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. [1]
The UK Environment Agency has guidelines [1] 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 the eel ladder interrupts the flow of water at each point in the ladder. In contrast, eel and elver passes are distinct by either employing a tube which bypasses the main flow or current and/or employing a bristle surface that presents a greater length of continuous disruption to the flow of water. [2]
Eel and elver passes have a dual purpose. By separating the eel traffic in the flow of water more accurate measurement of eel and elver migration is made possible. The results also prove the benefits. Wisbech Standard 12 July 2014 [3] report large numbers of eels return to the Fens also being able to migrate into the Middle Level along a bristle and duct type eel and elver pass.
The Eels (England and Wales) Regulations 2009 [4] implement Council Regulation (EC) No 1100/2007 [5] of the Council of the European Union, establishing measures for the recovery of the stock of European eel.
Some requirements of the regulations are, where appropriate, to:
Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear.
The European eel is a species of eel. They are critically endangered due to hydroelectric dams, overfishing by fisheries on coasts for human consumption, and parasites.
The American eel is a facultative catadromous fish found on the eastern coast of North America. Freshwater eels are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts. The American eel has a slender, supple, snake-like body that is covered with a mucus layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fins can be found near the midline, followed by the head and gill covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are often lighter than those from dark, tannic acid streams.
Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was long a mystery. Of particular interest has been the search for the spawning grounds for the various species of eels, and identifying the population impacts of different stages of the life cycle.
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. There is no single definition as to what constitutes a weir.
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 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 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.
The Hiram M. Chittenden Locks, or Ballard Locks, is a complex of locks at the west end of Salmon Bay in Seattle, Washington's Lake Washington Ship Canal, between the neighborhoods of Ballard to the north and Magnolia to the south.
The Uttoxeter Canal was a thirteen-mile extension of the Caldon Canal running from Froghall as far as Uttoxeter in Staffordshire, England. It was authorised in 1797, but did not open until 1811. With the exception of the first lock and basin at Froghall, it closed in 1849, in order that the Churnet Valley line of the North Staffordshire Railway could be constructed along its length. The railway has since been dismantled and there are plans to reinstate the canal.
A culvert is a structure that channels water past an obstacle or to a subterranean waterway. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete or other material. In the United Kingdom, the word can also be used for a longer artificially buried watercourse.
A fishing weir, fish weir, fishgarth or kiddle is an obstruction placed in tidal waters, or wholly or partially across a river, to direct the passage of, or trap fish. A weir may be used to trap marine fish in the intertidal zone as the tide recedes, fish such as salmon as they attempt to swim upstream to breed in a river, or eels as they migrate downstream. Alternatively, fish weirs can be used to channel fish to a particular location, such as to a fish ladder. Weirs were traditionally built from wood or stones. The use of fishing weirs as fish traps probably dates back prior to the emergence of modern humans, and have since been used by many societies around the world.
The Hacking River is a watercourse that is located in the Southern Sydney region of New South Wales in Australia. For thousands of years traditional owners called the river Deeban, however the colonial settlers renamed the river after Henry Hacking, a British seaman who killed Pemulwuy and was a pilot at Port Jackson in colonial New South Wales.
The New Zealand longfin eel, also known as ōrea, is a species of freshwater eel that is endemic to New Zealand. It is the largest freshwater eel in New Zealand and the only endemic species – the other eels found in New Zealand are the native shortfin eel, also found in Australia, and the naturally introduced Australian longfin eel. Longfin eels are long-lived, migrating to the Pacific Ocean near Tonga to breed at the end of their lives. They are good climbers as juveniles and so are found in streams and lakes a long way inland. An important traditional food source for Māori, who name them ōrea, longfin eel numbers are declining and they are classified as endangered, but over one hundred tonnes are still commercially fished each year.
A drop structure, also known as a grade control, sill, or weir, is a manmade structure, typically small and built on minor streams, or as part of a dam's spillway, to pass water to a lower elevation while controlling the energy and velocity of the water as it passes over. Unlike most dams, drop structures are usually not built for water impoundment, diversion, or raising the water level. Mostly built on watercourses with steep gradients, they serve other purposes such as water oxygenation and erosion prevention.
Eels are ray-finned fish belonging to the order Anguilliformes, which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.
Low-head hydro power refers to the development of hydroelectric power where the head is typically less than 20 metres, although precise definitions vary. Head is the vertical height measured between the hydro intake water level and the water level at the point of discharge. Using only a low head drop in a river or tidal flows to create electricity may provide a renewable energy source that will have a minimal impact on the environment. Since the generated power is a function of the head these systems are typically classed as small-scale hydropower, which have an installed capacity of less than 5MW.
The Salmon and Freshwater Fisheries Act 1975 is a law passed by the government of the United Kingdom in an attempt to protect salmon and trout from commercial poaching, to protect migration routes, to prevent willful vandalism and neglect of fisheries, ensure correct licensing and water authority approval. This helps to sustain the rural inland freshwater fisheries industry, which employs around 37,000 people in the UK.
The Nimbus Fish Hatchery is located in eastern Sacramento County, built on the downstream side of the Nimbus Dam. It is one of the 21 fish hatcheries the California Department of Fish and Wildlife oversees. Chinook salmon and steelhead are raised, and about 4 million Chinook salmon and 430,000 steelheads released each year.
The Cut-off Channel is a man-made waterway which runs along the eastern edge of the Fens in Norfolk and Suffolk, England. It was constructed in the 1950s and 1960s as part of flood defence measures, and carries the headwaters of the River Wissey, River Lark and River Little Ouse in times of flood, delivering them to Denver Sluice on the River Great Ouse. In the summer months, it is also used as part of a water supply scheme for drinking water in Essex.
A tilting weir or tilting gate is a moveable weir that is used for raising and lowering a head of water by controlling the flow of water to a lower catchment area or drainage basin. Typically the plate or paddle of the tilting weir moves up and down in a narrow duct by titling, pivoting or rotating on its bottom horizontal axis - which opens or closes the tilting weir thus controlling the flow of water out of the higher drainage basin. For example, a reservoir, lake, duct, channel, river, pond, dyke or ditch to a lower-lying area or catchment or drainage basin.
Lake Āniwaniwa is a small man-made lake on the Rangitaiki River, in the Bay of Plenty region of New Zealand. The lake is situated 13 km north of the town of Murupara, and about 16 km upstream of the Matahina Dam. The lake was created as a result of the construction of a 10 m high dam, part of the Aniwhenua hydroelectric scheme.