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WREG /CP-002 

I ES-66 

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m .c y" LARVAL EXCLUSION SYSTEMS FOR POWER PLANT - 

w 

COOLING WATER INTAKES 

Proceedings of the Workshop Held at 

Shelter Island Inn, San Diego, 

California, February 7-8, I978 

ARGONNE NATIONAL LABORATORY, ARGONNE, ILLINOIS 

Operated for the U. S. DEPARTMENT OF ENERGY 

under Contract W-31-109-Eng-38 
The facilities of Argonne National Laboratory are owned by the United States Government. Under the terms of a contract (W-31-109-Eng-38) between the U. s. Department of Energy, Argonne Universities Association and The University of Chicago, the University employs 

the staff and operates the Laboratory in accordance with policies and programs formulated, approved and reviewed by the Association. 

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NOTICE 

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Available from 

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Code: RE) 

ARGONNE NATIONAL LABORATORY 

9700 South Cass Avenue 

Argonne, Illinois 60439 

LARVAL EXCLUSION SYSTEMS FOR POWER PLANT 

COOLING WATER INTAKES 

PROCEEDINGS OF THE WORKSHOP HELD AT 

SHELTER ISLAND INN,-SAN DIEGO, 

CALIFORNIA, FEBRUARY 7-8, 1978 

Rajendra K. Sharma 

Argonne National Laboratory 

and 

John B. Palmer 

Southern California Edison Co. 

Editors 

August 1978 

COSPONSORS: 

ARGONNE NATIONAL LABORATORY 

ELECTRIC POWER RESEARCH INSTITUTE 

SOUTHERN CALIFORNIA EDISON COMPANY 
237 

to the source water body. Since considerable "handling" of organisms is involved in use of this 

concept, biological effectiveness depends on efficient handling at various stages in the system. 

The intake velocity should be very low so that if there is any impingement of larvae on the 

screens, it is gentle enough not to result in damage or mortality; the wash spray for the screen 

panels or the baskets should be low-pressure so as not to result in mortality; the sluiceway 

should provide smooth flow so that there are no areas of high turbulence; and enough flow should 

be maintained so that the sluiceway is not dry at any time. 

returned to the source water body, their mortality should not be significantly in excess of the 

expected natural mortality for their stages. 

velocity can be reduced to the point that impingement of larvae, if any, is not detrimental and 

the wash system can be designed so that debris and organisms are separated to a great extent and 

spray wash for the organisms is not too forceful. The design of the sluiceway, however, leaves 

much to be desired. 

rates for larvae under natural conditions and under the influence of such an impingement-return 

cycle are needed before any definitive and long-term commitments are made to develop and improve 

upon this concept. 

up water as well as once-through cooling for sites on freshwater, estuarine, and marine locations. 

is recommended that investigations be conducted which will result in further development of this 

concept. Also, it appears that, due to design flexibility, the single-entry, double-exit screen 

has a slight advantage over the conventional vertical traveling screen. 

Finally, after the organisms are 

In this whole sequence of. operation, the intake 

Also, comparative determination, evaluation, and assessment ofmortality 

This system offers proven hardware technology which is feasible for the screening of makeConsidering the technologicat advantages and flexibility in the use of this concept, it 

RECOMMENDATIONS 

As a result of discussions at the workshop, the following recommendations are made: 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

On basis of present knowledge, no sound arguments on an ecological basis can be forwarded to screen fish larval forms at all power plants. However, if economics are 

favorable, or if the cost-benefit analysis dictates it, there are technological 

options which should be investigated for screening fish larval forms at the cooling 

water intakes of power plants. 

A detailed comparative cost evaluation of various concepts is needed. 

evaluation should be in terms of the design, construction, operation, and maintenance of various alternatives. A cost-benefit evaluation should be attempted only 

on a site-specific basis because the value of the species to be protected can significantly a'lter such an evaluation. 

Geologic and hydrologic factors permitting, the subsurface collector concept is 

the most effective for larval exclusion. 

Further investigations are warranted on screening efficiency, debris removal, and 

biofouling control of perforated-pipe, profile-wire screen, and other such intakes. 

The hydrodynamic characteristics of screening--such as orientation of screening 

surface to flow, which could improve biological effectiveness of this screening 

concept--should be investigated further. 

Biological effectiveness of porous dikes is unknown at this time. Field demonstrations are essential prior to any long-term comnitments to development of this 

technology. 

