Fish Screening Criteria

Justifications for Fish Screens

Endangered Species Act Salmon 4(d) Rule

Section 4(d) of the Endangered Species Act (ESA) directs NOAA Fisheries to issue regulations to conserve species listed as threatened. This applies particularly to “take,” which can include any act that kills or injures fish, and may include habitat modification. The ESA prohibits ANY take of species listed as endangered, but some take of threatened species that does not interfere with salmon survival and recovery can be allowed.

Before 2000, NOAA Fisheries Service had simply adopted 4(d) rules that prohibited take of threatened species. In a salmon and steelhead 4(d) rulesigned in July of 2000, the agency pioneered a new approach. It applied take prohibitions to all actions except those within 13 “limits” to the rules (described in detail in the rules) where the specified categories of activities contribute to conserving listed salmon. A separate but closely related tribal 4(d) rule created an additional limit for tribal resource management plans. For more information on the ESA 4(d) rule visit NOAA National Marine Fisheries website.

Fish Screening Bibliography

Documents Specifying the Need/Requirement to Screen Water Diversions

CALFED Bay-Delta Program, National Marine Fisheries Service Programmatic Biological Opinion, August 28, 2000, 6. Ecosystem Restoration, Page 60.

“Preliminary, significant steps towards the largest ecological restoration project yet undertaken in the United States have occurred during the past four years and continue to proceed in California’s Central Valley.  The CALFED Bay-Delta Program, in coordination with other Central Valley efforts including those implemented through the CVPIA, has implemented numerous habitat restoration actions that benefit Sacramento River winter-run Chinook salmon, Central Valley spring-run salmon, Central Valley steelhead, and their critical habitat.  These restoration actions include the installation of fish screens, modifications of barriers to improve fish passage, and habitat acquisition and restoration.”

CALFED Bay-Delta Program, Record of Decision, August 28, 2000, Page 19.

“Representative Ecosystem Restoration Program actions include:”

“Modifying of eliminating fish passage barriers, including the removal of some dams, construction of fish ladders, and construction of fish screens that use the best available technology.”

CALFED Bay-Delta Program, Record of Decision, August 28, 2000, Section 2.1.5 Environmental Preferable/Superior Alternative, Page 27-28.

“….Accordingly, the Preferred program alternative is the “Environmentally Preferred Alternative” under NEPA and the “Environmentally Superior Alternative” under CEQA.”

“….The Preferred Program Alternative meets the programs multiple purposes, reduces adverse environmental effects, and provides a system of research and monitoring to determine whether modifications or additional actions are needed.  It provides multiple benefits, including but not limited to:

Constructing fish screens that use the best available technology”

CALFED Bay-Delta Program, Ecosystem Restoration Program, Draft Stage1 Implementation Plan, August 6, 2001, Pg. 13.

“CALFED Science Program Goals in Relation to the Ecosystem Program.  The CALFED Program covers one of the largest and most modified watersheds on the West coast of North America (Nichols et al, 1986).  Loss of habitat, water diversions, pollution, and species introductions are among the stressors considered responsible for substantial reductions in the abundance of many native fish populations and massive modifications of ecosystems.

 CALFED Bay-Delta Program, Ecosystem Restoration Program, Draft Stage1 Implementation Plan, August 6, 2001, Pg. 19.

Anadromous Fish Screen Program (AFSP) – Section 3406(b)(21)
The goal of the AFSP is to encourage and facilitate fish screen and other physical fish passageway facilities construction to avoid or minimize the entrainment and impingement of juvenile Chinook salmon (all runs), steelhead trout, green and white sturgeon, American Shad, and striped bass.  …Activities eligible for these cost-share funds under AFSP include, but are not limited to: constructing fish screens on unscreened diversions; rehabilitating existing fish screens; replacing existing, nonfunctioning screens; and relocating water diversions to less fishery sensitive areas.

CALFED Bay-Delta Program, Ecosystem Restoration Program, Draft Stage1 Implementation Plan, August 6, 2001, Pg. 25.

“Fish Screens: ….The smaller diversions also the potential to entrain juvenile fish.  A large number of screen projects are underway and additional screens are needed.   At the same time, studies are needed to better understand how effectively fish screens protect species to better prioritize allocation of expenditures.”

A Citizen’s Guide to the 4(d) Rule For Threatened Salmon and Steelhead on the West Coast, National Marine Fisheries Service, Northwest and Southwest Regions, June 20, 2000, Page 4.

“’Take’ is defined as ‘harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or attempt to engage in any such conduct’ (ESA section 3[19]).  It is also illegal under ESA section 09 to possess, sell, deliver, carry, transport, or ship any species that has been taken illegally (ESA section 9[a][1]).  Violating the take prohibitions may result in civil or criminal penalties.”

