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The Thames Barrier Information Centre is accessed by bus from North Greenwich Underground station and at weekends in the summer regular boat trips leave from Greenwich and Westminster Pier. Pay and display parking is available at 51° 29.677 N E000’ 02.486 Please refer to the Thames Barrier Information Centre website for admission costs and opening times http://www.environment-agency.gov.uk/homeandleisure/floods/38375.aspx . It is not a requirement to visit the Centre to complete this cache. THE RIVER THAMES TIMELINE – 1. 170 -140 million years ago Southern England was covered by sea, Marine organisms were laid down to create the oolitic limestone of the Cotswold Hills – the source of the River. 2. 140 million years ago the sea became clear allowing for the deposit of marine creatures forming the chalklands of the Thames valley. Each inch of the Kent North Downs took 2,500 years to form and thus would have taken around 30 million years to form totally. 3. 30 million years ago earth upheavals and spasms shaped the earths crust. England was pushed up and the clay covered chalklands of the Thames Valley formed ridges. 4. During the last glacial period 25,000 years – 8,500 years BC England was still physically connected to Continental Europe. The Thames was a tributary of the River Rhine in Germany. 5. 12,000 BC the temperatures began to rise and the ice started to melt. The sea level began to rise. 6. 6,500BC the water of the North Sea rose breaking the remaining ridge between Kent and the North of France, the Straits of Dover were created and Great Britain became an island. 7. Now … the Thames rises in the Cotswolds at Trewsbury Mead 108.5m above sea level. A stone marks the source as for most of the year there is no sign of water. THE THAMES ESTUARY – The Thames Estuary is particularly vulnerable to flooding for a number of reasons. The South-eastern corner of the British Isles is slowly tilting downwards and sea levels are rising. As a result, the high tide in central London is rising at a possible rate of 75cm per century. Storm surges are an even more compelling reason. When an area of low pressure, perhaps hundreds of miles across, moves eastwards across the Atlantic towards the British Isles, it raises the level of seawater beneath it by up to a third of a metre. If this 'plateau' of sea water passes north of Scotland and then down into the shallow basin of the North Sea, perhaps further heightened by strong winds from the north, it can cause excessively high surge tides in the Thames Estuary of up to 4 metres leading towards London. If a spring tide combines with a surge tide the risk of serious flooding rises dramatically. The problem is made much worse when floodwater from upstream meets a high surge tide coming up from the Thames Estuary. On a typical summers day about 3,000 million litres of fresh water will pass over it. On a typical winters day the quantity will be at least four times greater, and sometimes eight times. In the winter of 1947, the peak flow at Teddington was 61,698 million litres a day. This flow was nearly three times that of a typical winter's day and more than 20 times that of a typical summer's day. THE THAMES BARRIER – The Thames Barrier is one of the largest movable flood barriers in the world. The Environment Agency runs and maintains the Thames Barrier. The barrier spans 520 metres across the River Thames near Woolwich, and it protects 125 square kilometres of central London from flooding caused by tidal surges. The site was chosen because of the solid chalk table and the high riversides at that point. It became operational in 1982 and has 10 steel gates that can be raised into position across the River Thames. When raised, the main gates stand as high as a five-storey building and as wide as the opening of Tower Bridge. Each main gate weighs 3,300 tonnes. The questions to complete this cache are: 1. From the Barrier, how far is it to the source of the Thames River? 2. As indicated by the mural, what is the ‘Mean High Water’ level at the Thames Barrier? 3. In the 1953 storm, there was a surge of 5.6m. If this storm surge occurred when the water level was at the ‘Mean High Water’ level (as indicated in question 2), what would the total water level add up to, and what are the last two towns that the water would have reached? 4. Take a photo of you and/or your GPS with the barriers in the background Please send us the answers of the questions and we'd love to see your photo if one is taken.” Congratulations and FTF honours to aB5dEglYeS5P
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Coordinates are in the WGS84 datum