Further research and development of artificat filter beds is not warranted because of 

operational and maintenance problems. 

Fine-mesh traveling screens offer long-term, proven technology. 

effectiveness for the whole cycle, from impingement to survival in the source water 

body, should be investigated thoroughly prior to implementation of this option. 

The cost 

However, biological 

$7 U.S. GOVERNMENT PRiNTlNG OFFICE: 1978-750-186/2801 
FOREWORD 

Section 316(b) of the Federal Water Pollution Control Act Amendments of 1972 (PL 92-500) 

states, “Any standard established ... applicable to a point source shall require that the location, design, construction, and capacity of cooling-water intake structures reflect the best 

technology available for minimizing adverse environmental impact.” 

the act because of concern about the potential ecological impact resulting from passing a large 

amount of water through intake screens at thermal power plants. 

Passage of aquatic organisms through the power plant is called entrainment. The designing 

of intakes and cooling systems to reduce entrainment losses to fish populations and the testing 

of their effectiveness require a combination of engineering and biological expertise. 

several approaches to reducing entrainment losses. 

entering the cooling system by application of various diversion and screening devices. 

is to reduce the mortality rate among those organisms passing through the cooling system by 

minimizing the stress to which they are subjected. 

Intakes was to evaluate the status of various methods for prevention of larval fish entrainment. 

Concepts covered include: artificial filter beds; subsurface collectors (wells); porous dikes; 

fine-mesh screens ; perforated pipes; single-entrance, doubl e-exi t screens; and prof ile-wire screens. 

promising domain of applicability (e.g., ocean, estuary, lake, river; once-through cooling system; offstream cooling system), and to define the status of current knowledge and investigations 

on the engineering and biological effectiveness of each concept. For most concepts, the demonstration of engineering feasibility is farther ahead than the demonstration of biological effectiveness. Recommendations for future research are also identified in the synthesis section. 

This section was included in 

There are 

A second 

One is to reduce the number of organisms 

The objective of the Workshop on Larval Exclusion Systems for Power Plant Cooling lJater 

An attempt has been made in the synthesis section of this report to specify the most 

It was c’lear at the workshop that substantial progress is being made in understanding 

larval behavior and avoidance. Several years ago, it was usually assumed that fish larvae were completely planktonic, i.e., they exerted no control over their positions in the water body. 

However, recent experiments indicate that fish larvae are capable of swimming and actively 

avoiding certain objects. 

ing intakes that would produce a hydrodynamic field to promote larval avoidance. 

Increased understanding in this area should prove valuab7e in developAugust 1978 Robert Goldstein 

Environmental Assessment Department 

Electric Power Research Institute 

Palo Alto, California 

iii 
ACKNOWLEDGEMENTS 

The workshop was cosponsored by Argonne National Laboratory (ANL) , Electric Power Research 

Institute (EPRI), and Southern California Edison Company (SCE). 

funding, SCE hosted the workshop, and ANL prepared and printed the proceedings. ANL effort and 

involvement was made possible as a result of grants from the U. S. Nuclear Regulatory Commission 

We thank the authors whose cooperation has resulted in timely publication of these proceedings, 

and we thank the participative audience whose involvement in discussions made this a worthwhile 

and productive workshop. 

efforts in editing the manuscripts. 

EPRI provided most of the 

Thanks are also due to Shari Zussman and Dee Wyman for painstaking 

iV 
CONTENTS 

Foreword. R. Goldstein ................................. 

Acknowledgements .................................... 

Introductory Remarks. P. F. Gustafson ......................... 

Objectives of the Workshop. J. B. Palmer ...................... 

Engineering Considerations in the Use of Artificial Filter Beds. 2. T. Eichards .... 

High-Capacity Filters for Power Plant Cooling Water Intakes. 9. J. Stober ....... 

Cooling Water Intakes Utilizing Ranney Collectors or Ranney Intakes. 

Hydrologic Engineering Considerations for Ranney Collector Well Intake Systems. 

F. C. Mikels, T. W. Bennett .............................. 

N. J. Beskid ..................................... 

iii 

An Engineering Evaluation of Porous-Dike Intake Screening Systems. J. 2. Qoberge .... 

Biological Aspects of Porous-Dike Intake Structures. B. P. Schrader, 9. P.. Ketschke . . 

Engineering Aspects of Passavant Screening. K. R. Siddle, R. K. Sharma ......... 