“‘Harass’ is defined as an intentional or negligent act that creates the likelihood of injuring wildlife by annoying it to such an extent as to significantly disrupt normal behavior patterns such as breeding, feeding, or sheltering (50 CFR 17.3).”

“’Harm’ is defined as an act that actually kills or injures a protected species (50 CFR 222.102 (64FR 60727)).  Harm can arise form significant habitat modification or degradation where it actually kills or injures protected species by significantly impairing essential behavioral patterns, including breeding, spawning, rearing, migrating, feeding, or sheltering.”

A Citizen’s Guide to the 4(d) Rule For Threatened Salmon and Steelhead on the West Coast, National Marine Fisheries Service, Northwest and Southwest Regions, June 20, 2000, Take Guidance, Page 4-5.

“Based on available information, NMFS believes the categories of activities listed below are those activities that, as a general rule, are most likely to harm listed fish…..These types of activities are, however, those most likely to cause harm and thereby violate this rule.  NMFS’ ESA enforcement will focus on these categories of activities.”

“…G.  Constructing or operating dams or water diversion structures with inadequate fish screens or passage facilities.”

A Citizen’s Guide to the 4(d) Rule For Threatened Salmon and Steelhead on the West Coast, National Marine Fisheries Service, Northwest and Southwest Regions, June 20, 2000, Limit No. 9 – Water Diversion Screening, Page 12-13.

“Operating water diversion without adequate screening is a widely recognized cause of mortality among salmon and steelhead.  Juveniles may be sucked or attracted into diversion ditches where they later die from a variety of causes, including stranding.  Adult and juvenile migration may be blocked by diversion structures such as pus-up dams.  Juveniles are often injured and killed when caught in pumping facilities or forced against screens.”

“State laws and Federal programs have long recognized these problems in varying ways, and encouraged or required adequate screening of diversion ditches and structures.  Nonetheless, large numbers of diversion are not adequately screened and remain a threat, particularly to juvenile fish.  Eliminating that source of injury or death is vital to conserving listed stocks.”

“The final rule encourages all diverters to move quickly to provide adequate screening or other protections for their diversion.  The rule does not apply take prohibitions provided that NMFS’ engineering staff–or any resource agency or tribal representative NMFS designates as an authorized officer—has agreed in writing that the diversion facility is screened, maintained, and operated in compliance with NMFS’ Juvenile Fish Screening Criteria (NMFS 1996) or, in California, in compliance with NMFS Southwest Region’s Fish Screening Criteria for Anadromous Salmonids (NMFS 1997) or any subsequent revision.  If a diversion is screened, operated, and maintained in a manner consistent with those criteria, adequate safeguards will be in place and no additional Federal protection is necessary or advisable for conserving listed fish.”

“The final rule also provides that NMFS or its authorized officer may review and approve for a take limit a proposed juvenile fish screen design and construction plan.  The plan must describe interim operations measures that will avoid taking threatened fish.”

Letter to Family Water Alliance from Rick Wantuck, National Marine Fisheries Service, June 26, 1998.

“Such a rule could call for all water diversions to be screened with NMFS-approved technology by some date certain, or else compliance measures would presumable be enforced (up to, and possible including, a prohibition against unscreened water diversion devices).  I must emphasize that this debate is strictly pre-decisional, but it is consistent with NMFS’ unpublished goal of protecting anadromous fish within their range by screening all unscreened water diversions.

It is documented that unscreened water diversions present a real and probable danger of entrainment to immature salmonid, as well as other tiny fishes and aquatic life forms.  With over 3000 unscreened diversions remaining to be screened in California, it is imperative that we aggressively pursue a solution to the problem of fish entrainment into water diversions.”

NMFS Proposed Recovery Plan for the Sacramento River Winter-run Chinook Salmon, National Marine Fisheries Service, Southwest Region, Long Beach, California, August 1997, Goal II Improve Survival of Downstream Migrants, Page V-34.

Objective/Action: 1. Maximize survival of juveniles at unscreened or inadequately screened diversions on the Sacramento, River, Sacramento-San Joaquin Delta, and Suisun Marsh (Priority 1) 1.  Develop and implement a comprehensive plan to install positive barrier fish screens at unscreened or poorly screened diversion on the Sacramento River, Sacramento-San Joaquin Delta, and Suisun Marsh sloughs.

Upper Sacramento River Fisheries and Riparian Habitat Management Plan, January 1989,The Resources Agency, State of California, Page 95, #3.

“Require screening and screen maintenance on all diversions on the Sacramento River that significantly impact the fishery and develop a process for funding this work.”

Upper Sacramento River Fisheries and Riparian Habitat Management Plan, January 1989, Resources Agency, State of California, Page 96, #4.

