Flood Risk Assessment in St Ives, Cornwall

A flood risk assessment in St Ives, Cornwall is usually about water that arrives fast. The town climbs steeply from its harbour and beaches, and the Stennack stream comes down off the high ground behind it, partly in open channel and partly in culverts, to a tidal outfall in the lower town. In a cloudburst the streets carry rain downhill quicker than the drains can take it. On a big spring tide with a swell running, the sea comes over the harbour front instead.

Our work in St Ives covers flood risk assessments for planning applications, purchases, mortgages and insurance, sequential and exception tests, and surface water drainage strategies. Here St Ives means the town in the TR26 postcode district: Downalong and the harbour, Porthmeor and Porthminster beaches, and the Stennack valley rising inland. Carbis Bay, Lelant and Halsetown lie just outside the town's built-up area but share its council and its coast, and Carbis Bay shares some of its drainage. Cornwall Council is a unitary authority, so it decides planning applications and also acts as the lead local flood authority.

Between 1992 and August 2004 the Stennack flooded the lower town eight times, and a single event could reach up to 190 businesses. In November 2002 the lifeboat was taking people out of homes and harbourside pubs.

Got a plot in Downalong, on the Stennack or up towards Penbeagle? Ring 01293 214444 or email enquiries@unda.co.uk.

Why does St Ives flood so quickly?

Because nearly all of the town drains to one short, steep stream and a flat lower town. The Environment Agency's St Ives Critical Drainage Area sheet (May 2015) describes a small catchment that responds quickly to rain. In many places the Stennack no longer runs along the bottom of its valley, and its old floodplain has been built on, so water running off the streets does not always reach the channel. It gathers in the low streets near the harbour, where the culvert meets the sea.

• Upper Stennack and Penbeagle. Housing spread west up the valley through the twentieth century, according to the neighbourhood plan. Roofs and roads there send rain quickly to the stream.
• The culvert under the lower town. The 2005 to 2008 flood scheme relined and sealed it, blocked the highway drains that used to empty into it and fitted bolt-down covers so it can run under pressure. Smaller culverts upstream were replaced with larger ones and the channel walls raised.
• Tregenna Place, St Andrew's Street and Gabriel Street. The flat centre where the water ends up. Debris was piled five feet high across Tregenna Place in 1894, and the same streets stood under about five feet of water in 2002.
• Carbis Bay. A steep catchment with its own flooding problems. The drainage area sheet notes that flows may cross from Carbis Bay into St Ives in heavy rain.

The Environment Agency measures the stream at St Ives Consols Farm, upstream of the town. Its usual range is 0.03 m to 0.66 m, and the highest reading on record is 1.23 m, taken on 7 January 2009. That gauge and the sea level gauge in St Ives both appear on our live river levels map. A culvert like this depends on its inlet screens staying clear. Debris turns up again and again in the town's flood record.

Screen a St Ives address against the flood zones

Type a postcode to see the Environment Agency's flood zones, surface water risk and climate change outlook at that point, or open our full flood risk map for any address in England. The coral line is St Ives as the Office for National Statistics maps it: a built-up area of about 1.6 km² taking in the harbour, Porthmeor, the Stennack valley, Penbeagle and Trenwith and reaching towards Porthminster. Carbis Bay, Lelant and Halsetown are counted as separate places, so they sit outside the line.

How much of St Ives is in Flood Zone 2 or 3?

Not much. That is why the flood zones on their own are a poor guide here. We overlaid the Environment Agency's Flood Map for Planning on the town's built-up area on 26 October 2026: about 5% of it, roughly 8.5 hectares, is in Flood Zone 3, and about 1% more is in Flood Zone 2. Most of the Flood Zone 3 land follows the Stennack, with smaller strips behind the harbour and at Porthmeor. The rest is Flood Zone 1. But the town's urban area is a Critical Drainage Area, and that brings its own rules.

A Flood Zone 1 address in St Ives can therefore still need a flood risk assessment, because the national rules ask for one for development in an area with critical drainage problems. Our guide to surface water flooding and planning explains how that risk is assessed on a site.