Investigations on the Protection of Fish Larvae at Water Intakes Using Fine-Mesh 

Screening. Impingement-Release Concept: Laboratory Study of a Single-Entrance, 

Double-Exit, Vertical Traveling Screen Concept. S. H. Maoiiente, 2. A. Tonljanovich, 

J. H. Heuer, S. Vigander, M. N. Smith ......................... 

Survival of Dominant Estuarine Organisms Impinged on Fine-Mesh Traveling Screens 

at the Barney M. Davis Power Station. L. S. Murray, T. S. Jinnette .......... 

iv 

1 

3 

5 

13 

15 

27 

37 

51 

65 

69 

79 

Larval Exclusion with Woven-Slot, Fine-Mesh Screening. W. D. Cheesrnan, 

Current TVA Work on the Fluid Mechanics of Screens with Very Small Openings for 

Biological and Engineering Considerations in the Fine-Screening of Small Organisms 

Investigations on the Protection of Fish Larvae at Water Intakes Using Fine-Mesh 

R. R. Cheesrnan .................................... 89 

the Exclusion of Larvae at Power Plant Cooling-Water Intakes. S. Vigandsr ...... 91 

from Cooling Water Intakes. Y. G. Mussalli, E. P. Taft, P. Hofmann .......... 107 

Screening. D. A. Tornljanovich, J. H. Heuer, C. W. Voigtlander ............ 125 

Engineering and Hydraulics of the Modified Perforated-Pipe Intake. FI. T. Richards ... 141 

The Johnson Screen for Cooling Water Intakes. L. E. Cook ................ 149 

In-situ Testing of Profile Wire Screens for Long-Term Engineering Feasibility. 

A Study on the Protection of Fish Larvae at Water Intakes Using Wedge-Wire Screening. 

Practicality of Profile-Wire Screen in Reducing Entrainment and Impingement. 

Larval Exclusion Systems for Power Plant Cooling Water Intakes: 

J. C. Mi Iler, K. E. Charles; T. H. Key ........................ 159 

. 

J. H. Heuer, D. A. Tomljanovich ............................ 169 

B. N. Hanson, W. H. Bason, B. E. Beitz, K. E. Charles ................. 195 

Views Presented at the Workshop. R. K. Sharrna .................... 235 

a Synthesis of 

V 
INTRODUCTORY REMARKS 

Philip F. Gustafson 

Pivisisc 0: Environnenial im;iact SttiCier 

, Arco:~:~ ::at i on3 I Laborator, 

?7G2 Zouth Ca;s Avenue 

P.rpnne, I I I i noi s SC’37 

Within less than a decade, environmental impact analysis and. pollution control have become 

part of our national vocabulary, and have movgd from being a more or less ad hoc art to a fairly 

well-defined and respectable science. Concern with environmental quality--an environmental con- science, if you will--is a social attitude reaching widest expression in an affluent, hightechnology society such as ours. first, until a modest degree 

of personal and societal well-being is reached, people are too busy with basic subsistence to 

worry about even their immediate environment; second, there is a suspicion, which is sometimes 

correct but often incorrect, that technology or its use per se is the cause of environmental 

degradation. Sheer population pressure and prolonged human activity or occupation may, in and 

of themselves, lead to profound environmental alteration and degradation: to wit, water pollution in Europe, Asia, and the Americas prior to sewage treatment practices, and the denuding of 

coastal areas along the Mediterranean in North Africa and the Middle East due to excessive timber cutting and intensive agricultural use of the land (although this effect may also have been 

aided and abetted by subtle large-scale climatic changes). 

ing, with some basis in fact, that our affluence has been gained at the expense of the 

environment. 

The reason is at least two-fold: 

In any event, there is a guilt feefAfter several significant court cases, the growing attitudes of environmental concern 

reached fruition in this country with the passage of Federal legislation designed to regulate 

emissions or releases to air and water. The United Nations--through the United Nations Educational, Scientific, and Cultural Organization--took a similar, though less legally tough, position globally. Whereas the initial air and water quality legislation was directed at remedial 

action for existing facilities and provided a prescription or guidelines for new facilities, the 