“Obtain funding to design and install screens at private diversions currently not under permit from the Crops of Engineers.”

State of California, Resources Agency, Department of Fish and Game, Statewide Fish Screening Policy, Diversions Covered by Section 6020, June 19, 2000.

“The Department of Fish and Game may consider for screening any diversion with a capacity of 250 cubic-feet per second or less. Activities in this category will be assigned a lower priority than those covered by Section 5980 until all of the Department of Fish and Game obligations for both its own diversions, and for those diversions with a capacity greater than 250 cubic-feet per second, have been fulfilled.”

“In addition, all diversions covered by this section which are located within the essential habitat of a State (CESA) listed species, or the critical habitat of a federally (ESA) listed species, shall be deemed to require screening.”

“Variances from these requirements shall be supported by a report, prepared by the diverter, which includes data from onsite monitoring and a review of historical entrainment and diversion data. The scope of the report and the sampling effort shall be approved by the Department of Fish and Game prior to the initiation of work.”

Central Valley Project Improvement Act (CVPIA),Section: 3406(b)(21),Title: Anadromous Fish Screen Program.

“This section authorizes the Secretary to assist the State of California in its effort to develop and implement measures to avoid losses of juvenile anadromous fish resulting from poorly sited, unscreened, or inadequately screened diversions on Central Valley waterways. The Anadromous Fish Screen Program is voluntary; making it difficult to predict the number of program related screening projects in the future. However, of those diverters applying for inclusion, the program applies standards to ensure selected projects are of high priority.”

“Restoration Objectives: Appropriate screening of diversions is anticipated to reduce a substantial cumulative source of mortality for anadromous and resident fish species. Unscreened diversions, from small tributaries such as Butte Creek, to the salt-water interface near Suisun Bay, affect anadromous fish throughout their juvenile stages. The development of a basin-wide screen program, in a context of cooperation and partnership, is the most promising strategy for control of juvenile anadromous fish losses associated with agricultural, municipal, and industrial diversion.”

California Salmonid Stream habitat Restoration Manual, State of California Resources Agency, Department of Fish and Game, third Edition, January 1998,Policy and Regulations, A-7,

Fish and Wildlife Coordination Act of 1934. “Under the provisions of this Federal legislation enacted in 1934, the Department of Fish and Game shall require installation of fish screens on all unscreened diversions where fish are present.”

“The ‘General Fish Screening Criteria’ shall be used as the basis for design of fish screens required under this policy.  The need-to-screen criteria may be modified by the Department of Fish and Game, and it is the responsibility of the project proponent to have the most recent copy of these agreement criteria.  Copies are available from either the Environmental Services Division or the Inland Fisheries Division of the Department of Fish and Game.

Salmon, Steelhead Trout, and Anadromous Fisheries Program Act, Chapter 8, Article 1. 6901 (d).

“Protection of, and in increase in, the naturally spawning salmon and steelhead trout resources of the state would provide a valuable public resource to the residents, a large statewide economic benefit, and would, in addition, provide employment opportunities not otherwise available to the citizens of this state, particularly in rural areas of present underemployment.”

Salmon, Steelhead Trout, and Anadromous Fisheries Program Act, Chapter 8, Article 1.  6902 (a).

“The Department shall develop a plan and a program that strives to double the current natural production of salmon and steelhead trout resources.

Salmon, Steelhead Trout, and Anadromous Fisheries Program Act, Chapter 8, Article 1.  6902 (b).

“It is the policy of the state to recognize and encourage the participation of the public in privately and publicly funded mitigation, restoration, and enhancement programs in order to protect and increase naturally spawning salmon and steelhead trout resources.”

California Department of Fish and Game Criteria

Fish Screening Criteria
June 19, 2000


A. Streams And Rivers (flowing water): The screen face shall be parallel to the flow and adjacent bankline (water’s edge), with the screen face at or streamward of a line defined by the annual low-flow water’s edge.

The upstream and downstream transitions to the screen structure shall be designed and constructed to match the bankline, minimizing eddies upstream of, in front of, and downstream of, the screen.

Where feasible, this “on-stream” fish screen structure placement is preferred by the California Department of Fish and Game.

B. In Canals (flowing water): The screen structure shall be located as close to the river source as practical, in an effort to minimize the approach channel length and the fish return bypass length. This “in canal” fish screen location shall only be used where an “on-stream” screen design is not feasible. This situation is most common at existing diversion dams with headgate structures.

The current National Marine Fisheries Service – Southwest Region criteria for these types of installations shall be used.

C. Small Pumped Diversions: Small pumped diversions (less than 40 cubic-feet per second) which are screened using “manufactured, self-contained” screens shall conform to the National Marine Fisheries Service – Southwest Region criteria.

