-- 

Biological Services Program 'Flsul si"~6 

FWS/0BS-76120.9 Topical Briefs: Fish and Wildlife 8 

July 1980 and Electric Power 

Cooling Water Intake Screening 

Devices Used to Reduce 

Entrainment and Impingement v 

Fish and Wildlife Service 

US. Department of the Interior #. 
Biological Services Program 

FWS/OBS-76/20.9 Topical Briefs: Fish and Wildlife Resources 

July 1980 and Electric Power Generation, no. 9 

COOLING WATER INTAKE SCREENING 

DEVICES USED TO REDUCE ENTF?AINI\IENT 

AND IMP INEEKENT 

Eugene S. Fritz 

National Power Plant Team 

2929 Plymouth Road, Room 206 

Ann Arbor, Michigan 48105 

Power P1 ant Project

Office of Biological Services 

Fish and Wildlife Service 

U.S. Department of the Interior 

Fish and Wildlife Service 

U.S. Department of the Interior 
Preface 

The series Topical Briefs: Fish and Wildlife Resources and Electric 

Power Generationys 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 

wild1 ife 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. 

This series is designed to provide synthesized technical information in a convenient format. It is, of course, possible to treat only

the basic aspects of each topic within this abridged format. Also, the 

reader should note that this series addresses solely the technical 

issues concerning electric power generation and transmission. There may

be additional informaton sources and considerations, not covered by

this series, which should be incorporated into electric power development

decisions, 

We solicit open discussion and comment on the topic addressed. 

Documentation of differing points of view would be appreciated. We 

request that any suggestions or questions regarding Topical Briefs be 

directed to: 

Information Transfer Special ist 

National Power Plant Team 

2929 Plymouth Road, Room 206 

Ann Arbor, Michigan 48105 

(313) 668-2365 

FTS: 378-2365 
COOLING WATER INTAKE SCREENING DEVICES USED 

TO REDUCE ENTRAINMENT AND IMPINGEMENT 

ABSTRACT 

Cooling water intake screening devices that Fish and Wildlife 

Service personnel may be expected to assess are identified and described. 

The devi ces incl uded are modified vertical travel i ng screens , singleentrance double-exi t screens, horizontal traveling screens , passive

intake screens, radial wells, artificial filter beds, and porous dikes. 

For each device the location, limitations or restrictions, evidence for 

reducing entrainment and impingement, and major unresolved problems are 

also discussed. 

INTRODUCTION 

Section 316(b) of the Clean Water Act requires that 'I ... the location, 

design, construction, and capacity of cooling water intake structures 

reflect the best available technology available for minimizing adverse 

environmental impact." The best available technology, exclusive of 

cost, is most often represented by closed-cycle cooling systems (e.g. , cooling towers, ponds, canals) that reduce the volume of water that must 

be withdrawn from the source of the cooling water. The reduction in the 

volume of water results in a subsequent decline in the number of organisms

drawn toward or into the cooling system, or both. Due to the expense of 

some closed-cycle cooling systems and their potential environmental 

impacts (e.9- , salt drift, icing, unproductive land use), substantial 

effort has been expended to identify or develop alternative intake 

systems and devices . 

The purposes of this Topical Brief are to identify and to describe 

some of the screening devices that Fish and Wildlife Service biologists 

may be expected to assess, and to discuss the major problems associated 

with each. The information presented can be used in assessing any type 

of water intake system including those used in irrigation, industrial, 

and municipal withdrawals. 

Most screening devices or systems presently available can be included 

within seven general categories. These are: modified vertical traveling 

screens, single-entrance double-exit screens , horizontal traveling 

screens, passive intake screens, radial wells, artificial filter beds, 

and porous dikes. This Topical Brief focuses on each of the categories

rather than on the variation found within each. 

BAC KGRO UNO 

Thermal electric power plants require water to cool steam in their 

condensers. This water is withdrawn from an external water source (Figure 

11. Power plants with a once-through cooling system must withdraw water 

continuously during plant operation. Among power plants with closed-
-- 

2 Screening Devices 

cycle cooling systems, make-up water must be withdrawn periodically to 

replenish that lost by evaporation, blow-down, and other consumptive 

uses. 

POWER PLANT 

IS 

II WASTES 7

11/I 

Figure 1. The cooling water system of a thermal electric power plant

(Shoreham Nuclear Power Station). The stresses that aquatic organisms 

encounter in each portion of the cooling system are identified (Coutant

1974.). 

