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Elver Pass
An elver pass or eel pass is a waterway modification constructed to mitigate the effects of obstructions, especially manmade weirs, on waterways, watercourses, ditches, drains, channels and flumes, on the movement of eels, fish and elvers (juvenile eels). Powerful swimmers, including salmon and sea trout, find it easy to pass through many structures. However, it is widely accepted that some structures make fish migration more difficult upstream. Construction The UK Environment Agency has guidelines for the design of eel and elver passes for employment in weirs, tidal flaps & gates and sluice structures. A variety of materials for example HDPE and stainless steel are used to construct brush and bristle surfaces, pipes, ducts, mouse holes, cat flaps and pet door types of eel and elver passes. Eel and elver passes are distinctive from fish ladders which in turn are distinct from eel ladders. The eel ladder is constructed by introducing steps or uprights. Each step or upright of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elver (fish)
Fish go through various life stages between fertilization and adulthood. The life of a fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish. Growth stages Ichthyoplankton ''(planktonic or drifting fish)'' are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 met ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish Ladder
A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as movements of potamodromous species. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ''ladder'') into the waters on the other side. The velocity of water falling over the steps has to be great enough to attract the fish to the ladder, but it cannot be so great that it washes fish back downstream or exhausts them to the point of inability to continue their journey upriver. History Written reports of rough fishways date to 17th-century France, where bundles of branches were used to make steps in steep channels to bypass obstructions. A pool and weir salmon ladder was built around 1830 by James Smith, a Scottish engineer on the River Teith, near Deanston, Perthshire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eels
Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators. The term "eel" is also used for some other eel-shaped fish, such as electric eels (genus ''Electrophorus''), spiny eels (family Mastacembelidae), swamp eels (family Synbranchidae), and deep-sea spiny eels (family Notacanthidae). However, these other clades evolved their eel-like shapes independently from the true eels. Eels live both in salt and fresh water, and some species are catadromous. Description Eels are elongated fish, ranging in length from in the one-jawed eel (''Monognathus ahlstromi'') to in the slender giant moray. Adults range in weight from to well over . They possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal fin, formin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Council Of The European Union
The Council of the European Union, often referred to in the treaties and other official documents simply as the Council, and informally known as the Council of Ministers, is the third of the seven Institutions of the European Union (EU) as listed in the Treaty on European Union. It is one of two legislative bodies and together with the European Parliament serves to amend and approve or veto the proposals of the European Commission, which holds the right of initiative. The Council of the European Union and the European Council are the only EU institutions that are explicitly intergovernmental, that is, forums whose attendees express and represent the position of their Member State's executive, be they ambassadors, ministers or heads of state/government. The Council meets in 10 different configurations of national ministers (one per state). The precise membership of these configurations varies according to the topic under consideration; for example, when discussing agri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Middle Level Commissioners
The Middle Level Commissioners are a land drainage authority in eastern England. The body was formed in 1862, undertaking the main water level management function within the Middle Level following the breakup of the former Bedford Level Corporation. The Middle Level is the central and largest section of the Great Level of The Fens, which was reclaimed by drainage during the mid-17th Century. The area is bounded on the northwest and east by the River Nene and Ouse washes, on the north by previously drained Marshland silts and to the south and west by low clay hills. The Middle Level river system consists of over of watercourses most of which are statutory navigations and has a catchment of over . History In the distant past Great Britain was part of continental Europe with the rivers of eastern England being tributaries of the River Rhine, which flowed across a flat, marshy plain, which is now the southern North Sea. Around 12,000 years ago, following the end of the last Ice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Fens
The Fens, also known as the , in eastern England are a naturally marshy region supporting a rich ecology and numerous species. Most of the fens were drained centuries ago, resulting in a flat, dry, low-lying agricultural region supported by a system of drainage channels and man-made rivers ( dykes and drains) and automated pumping stations. There have been unintended consequences to this reclamation, as the land level has continued to sink and the dykes have been built higher to protect it from flooding. Fen is the local term for an individual area of marshland or former marshland. It also designates the type of marsh typical of the area, which has neutral or alkaline water and relatively large quantities of dissolved minerals, but few other plant nutrients. The Fens are a National Character Area, based on their landscape, biodiversity, geodiversity and economic activity. The Fens lie inland of the Wash, and are an area of nearly in Lincolnshire, Cambridgeshire, and Norfol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elver Pass During Manufacture Exposing Bristles
Elver may refer to: * Elver (fish), a juvenile eel * Elver pass, a river construction that allows fish & eels to migrate freely * Elver Eating World Championships People * Elmore Elver * Hilal Elver * Helena Elver Helena Elver (born 1 March 1998) is a Danish handball player who plays for Odense Håndbold and the Danish national team. She made her debut on the Danish national team on 27 July 2019. She also represented Denmark in the 2015 European Women's ... * Élver James Melchor Bañol {{disambiguation, given name, surname ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eel Ladder
A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as movements of potamodromous species. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ''ladder'') into the waters on the other side. The velocity of water falling over the steps has to be great enough to attract the fish to the ladder, but it cannot be so great that it washes fish back downstream or exhausts them to the point of inability to continue their journey upriver. History Written reports of rough fishways date to 17th-century France, where bundles of branches were used to make steps in steep channels to bypass obstructions. A pool and weir salmon ladder was built around 1830 by James Smith, a Scottish engineer on the River Teith, near Deanston, Perthshire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eel Ladder
A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as movements of potamodromous species. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ''ladder'') into the waters on the other side. The velocity of water falling over the steps has to be great enough to attract the fish to the ladder, but it cannot be so great that it washes fish back downstream or exhausts them to the point of inability to continue their journey upriver. History Written reports of rough fishways date to 17th-century France, where bundles of branches were used to make steps in steep channels to bypass obstructions. A pool and weir salmon ladder was built around 1830 by James Smith, a Scottish engineer on the River Teith, near Deanston, Perthshire ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stainless Steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corrosion resistance, resistance to corrosion results from the chromium, which forms a Passivation (chemistry), passive film that can protect the material and self-healing material, self-heal in the presence of oxygen. The alloy's properties, such as luster and resistance to corrosion, are useful in many applications. Stainless steel can be rolled into Sheet metal, sheets, plates, bars, wire, and tubing. These can be used in cookware, cutlery, surgical instruments, major appliances, vehicles, construction material in large buildings, industrial equipment (e.g., in paper mills, chemical plants, water treatment), and storage tanks and tankers for chemicals and food products. The biological cleanability of stainless steel is superior to both alumi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weir
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] |
High-density Polyethylene
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code. In 2007, the global HDPE market reached a volume of more than 30 million tons. Properties HDPE is known for its high strength-to-density ratio. The density of HDPE ranges from 930 to 970 kg/m3. The standard method to test plastic density is ISO 1183 part 2 (gradient columns), alternatively ISO 1183 part 1MVS2PRO density analyzer. Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