D. Non-Flowing Waters (tidal areas, lakes and reservoirs): The preferred location for the diversion intake structure shall be offshore, in deep water, to minimize fish contact with the diversion. Other configurations will be considered as exceptions to the screening criteria as described in Section 5.F. below.

2. APPROACH VELOCITY (Local velocity component perpendicular to the screen face)

A. Flow Uniformity: The design of the screen shall distribute the approach velocity uniformly across the face of the screen. Provisions shall be made in the design of the screen to allow for adjustment of flow patterns. The intent is to ensure uniform flow distribution through the entire face of the screen as it is constructed and operated.

B. Self-Cleaning Screens: The design approach velocity shall not exceed:

1. Streams and Rivers (flowing waters) – Either:

a. 0.33 feet per second, where exposure to the fish screen shall not exceed fifteen minutes, or

b. 0.40 feet per second, for small (less than 40 cubic-feet per second) pumped diversions using “manufactured, self-contained” screens.

2. In Canals (flowing waters) – 0.40 feet per second, with a bypass entrance located every one-minute of travel time along the screen face.

3. Non-Flowing Waters (tidal areas, lakes and reservoirs) – The specific screen approach velocity shall be determined for each installation, based on the species and life stage of fish being protected. Velocities which exceed those described above will require a variance to these criteria (see Section 5.F. below).

(Note: At this time, the U.S. Fish and Wildlife Service has selected a 0.2 feet per second approach velocity for use in waters where the Delta smelt is found. Thus, fish screens in the Sacramento-San Joaquin Estuary should use this criterion for design purposes.)

C. Screens Which Are Not Self-Cleaning: The screens shall be designed with an approach velocity one-fourth that outlined in Section B above. The screen shall be cleaned before the approach velocity exceeds the criteria described in Section B.

Frequency Of Cleaning: Fish screens shall be cleaned as frequently as necessary to prevent flow impedance and violation of the approach velocity criteria. A cleaning cycle once every 5 minutes is deemed to meet this standard.

Screen Area Calculation: The required wetted screen area (square feet), excluding the area affected by structural components, is calculated by dividing the maximum diverted flow (cubic-feet per second) by the allowable approach velocity (feet per second). Example: 1.0 cubic-feet per second / 0.33 feet per second = 3.0 square feet. Unless otherwise specifically agreed to, this calculation shall be done at the minimum stream stage.

3. SWEEPING VELOCITY (Velocity component parallel to screen face)

A. In Streams And Rivers: The sweeping velocity should be at least two times the allowable approach velocity.

B. In Canals: The sweeping velocity shall exceed the allowable approach velocity. Experience has shown that sweeping velocities of 2.0 feet per second (or greater) are preferable.

C. Design Considerations: Screen faces shall be designed flush with any adjacent screen bay piers or walls, to allow an unimpeded flow of water parallel to the screen face.


A. Porosity: The screen surface shall have a minimum open area of 27 percent. We recommend the maximum possible open area consistent with the availability of appropriate material, and structural design considerations.

The use of open areas less than 40 percent shall include consideration of increasing the screen surface area, to reduce slot velocities, assisting in both fish protection and screen cleaning.

B. Round Openings: Round openings in the screening shall not exceed 3.96mm (5/32in). In waters where steelhead rainbow trout fry are present, this dimension shall not exceed 2.38mm (3/32in).

C. Square Openings: Square openings in screening shall not exceed 3.96mm (5/32in) measured diagonally. In waters where steelhead rainbow trout fry are present, this dimension shall not exceed 2.38mm (3/32in) measured diagonally.

D. Slotted Openings: Slotted openings shall not exceed 2.38mm (3/32in) in width. In waters where steelhead rainbow trout fry are present, this dimension shall not exceed 1.75mm (0.0689in).


A. Material Selection: Screens may be constructed of any rigid material, perforated, woven, or slotted that provides water passage while physically excluding fish. The largest possible screen open area which is consistent with other project requirements should be used. Reducing the screen slot velocity is desirable both to protect fish and to ease cleaning requirements. Care should be taken to avoid the use of materials with sharp edges or projections which could harm fish.

B. Corrosion and Fouling Protection: Stainless steel or other corrosion-resistant material is the screen material recommended to reduce clogging due to corrosion. The use of both active and passive corrosion protection systems should be considered.

Consideration should be given to anti-fouling material choices, to reduce biological fouling problems. Care should be taken not to use materials deemed deleterious to fish and other wildlife.

C. Project Review and Approval: Plans and design calculations, which show that all the applicable screening criteria have been met, shall be provided to the Department before written approval can be granted by the appropriate Regional Manager.