Cooling water is withdrawn at some type of intake structure, the 

offshore intake, the shoreline intake, or the approach channel intake 

(Cada et al. 1979). Somewhere between the point that water enters the 

intake structure and before it enters the power plant it must pass

through a screening device (Figure 1). The original function of the 

screening device was to exclude debris in the water from entering and 

clogging the condenser tubes. Inspection of these screening devices 

showed that many fish and shellfish were held against the screening

material (impinged) and many of these organisms died. Further investigation

demonstrated that water passing through the screens contained many of 

the younger and smaller stages of aquatic organisms (entrained). Many of 

the entrained organisms were killed or made more susceptible to natural 

mortality as a result of plant passage. 

VERTICAL TRAVELING SCREEN 

The most common screening device presently being used at power

plants, and the device most commonly associated with the impacts resulting 
i 

Screening Devices 3 

from entra nment and impingement, is the Vertical Travel i ng Screen 

(VTS). 

u i I 

SCREEN BASKETS i

LOR “TRAYS”) 

WATER 

-FLOW 

f CLEAN 

a 

I [FLCOR OF SCREEN 

STWCTURE 

Figure 2. A conventional vertical traveling screen (from U.S. Environmental 

Protection Agency 1976). 

CHAR 

spec 

?TER ISTICS 

Conventional VTS’s (Figure 2) may be modified slightly to suit a 

fic site, but the following characteristics are common to all. 

O They are installed in concrete structures that act as the 

screen arid circulating-water pump well. 

O Trash bar racks are located ahead of the screen to remove 

large debris. 

O They consist of a chain belt with individual screen pane1

attached. 

O Screens revolve in the vertical plane between a set of two 

sprockets . J 

O Screen panels are slightly inclined to retain debris, 
-- 

-- 

4 Screening Devices 

O Generally the screen panels are comprised of 9.5-m woven 

mesh . O Screens are rotated either at predetermined intervals or with 

predetermined differential pressure across the screen. 

O Debris is washed off screens with a high pressure spray. 

MODIFIED VERTICAL TRAVELING SCREEN 

Modified vertical traveling screens (Figure 3) are conventional 

vertical traveling screens fitted with a collection "bucket" or ''pan"

beneath the screen panel. The most commonly encountered synonyms for 

this type of screening device are "the bucket screen," "Ristroph screen," 

or the "Surry type screen." The latter name arises from the fact that 

Virginia Electric Power Company's Surry Power Station was one of the 

original sites that this type of screen was used. 

LOW PRESSURE 

FISH WASHING 

CONVENTIONAL 

.SIDE ELEVATION 

FISH SCREEN 

Figure 3. The fish-bucket traveling screens at the Surry Power Station 

(White and Brehmer 1976). 

CHARACTERISTICS 

Although there are many variations of the modif'ied VTS's they all 

have the following characteristics: 
-- 

Screening Devices 5 

O They are structural y simi ar to conventional VTS's. 

O They utilize screen panel s that are fitted with a basket 

capable of retaining' water. 

O Impinged fish are washed into the basket with a low pressure 

spray, thus reducing desiccation. 

O They typically have a high pressure spray to clean debris. 

O They must be operated continuously when fish are present to 

attain maximum effectiveness (typically 3-6 m/min). 

O They must be fitted with fine mesh screen (1 mm or less) to 

reduce entrainment, this increases impingement. 

O They must have a through screen velocity sufficiently low to 

minimize impingement stress. 

LOCATION LIMITATIONS OR RESTRICTIONS 

Modified VTS's can be utilized in any location within design limitations 

of VTS's because the two are structurally almost identical. 

EVIDENCE FOR SUCCESSFUL REDUCTION OF ENTRAINMENT AND IMPINGEMENT 

A number of in situ impingement studies have been conducted at a 

number of power pznWCada et a1 . 1979). Most of these studies showed 

a relatively high initial survival rate for impinged fish (as high as 

93.3% at Salem Nuclear Generating Station in New Jersey). However, 

little information has been obtained on long-term or latent survival. 

One of the few studies that did provide evidence for latent survival was 

conducted at the tlanford Generating Plant on the Columbia River (Page et 

al. 1975). In this study 79-95% of the chinook salmon fry, that were 

released and collected on the screens, survived for over 96 hrs. 

