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and Electric Power Generation, no. 1 

Impactsof 

Power PlantIntake 

VelocitiesonFish 

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_-- Fish and Wildlife Service 

US. Department of the Interior 
FWS/OBS-76/20.1 

March 1977 

Topical Briefs: Fish and Wildlife Resources and 

Electric Power Generation, no. 1 

IMPACTS OF POWER PLANT 

INTAKE VELOCITIES ON FISH 

John Boreman 

National Power Plant Team 

1451 Green Road 

Ann Arbor, Michigan 48105 

Power Plant Project 

Office of Biological Services 

Fish and Wildlife Service 

U.S. Department of the Interior 
Preface 

The series Topical Briefs: Fish and Wildlife Resources and Electric 

Power Generation is published by the National Power Plant Team of the 

Power Plant Project to provide a set of concise summaries on topics 

related to electric power generation and transmission and their effects 

on fish and wildlife resources. The briefs are written for fish and 

wildlife biologists who review and make recommendations regarding electric 

power projects. Each brief contains background information on and a 

discussion of the particular topic, a selected bibliography of additional 

information sources, and, in some cases, a strategy to address the 

problem. 

Any suggestions or questions regarding Topical Briefs should be 

directed to: 

Information Transfer Specialist 

National Power Plant Team 

1451 Green Road 

Ann Arbor, Michigan 48105 

(313) 994-3331 ext. 238 

PTS: 378-1238 
IMPACTS OF POWER PLANT INTAKE VELOCITIES ON FISH 

Abstract 

This report outlines biological problems associated with power 

plant intake velocities. Information needed to assess impacts of intake 

velocities on fishery resources and a list of technical references containing more detailed analyses of the problems and mitigation alternatives are included. 

INTRODUCTION 

There is growing recognition that mortality of aquatic biota due to 

entrainment or impingement at power plant intakes produce substantial 

impacts on estuarine, riverine, lacustrine, and coastal ecosystems. In 

some power plants water withdrawal may produce greater losses to fishery 

resources than thermal pollution. For example, up to 165.5 million 

menhaden larvae were killed per day by entrainment at the Brayton Point 

Plant in Massachusetts during the summer of 1971 (U.S. Environmental 

Protection Agency 1972). The ecological implications of this mortality 

are not yet known. 

L R PLANT 1 ENTRAINMENT EVENT 

Brayton Point, 7.0 to 165.5 million menhaden 

Mt. HoDe Bay. Mass. (some river herring) killed

I .. per day 

50 million fish killed in 

11 days 

Hillstone, 36 million fish killed in 

Niantic Bay, Conn. 16 days (probably menhaden 

blueback herring) 

I 2.5 million flounder 

entrained 

Connecticut Yankee, 

Conn. River, Conn 179 million fish larvae 

killed per year 

1 I 

Indian Point, Predicted 7.3 million 

Audson Estuary, N.P. striped bass killed per year, 

larvae and juveniles 

Seabrook, Predicted kill of 74 million 

Hampton-Seabrook clam larvae per day 

Estuary, N.H. 

-~ 

DATE COMMENT 

Summer. L371 Estimated from EPA's 

sampling techniques. 

164.5 million kill on 

July 2; fish mangled. 

August 10-21, Estimated from net tons 

1971 

Nov. 2-18, 

1971 

Apr. -June 

1972 

196961970 

Future 

Future 

at discharge; menhaden and 

blueback herring; tests 

showed all fish died. 

Estimated by sampling of 

vertebrae of dean fish in 

discharge channel. 

Death rate not estimated 

I 

Estimated by B. Marcy. 

For Units 162; estimated 

Prom estuary sampling in 

1966 and 1967. 

Estimate for.proposed plant; 

74 million is initial kill at 

plant startup, lower rate after 

equilibrium reached. 

Table 1. Reports and Predictions of Power Plant Entrainment 

(U.S. 'EnvironmentalProtection Agenc:y 1976a) 

1 
I 2 Intake Velocities 

WER PLANT IMPINGEMENT EVENT 

I 

/Millstone, Niantic Ba? Massive kill of small menhaden (more 

than 2.0 million), screens clogged. 

. H. Robinson, 7,191,785 fish impinged in one year. 

lalveston Bay, Tex. 