The approval shall be documented in writing to the project sponsor, with copies to both the Deputy Director, Habitat Conservation Division and the Deputy Director, Wildlife and Inland Fisheries Division. Such approval may include a requirement for post-construction evaluation, monitoring and reporting.

D. Assurances: All fish screens constructed after the effective date of these criteria shall be designed and constructed to satisfy the current criteria. Owners of existing screens, approved by the Department prior to the effective date of these criteria, shall not be required to upgrade their facilities to satisfy the current criteria unless:

1. The controlling screen components deteriorate and require replacement (i.e., change the opening size or opening orientation when the screen panels or rotary drum screen coverings need replacing),

2. Relocation, modification or reconstruction (i.e., a change of screen alignment or an increase in the intake size to satisfy diversion requirements) of the intake facilities, or

3. The owner proposes to increase the rate of diversion which would result in violation of the criteria without additional modifications.

E. Supplemental Criteria: Supplemental criteria may be issued by the Department for a project, to accommodate new fish screening technology or to address species-specific or site-specific circumstances.

F. Variances: Written variances to these criteria may be granted with the approval of the appropriate Regional Manager and concurrence from both the Deputy Director, Habitat Conservation Division and the Deputy Director, Wildlife and Inland Fisheries Division. At a minimum, the rationale for the variance must be described and justified in the request.

Evaluation and monitoring may be required as a condition of any variance, to ensure that the requested variance does not result in a reduced level of protection for the aquatic resources.

It is the responsibility of the project sponsor to obtain the most current version of the appropriate fish screen criteria. Project sponsors should contact the Department of Fish and Game, the National Marine Fisheries Service (for projects in marine and anadromous waters) and the U.S. Fish and Wildlife Service (for projects in anadromous and fresh waters) for guidance.

For more information visit the California Dept. of Fish & Game website.

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National Marine Fisheries Service

Fish Screening Criteria

I. General Considerations

This document provides guidelines and criteria for functional designs of downstream migrant fish passage facilities at hydroelectric, irrigation, and other water withdrawal projects. It is promulgated by the National Marine Fisheries Service (NMFS), Southwest Region as a result of its authority and responsibility for prescribing fishways under the Endangered Species Act (ESA), the Federal Power Act, administered by the Federal Energy Regulatory Commission (FERC), and the Fish and Wildlife Coordination Act (FWCA), administered by the U.S. Fish & Wildlife Service.

The guidelines and criteria are general in nature. There may be cases where site constraints or extenuating circumstances dictate a waiver or modification of one or more of these criteria. Conversely, where there is an opportunity to protect fish, site-specific criteria may be added. Variances from established criteria will be considered on a project-by-project basis.

The swimming ability of fish is a primary consideration in designing a fish screen facility. Research shows that swimming ability varies depending on multiple factors relating to fish physiology, biology, and the aquatic environment. These factors include: species, physiological development, duration of swimming time required, behavioral aspects, physical condition, water quality, temperature, lighting conditions, and many others. Since conditions affecting swimming ability are variable and complex, screen criteria must be expressed in general terms and the specifics of any screen design must address on-site conditions.

NMFS may require project sponsors to investigate site-specific variables critical to the fish screen system design. This investigation may include fish behavioral response to hydraulic conditions, weather conditions (ice, wind, flooding, etc.), river stage-discharge relationships, seasonal operations, sediment and debris problems, resident fish populations, potential for creating predation opportunity, and other pertinent information. The size of salmonids present at a potential screen site usually is not known, and can change from year-to-year based on flow and temperature conditions. Thus, adequate data to describe the size-time relationship requires substantial sampling over a number of years. NMFS will normally assume that fry-sized salmonids are present at all sites unless adequate biological investigation proves otherwise. The burden of proof is the responsibility of the owner of the screen facility.

New facilities which propose to utilize unproven fish protection technology frequently require: 1) development of a biological basis for the concept; 2) demonstration of favorable behavioral responses in a laboratory setting; 3) an acceptable plan for evaluating the prototype installation; 4) an acceptable alternate plan should the prototype not adequately protect fish. Additional information can be found in Experimental Fish Guidance Devices, position statement of the National Marine Fisheries Service, Southwest Region, January 1994.

Striped Bass, Herring, Shad, Cyprinids, and other anadromous fish species may have eggs and/or very small fry which are moved with any water current (tides, streamflows, etc.). Installations where these species are present may require individual evaluation of the proposed project using more conservative screening requirements. In instances where state or local regulatory agencies require more stringent screen criteria to protect species other than salmonids, NMFS will generally defer to the more conservative criteria.