St Ives flood history: the Stennack and the sea

The record splits two ways: flash floods down the Stennack after heavy rain on the moors, and storm tides breaking over the harbour and beaches. These dates come from council, fire service, Environment Agency and local history sources.

1. 11 November 1894. After weeks of rain, water poured off the moors through St Ives Consols and turned the Stennack into a floodway. Several hundred tons of sand, gravel and granite piled up across Tregenna Place, and people were rescued by boat from upstairs windows (Penwith Local History Group).
2. 1992 to August 2004. Eight Stennack floods. Each could affect up to 190 businesses and access to about 2,500 homes.
3. November 2002. On the first night of the national fire strike, the Stennack burst its banks hours after its debris screens had been cleared. Streets around St Andrew's Street, Tregenna Place and Gabriel Street flooded to about five feet, and the lifeboat rescued twelve people (Cornwall Fire and Rescue newsdesk).
4. 2005 to 2008. The Environment Agency, Cornwall County Council and Penwith District Council built the flood scheme. The lower-town drainage and pumping station were finished in April 2006, and a second phase on the culvert and channel began in May 2006, aiming to finish in 2008.
5. 10 March 2008. A wave broke through the window of a house in Sea View Place and flooded it.
6. 7 January 2009. The Stennack gauge reached 1.23 m, its highest level on record.
7. 25 April 2009. An overnight downpour put 125 mm of rain on the Zennor area in 24 hours. Shop owners in St Ives reported up to 1 m of water, crews pumped out a basement on Tregenna Hill and residents were moved out of two hotels (fire service log; council report).
8. 3 February 2014. Very high tides and a heavy swell overtopped defences all along the harbour front. Fifteen properties flooded, and flats at Porthmeor were damaged, one evacuated after a window was smashed (council flood investigation). Around 360 properties flooded across Cornwall that winter.

None of the council's flood investigation reports since then covers St Ives. From 2019 the council has logged floods in its annual flood and coastal reports rather than separate investigations, so a quiet decade on paper is no proof that streets have stayed dry. A flood risk assessment checks the council's records and the Environment Agency's for the site itself.

Porthmeor, the harbour and Porthminster: holding the line

The shoreline management plan for Cornwall and the Isles of Scilly holds the line along the whole built frontage of St Ives in all three of its epochs, out to 2105. The existing walls and defences are to be kept and replaced roughly where they stand. That does not remove the risk: the plan's notes for the St Ives Harbour unit warn that continued protection may bring coastal squeeze and more wave overtopping, and call for property resilience and better flood warning and drainage alongside the defences.

• Porthmeor (unit 25.2). Hold the line in every epoch. The beach faces the open Atlantic, and it is where flats were damaged in February 2014.
• Porthgwidden to the Pier (25.3). Hold the line in every epoch, round the east side of the headland.
• St Ives Harbour (25.4). Hold the line in every epoch. The plan expects sediment to keep building up here, which may offset some sea level rise.
• Porthminster beach (25.5). Hold the line in every epoch. West of Porthmeor and east of Porthminster the plan's units are undefended cliffs.

Erosion is handled separately. Cornwall's Climate Emergency Development Plan Document draws a Coastal Vulnerability Zone around the entire coast, and its policy CC1 asks for a coastal vulnerability assessment before new buildings go inside it. That is a different report from a flood risk assessment and not one we prepare; on the St Ives coast our work is flood risk assessment and due diligence. CC1 also rules out soakaways within 5 m of the zone and surface water discharged over a cliff face, unless that assessment shows the cliff will not be harmed. St Ives is not one of the candidate Coastal Change Management Areas listed under policy CC2. Our explainers on shoreline management plans and sea defences go into the policies and structures in more detail.

What planning policy asks of a flood risk assessment in St Ives

An application in St Ives is tested against the Cornwall Local Plan, the Climate Emergency Development Plan Document, the Environment Agency's drainage area standards and the town's own neighbourhood plan. Nationally, chapter 18 of the NPPF sets out when an assessment is needed (policy F4), the sequential and exception tests (F5 and F6), and the expectation that all development follows the 2025 National Standards for sustainable drainage (F8).