I

Indian Point, No. 1 Yearly kill of 1.0 to 1.5 million fish. 

udson River, N.Y. Kill of 1.3 million in 9 112 weeks 1ndian Point, No. 2 Massive kills; maximum per day 120,000 

175,003 fish killed in 5 days. 

ndian Point. No. 1.2 Predicted total kill 6.5 million fish p 

ort Jefferson 2 truckloads (at least) of fish killed 

on screens in 3 days. 

I 

rystal River Predicted annual kill of 400,000 fish 

and 100,000 shellfish. 

I brayton Point 350,000 fish inpinged in one year; 

mostly menhaden 

yster. Creek, 10,000 fish, 5,000 crabs, destroyed pel 

arnegat Bay, N.J. month in spring and summer. 

urry Power Station 6 million river herring destroyed in 

2-3 monrhs 

DATE 

1971 

1969-70 

1965-72 

1969-70 

Jan. 71 

Feb. 72 

:year 

Jan. 26-28 

1966 

1969 

1971-TZ 

1971 

Oct .-Dec. 

1972 

COMMENT 

Occurring late summer, early 

fall; plant shut down on 8121i71; 

persistent low kill of 10 other 

species. 

Projected from sampling of 

operating plant; principal species 

were menhaden, anchovy, croaker; 

highest in ?larch. 

Primarily white perch with 4-10% 

srriped bass. 

10% striped bass; plant closed 

Feb. 8. 

Testing cooling system of new plant 

(no heat); white perch 6 other 

species 

Testing again (no heat) Con. Ed. 

fined $1.6 million by N.Y. for kills. 

With both ulants in full overation 

Mostly sinail menhaden; also white 

perch. 

Based upon operation of 3 units (2 

units now destroy 1.2 this amount). 

Heaviest from Nov-March; flounder, 

silverside, 6 other also impinged. 

Estimated from 19 days of 

sampling; screen kill in cold 

season unknown. 

Estimated by AEC from screen 

samplings during partial power runs. 

Power Plant Impingement 

STATEMENT OF THE PROBLEM 

Rates of entrainment and impingement of aquatic resources are 

directly related to intake velocities at and around the intake structures, and also to numerous other physical and biological phenomena. An 

understanding of these phenomena is necessary to make effective recommendations concerning intake velocities. 

Hydrodynamic conditions in the water body are the principal physical phenomena controlling entrainment and impingement. Three types of 

hydrodynamic conditions may exist (with associated site-specific modifications): a stagnant pool system, such as a lake or pond with no 

prevailing currents; an uni-directional system, such as a stream, river, 

or coastal system with one prevailing current in the vicinity of the 

intake; and a multi-directional flow system, such as in an estuary. 
Intake Velocities 3 

Relative location and construction details of the intake structure 

are also important, because they control flow conditions in the immediate vicinity of the intake. The location of the structure in relation 

to the shoreline, bottom, and water surface influences the abundance, 

variety, and extent of withdrawal of aquatic organisms. Construction of 

skimmer wall%, submerged weirs, velocity caps, etc., can limit the zone 

of power plant water withdrawal, and screens set at an angle to the 

direction of inflow may reduce the impingement of small fish considerably (Stone & Webster Engineering Corporation 1976). 

I dealized Velocitj/ Distributi0n [dealized Velocity Distribution 

Without Cap With Cap 

Figure 1. Operation of the Velocity cap 

(U.S. Environmental Protection Agency 1976a) 

Biological phenomena that influence the magnitude of entrainment 

and impingement of aquatic organisms include their: (1) motility; (2) 

physiological and behavioral responses to factors such as temperature, 

salinity, oxygen concentration, currents, etc.; (3) vertical and horizontal distribution in the vicinity of the power plant intake; and (4) 

growth rate which governs the period of vulnerability to entrainment or 

impingement during each life stage. 

The biologist should be aware of the following problems inherent in 

discussions of entrainment and impingement impacts on critical fishery 

resources that appear in environmental reports, environmental impact 

statements, 316(b) demonstrations and other such reports. The biologist

should also conskder the design stage. 
I 4. Intake Velocities 

method has yet been established for predicting the zone of influence on 

aquatic organisms around power plant intake. Three-dimensional velocity 

profile models superimposed on movement patterns of aquatic species are 

one approach to this problem. However, these models are still in the 

formulative stage. Simplistic mathematical models neglect important 

hydrodynamic phenomena necessary for predicting flow conditions in the 

studies do not reflect the reaction of aquatic organisms to the higher 

velocities in the immediate vicinity of intakes and. therefore. are 

Relating swimming speeds of fishes to intake vulnerability. Impingement and entrainment rates of fishes are dependent on much more 

than simply their ability to maintain position in a given velocity for a 

given period of time. For example, available data indicates that impingement rates of fishes are strongly influenced by temperature and 

salinity conditions in the vicinities of estuarine power plant intakes. 