General screen criteria and procedural guidelines are provided below. Specific exceptions to these criteria occur in the design of small screen systems (less than 40 cubic feet per second) and certain small pump intakes. These exceptions are listed in Section K, Modified Criteria for Small Screens, and in the separate addendum entitled: Juvenile Fish Screen Criteria For Pump Intakes, National Marine Fisheries Service, Portland, Oregon, May 9, 1996.

II. General Procedural Guidelines

For projects where NMFS has jurisdiction, such as FERC license applications and ESA consultations, a functional design must be developed as part of the application or consultation. These designs must reflect NMFS design criteria and be acceptable to NMFS. Acceptable designs typically define type, location, method of operation, and other important characteristics of the fish screen facility. Design drawings should show structural dimensions in plan, elevation, and cross-sectional views, along with important component details. Hydraulic information should include: hydraulic capacity, expected water surface elevations, and flows through various areas of the structures. Documentation of relevant hydrologic information is required. Types of materials must be identified where they will directly affect fish. A plan for operations and maintenance procedures should be included- i.e., preventive and corrective maintenance procedures, inspections and reporting requirements, maintenance logs, etc.- particularly with respect to debris, screen cleaning, and sedimentation issues. The final detailed design shall be based on the functional design, unless changes are agreed to by NMFS.

All juvenile passage facilities shall be designed to function properly through the full range of hydraulic conditions expected at a particular project site during fish migration periods, and shall account for debris and sedimentation conditions which may occur.

III. Screen Criteria for Juvenile Salmonids

A. Structure Placement

1. General:

The screened intake shall be designed to withdraw water from the most appropriate elevation, considering juvenile fish attraction, appropriate water temperature control downstream or a combination thereof. The design must accommodate the expected range of water surface elevations.

For on-river screens, it is preferable to keep the fish in the main channel rather than put them through intermediate screen bypasses. NMFS decides whether to require intermediate bypasses for on-river, straight profile screens by considering the biological and hydraulic conditions existing at each individual project site.

2. Streams and Rivers:

Where physically practical, the screen shall be constructed at the diversion entrance. The screen face should be generally parallel to river flow and aligned with the adjacent bankline. A smooth transition between the bankline and the screen structure is important to minimize eddies and undesirable flow patterns in the vicinity of the screen. If trash racks are used, sufficient hydraulic gradient is required to route juvenile fish from between the trashrack and screens to safety. Physical factors that may preclude screen construction at the diversion entrance include excess river gradient, potential for damage by large debris, and potential for heavy sedimentation. Large stream-side installations may require intermediate bypasses along the screen face to prevent excessive exposure time. The need for intermediate bypasses shall be decided on a case-by-case basis.

2. Canals:

Where installation of fish screens at the diversion entrance is undesirable or impractical, the screens may be installed at a suitable location downstream of the canal entrance. All screens downstream of the diversion entrance shall provide an effective juvenile bypass system- designed to collect juvenile fish and safely transport them back to the river with minimum delay. The angle of the screen to flow should be adequate to effectively guide fish to the bypass. Juvenile bypass systems are part of the overall screen system and must be accepted by NMFS.

3. Lakes, Reservoirs, and Tidal Areas:

a. Where possible, intakes should be located off shore to minimize fish contact with the facility. Water velocity from any direction toward the screen shall not exceed the allowable approach velocity. Where possible, locate intakes where sufficient sweeping velocity exists. This minimizes sediment accumulation in and around the screen, facilitates debris removal, and encourages fish movement away from the screen face.

b. If a screened intake is used to route fish past a dam, the intake shall be designed to withdraw water from the most appropriate elevation in order to provide the best juvenile fish attraction to the bypass channel as well as to achieve appropriate water temperature control downstream. The entire range of forebay fluctuations shall be accommodated by the design, unless otherwise approved by NMFS.

B. Approach Velocity

Definition: Approach Velocity is the water velocity vector component perpendicular to the screen face.

Approach velocity shall be measured approximately three inches in front of the screen surface.

1. Fry Criteria – less than 2.36 inches {60 millimeters (mm)} in length.

If a biological justification cannot demonstrate the absence of fry-sized salmonids in the vicinity of the screen, fry will be assumed present and the following criteria apply:

Design approach velocity shall not exceed:

  • Streams and Rivers: 0.33 feet per second
  • Canals: 0.40 feet per second
  • Lakes, Reservoirs, Tidal: 0.33 feet per second (salmonids)

2. Fingerling Criteria – 2.36 inches {60 mm} and longer

If biological justification can demonstrate the absence of fry-sized salmonids in the vicinity of the screen, the following criteria apply:

Design approach velocity shall not exceed:

  • All locations: 0.8 feet per second

3. The total submerged screen area required (excluding area of structural components) is calculated by dividing the maximum diverted flow by the allowable approach velocity. (Also see Section K, Modified Criteria for Small Screens, part 1).

