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Weirs
A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of lakes, ponds, and reservoirs. There are many weir designs, but commonly water flows freely over the top of the weir crest before cascading down to a lower level. Etymology There is no single definition as to what constitutes a weir and one English dictionary simply defines a weir as a small dam, likely originating from Middle English ''were'', Old English ''wer'', derivative of root of ''werian,'' meaning "to defend, dam". Function Commonly, weirs are used to prevent flooding, measure water discharge, and help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but normally there is a clear distinction made between the structures. Usually, a dam is designed specifically to impound water behind ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weir At Bray Lock, May 2018
A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of lakes, ponds, and reservoirs. There are many weir designs, but commonly water flows freely over the top of the weir crest before cascading down to a lower level. Etymology There is no single definition as to what constitutes a weir and one English dictionary simply defines a weir as a small dam, likely originating from Middle English ''were'', Old English ''wer'', derivative of root of ''werian,'' meaning "to defend, dam". Function Commonly, weirs are used to prevent flooding, measure water discharge, and help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but normally there is a clear distinction made between the structures. Usually, a dam is designed specifically to impound water behind ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Locks And Weirs On The River Thames
The English River Thames is navigable from Cricklade (for very small, shallow boats) or Lechlade (for larger boats) to the sea, and this part of the river falls 71 meters (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 involv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
River Thames
The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, second-longest in the United Kingdom, after the River Severn. The river rises at Thames Head in Gloucestershire, and flows into the North Sea near Tilbury, Essex and Gravesend, Kent, via the Thames Estuary. From the west it flows through Oxford (where it is sometimes called the Isis), Reading, Berkshire, Reading, Henley-on-Thames and Windsor, Berkshire, Windsor. The Thames also drains the whole of Greater London. In August 2022, the source of the river moved five miles to beyond Somerford Keynes due to the heatwave in July 2022. The lower reaches of the river are called the Tideway, derived from its long tidal reach up to Teddington Lock. Its tidal section includes most of its London stretch and has a rise and fall of . From Oxford to th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes, which are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, Huron, Lake Erie, Erie, and Lake Ontario, Ontario and are in general on or near the Canada–United States border. Hydrologically, lakes Lake Michigan–Huron, Michigan and Huron are a single body joined at the Straits of Mackinac. The Great Lakes Waterway enables modern travel and shipping by water among the lakes. The Great Lakes are the largest group of freshwater lakes on Earth by total area and are second-largest by total volume, containing 21% of the world's surface fresh water by volume. The total surface is , and the total volume (measured at the low water datum) is , slightly less than the volume of Lake Baikal (, 22–23% of the world's surface fresh water ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spawning
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquatic mammals and reptiles, reproduce through the process of spawning. Spawn consists of the reproductive cells (gametes) of many aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing ova (unfertilized eggs) into the water, often in large quantities, while males simultaneously or sequentially release spermatozoa (milt) to fertilize the eggs. Most fish reproduce by spawning, as do most other aquatic animals, including crustaceans such as crabs and shrimps, molluscs such as oysters and squid, echinoderms such as sea urchins and sea cucumbers, amphibians such as frogs and newts, aquatic insects such as mayflies and mosquitoes and corals, which are actually small ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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