In situ studies have not yet been conducted on impingement of 

larval fishes on fine mesh bucket screens. 

PROBLEMS 

Evidence from impingement studies suggests that juvenile fishes are 

less affected by modified vertical traveling screens than by conventional 

screens. Survival rate, however, appears to be dependent on the physiological

characteristics of the organism and hydrological characteristics of the 

site (e.g., if water is recirculated survival could be reduced by reimpingement or long-term exposure to thermal stress). The physical

shape of impinged organism also appears to influence survival rate. For 

example, filiform larvae tend to become entangled in fine screen mesh 

(Joseph Johnson, personal communication). 
61 Screening Devices 

Benefits derived from uti1 izing modified vertical traveling screens 

appear to be site specific and dependent on the physiological capacity

of a fish to survive impingement force (pinned to the screen) for a 

certain duration. In order to reduce the duration of impingement, the 

screens must be continuously operated. Operation in this manner is 

energy expensive and reduces re1 iabil ity due to breakdowns resulting

from wear of the moving parts. 

The use of fine mesh screen panels, and a reduction of the clearance 

between buckets, shows promise for a reduction in entrainment of fish 

eggs and larvae. However, reduction of entrainment suggests an increase 

in larval impingements, the consequences of which are species and lifestpage dependent. 

SINGLE-ENTRANCE DOUBLE-EXIT VERTICAL TRAVELING SCREENS 

In single-entrance double-exi t vertical traveling screens (Figure

4) water enters the center of the screen and passes from the inside to 

thle outside of the screening surface. Thus debris arid biota are impinged 

on the inner surface of the screen. The most common device is the pearshaped Passavant Screen which has been used in Europe for over 30 years. 

SPROCKET 

WHEEL 

DEBRIS TROUGH 

-SEMlCYLlNDRlCAL 

SCREEN PANEL 

F,igure 4. A single-entrance double-exit screen (Mag1 iente et al. 

1Y78). 

CHARACTER I STICS 

The major characteristics of single-entrance doubl e-exit screens 

are: 

O The screen surface is theoretically double that of a comparable

conventional VTS . 
-- 

. ' Screening Devices 7 

0 Various shapes of screen panels can be utilized but the semicircular screen basket fitted with a water proof membrane and 

water retaining lip (Figure 5) appears most promising for 

impact reduction (Mag1iente et a1 . 1978). 

0 Screen baskets can be constructed of any mesh size, however, 

0.5-mm fine mesh or smaller is the most effective for reducing

entrainment impacts on larval fish and eggs. 

The system has a low pressure wash to flush eggs and larvae into 

the water retaining portion of the bucket. 

The top of the system has a high pressure spray wash which 

directs debris, fish eggs, larvae, and post larval stages of 

fish to a collecting trough which returns them to the receiving 

water. 

Figure 5. Semi-circular screen basket used in single-entrance doubleexjt screen systems (Magliente et al. 1978). 

LOCAT ION LIMITATIONS OR RESTRICT IONS 

Based upon manufacturers ' claims, sing1e-entrance doluhl e-exi t Screens 

can be used in any site that will accommodate a conventional VTS. 

EVIDENCE FOR SUCCESSFUL REDUCTION OF ENTRAINMENT AND IMPINGEMENT 

Only one -in situ study has been completed (Barney M. Davis Generating

Station, Corpus Christi, Texas) which evaluated the effectiveness of 

si ngl e-entrance doubl e-exi t screens; 86% of the impinged organisms survived. Although survival appears high, one must realize that all 

observations were made 10-15 min after collection. No results were 

available for latent mortality or for survival rates of larvae. 
8 Screening Devices 

PROBLEMS 

Results of the study conducted at the Barney Davis Generating

Station (Murray and Jinnette 1978) do not indicate that the singleentrance double-exit screen is any more effective in reducing impingement

mortality than is 'the modified VTS. The use of fine mesh screen (0.5-mm

slot size) should reduce entrainment, but cause simultaneous increase in 

impingement of fish eggs and larvae. Any fish impinged on the downtravel side of the screen would also remain impinged for a longer period

than those on the up-travel side. Although results of the Barney Davis 

study suggest increased survival rates among fishes (juveniles and 

larger), no field data have been obtained which demonstrates that larval 

impingement survival rates are greater than entrainment survival rates. 