National Environmental Policy Act of 1969 (NEPA) required that the probable environmental impacts 

of a.specific action be examined before the action was taken--a look forward rather than a look 

backward at what had already happened. NEPA also required examination of practical or feasible 

alternatives for eliminatins or minimizing unnecessary and undesirable impacts; a balancing of 

costs--both monetary and environmental--against the benefits, including those to society as a 

whole; and finally, a disclosure of possible impacts (even of a secondary or tertiary nature) 

with no attempt to quantify or judge whether they are good or bad. NEPA has been used effectively, and it has been sadly abused. It has been used in the critical evaluation of nuclear 

power plant sites; for example, water availability for downstream communities was a major factor 

in the rejection of the Koshkonong site in Wisconsin. NEPA has at times tended to be used as a basis, along with air and water quality considerations, for adoption of a zero-release position 

which, if carried to extreme, will lead to zero-growth, at least regionally. 

one hand, and the orderly continuance of our national economy--or life-style, if you will--on 

the other. 

nature in terms of extremes. Thus, the attitudinal pendulum regarding concerns for the environment has, in one decade. swung from a position of essentially no concern at all, to a position 

of almost virtual overkill for protecting the environment from all possible impacts, and is now 

moving toward a more central position. Both extremes are costly in terms of material and mone- tary resources (the influence of environmental protection on inflation is presently a subject of 

heated debate). 

Clearly there is a need for a reasonable balance between protection of the environment, on 

It seems part of human nature to regard matters of a societal or sociopolitical 

A balanced or middle-of-the-road position is being achieved, albeit somewhat tortuously, 

through the judicial system and the public hearing process, along with a certain amount of just 

plain common sense. As a result of these processes, technical problems have been identified, 

and solutions or remedial procedures in many cases have been developed. Generally, this has 

1 
been a healthy interactive relationship and one which has shown that often the proper application of existing or new technologies can, in fact, solve problems due to technology in the first 

. place. Overall, this has led to environmental improvements accompanied by increased application 

of technology--primarily, in the cases considered here, the production of increased quantities 

of electric power. 

This workshop is a direct outgrowth of the continuing effort to strike a reasonable balance 

between energy needs and environmental protection mentioned above. 

that the cooling-water intake end of the system (the steam power plant in this case) had the 

potential to ingest and destroy biota to the detriment of the adjacent ecosystem. Indeed, a 

power plant may be thought of as a man-made predator, often of appreciable magnitude. 

the strong features of impact assessment is to identify possible problems or problem areas, and 

to indicate the need for Research & Development to fill a knowledge gap or to correct an undesirable situation (a fact that is often overlooked). Fish impingement and larval entrainment is an 

excellent example of biological research and engineering development working hand-in-hand to 

eliminate or minimize a problem, real or potential, in an effective, publicly acceptable manner. 

Early on, it was recognized 

One of 

The contributors at the workshop described arid discussed, in detail, the theory and design 

of various systems and schemes employed to reduce larval entrainment, and, where possible, the 

real-world success of these methods as judged by operating experience. Whereas procedures to 

reduce impingement may have little effect on larval entrainment, the converse is one in which 

both are reduced--i.e., reducing entrainment by diversion, velocity-reduction, or fine-screening 

techniques essentially eliminates impingement, if done wisely and properly. 

these investigations will be of direct value to those designing new facilities and upgrading 

present ones, as well as to those engaged in environmental impact analysis, 316(b) demonstration 

efforts, and like matters. 

The results of 
OBJECTIVES OF THE WORKSHOP 

John B. Palmer 

Research 8 Development 

Southern California Edison Company 

P. 0. Box 800 

Rosemead, California 91770 

The objectives of this workshop are based on two aspects of today's electric utility industry. 

research can be incorporated into the design of specific power systems. This potential for 

incorporation is made possible by an explicit corporate commitment to natural resource conservation--a commitment which is supported by the utility rate base, as is now the case in 

California. The second underlying aspect is the necessity for long-range planning within the 

utility industry. 

ability of the information necessary for making decisions which will permit those goals to be 

achieved . 

The first is provision that environmental design criteria developed through responsible 

Planning is possible only in an atmosphere of well-defined goals and availIn the papers presented at this workshop we look beyond minimizing adult losses, and we 

review the state of information on intake designs which have the potential for excluding the 

smaller life stages of aquatic organisms: It seems likely that 

planning for future utility generating capacity will involve decisions as to whether or not larval exclusion capability is a viable design feature of power plant cooling water intake systems. 

