brooks that flood Newport and Ryde

Island rivers are short and rise fast. The Medina runs north through Newport to Cowes, the Eastern Yar from the south of the Island past Sandown and Brading to Bembridge Harbour, and the Western Yar from Freshwater to Yarmouth. In Newport and Ryde the town brooks and the sewers matter as much as the rivers, and at Binstead in 2021 flooding followed within 10 to 15 minutes of the heaviest rain.

Altogether the Environment Agency runs 27 flood warning and alert areas on the Island, 18 of them warning areas, all managed by its Solent and South Downs area. Gauges on the Eastern Yar at Alverstone and Sandown, on the Lukely Brook at Carisbrooke and on Monktonmead Brook at St Johns, with tide gauges at Cowes, Newport, Ryde and Yarmouth, can be followed on our live river levels map.

Flooding on the Isle of Wight from 1999 to 2023, from the council's records

Most of what is known about Island flooding comes from the council's own investigations as lead local flood authority. Ryde appears in 2000, 2014, 2021 and 2023, which is why a site there needs evidence beyond the national maps.

1. December 1999 and autumn 2000. Flooding in Cowes, Newport and Seaview from 24 December 1999 was followed in autumn 2000 by weeks of rain that raised groundwater and river levels; in Ryde about 70 houses flooded as groundwater rose and the combined sewers overflowed.
2. Winter 2013 to 2014. About 50 properties flooded across the Island, probably an undercount, and the council investigated in Alverstone, Carisbrooke and Newport, Cowes and East Cowes, the Eastern Yar valley, and Ryde and Binstead.
3. 25 July to 2 August 2021. Three storms in Ryde got inside at least 32 properties, most on 25 July, when the rainfall was rated between a 1 in 42 and a 1 in 107 year event. Great Preston Road, Argyll Street, Bettesworth Road and Buckland Gardens were worst hit (Section 19 report, April 2022).
4. 24 and 25 October 2023. Overnight rain got inside at least 107 properties across Ryde, where the gauge recorded a 1 in 144 to 1 in 190 year storm; at least 56 in Newport, with 22 at Gunville and 9 on Carisbrooke High Street; and at least 22 in East Cowes, 12 of them commercial.
5. Brading, the same morning. At Knighton, 83.79 mm fell in 12 hours, about a 1 in 322 year event, and a tributary of the Eastern Yar overtopped into Nicholas Close as the river rose by about a metre at Alverstone.

The council published its reports on the 2023 flooding in Newport, East Cowes, Ryde and Brading in September and October 2024, using evidence gathered by JBA Consulting, and the Environment Agency added its own Ryde investigation in July 2025. Our explainer on Section 19 investigations says when a council has to carry one out.

Which policies decide a flood risk assessment in the Isle of Wight under the new Island Planning Strategy?

The Island Planning Strategy became the Island's local plan in September 2026, running from 2025 to 2037, and replaced the 2012 Core Strategy, whose flood and coast policies, DM14 and DM15, no longer apply. Seven policies in the new plan now carry the flood, drainage and coastal tests, alongside chapter 18 of the NPPF.

Allocated sites still need an assessment. The inspectors' report on the plan noted that large parts of the Newport Harbour priority site lie in Flood Zones 2 and 3a and will face the exception test, and the Medina Yard allocations in Cowes were deleted because of tidal flood risk. The council's flood risk and investigation page lists every investigation published since 2014, and our guide to the lead local flood authority explains the council's part in the drainage decision.

What the council's SuDS SPD asks of drainage on the Island

Since 23 May 2024 every planning application on the Island, of any size, has been expected to include sustainable drainage under the council's Sustainable Drainage Systems Supplementary Planning Document. Major schemes need an outline drainage strategy at outline stage and a detailed one with a full application; smaller schemes need a surface water drainage management plan.

• Where the water goes. Re-use first, then shallow infiltration, then a watercourse, lake or the sea, then a surface water sewer; a combined sewer only as a last resort, offset by taking rainwater out of the sewers elsewhere in the catchment.
• How fast it leaves. For the 1 in 1, 1 in 30 and 1 in 100 year storms, discharge must never exceed the greenfield peak rate for the same storm, and the 1 in 100 year, six-hour volume must not exceed the greenfield volume, with climate change and urban creep added.
• How much rain to plan for. Peak rainfall for the 1 in 100 year storm is raised by 25% to 45% for climate change, with the upper figure expected in the drainage calculations.
• The tide and the slopes. Where an outfall reaches tidal water the effect of tide-locking on storage must be shown, and infiltration is ruled out in the Ventnor Undercliff, on the Cowes to Gurnard slopes and inside the Coastal Change Management Areas.
• Proving the ground. Infiltration testing and winter groundwater monitoring on high-risk sites, with the base of any soakaway at least a metre above the highest likely water table, and a ground investigation before a full application.

Major development is also tested against the 2025 national standards for sustainable drainage. The geology and ground conditions map and the BRE 365 infiltration rate calculator give a first indication of whether the ground will take water before any trial pit is dug.

Flood schemes at Ryde, East Cowes and Sandown Bay

Three schemes and a road embankment hold back water at Ryde, East Cowes, Sandown and Bembridge. Each lowers the chance of flooding without taking land out of the flood zone, so an assessment for a site behind one still has to deal with what happens if it is overtopped or fails.

