Fish screen
Encyclopedia
A fish screen is designed to prevent fish
from swimming or being drawn into an aqueduct
, cooling water intake, dam
or other diversion on a river
, lake
or waterway where water is taken for human use. They are built to supply debris-free water without harming aquatic life. Fish screens are typically installed to protect endangered species
of fishes that would otherwise be harmed or killed when passing through industrial facilities such as steam electric power plants, hydroelectric
generator
s, petroleum refineries
, chemical plant
s, farm irrigation
water and municipal drinking water treatment
plants.
Positive barriers are often effective at keeping aquatic organisms from entering a cooling system, but may also kill them by impinging them on the screens. These barrier types are widely used and include:
Besides simply preventing fishes from passing, fish screens are designed to minimize stress and injury that occur when fishes impact the screen or are subjected to changes in water velocity and direction caused by the diversion.
The U.S. Environmental Protection Agency (EPA) has evaluated other barrier technologies and identified some as potentially effective, although not widely demonstrated (as of 2004):
Some fish screens are designed to protect a single species of fish (for example, salmon
) and are not necessarily effective at protecting other fish species. Some screens are capable of protecting more than one species or type of life. Additionally, some screens may effectively protect juvenile and adult fish, but not fish eggs and larva
e. Organisms that pass through the screens are killed or stressed (depending on the species) as they become entrained in the cooling system.
The cost of a fish screen varies from thousands of US dollars for small, low-flow-rate screens to millions of US dollars, in the case of very large custom-designed systems that filter a large flow of water. Maintenance costs can be significant, including repairs, removing trash, and adjusting the equipment for changes in stream conditions. Some manufacturers are able to produce a screen that has no moving parts, requires no electricity, and has very little need for maintenance.
, the National Marine Fisheries Service
, a division of NOAA, mandates positive-barrier fishscreens in most new diversions from waterways where endangered or threatened fish species occur. Some existing unscreened diversions whose construction pre-dates fish-screen mandates are allowed to continue operating by grandfather rule
.
The U.S. Clean Water Act
requires EPA to issue regulation
s on industrial cooling water intake structures. EPA issued final regulations for new facilities in 2001 (amended 2003). Other EPA regulations for existing facilities were challenged in litigation and EPA published new proposed regulations in April 2011.
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
from swimming or being drawn into an aqueduct
Aqueduct
An aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose....
, cooling water intake, dam
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
or other diversion on a river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
, lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
or waterway where water is taken for human use. They are built to supply debris-free water without harming aquatic life. Fish screens are typically installed to protect endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of fishes that would otherwise be harmed or killed when passing through industrial facilities such as steam electric power plants, hydroelectric
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...
generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
s, petroleum refineries
Oil refinery
An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...
, chemical plant
Chemical plant
A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...
s, farm irrigation
Irrigation
Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...
water and municipal drinking water treatment
Water purification
Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...
plants.
Design
Fish screens may be positive barriers (devices such as a perforated metal plate that physically prevents fishes from passing) or behavioral barriers (devices that encourage fishes to swim away). Most behavioral barriers are experimental and of unproven effectiveness.Positive barriers are often effective at keeping aquatic organisms from entering a cooling system, but may also kill them by impinging them on the screens. These barrier types are widely used and include:
- Modified traveling screens
- Fish handling and return systems
- Cylindrical wedgewire screens
- Fine-mesh screens
- Fish net barriers.
Besides simply preventing fishes from passing, fish screens are designed to minimize stress and injury that occur when fishes impact the screen or are subjected to changes in water velocity and direction caused by the diversion.
The U.S. Environmental Protection Agency (EPA) has evaluated other barrier technologies and identified some as potentially effective, although not widely demonstrated (as of 2004):
- Aquatic microfiltration barriers
- Angled and modular inclined screens
- Velocity caps.
Some fish screens are designed to protect a single species of fish (for example, salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
) and are not necessarily effective at protecting other fish species. Some screens are capable of protecting more than one species or type of life. Additionally, some screens may effectively protect juvenile and adult fish, but not fish eggs and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. Organisms that pass through the screens are killed or stressed (depending on the species) as they become entrained in the cooling system.
The cost of a fish screen varies from thousands of US dollars for small, low-flow-rate screens to millions of US dollars, in the case of very large custom-designed systems that filter a large flow of water. Maintenance costs can be significant, including repairs, removing trash, and adjusting the equipment for changes in stream conditions. Some manufacturers are able to produce a screen that has no moving parts, requires no electricity, and has very little need for maintenance.
Legal requirements
In the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, the National Marine Fisheries Service
National Marine Fisheries Service
The National Marine Fisheries Service is a United States federal agency. A division of the National Oceanic and Atmospheric Administration and the Department of Commerce, NMFS is responsible for the stewardship and management of the nation's living marine resources and their habitat within the...
, a division of NOAA, mandates positive-barrier fishscreens in most new diversions from waterways where endangered or threatened fish species occur. Some existing unscreened diversions whose construction pre-dates fish-screen mandates are allowed to continue operating by grandfather rule
Grandfather clause
Grandfather clause is a legal term used to describe a situation in which an old rule continues to apply to some existing situations, while a new rule will apply to all future situations. It is often used as a verb: to grandfather means to grant such an exemption...
.
The U.S. Clean Water Act
Clean Water Act
The Clean Water Act is the primary federal law in the United States governing water pollution. Commonly abbreviated as the CWA, the act established the goals of eliminating releases of high amounts of toxic substances into water, eliminating additional water pollution by 1985, and ensuring that...
requires EPA to issue regulation
Regulation
Regulation is administrative legislation that constitutes or constrains rights and allocates responsibilities. It can be distinguished from primary legislation on the one hand and judge-made law on the other...
s on industrial cooling water intake structures. EPA issued final regulations for new facilities in 2001 (amended 2003). Other EPA regulations for existing facilities were challenged in litigation and EPA published new proposed regulations in April 2011.
External links
- Cooling Water Intake Structure Technology Fact Sheets - U.S. EPA
- Farmers Irrigation Fish Screen Webcam - Farmers Conservation Alliance, Hood River, Oregon
- Video: "Preserving Utah's Bonneville Cutthroat Trout" - News story about fish screen