In this workshop, the hardware end of this problem is addressed: Are such things feasible at 

all and, if so, under what conditions are they reliable, at what costs, and with what degree of 

biotic protection? 

eggs, larvae, and juveniles. 

The charter for this workshop reads as follows: 

The aim of the workshop is to reach an evaluation of the status of various design 

concepts which could exclude the meroplanktonic larvae or juveniles of fish and invertebrates from the cooling water of steam electric power stations. 

the possible domain of applicability for each concept (coastal, estuarine, riverine, 

lentic; once-through or off-stream) and the status of current research to determine 

engineering and biological effectiveness. 

neering aspects which require further research in order to bring all concepts on a par 

by, say, 1983; so at that time the power industry will be able to determine if there 

exist best technology options in this general area. 

The papers presented are published as the Proceedings of this Workshop. 

We plan to explore 

For those concepts which have promise, we intend to identify biological or engiIn the summary we 

have incorporated the consensus of the participants as to where research and development in this 

area stands and where it ought to be directed. 

this field presented a paper at this workshop. 

discussions, and we have incorporated several of these valuable comments in the proceedings. 

the next several years. 

We realize that not everyone who is active in 

However, all those present contributed to the 

It seems likely that research and development in this area will proceed at a good pace over 

If this proves to be the case, we plan to reconvene in about two years. 

3 
ENGINEERING CONSIDERATIONS IN THE USE OF ARTIFICIAL FILTER BEDS 

Richard T. Richards 

INTRODUCTION 

The artificial filter bed is one of several water screening methods proposed to eliminate 

or reduce the entrainnieni of small aquatic organisms in the cooling water supplied to power 

plants. I say "proposed" because its actual power plant use has been minimal to date. The 

engineering problems involved in developing an intake filter of high reliability and large 

capacity are formidable and as yet largely unresolved. This discussion is a brief review of some of these problems, and is generally related to the development of a filter intake for one 

specific, reasonably favorable 1 ocation. 

Entrainment is a growing concern because of the large volumes of water withdrawn from our water sources for power plant cooling, including withdrawal of makeup water for cooling towers. 

Although the water requirements are no more than about 5' of once-through cooling, it can be 

assumed that all entrained organisms will be destroyed in the cooling tower cycle. On the other 

hand, continuing biological studies indicate that a large proportion of the organisms entrained 

in the once-through cooling flow may well survive. From a practical standpoint we should con- centrate present research efforts on developing a filter suitable for makeup flows in the range 

of 0.6 m3/s (10.000 gpm) to about 3.1 m3/s (50,000 gpm). The problems in that range are enough 

of a challenge without considering the artificial filtering of once-through cooling water flows 

in the range of 12.6 to 63 m3/s (200,000 to 1,000,000 gpm). 

HISTORICAL NOTES 

For many years artificial filters have been used for small water supply withdrawals. 

primary purpose has been to produce a well-filtered water rather than to protect aquatic organ.- 

isms from damage. 

suspended sediiiients and algae growth are low. 

The 

A few of these filters have been successful, usually in waters where the 

Many have been failures. 

5 
6 

The subject of filters for power plant use was discussed in two papers at the Second Workshop on Entrainment and Intake Screening in 1973. At that workshop Stober’ covered the details 

of a test filter design for a salt-water environment. 

neering design concept for a very large filter applicable to a once-through system. 

Strandberg’ presented a paper on an engiOne recent attempt to use an artificial filter for power plant makeup water ended in abandonment of the filter after construction, and its replacement with a perforated-pipe intake. 

This filter was designed for a Z.0-m3/s (33,000-gpm) flow, typical of the capacity we are considering here. 

for the Montour Steam Electric Station of the Pennsylvania Power and Light CO.~ Several field 

modifications were made in the original design, but ultimately it could not be prevented from 

clogging at a rate considered unacceptable. 

It was placed on the west branch of the Susquenhanna River to draw makeup water 

THE ARTIFICIAL FILTER 

Figure 1 is a schematic drawing of an artificial filter. An area is excavated and backFor the periodic removal of undesirable 

filled with a specially graded filter medium. 

filtered water and carries it to the pump structure. 

material which has settled out on the bed, water and/or air may be backwashed through the collector pipe or through separate pipes. 

Figure 1, or in concrete box units, removable wire basket units, etc. 