The keyhole shape of the Passavant Screen can itself contribute to 

higher incidence of impingement because the required screen well can act 

as an entrapment device. 

HORIZONTAL TRAVELING SCREENS 

Horizontal traveling screens (Figure 6) are continuously moving 

screens that traverse the water source being screened. Although much 

discussion has surrounded the use of the latter screening device, such 

screens have not been successfully operated at power plants. 

-BAR RACK 

WATER FLOW 

TRASH REMOVAL S 

\ 

DEBRIS 

5LUI CEWAY 

Figure 6. Vertical view of the original design concept for horizontal 

tlravelina screens in steam-electric power plant intakes (Chezar 1976). 
SPRAY HEADER 

TRASH REMOVAL 

4 CIRCULATING WATER PUMPS 

Screening Devices 9 

CHARACTER I STICS 

Although many designs have been developed for horizontal traveling 

screens, they all have the following in comon: 

O The screening surface remains submerged thoughout each cycle. 

O The screen is usually oriented at some angle (usually between 

20" and 30') to.the flow. 

O Fish and shellfish impinged on or approaching the screen are 

carried or directed to a return or bypass system. 

O Screens can be fitted with fine mesh to reduce larval entrainment. 

LOCATION LIMITATIONS OR RESTRICTIONS 

Horizontal screens have the potential for being utilized at any 

location that can accomodate conventional vertical travel.ino screens. P

number of designs have been developed that can be used with a very short 

canal although most horizontal traveling screen pl-ototypes indicate the 

need for a relatively long intake canal (Figure 7). 

r -TRASH BARS 

SPRAY HEADER 

TRASH REMOVAL 

4 CIRCULATING WATER PUMPS 

Figure 7. A screenwell with flushmounted horizontal travel ing screen 

(U.S. Environmental Protection Agency 1976). 
I 

I 10 Screening Devices 

I 

EVIDENCE FOR SUCCESSFUL REDUCTION OF ENTRAINMENT AND IMPINGEMENT 

The evidence for reduced impingement mortality comes from experiments 

with prototypes (Cada et a1 . 1979). These experiments yielded results 

that showed over 90% diversion efficiency and survival rates of impinged fr.y and fingerlings between 39% and 100% (the experiments utilized 

chinook salmon, Oncorhynchus tschawt scha, fry and fingerlings). Little 

evidence has been developed for -+-iological effectiveness of ful 1-scale

screens. 

PROBLEMS 

The results of experiments with prototypes are insufficient to 

evaluate the effectiveness of the horizontal screens to reduce the 

impact of entrainment and impingement. 

One of the major problems that has not yet been solved, particularly

in areas with fluctuating high and low water levels, is mechanical 

re'l iabil i ty. The screens must move continuously to operate appropriately

and effectively. Most of the prototype systems have had problems with 

excessive mechanical wear. 

PASSIVE INTAKE SCREENS 

Passive intake screens (Figure 8) are a generic name given to those 

devices which screen-out debris and biota with little or no mechanical 

activity required. The most commonly discussed passive screening systems 

are those manufactured by the Johnson Division, UOP Imc. (the Johnson 

Screen). Other devices include the Ranney Surface Water Intake, Ranney

Co. and the large number of perforated or screened pipe intakes. 

CHARACTER1STICs 

O The screening units are self supporting. 

0 The screening units can be cylindrical, drum shaPed, or Danels. 

O Screens are mostly fine mesh or with very small perforations

(0.5 - 2 mm). Slots may be as large as 9.5 mm. 

O Screening material is typically wedge wire (Figure 9), "Smoothtex" or perforated pipe. 

O Systems may be self-cleaning in locations where flowing water 

passes by the screens, but most utilize back-up backflushing 

components. 
a. 

b. 

if 4 

a ---3 

Screening Devices 11 

7_----

NOT SHOWN) 

C. 

23rn PERFORATED 

I 

C 

Figure 8. Passive intake screens: (a) design concept for cylindrical

wedge-wire screens at power plant cool ing-water intakes (Pagan0 and 

Smith 1979), (b) a Ranney surface water intake (Mickels and Bennett 

1978), (c) a perforated pike intake system (Richards and Hronich 1976). 
"7 MATERIAL STAINLESS STEEL kLOTSLOT WIDTHS: 1.0-2.5mm

w,OTH OPEN AREA: 22.3 -39.5 7. 

