|
The English River Thames is navigable from Cricklade (for small boats) or Lechlade (for larger boats) to the sea, and this part of the river falls 71 metres (234 feet). There are 45 locks on the river, each with one or more adjacent weirs. These lock and weir combinations are used for controlling the flow of water down the river, most notably when there is a risk of flooding, and provide for navigation above the tideway. ==History== From ancient times there were many obstructions across the Thames, for fish-pounds and millers' weirs. They are referred to by Asserius Menevensis in the ninth century and Magna Carta (1215) states that "weirs, for the time to come, shall be demolished in the Thames and Medway, except on the sea coast." It appears this never happened.〔 〕 In the Middle Ages, the fall on the river in its middle and upper sections was used to drive watermills for the production of flour and paper and various other purposes such as metal-beating. This involved the construction of weirs in order to divert water into the mills. The weirs, however, presented an obstacle to navigation and to solve this problem locks were built alongside the weirs to enable boats to be moved between levels. Originally these were flash locks that were essentially removable sections of weir. A boat moving downstream would wait above the lock until the lock was opened, which would allow a "flash" of water to pass through, carrying the boat with it. In the opposite direction boats would be winched or towed through the open lock. The difficulty of using flash locks, and the consequent loss of water and income to the miller, eventually led to their replacement with pound locks. Locks similar to these early pound locks still exist on the river, although in many cases they have been enlarged and mechanised. On the lower section, the river was tidal as far as Staines until the beginning of the 19th century and was under the control of the City of London. The City's jurisdiction was marked by the London Stone. The principle of lock/weir combination, which maintained the depth of water for navigation and reduced the danger of flooding, was extended over the tidal section as far as Teddington in a series of locks built after 1810.〔 The first authority charged with managing navigation and lock building was the Oxford-Burcot Commission, which built the locks at Iffley and Sandford below Oxford in 1633 and at Swift Ditch near Abingdon. In 1751, the Thames Navigation Commissioners were established and built eight locks between Shiplake Lock and Boulters lock between 1770 and 1773. The opening of the Thames and Severn Canal from Lechlade in 1789 led to the building of many of the locks upstream of Shiplake. The locks built on the tidal section required individual Acts of Parliament, and the Thames Conservancy took over their management from the City in 1857. In 1866 the Thames Conservancy became responsible for all river management and installed more locks over the years, the last being Eynsham and King’s in 1928. In 1908 an Act transferred responsibility for the Thames from a point below Teddington Lock to the Port of London Authority, and this included Richmond Lock.〔Fred S. Thacker ''The Thames Highway: Volume 1 General History'' David & Charles 1968〕 The Thames Conservancy was subsumed into the Thames Water Authority in 1974. With the privatization of water supply in 1990 the river management functions passed to the new National Rivers Authority and in 1996 to the Environment Agency. Only Richmond Lock remains under the jurisdiction of the Port of London Authority. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Locks and weirs on the River Thames」の詳細全文を読む スポンサード リンク
|