• Monktonmead Brook, Ryde. A £5 million Environment Agency scheme started in March 2018 with a new outfall through the sea wall and a flood wall around Simeon Street recreation ground, for more than 300 homes and businesses. After the 2023 flood, the investigations asked for a review of how the scheme performed and how the recreation ground wall affects surface water.
• East Cowes. The Environment Agency scheme, approved in 2020 for 68 homes and 26 commercial properties, abandoned its temporary barrier, which could not be put up safely and in time there, and turned to measures fitted to individual homes; no scheme funding was available for the commercial properties.
• Yaverland and Sandown. The Yaverland Coastal Defence Scheme will refurbish 1.2 km of sea wall and groynes at their present height; failure of the existing defences would affect 138 homes and 136 businesses. Detailed design began in spring 2025.
• Embankment Road, Bembridge. The road itself holds back the harbour, and the council's strategy says around 450 properties would be at risk without it.

Our notes on residual flood risk and on why land stays in a flood zone after new defences explain how an assessment treats a defended site.

Does a flood risk assessment in the Isle of Wight apply to your scheme?

Policy F4 in chapter 18 of the NPPF requires one for any site in Flood Zone 2 or 3, for a Flood Zone 1 site of a hectare or more, and for land the Environment Agency's maps or the council's evidence show at risk from other sources. Policy EV14 adds its own expectation of a site-specific assessment wherever risk exists now or is expected in future.

Where a site is at risk only from surface water, policy F5 allows the sequential test to be skipped if the assessment shows the development will be safe. Our NPPF flood risk guidance explains how chapter 18 sits above the Island's own policies, and our guide to holiday lets and cabins covers the rules for small sites.

Reports for Island sites, from the Cowes waterfront to the Undercliff

A flood risk assessment asks whether a development and its occupants will be safe, the sequential and exception tests ask whether it should be built there at all, and a drainage strategy shows where the rain goes. On the Island the three often travel together. Island reports are written by chartered consultants and checked by a senior consultant before they leave Unda, which is a CIWEM Business Partner.

• Several sources at once. The tide, a brook and a tide-locked sewer flooded East Cowes together in 2023, and a flood risk assessment weighs each source against the others.
• Planning applications. A flood risk assessment for planning answers Island Planning Strategy Policy EV14 and chapter 18 of the NPPF, with sea level rise taken to the end of the building's life.
• Buying a home. Streets in Ryde, Gunville and East Cowes named in the Section 19 reports can be flagged by a search or a lender, and a flood risk survey for property purchase sets out what the flag means for that house before exchange.
• Homes in the tidal zones. Where housing is proposed in Flood Zone 2 or 3 on an unallocated site, the sequential and exception test looks for reasonably available Island sites at lower risk and, where needed, shows the scheme is safe and brings wider benefits.
• Major schemes. On ten homes or more, or half a hectare, the council is consulted as lead local flood authority and checks the drainage strategy against the SPD's greenfield rates and the national standards.
• Greenfield rates. A surface water drainage strategy works out the greenfield peaks and volume the 2024 SuDS SPD asks for and sizes the storage, allowing for outfalls that the tide can close.
• Conditions before work starts. Island permissions often reserve the drainage details, and discharge of drainage conditions supplies the calculations, layout and five-year maintenance plan the council asks for.
• Premiums after 2023. Owners among the 317 properties that flooded in Storms Babet and Ciaran can use a flood risk assessment for insurance to show an insurer the risk to the building as it stands now.
• Waterfront land. With the Medina Yard allocations deleted over tidal risk, flood risk due diligence tests a boatyard, marina or harbourside site before it is bought or refinanced.
• Shops and the ferry terminals. Twelve of the 22 properties that flooded inside in East Cowes in 2023 were commercial, and a business continuity flood risk assessment plans how a business keeps trading when water reaches the door.
• Off the mains. Holiday lets, barn conversions and farm sites beyond the reach of Southern Water's 1,455 km of Island sewers need a foul drainage strategy showing how waste water will be treated.
• Rising groundwater. About 70 Ryde houses flooded as groundwater rose in autumn 2000, and a groundwater flood risk assessment tests basements and soakaways against the water table.
• Brooks without flood levels. Where national data gives no level for a site on the Lukely Brook, the Eastern Yar or a smaller stream, flood modelling provides one.
• Tidal frontages. The council and the Island's fire and rescue service publish guidance for a flood warning and evacuation plan on sites in Cowes, Ryde, Yarmouth and the other tidal warning areas.
• Land for the new plan. With the Island Planning Strategy running to 2037 and Newport Harbour facing the exception test, a flood risk feasibility study tests land before it is promoted.
• Solar and battery parks. Panels and storage on Island farmland, such as a solar park proposed near Wootton with its edges in Flood Zones 2 and 3a beside Palmers Brook, need a flood risk assessment for renewable energy.

Neighbouring pages across the Solent

The Island shares its Environment Agency area, its regional flood committee and its resilience forum with most of Hampshire, though its planning and drainage rules are its own. For a mainland site opposite, our pages on Portsmouth and Southampton cover the harbour cities, and every place we cover is listed on our areas page.

Who to contact about flooding on the Isle of Wight

If floodwater threatens anyone's safety, dial 999; a power cut goes to 105. For everything else, which body to call depends on where the water comes from: the sea and the main rivers, a brook or ditch, a road gully or a sewer.

Southern Water's drainage and wastewater management plan for the Island counts 20 sewerage catchments and 103 storm overflows, and names Sandown, Brighstone, St Helens and Chillerton as already at very significant risk of sewer flooding in heavy rain.

Flood risk assessment in the Isle of Wight: what Island clients ask

Whether the site is a boatyard on the Medina, a terrace in Ryde or a garden on the Undercliff, our consultants can tell you what it needs. Call 01293 214444 or email enquiries@unda.co.uk.