FLOW 

___c 

i 4 4!kr.0 

I SECTION A-A 

A d DIMENSIONS(mmj SECTION 8-8 

Figure 9. Flat wedge-wire screen panels used in the TVA hydraulic test 

(Vigander 1978). 

LOCATION LIMITATIONS OR RESTRICTIONS 

Passive intake systems can be designed for use in virtually any 

type of water body; hiowever, their self cleaning characteristic depends 

upon the bypass velocity of the source water. The physical size of the 

screening devices is limiting in most passive systems, thus, necessitating

the clustering of a number of screening units. Perforated pipes, Ranney

Intakes, and large Johnson Screen intakes cannot be utilized in areas 

where their presence would affect navigation. 

Siltation, biofouling, and frazzle ice also limit areas where 

passive screens can be utilized. Most manufacturers claim that these 

problems can be overcome through engineering (e.g. , raising the units 

above sediments), with backflushing systems, and, in the instance of 

biofoul ing, by using antifouling copper alloys. However, site-specific

demonstrations are needed. 

EVIDENCE FOR SUCCESSFUL REDUCTION OF ENTRAINMENT AND IMPINGEMENT 

Laboratory studies have indicated that passive intake wedge wire 

screens are effective in reducing larval entrainment (Hanson et al. 

1978, Heuer and Tom1 janovich 1978). In experimental studies using 1.Olmm mesh, Hanson et al. (1978) noted that striped bass less than 40 fork 

length (FL) showed no impingement stress at intake velocities of 15.24 

cm/s. Field studies conducted in the St. Johns River, Florida with 

prototype screens (Lifton 1980) demonstrated very 1ittle entrainment of 

fish and larvae, minimal impingement of larvae, and no impingement of 

small fishes. Similar types of studies have not yet been reported for 

other types of passive screening systems. 
Screening Devices 13 

PROBLEMS 

There is no evidence that a full-scale passive intake system will 

significantly reduce entrainment and impingement. The wedge wire screens 

that have been tested under field conditions are much smaller than the 

type that may be eventually employed (e.g., 0.6-m long by 0.3-m diameter 

screens have been used as prototypes for 6-m long by 3-m diameter screens).

The difference in scale makes evaluating the effectiveness of the screens 

difficult. +.. 

i The size and configuration of offshore passive intakes are such 

i that they could potentially act as artificial reefs. Such a phenomenon, 

could attract organisms to the intake, thus, increasing their vulnerability 

to impacts. 

As stated previously, the utilization of passive intake systems in 

water with high concentrations of suspended particles, high potential

for frazzle ice formation, or high biofouling potential may pose a 

number of maintenance problems. The solution of these problems requires

information that can only be obtained at facilities using passive intake 

systems. 

RADIAL WELLS 

Radial we1 1s (Figure 10) are subsurface collectors located in 

highly permeable alluvial aquifers where the water table is high and in 

direct contact with a surface stream or lake (recharge source). The 

most popular brand3name is the Ranney Collector. Yields of radial wells 

range up to 0.93 m /s (Mikels and Bennett 1978). 

. .' SAND & GRAVEL . ' APUIFER 

Figure 10. A radial well intake system (Ray et al. 1976). 
The fundamenta.1 characteristics of the radial well intake are: 

O A submerged concrete caisson sunk into the base of an aquifer

adjacent to a recharge source. 

O A number of perforated pipes that radiate from the base of the 

caisson into the aquifer. 

O A pump to move water from the well to the plant. 

LOCAT ION L IMITATIOMS AND RESTRICTIONS 

I to’provide a reliable-source of water, the recharge source must be at a 

higher level than the aquifer. 

I Water is obtained directly from the aquifer, thus, aquatic resources 

are not affected unless the recharge source is reduced to a level that 

The major problem associated with radial wells is the necessity to 

locate them in a sand or gravel aquifer. The volume of water that can 

be obtained is limited by the aquifer and the recharge source. These 

problems limit the application of radial wells to relatively specific 

areas. 

ARTIFICIAL FILTER BEDS 

Artificial filter beds (Figure 11) are man-made filtering facilities 

designed to reduce the impact Of Water withdrawals on aauatic oraqnisrns.

The s.$ate-of-the-art artificial filter bed may be capable of providing

3.1 m /s at maximum performance (Richards 1978). 
Screening Devices 15 

PUMP 

WATER BACKWASH PIPE 

A PERFORATED COLLECTOR 

AIR BACKWASH PIPE PIPE 

Figure 71. An infiltration barrier intake (Richards 1978). 