4. The screen design must provide for uniform flow distribution over the surface of the screen, thereby minimizing approach velocity. This may be accomplished by providing adjustable porosity control on the downstream side of the screens, unless it can be shown unequivocally (such as with a physical hydraulic model study) that localized areas of high velocity can be avoided at all flows.

C. Sweeping Velocity

Definition: Sweeping Velocity is the water velocity vector component parallel and adjacent to the screen face.

1. Sweeping Velocity shall be greater than approach velocity. For canal installations, this is accomplished by angling screen face less than 45 relative to flow (see Section K, Modified Criteria for Small Screens). This angle may be dictated by specific canal geometry, or hydraulic and sediment conditions.

D. Screen Face Material

1. Fry criteria

If a biological justification cannot demonstrate the absence of fry-sized salmonids in the vicinity of the screen, fry will be assumed present and the following criteria apply for screen material:

  • Perforated plate: screen openings shall not exceed 3/32 inches (2.38 mm), measured in diameter.
  • Profile bar: screen openings shall not exceed 0.0689 inches (1.75 mm) in width.
  • Woven wire: screen openings shall not exceed 3/32 inches (2.38 mm), measured diagonally. (e.g.: 6-14 mesh)
  • Screen material shall provide a minimum of 27% open area.

2. Fingerling Criteria

If biological justification can demonstrate the absence of fry-sized salmonids in the vicinity of the screen, the following criteria apply for screen material:

  • Perforated plate: Screen openings shall not exceed 1/4 inch (6.35 mm) in diameter.
  • Profile bar: screen openings shall not exceed 1/4 inch (6.35 mm) in width
  • Woven wire: Screen openings shall not exceed 1/4 inch (6.35 mm) in the narrow direction
  • Screen material shall provide a minimum of 40% open area.

3. The screen material shall be corrosion resistant and sufficiently durable to maintain a smooth and uniform surface with long term use.

E. Civil Works and Structural Features

1. The face of all screen surfaces shall be placed flush with any adjacent screen bay, pier noses, and walls, allowing fish unimpeded movement parallel to the screen face and ready access to bypass routes.

2. Structural features shall be provided to protect the integrity of the fish screens from large debris. Trash racks, log booms, sediment sluices, or other measures may be needed. A reliable on-going preventive maintenance and repair program is necessary to ensure facilities are kept free of debris and the screen mesh, seals, drive units, and other components are functioning correctly.

3. Screens located in canals – surfaces shall be constructed at an angle to the approaching flow, with the downstream end terminating at the bypass system entrance.

4. The civil works design shall attempt to eliminate undesirable hydraulic effects (e.g.- eddies, stagnant flow zones) that may delay or injure fish, or provide predator opportunities. Upstream training wall(s), or some acceptable variation thereof, shall be utilized to control hydraulic conditions and define the angle of flow to the screen face. Large facilities may require hydraulic monitoring to identify and correct areas of concern.

F. Juvenile Bypass System Layout

Juvenile bypass systems are water channels which transport juvenile fish from the face of a screen to a relatively safe location in the main migratory route of the river or stream. Juvenile bypass systems are necessary for screens located in canals because anadromous fish must be routed back to their main migratory route. For other screen locations and configurations, NMFS accepts the option which, in its judgement, provides the highest degree of fish protection given existing site and project constraints.

1. The screen and bypass shall work in tandem to move out-migrating salmonids (including adults) to the bypass outfall with minimum injury or delay. Bypass entrance(s) shall be designed such that out-migrants can easily locate and enter them. Screens installed in canal diversions shall be constructed with the downstream end of the screen terminating at a bypass entrance. Multiple bypass entrances (intermediate bypasses) shall be employed if the sweeping velocity will not move fish to the bypass within 60 seconds assuming the fish are transported at this velocity. Exceptions will be made for sites without satisfactory hydraulic conditions, or for screens built on river banks with satisfactory river conditions.

2. All components of the bypass system, from entrance to outfall, shall be of sufficient hydraulic capacity to minimize the potential for debris blockage.

3. To improve bypass collection efficiency for a single bank of vertically oriented screens, a bypass training wall may be located at an angle to the screens.

4. In cases where insufficient flow is available to satisfy hydraulic requirements at the main bypass entrance(s), a secondary screen may be required. Located in the main screen’s bypass channel, a secondary screen allows the prescribed bypass flow to be used to effectively attract fish into the bypass entrance(s) while allowing all but a reduced residual bypass flow to be routed back (by pump or gravity) for the primary diversion use. The residual bypass flow (not passing through the secondary screen) then conveys fish to the bypass outfall location or other destination.