A perforated pipe under this filter collects the 

The filter could be in a simple excavation, as shown in 

WATER BACKWASH PIPE 

RATED COLLECTOR 

AIR BACKWASH PIPE 

Fig. 1. Schematic of Artificial Filter 

The filter itself must be a very carefully graded material (sand, stone, and possibly other 

additives) of a certain area and depth to meet the filtering criteria for a given site. It must 

also be protected from scouring. 

GENERAL DESIGN CRITERIA 

Power plant cooling water supply requirements are particularly stringent. With a oncethrough cooling system, the plant cannot operate even for minutes without a cooling water supply. 

This means a system that must operate 24 hours a day, 7 days a week for 30 or 40 years. 

not be shut down for normal maintenance unless duplicate facilities are provided. 

are nearly as stringent for cooling tower makeup supply. 

to the towers., there is enough water storage capacity in the cooling tower basins to permit a 

water supply shutdown of only one half to one hour. Unless there is a storage pond or lake 

associated with the cooling tower system (a relatively rare provision), the requirement for 

makeup water is essentially continuous. 

It canThe criteria 

If the makeup water is going directly 

Power plant shutdown due to a cooling water interruption could cost in the range of $200,000 

per day for a 400-MWe unit. 
7 

The criteria for a filter design include the following items: 

Reliability. The facility must be capable of functioning at full output for the life of 

the plant. 

Operability. 

Maintainability. 

Operation must be possible with reasonable operator attention. 

There must be duplicate filters to permit backwash, and there must be 

accessibility for maintaining the filter beds (periodic replacement or rebuilding). Implied 

here too is the necessity for providing a facility that does not require excessive maintenance. 

Environmental Acceptability. The facility must be environmentally acceptable. For example, the turbidity during backwash may have to meet certain stringent standards, as in the 

example described in the next section. 

Reasonable Costs. This may be a sensitive subject where the environment is involved, but 

it is nonetheless an important factor which ultimately will determine whether the filter system 

is to be used. 

ENGINEERING ASPECTS OF A TYPICAL FILTER DESIGN 

In 1972 a filter design was prepared and submitted to regulatory authorities in connection 

with the makeup water system for Nuclear Project #2 of the Washington Public Power Supply System 

(WPPSS-2) on the Columbia River. The WPPSS-2 facility was designed to handle a maximum flow of 

1.6 m3/s (25,000 gpm). A pumping station pumps the water to cooling tower basins about three 

miles from the river. There is no storage capacity at the power plant site except in the cooling tower basins themselves. 

Several filter concepts were studied, including a filter placed directly in the bed of the 

river, an infiltration gallery in the river bank, and a filter placed in the bed of an artificial off-stream channel. The final selection, shown in Figure 2, was a system of seven offstream individual filter units contained by sheet piling and preceded by a river diversion 

system and a stilling basin. 

successfully, but that certain major research (described in Research Needed) would be required 

for a final design. 

perforated-pipe intake described in Reference 4. 

It was concluded that the filter concept could be developed 

Ultimately, the filter concept was set aside in favor of the modified 

.-c-- ,360 

0 

0 - 50 100 200 300 

SCALE IN FEET 

Fig. 2. Schematic of Proposed Artificial Filter Facility 
8 

It can readily be seen that the artificial filter system selected would have been a very 

complex facility. The system might have become even more complex if proposed model and field 

studies had dictated changes in the design. 

lighted as we discuss the passage of water from the river to the filter and back to the river, 

through the various components of such a system. 

Engineering factors and problems will be highDiversion Wall. A river diversion wall, to be developed in part by model tests, would 

direct water into the channel in sufficient quantity for proper performance not only of the 

intake but of the backwash system. 

back to the river. 

Backwash requires a continuous flow across the filter and 

Flow Control Structure. A sheet pile channel would extend from the river diversion wall to 

a flow control structure at the head of twin stilling basins, shown in Figure 3: The flow control structure was required to limit the inflow to the proper volume for intake and backwash and 

to permit diversion of flow to either or both stilling basins. 

ability were factors which dictated the sheet pile channel side walls. Channel velocity would 

be limited to an average of 1 m/s (3 fps) to avoid bottom erosion, as determined by a study of 

the characteristics of the bottom material. 