CHARACTERISTICS 

O A large excavated area filled with suitable filter material. 

O A perforated pipe or series of pipes imbedded in the filter 

material. 

O A pumping facility. 

O A backflush system. 

I-OCAT I ON LIMITATIONS OR RESTRICTIONS 

Artificial filter beds can only be sited on water bodies that have 

11 ow concentrations of suspended particles and where the potential for 

biofouling is low. 

EVIDENCE FOR SUCCESSFUL REDUCTION OF ENTRAINMENT AND IMPINGEMENT 

Filtration waters as high as 407.3 1/ rnin/rn' (0.61 cm/s filter 

velocity) have been evaluated and do not appear to affect juvenile fish 

(Stober 1978). Although filters are not presently operational at a 
-- 

16 Screening Devices 

power plant site, some engineers believe that filters can eventually be 

designed to effectively eliminate entrainment and impingement of fish 

eggs and larvae. 

PROBLEM 

Most authorities believe that technology is not sufficiently advanced 

to permit the construction and operation of a reliable filter. The 

major problems are clogging and biofoul ing. 

POROUS DIKES 

Porous dikes (Figure 12) are f i 1ters resembl ing a breakwater surrounding 

a cooling water intake. The core of the dike consists of cobble or 

gravel which permits free passage of water. The dike acts both as a 

physical and behavioral barrier to aquatic organisms. 

A 

POROUS DIKE k 

SECTION OF POROUS DIKE Y@ 

Figure 12. A Gabion dam (Schrader and Ketschke 1978). 

CHARACTERISTICS 

The main characteristics of porous dikes are: 

' The filtering mechanism includes a breakwater or some other 

type of barrier and the filtering core. Both components can 

be built of the same type and size material. 

O Filtering material must be a size that permits free passage of 

water but still prevents entrainment and impingement. 
Screening Devices 17 

LOCATION LIMITATIONS OR RESTRICTIONS 

Porous dikes c'an be utilized in large lakes and coastal areas. 

However, this type of screening device may have limited application in 

lareas with high conlcentration of suspended particles and biofoul ing

ipotential. 

EVIDENCE FOR SUCCESSFUL REDUCTION OF ENTRAINMENT AND IMPINGEMENT 

Controlled studies in the laboratory and under field conditions 

'indicate that filtering material of the dike and behavioral responses to 

the dike can effectively exclude fish larvae and juveniles. Schrader 

iind Ketschke (1978) studied the porous dike at Wisconsin Electric Service 

Company's Lakeside Plant on Lake Michigan and found that numerous fish 

penetrated large void spaces but for most fish accessability was 1imited 

PROBLEMS 

The technology for porous dikes is presently bein developed and 

rriuch evidence, from operating facilities, is needed be 9ore they can be 

thoroughly evaluated. 

Dikes have the potential problems of being clogged by settling

suspended particulates and biofoul i ng. These problems could reduce 

reliability, thus necessitating costly maintenance (e.g. , cleaning or 

bisciding). The dike can also act as an artifical reef, thereby attracting

organisms and increasing the potential for some type of adverse impacts

(e. g., increased predation, mortality due to biocide additions, increased 

l'i shi ng pressure). 

CONCLUSION 

C1osed cycle cool ing systems reduce the volume of cool ing water 

withdrawn from a water body by at least 90%of that required for oncethrough cooling systems. In estimating the effectiveness of closed 

cycle cooling with once through cooling systems fit,ted with a, VTS, Boreman 

et al, (1979) concluded that closed cycle cooling minimizes the biological

impact by at least 90%. To be considered an alternative to closed cycle

cooling a once-through cooling system with its screening device must be 

shown to reduce impingement and entrainment mortality by 90% of that 

evected of a once through system fitted with a VTS. 

The intake technologies described in this topilcal brief show some 

promise for reducing the impacts of entrainment and impingement. However, 

evidence is insufficient to demonstrate that any of these intake systems

ailone, or in combination, can afford the protection that is presently

attainable by closed cycle cooling. The most effective systems, the 

radial well and artificial filter bed, can only provide enough water for 

make up water in closed cycle systems. The screening devices, both 

aictive and passive, do not yet have a sufficient data base to demonstrate 
18, Screening Devices 

effectiveness or re1 iability. More experience is needed operating and 

maintaining these devices before they can be considered as a1ternatives 

to closed cycle cooling for minimizing the adverse impact of cooling

waiter intakes. 

