Fish screen

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 generators, petroleum refineries, chemical plants, farm irrigation water and municipal drinking water treatment plants.

Contents

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.[1]:p. 4-19

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.[2] 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.[1]:pp.4-3ff

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 larvae. Organisms that pass through the screens are killed or stressed (depending on the species) as they become entrained in the cooling system.[3]

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 States, 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 regulations on industrial cooling water intake structures.[4] EPA issued final regulations for new facilities in 2001 (amended 2003).[5] Other EPA regulations for existing facilities were challenged in litigation and EPA published new proposed regulations in April 2011.[6]

See also

References

  1. ^ a b c U.S. Environmental Protection Agency (EPA), Washington, DC. (2004). "Efficacy of Cooling Water Intake Structure Technologies." Chapter 4 of Technical Development Document for the Final Section 316(b) Phase II Existing Facilities Rule. Doc. No. EPA-821-R-04-007.
  2. ^ "One Fish, Two Fish, 46 Million Lake Erie Dead Fish." Toledo City Paper. 2009-08-19.
  3. ^ EPA (2002). "National Pollutant Discharge Elimination System—Proposed Regulations to Establish Requirements for Cooling Water Intake Structures at Phase II Existing Facilities; Proposed Rule." 67 F.R. 17136. 2002-04-09.
  4. ^ Clean Water Act, Section 316(b), 33 U.S.C. § 1316.
  5. ^ EPA. "Phase I—New Facilities." Cooling Water Intake Structures. Final rule: 2001-12-18, 66 F.R. 65255. Amended: 2003-06-19, 68 F.R. 36749.
  6. ^ EPA. "National Pollutant Discharge Elimination System—Cooling Water Intake Structures at Existing Facilities and Phase I Facilities." Proposed rule. 76 F.R. 22174. 2011-04-20.

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