Bank stability and maintainPLAN 

EL 354 GRADE 

MANUAL GATEOPERATOR S 

1 4 FLUSH BOTTOM /- 22' ' 22'L-i SLIDE GATES 

I 

SECTION A-A 

Fig. 3. Schematic of Flow Control Structure 
9 

Stilling Basins. 

the river suspended sediment, thus taking the burden off the filters. 

lated and dredged while the other continued to operate. a relatively clean river. 

use of such an artificial filter. 

ities were determined by the settling rate of the sediment to be removed under the worst river 

conditions. 

periods of high level water. 

would reduce filter performance. 

by 9.1 m (19 ft by 30 ft) as shown schedmatically in Figure 4. 

ters were studied in detail and a design developed as far as possible without the final mode'l 

and prototype field tests. The complexity of water piping required is shown in Figure Q. 

additional air backwash piping is not shown at all in the plan. The typical filter bed shown in 

Figure 4 is approximately 2 m (6 ft) deep, and is to be covered by a minimum depth of 0.6 m 

(2 ft) of water. 

Stilling (sedimentation) basins would settle cut as much as possible of 

One basin could be isoIt should be noted that the Columbia is 

The length of the stilling basins and the flow-through velocEven modest seasonal sediment could be a major factor ruling out the 

The basins were to be protected by dikes which would prevent flooding during 

Periodic flooding of the facility, with attendant sediment loads, 

Filter Beds. A filter bed array would consist of seven separate filter cells, each 5.8 m 

Fine- and coarse-textured filThe 

Distribution Structure. A distribution structure would be required to isolate the seven 

filter sections for operation, backwash, and maintenance, and is shown conceptually in Figure 5. 

Road System. Not shown in the figures is the road system to permit access to both the 

stilling basin and the filter system for trucks, cranes, and other maintenance equipment. 

Material periodically dredged from the stilling basins would be disposed of on land. 

necessary auxiliary features would add considerably to the cost of the filter intake facility. 

Enough water flow 

must be maintained across the filter to carry the backwashed material downstream. 

sented a major problem in that the limitations on raising river turbidity were very stringent. 

The regulatory authorities limited the increase to five Jackson Turbidity Units (JTU) above the 

natural river turbidity at any river stage. 

flow over the filter had to be sufficient to keep the clarity of the water reentering the river 

within the sDecified limits. Preliminary oDeratins studies called for continuous operation of 

Such 

Backwash. Backwash is achieved by air flow up through the filter bed. 

This pre- 

(Normal river turbidity is about six JTU.) The 

the system with five filter units delivekng water-and two filter 

Return Channel. The final element in the filter facility is 

river. 

RESEARCH NEEDED 

A major model and field testina Droqram is required to final 

units being backwashed. 

the return channel to the 

ze the desisn details of such 

a fi1,ter iystem. 

several hundred thousand dollars. For this particular project no tests were undertaken because 

an alternative perforated-pipe intake4 was adopted before the filter testing program could be 

initiated; however, the following tests were among those recommended: 

suitable gradation of filter material, test the rate of clogging, and perfect the backwash system. Columbia River water must be used and the temporary laboratory facility must therefore be 

located near the site of the intake. 

Sound indicates the complexity of such an installation.] It should be noted, however, that the 

salt-water environment of Puget Sound imposes more biological fouling problems than would be 

expected for Columbia River fresh water. 

It is quite possi6le that the expense of this program would-be in the order of 

- An on-site laboratory test of one or more short sections of the filter bed to develop a 

Stober's description of a similar test facility in Puget 

- An extended field test of a prototype filter section in the river, located such that the 

characteristics of the test unit would duplicate those of the final installation. This test 

should be run for all river stages to assess the influence of actual river conditions on the 

performance of the filter bed. 

backwash, and monitoring facilities. 

The test facility must be complete with appropriate pumping, air 

- A reduced-scale laboratory model test of the entire filter complex (approach channel, 

sedimentation basin, etc.) and as much of the Columbia River as is necessary to accurately 

simulate the filter system entrance and exit conditions. This model is essential to determine 

the optimum angle of channel approach and the proper orientation and length of the river diversion wall and to refine some of the details of the gate structure. 

testing of this model, extensive field work must be done to determine the river physical and 

flow characteristics for accurate modeling. Model verification will be required to assure that 

the model does in fact duplicate the actual river flow conditions at the intake site. 

