Protecting Pentewan

e a s o u th w e s t r4LwYW*'#* A \ ' \ 5 “ Protecting Pentewan Restormel En v ir o n m en t Borough Council Agency CORNWALLCOUNTY COUNCIL Protecting Pentewan Pentewan - a history of flooding ▲ The Square, Pentewan Nowadays Pentewan is a small busy holiday Floodwater rose quickly so that soon the centre, on the south Cornish coast. But in village centre was under four feet of water. the 19th and 20th centuries it was a About 40 families were evacuated. On the bustling port and industrial centre. same day the nearby St Austell River also Evidence of this is still there - although flooded, so that some Pentewan homes blocked off from the sea, the old harbour is were flooded twice. a reminder of when cargo ships visited, trading in coal, timber and china clay, and What caused the flooding? fishing vessels moored alongside the village. The principal cause of the flooding was a There was a purpose-built narrow-gauge small culvert running beneath houses in the railway that transported goods between St Square. Debris washed downstream by Austell's china clay mines and Pentewan. floodwater also blocked the culvert, contributing to the flooding. Also, Pentewan has a long history of flooding floodwater was unable to escape from the from the Pentewan Stream, which is only harbour as it is blocked off from the sea. two kilometres long and flows down to the disused harbour in the centre of the village. The stream drains a small wooded valley to the north of the village and becomes a mere trickle in summer. However, on 26 November 1997, the Pentewan Stream caused a devastating flood. An intense thunderstorm dropped more than 80 mm of rain in seven hours - 30mm of which fell in just half an hour. ▲ 26 November 1997 3 ▲ Special low vibration equipment was used to install the sheet piles that supported the excavation for the culvert ^ Construction of the culvert. Its alignment and shape- had to take occount of dll the underground services ■ and obstructions in the I Square K - * 5 ,Jr5j5>^59 - "*3; - ^ - r v" ^ w Protecting Pentewan Reducing the risk of flooding The Environment Agency considered several A new spillway was built opposite the Ship options to speed the flow of water past Inn to carry away floodwater that collects in houses in Pentewan Square. A key the road (West End) when the St Austell consideration was the possibility of damage River floods. to the many old cottages in the centre of Floodwater in Pentewan drains to the the village if tunnelling or pipe laying was disused harbour, therefore it was necessary used to provide the extra flow capacity. to ensure the water could flow out to the The chosen solution had an unusual feature sea. Some sand was removed from the old - the demolition of a holiday cottage to harbour entrance channel and modifications make way for a new larger culvert. Its made to the harbour gates to allow quicker controlled demolition reduced the risk of flows. other property damage and gave an extra Design of the scheme was mindful of the construction access point to other works on long-term aspirations to reopen the the Pentewan Stream. The cottage was harbour as part of a wider regeneration rebuilt to look exactly the same and the scheme. Therefore, the scheme can cope integrity of the Conservation Area in the with floods that occur at the same time as centre of the village was retained. high tides that would effect harbour water Other works included the construction of levels. 80 metres of stone-faced walls to protect A public exhibition was held in the village properties next to the Pentewan Stream in summer 1999 and the scheme gained and a large debris screen at the entrance to the support of the ma|ority of residents. the culvert. ▲ Installing sheet piles where the culvert enters Pentewan Harbour 5 Pentewan Stream New stone faced flood defence walls New debris screen Landscape works to pond Cove Cottac and rebuilt 1.50m dia. new culvert Harbour West End flood relief - new spillway to harbour St Austell River Protecting Pentewan Construction Demolition of the cottage began in December 2001 and the main road through the village was closed for six weeks to allow construction of the new pipeline beneath it and the cottage. A special low vibration technique - a silent piler - was used to install sheet piles to support the main trench. The new culvert had to weave through existing utility services and avoid the old culvert that was still conveying the Pentewan Stream. These restrictions meant the culvert was constructed using different techniques along its length - sometimes pipes, sometimes a rectangular culvert that was cast in situ. The new culvert was at least 1.5 metres in diameter, replacing an irregular 0.75 metre diameter culvert. The stone-clad floodwalls needed deep foundations to prevent water seeping through the permeable soils beneath the defence. Significant efforts were made to blend the walls into the rear gardens and an existing pond on the stream was enlarged to include a new fringe of reeds and similar plants. ▲ Stone clad flood walls to keep the character of the village Protecting Pentewan Reconstruction of the cottage was ▲ Rebuilding the cottage above the new enlarged culvert particularly complex. It had to achieve modem building regulations, yet be no Support and funding larger than the original. There is no visible The £1.75 million scheme was indication that a large culvert flows just coordinated by a steering group made below the ground floor. The character of up of the Environment Agency, the cottage was maintained by retaining Restormel Borough Council and Cornwall the various changes of floor levels and County Council, with support from the reinstating exposed beams. Pentewan Residents Association. Funding The original walling stone was reclaimed for partners were the Department for use on both the frontage and some Environment, Food and Rural Affairs exposed walls inside. Every opportunity was (DEFRA), the Environment Agency, taken to enhance the cottage for the good borough and county councils. The of the built conservation area, with a slate Agency managed the implementation of roof replacing old asbestos cement tiles. the scheme. During much of the construction period Outline design of the scheme was by water levels in the harbour were lowered, Lewin Fryer and Partners of Bradford-on- and fish were removed before work began. Avon and Plymouth and detailed design Several unexpected migratory species were and construction by E Thomas Civil found e.g. brown trout and flounder, plus a Engineering of Truro with Hyder healthy rudd population. The design of a Consulting of Plymouth. Contract small weir on the stream was adapted to management was by Halcrow Ltd of make it easier for fish to pass over, and eel Exeter. ramps were incorporated at each side. 11 SOUTH WEST REGION ADDRESSES REGIONAL OFFICE SOUTH WESSEX DEVON AREA OFFICE Environment Agency AREA OFFICE Environment Agency South West Region Environment Agency Exminster House Manley House Rivers House Miller Way Kestrel Way Sunrise Business Park Exminster Exeter EX2 7LQ Higher Shaftesbury Road Devon EX6 8AS Tel: 01 392 444 000 Blandford DT11 8ST Tel: 01392 444 000 Fax: 01 392 444 238 Tel: 01258 456 080 Fax: 01392 316 016 Fax: 01258 455 998 CORNWALL AREA OFFICE — Area Administrative Boundaries Environment Agency Sir John Moore House — Regional Boundary Victoria Square • Area Office Bodmin PL31 1 EB Tel: 01208 78301 a Regional Headquarters Fax: 01208 78321 NORTH WESSEX AREA OFFICE Environment Agency Rivers House, East Quay Bridgwater TA6 4YS Tel: 01278 457 333 SOUTH WESSEX AREA Fax: 01278 452 985 www.environment-agency.gov.uk ENVIRONMENT AGENCY GENERAL ENQUIRY LINE 0845 933 3111 ENVIRONMENT AGENCY FLOODLINE 0845 988 1188 ENVIRONMENT AGENCY EMERGENCY HOTLINE E n v ir o n m e n t 0800 80 70 60 Ag e n c y.

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