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Title: Tidal defences for Clevedon, North Somerset
Author: Environment Agency South West Region
Document Type: Monograph
Abstract:
The Land Yeo drains mainly rural land upstream of Clevedon - including the low-lying Tickenham, Nailsea and Kenn Moors Site of Special Scientific Interest. When the M5 motorway was built in the 1970s the River Yeo was divided into two watercourses upstream of Clevedon - the Land Yeo and the manmade Blind Yeo. They are connected by the Yearling Ditch, which takes flow south from the Land Yeo to the Blind Yeo via a sluice at Cooks Clyse. The Land Yeo outfall - where the river discharges into the Severn Estuary - was an old masonry structure, thought to date back to the 1880s. Records show there has been an outfall structure at this location since medieval times. Marshalls Bank - a 500-metre long embankment that stretches between the Land Yeo outfall and the Blind Yeo sluice - also dates back to medieval times. Work took place in 1958 and 1984 to raise and strengthen the bank. The Blind Yeo sluice is not as historic as the other two tidal structures, but its purpose is no less significant. The sluice lies at the tidal outlet of the Blind Yeo, where it meets Clevedon Pill and the Severn Estuary. The sluice comprises two gates, known as the north and south eyes. The south eye dates from around 1952 and the north eye was added in the early 1970s to handle the extra water run-off from the M5. The three tidal defence structures are located next to the Severn Estuary. The estuary has the second highest tidal range in the world. The most recent flooding happened in December 1981, when a large surge on a modest spring tide flooded 305 properties and land up to two kilometres from the sea. Since that time many hundreds of properties have been built in the tidal floodplain. Engineers found the previous Land Yeo outfall was in poor structural condition and nearing the end of its useful life. The outfall was also no longer watertight, did not control upstream water levels as required and did not meet health and safety requirements for operation and maintenance. Although Marshalls Bank was structurally stable, erosion and settlement had significantly reduced its height and width. In an extreme tidal event waves would overtop the low, narrow bank and cause further erosion and structural damage, and could eventually cause a breach of the defence. The Blind Yeos north and south eyes - constructed of reinforced concrete - were in need of structural, mechanical and electrical refurbishment. The three tidal defence structures were only capable of preventing flooding from an extreme tidal event with a 1 in 25 (4 per cent) chance of happening in any one year. The Environment Agencys national target is to provide protection against a flood with a 1 in 100 to 1 in 300 (1 per cent - 0.33 per cent) chance of happening in any one year. In 2004 we carried out a 1 million project to refurbish the Blind Yeo sluice, and in 2005/2006 a 3.2 million scheme was completed on the Land Yeo outfall and Marshalls Bank.
Publisher: Environment Agency
Publication Date: 2006
Publication Place: Exeter
Subject Keywords: CoastsBeachesCoastal managementFlood controlFlood barriersRiversSite of Special Scientific Interest
Geographic Keywords: Bristol Avon and North Somerset Streams catchmentSomersetEA South WestYeo (South Somerset)
Extent: 11
Permalink: http://www.environmentdata.org/archive/ealit:1194
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