An elver pass or eel pass is a waterway modification constructed to mitigate the effects of obstructions, especially manmade

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 l ...

, on

waterways A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other languages. A first distinction is necessary ...

watercourses A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams ar ...

ditches A ditch is a small to moderate divot created to channel water. A ditch can be used for drainage, to drain water from low-lying areas, alongside roadways or fields, or to channel water from a more distant source for plant irrigation. Ditches ar ...

, drains, channels and flumes, on the movement of

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 ...

, 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 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 thousa ...

more difficult upstream. River Welland Elver Pass at Duddington

Construction

The UK

Environment Agency The Environment Agency (EA) is a non-departmental public body, established in 1996 and sponsored by the United Kingdom government's Department for Environment, Food and Rural Affairs, with responsibilities relating to the protection and enha ...

has guidelines for the design of

eel 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 elver passes for employment in

, tidal flaps & gates and sluice structures. A variety of materials for example

HDPE 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, ...

and

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 corros ...

are used to construct brush and bristle surfaces, pipes, ducts, mouse holes, cat flaps and pet door types of

and elver passes. Eel and elver passes are distinctive from

fish ladders 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, Lock (water transport), locks and waterfalls) to facilitate Fish migration#Classification, ...

which in turn are distinct from eel ladders. The

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 move ...

is constructed by introducing steps or uprights. Each step or upright of the

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.

Elver pass during manufacture exposing bristles

Migration and measurement

Eel and elver passes have a dual purpose. By separating the

traffic in the flow of water more accurate measurement of

and elver migration is made possible. The results also prove the benefits. Wisbech Standard 12 July 2014 report large numbers of eels return to the

Fens A fen is a type of wetland. Fen, Fenn, Fens, Fenns, may also refer to: People * Fen (name), a Chinese given name and surname * Fen Cresswell (1915–1966), New Zealand cricketer * Fen McDonald (1891–1915), Australian rules footballer * Kees ...

also being able to migrate into the Middle Level along a bristle and duct type eel and elver pass.

Regulations

The Eels (England and Wales) Regulations 2009 implement Council Regulation (EC) No 1100/2007 of the

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 ...

, establishing measures for the recovery of the stock of European

. Some requirements of the regulations are, where appropriate, to: * Notify the

of the construction, alteration or maintenance of any structure likely to affect the passage of

. * Construct and operate an

pass to allow the free passage of

* Use

screens to exclude

from water abstraction and discharge points * Use of
by-wash
to return excluded

to the waters they came from.

References

{{reflist Eels Dams Fish migrations

Construction

Migration and measurement

Regulations

See also

References