The council's SuDS for Cornwall guidance collects the drainage area sheets with its guidance on factors of safety, urban creep and householder extensions, and the flood zones and main rivers can be checked on its strategic flood risk assessment map. Our article on Critical Drainage Areas explains what the designation changes for an application.

Do you need a flood risk assessment in St Ives for your scheme?

For most new building, yes. The town sits in a Critical Drainage Area, so development usually needs a flood risk assessment even on Flood Zone 1 land, and anything in Flood Zones 2 or 3 needs one anyway. What changes from scheme to scheme is how much the assessment has to cover, as the table shows.

Most of the neighbourhood plan's housing land is on the slopes above the town. Those greenfield sites drain towards streets that already flood, which is why the drainage area rules ask them to release less water than the fields do today. In the old town, where plots are small, storage usually has to be found on roofs, under yards or in permeable surfaces.

Reports we prepare for sites from Penbeagle down to the Wharf

A flood risk assessment asks whether a site is safe, a sequential test asks whether the development should be there at all, and a drainage strategy asks where the rain goes. In St Ives these questions come up for the following kinds of work.

• Every source in one report. A flood risk assessment for a St Ives site weighs the Stennack, the run-off coming down the hill, the sea at the harbour and the drains together, because the flood zone map shows only part of that picture.
• Applications to Cornwall Council. New homes, extensions and changes of use inside the drainage area or in Flood Zones 2 and 3 need a flood risk assessment for planning that answers Policy 26 and CC3.
• Buying in TR26. Where a search flags the Stennack or the harbour front, a flood risk survey for property purchase looks at the building, its floor levels and the town's flood record before you exchange.
• Homes and holiday lets on low ground. More vulnerable uses on the Flood Zone 3 land along the Stennack or behind the harbour usually have to pass the sequential and exception test.
• Drainage evidence at application stage. Because the town is a Critical Drainage Area, a drainage strategy for a St Ives scheme has to show run-off going down. Holding it level is not enough.
• Greenfield plots above the town. Housing on the allocated land needs a surface water drainage strategy that keeps the 1 in 100 year storm plus climate change on site and lets out no more than the greenfield rate, capped at 1 in 10.
• After permission is granted. Where the permission comes with a drainage condition, we put together the calculations, drawings and maintenance plan needed for discharge of drainage conditions so work can start.
• Harbour-front buildings. The harbour and Porthmeor lie in the Environment Agency's warning area for the north Cornwall coast from Land's End to Chapel Porth, and a flood warning and evacuation plan sets out what occupants do when a warning is issued.
• Homes with a flood history. The lower town flooded in 2002, 2004, 2009 and 2014, and an insurance flood risk assessment gives brokers and underwriters the property's own evidence.
• Commercial purchases by the sea. Hotels, shops and restaurants on the St Ives harbour front change hands with stream and sea risk attached, and a commercial due diligence flood report covers both before contracts are signed.
• Businesses in the lower town. Before the scheme, a single Stennack flood could reach up to 190 businesses; a business continuity flood assessment plans for the event the scheme does not stop.
• Sites on or over the Stennack. Where a scheme alters the channel, builds over the culvert or depends on its capacity at a tidal outfall, flood modelling tests the depths and flows at that spot.
• Land before it is bought. The neighbourhood plan allocates housing and mixed-use land at Trenwith Lane, the Belyars and the rugby club, and a flood and drainage feasibility study checks a site's drainage and flood constraints before money is committed.

Who to call about the Stennack, the drains or the sea in St Ives

Cornwall Council deals with surface water, ordinary watercourses, highway drainage and the coast; the Environment Agency deals with the sea and main rivers and sends out the warnings; South West Water deals with public sewers. If life is at risk, call 999.

For flooding from a road other than the A30 or A38, or from a stream that is not a main river, the council's 24-hour line is 0300 1234 222. Flooding from main rivers and the sea goes to the Environment Agency hotline.

Questions from St Ives owners, buyers and applicants

Unda Consulting Limited prepares flood risk assessments, sequential tests and drainage strategies across the county; our Cornwall page covers the wider picture, and our pages on Penzance and Helston cover two neighbouring west Cornwall towns. Call 01293 214444 or email enquiries@unda.co.uk to discuss a St Ives site.