Rheotaxis (response of an organism to current), phototaxis (response to 

light), and tactile responses also are important in determining the 

Vulnerability of a species. Furthermore, fish may hold a position 

inmediately in front of the intake structure and become susceptible to 

entrainment or impingement upon exhaustion. 

Reports may also mention an organism's capacity to exert a burst of 

speed to support arguments for reduced vulnerability to intakes. However, such arguments are seldom supportable because initial orientation, 

distance and direction travelled, and the types of stimuli that elicit a 

sudden burst of speed all are variables that can not be sufficiently 

documented. 

Meamirernents of intake velori ties. The rennrt shnnlrl crate t-yartlv 

where measurements or estimates of intake velocities have been made with 

respect to the intake structure, water surface and bottom, tide, river 

sitage, and other pertinent variables. Often an average intake velocity 

is reported with no indication of the range of velocities across the 

intake structure; some parts of the intake may have close to zero 

velocity, while others may have velocities much higher than the "average". Furthermore, low velocities are extremely difficult to measure, 

and the accuracy of these measurements may be auestisonable. 

i 

I I 
Intake Velocities 5 

0061 0.08E 

I 

007:

t 

NOTES: 

1. VELOCITIES SHOWN IN METERS/ SEC 

2-MEANREMENTS MADE BETWEEN DEICING LOCP PIPE AND BAR RACKS IN MARCH 1370 

3.ME4WRFMENTS MADE AT A WATER FlDW RATE 60'1. OF NU CAPABILITY 

Figure 2. Undesirable Intake Well Velocity Profiles 

(U.S. Environmental Protection Agency 1976a) 

Stagnant pool areas around the intake. All intakes are designed to 

prevent the pumps from running dry. To keep them from running dry some 

companies construct a reservoir. In such cases, a stagnant water area 

usually occurs in the vicinity of intakes, which allows material such as 

sand and silt to settle out and concentrations of aquatic organisms to 

increase. Vulnerability of the aquatic organisms to the intakes is also 

increased. These areas can be created by breakwaters in combination 

with a dredged-out area, sheet pile walls, ponds dredged adjacent to the 

river, intake canals, etc. 

Relation of intake location to plant discharge. Fish and shellfish 

often are attracted to the discharge, and more of them may be subjected 

to entrainment or impingement if the intake is located too near the 

discharge. 
SUGGESTED STRATEGY 

Entrainment: Eggs and early larval stages of aquatic organisms are 

particularly vulnerable to entrainment. Volume of intake flow is often 

more important than intake velocity in determining degree of impact. If 

important fishery resources are likely to be entrained at a power plant, 

the project report should include the following: 

* Accurate delineation of vertical and horizontal distribution 

of eggs and larvae by species in the expected zone of withdrawal. 

Information on the period of vulnerability of the resource to 

entrainment, including data on duration of the egg and larval 

stages, length of spawning season, and relationship of developmental periods to environmental factors (e.g., temperature) 

that are likely to affect them. 

Description of the physical and biological phenomena that 

could increase vulnerability, such as tidal cycles, current 

patterns, location in intake, behavior, etc. 

Indication of .thevolume of water withdrawal in relation to 

the net flow of the water body. 

- Estimates of the egg and larvae population sizes. 

- Evaluation of significance of entrainment losses to recreational and commercial fisheries. 

Reduction of entrainment losses can be accomplished by several 

methods, including use of skimmer walls, velocity caps, and submerged 

weirs to control the zone of withdrawal; relocation of the intake in 

areas of less critical habitat; or construction of a closed-cycle 

cooXing system to reduce the volume of water withdrawal. Seasonal mode 

operation of once-through cooling during periods of low potential impact 

may also be recommended. It cannot be overemphasized that the best way 

to minimize the impact of a power plant on important aquatic resources 

is t:o site the plaat in a location where such resources are very scarce. 

a 
Intake Velocities 7 

Impingement. Juvenile (post-larval) stages of fish are much more 

vulnerable to impingement losses than any other life stage. In some 

instances, however, substantial impingement of adult fish can occur. 