Another subject, that must be considered when assessing screening 

devices which require the impingement of an organism, is the fish bypass 

or return system. The success of the screening system is greatly dependent 

on aeturning or bypassing fish, eggs, and larvae to the source water 

with a high probability for their survival. Any system that minimizes 

dannage to organisms during their capture, but damages or overly stresses 

them when released, cannot be considered the best technology avail able. 

Siniilarly, a system that returns organisms to an area that is unsuitable 

for their survival cannot be considered best technology available. Fish 

return systems differ greatly at different power plants. These differences 

have inhibited the evaluation of the return portions of water intake 

syr;tems . 
 , 

li 

Screening Devices 19 

REFERENCES I 

Boreman, J., L. W. Barnthouse, D. S. Vaughan, C. P. Goodyear, and S. W. 

Christensen. 1979. Entrainment Impact Estimates for Six Fish 

Populations Inhabiting the Hudson River Estuary. Joint Testimony.

Prepared for the U.S. EPA. Kegion 11. no pagination. 

Cada, G. F., J. B. Cannon, and D. W. Lee. 1979. Alternative Screening

Devices at Indian Point Units 2 and 3, Bowline Point, and Roseton 

Generating Stations. Joint Testimony Prepared for the U.S. EPA 

Region 11. Oak Ridge National Laboratory, Oak Ridge, Tennessee. 

138 pp. 

Chezar, B. 1976. Mutifarious Power Plant Water Intake Structure (MWIS) - A Design Concept to R?duce the Environmental Effects of Cooling Water 

Intake Structures. t4ew York State Energy Research and Development Authority, 164 pp. 

Cloutant, C.C. 1974. Opening remarks at entrainment; and intake screening

workshop: "Evaluation of entrainment effect", pp. 1-11. In Proceedings

of the Second Workshop on Entrainment and Intake ScreeningrEPRI , Publ. 74-049-00-5. 

Hanson, B. M. , W. H. Bason, B. C. Beitz, and K. E. Charles. 1978. 

Practicality of profile-wire screen in reducing entrainment and 

impingement, pp. 195-233. In Larval Exclusion Systems for Power 

Plant Cooling Water Intakes. Proceedings of the workshop held 7-8 

February, 1978. San Diego, California. 

Heuer, J. H., and D. A. Tomljanovich. 1978. A study on the protection

of fish larvae at water intakes using wedge-wire screening, pp.

169-194. -In Larval Exclusion Systems for Power Plant Cooling Water 

Intakes. Proceedings of the Workshop held 7-8 February, 1978. San 

Diego, California. 

Lifton, W. S. 1980. Biological Aspects of Screen 'resting on the St. 

Johns River, Palatka, Florida. Dames and Moore, Cincinnati , Ohio. 

14 PPVlagliente, S. H., D. A. Tomljanovich, J. H. Heuer, S. Vigander, and M. 

N. Smith. 1978. Investigations on the protection of fish larvae 

at water intakes using fine-mesh screening. Impingement release 

concept: Laboratory study of single-entrance double-exit, vertical 

travel ing screen concept, pp. 69-77. & Larval Exclusion Systems

for Power Plant Cooling Water Intakes. Proceeding of the workshop 

held 7-8 February, 1978. San Diego, California. 

Mikels, F. C., and T. W. Bennett. 1978. Cooling water intakes utilizing 

Ranney Collectors and Ranney Intakes, pp. 15-25. In Larval Exclusion 

Systems for Power Plant Cooling Water Intakes. Proceedings of the 

Workshop held 7-8 February, 1978. San Diego, California. 
20 Screening Devices 

Murray, L. S., and 7. S. Jinnette. 1978. Survival of dominant estuarine 

organisms impinged on fine-mesh traveling screens at the Barney M. 

Davis Power Station, pp. 79-87. In Larval Exclusion Systems for 

Power Plant Cooling Water Intakes. Proceedings of the Workshop

held 7-8 February, 1978. San Diego, California. 

Pagano, R. and H. B. Smith. 1977. Recent developments in techniques to 

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Stock NO. 024-010-00553-0 * U.S. GOVERNMENT PRINTING OFFICE: 1980-654-500 

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