5. Access is required at locations in the bypass system where debris accumulation may occur.

6. The screen civil works floor shall allow fish to be routed to the river safely in the event the canal is dewatered. This may entail a sumped drain with a small gate and drain pipe, or similar provisions.

G. Bypass Entrance

1. Each bypass entrance shall be provided with independent flow control, acceptable to NMFS.

2. Bypass entrance velocity must equal or exceed the maximum velocity vector resultant along the screen, upstream of the entrance. A gradual and efficient acceleration into the bypass is required to minimize delay of out-migrants.

3. Ambient lighting conditions are required from the bypass entrance to the bypass flow control.

4. The bypass entrance must extend from floor to water surface.

H. Bypass Conduit Design

1. Smooth interior pipe surfaces and conduit joints shall be required to minimize turbulence, debris accumulation, and the risk of injury to juvenile fish. Surface smoothness must be acceptable to the NMFS.

2. Fish shall not free-fall within a confined shaft in a bypass system.

3. Fish shall not be pumped within the bypass system.

4. Pressure in the bypass pipe shall be equal to or above atmospheric pressure.

5. Extreme bends shall be avoided in the pipe layout to avoid excessive physical contact between small fish and hard surfaces and to minimize debris clogging . Bypass pipe centerline radius of curvature (R/D) shall be 5 or greater. Greater R/D may be required for supercritical velocities.

6. Bypass pipes or open channels shall be designed to minimize debris clogging and sediment deposition and to facilitate cleaning. Pipe diameter shall be 24 inches (0.610 m) or greater and pipe velocity shall be 2.0 fps (0.610 mps) or greater, unless otherwise approved by NMFS. (See Modified Criteria for Small Screens) for the entire operational range.

7. No closure valves are allowed within bypass pipes.

8. Depth of flow in a bypass conduit shall be 0.75 ft. (0.23 m) or greater, unless otherwise authorized by NMFS (See Modified Criteria for Small Screens).

9. Bypass system sampling stations shall not impair normal operation of the screen facility.

10. No hydraulic jumps should exist within the bypass system.

I. Bypass Outfall

1. Ambient river velocities at bypass outfalls should be greater than 4.0 fps (1.2 mps), or as close as obtainable.

2. Bypass outfalls shall be located and designed to minimize avian and aquatic predation in areas free of eddies, reverse flow, or known predator habitat.

3. Bypass outfalls shall be located where there is sufficient depth (depending on the impact velocity and quantity of bypass flow) to avoid fish injuries at all river and bypass flows.

4. Impact velocity (including vertical and horizontal components) shall not exceed 25.0 fps (7.6 mps).

5. Bypass outfall discharges shall be designed to avoid adult attraction or jumping injuries.

J. Operations and Maintenance

1. Fish Screens shall be automatically cleaned as frequently as necessary to prevent accumulation of debris. The cleaning system and protocol must be effective, reliable, and satisfactory to NMFS. Proven cleaning technologies are preferred.

2. Open channel intakes shall include a trash rack in the screen facility design which shall be kept free of debris. In certain cases, a satisfactory profile bar screen design can substitute for a trash rack.

3. The head differential to trigger screen cleaning for intermittent type systems shall be a maximum of 0.1 feet (.03 m), unless otherwise agreed to by NMFS.

4. The completed screen and bypass facility shall be made available for inspection by NMFS, to verify compliance with design and operational criteria.

5. Screen and bypass facilities shall be evaluated for biological effectiveness and to verify that hydraulic design objectives are achieved.

K. Modified Criteria for Small Screens (Diversion Flow less than 40 cfs)

The following criteria vary from the standard screen criteria listed above. These criteria specifically apply to lower flow, surface-oriented screens (e.g.- small rotating drum screens). Forty cfs is the approximate cut off; however, some smaller diversions may be required to apply the general criteria listed above, while some larger diversions may be allowed to use the “small screen” criteria below. NMFS will decide on a case-by-case basis depending on site constraints.

1. The required screen area is a function of the approach velocity listed in Section B, Approach Velocity, Parts 1, 2, and 3 above. Note that “maximum” refers to the greatest flow diverted, not necessarily the water right.

2. Screen Orientation:

  • For screen lengths six feet or less, screen orientation may be angled perpendicular to the flow.
  • For screen lengths greater than six feet, screen-to-flow angle must be less than 45 degrees. (See Section C Sweeping Velocity, part 1).
  • For drum screens, design submergence shall be 75% of drum diameter. Submergence shall not exceed 85%, nor be less than 65% of drum diameter.
  • Minimum bypass pipe diameter shall be 10 in (25.4 cm), unless otherwise approved by NMFS.
  • Minimum pipe depth is 1.8 in (4.6 cm) and is controlled by designing the pipe gradient for minimum bypass flow.

For more information visit the National Marine Fisheries Service website.