If critical fishery resaurces are likely to be impinged at power 

plant intakes, the project report should contain the following: 

- Accurate delineation movement patterns of the critical fishery 

resource through the zone of withdrawal. 

Description of the physical and biological phenomena that may 

increase the vulnerability of a species to impingement, such 

as temperature, salinity, currents, behavior, etc. 

If fish by-pass systems are utilized, evidence that fish 

returned to the water body will survive, grow, and reproduce 

successfully. 

- Estimation of the numbers and sizes of impinged species in 

relation to the quantity of wa.ter passing through the plant, 

intake current velocities, season, water temperatures, stage 

of tide, illumination, and other environmental conditions. 

* Population estimates of the impingeable stocks of aquatic 

organisms. 

Evaluation of the degree to which impingement losses will 

reduce recreational and comercial fisheries. 

Reduction of impingement can be accomplished by use of methods such 

as travelling screens, fish bypass systems, louvers, relocation of the 

intake, etc. Air bubbler screens and sound waves have not been shown to 

be effective measures. 

More detailed analyses of alternate intakes that will reduce entrainment and impingement are found in the Atomic Industrial Forum source 

book on cooling water intakes (Battelle 1975) and the U.S. Environmental 

Protection Agency's cooling water intake development document (1976a). 

Guidelines for studies related to power plant intake velocity impacts on 

aquatic resources are presented in the U.S. Environmental Protection 

Agency's 316(b) technical guidance manual (19762)). 

It is important to keep in mind that closed-cycle cooling is not 

the best available technology in all cases. Minor alterations in 

existing open-cycle systems to minimize impact should be recommended 

whenever possible. Each system must be judged on a case-by-case basis. 
CURRENT POLICY 

The U.S. Environmental Protection Agency (1973) recommends reducing 

intake velocities to below 0.5 ft/sec(fps) at the trash rack to enable 

fish to escape the screenwell. The U.S. Nuclear Regulatory Commission 

(1975) recommends that "...the site should have characteristics that 

allow placement of intake structures where the relative abundance of 

impbrtant species is small and where low approach velocities can be 

attained." Also "...approach velocity and screen face velocity are the 

p.rincipa1design criteria for controlling the impingement of larger 

organisms, principally fish, on intake screens. Acceptable approach and 

screen face velocities are based on fish swim speeds which will thus 

vary with the species, site and season. Maximum acceptable approach 

velocities are on the order of 0.5 fps." 

Fish and Wildlife Service concerns on intake velocities appeared in 

Dr. Willis King's Instructional Memorandum RB-44, dated February 5, 

1973, and in the Navigable Waters Handbook (U.S. Fish and Wildlife 

Service 1974). The memorandum reads: "The maximum velocity protecting 

most small fish is 0.5 fps but even lower velocities will entrain 

larvae and plankton and even small fish where intake channels are not 

provided with an effective escape bypass." 
Intake Velocities 9 

REFERENCES CITED 

Battelle. 1975. Environmental impact monitoring of nuclear power 

plants -- source book of moxitoring methods. Atomic Industrial Forum, 

Inc., New York. 2 vols. 

Stone & Webster Engineering Corporation. 1976. Studies to alleviate 

fish entrapment at power plant cooling water intakes: final report. 

Boston, Mass. 1 vol. 

U.S. Environmental Protection Agency. 1972. Proceedings in the matter 

of pollution of Mount Hope Bay and its tributaries. Washington, D.C. 

643 pp. 

U.S. Environmental Protection Agency. 1973. Reviewing environmental 

impact statements - power plant cooling systems, engineering aspects. 

Environmental Protection Technology Series EPA-660f2-73-016. Corvallis, 

Oregon. 93 pp. 

U.S. Environmental Protection Agency. 1976a. Development document for 

best technology available for the location design, constructioh and 

capacity of cooling water intake structure for minimizing adverse 

environmental impact. EPA 440f1-76f015-a. Washington, D.C. 263 pp. 

U.S. Environmental Protection Agency. 1976b. Guidance for determining 

best technology available for the location, design, construction and 

capacity of cooling water intake structures for minimizing adverse 

environmental impact. Section 316(b) P. L. 92-500. (draft 2) Washington, D.C. 50 pp. 

U.S. Fish and Wildlife Service. 1974. Navigable waters handbook. 

Loose-leaf pub. n.p. 

U.S. Nuclear Regulatory Commission. 1975. Regulatory guide 4.7. 

General site suitability criteria for nuclear power stations. Washington, D.C. 30 pp.