Prior to construction and 
.. .. I . CAPACITY(ISPARE) I I I - - - - t - -- -=$ 

I I 

PLAN - 

3-18"P PERF. IM 

MIN. W.L.EL.3437 I l+l I 

STONE FII 

SECTION 6-B 

:T PILING 

Fig. 4. Sketch of FilterBed and Typical Filter Cell 
11 

+‘ 

(D 

cu 0’: P ’, - 

PLAN 

SECTION 

Fig. 5. Schematic of Distribution Structure 

CONCLUSION 

We can see from this discussion how the simple filter concept illustrated in Figure 1 can 

grow into a relatively monstrous project from an engineering standpoint. Although some aspects 

of filter systems might be refined and used as standards at some future date, the majority of 

filter engineering will be site-related and will require a new design for each project. If the 

intake is to have the high degree of reliability required of a power plant installation, the 

engineering of an acceptable artificial filter system will continue to be difficult and costly- 
12 

REFERENCES 

1. Stober, Q- J., C. H. Hanson, and P. B. Swierkowski. 1974. A high capacity sand filter 

for thermal power plant cooling water intakes. Part I: Model studies and fouling control 

techniques, pp. 317-334. 

Entrainment and Intake Screening, The Johns Hopkins University, Baltimore, Md., Feb. 5-9, 

1973. EPRI Publ. No. 74-049-00-5. Electric Power Research Institute, Palo Alto, Calif. 

2. Strandberg, H. V. 1974. A high capacity.sand filter for thermal power plant cooling 

water intakes. Part 11: Design concept, pp. 335-343. In L. D. Jensen (ed.), Proceedings 

of the Second Workshop on Entrainment and Intake Screening, The Johns Hopkins University, 

Baltimore, Md., Feb. 5-9, 1973. EPRI Publ. No. 74-049-00-5. Electric Power Research 

Institute, Palo Alto, Calif. 

L. D, Jensen (ed.), Proceedings of the Second Workshop on 

3. Metzger, A. W., and F. J. Sawicki. 1974. Mountour Steam Electric Station Alternate River 

Intake Slotted Pipe Installation. 

Structures and Hydraulics Committee Winter Meeting, Feb., 1974. 

tion. J. Hydraul. Div. Proc. Am. Soc. ‘Civ. Eng. 102:139-149. 

Paper presented at the Pennsylvania Electric Association 

4. Richards, R. T., and M. J. Hroncich. 1976. Perforated-pipe water intake for fish protec- 
HIGH-CAPACITY FILTERS FOR POWER PLANT COOLING WATER INTAKES 

Quentin J. Stober 

Fisheries Research Institute 

University of kashinofon 

Seattle, tiashincton 98195 

SUMMARY 

A high-capacity model filter was tested as a method of preventing the entrainment and 

impingement of pelagic eggs and larval fishes at power plant intakes. 

proposed plant site in Puget Sound. 

engineering design concept developed and reported by Stober et al. (1974) and Strandberg (1974) 

were reviewed. 

Tests were conducted at a 

Model filter studies, fouling control techniques, and an 

The hydraulic considerations of seawater filtration through an anthracite-gravel filter 

indicated that the size of the anthracite media should range from 2.4 to 7.9 mm with the optimum 

from 3.2 to 6.4 mm. 

712.7 Lpm/m2 to achieve the desired filter bed expansion of 252. 

and 407.3 Lpm/m2, were not observed to affect the horizontal or vertical mobility of juvenile 

fishes or invertebrates even above the filter surface. 

larval stages of marine fouling organisms, was not practical. 

The coarseness of the media was restricted by the design backwash rate of 

Filter flow velocities of 0.305 to 0.610 cm/s, which related to filtration rates of 203.6 

The exclusion of plankton, including the 

The seasonal changes in water quality (turbidity, temperature and salinity) were determined 

on-site. Turbidity was subject to seasonal variations, due primarily to planktonic organisms 

(1-3 FTU) and to suspended sediment (3-6.5 FTU) from winter and spring flooding of the Skagit 

River, Suspended sediment caused the greatest short-term reduction in filter performance. 

A filtration rate of 244.4 Lpm/m2 through the 2.32-m2 model yielded a mean volume of over 

9462.5 m3 per run. 

ranged from 5.4 to 20 days, depending on influent turbidity. 

selected was 305.5 Lpm/m2 through an active filter area of 8361 m2, divided into seven units to 

yield a cooling water output of 42.5 m3/s. 

anoxia, single-dose chlorination, heat treatment, chlorination and heat treatment during backwash, and daily two-hour chlorination. Based on barnacle abundance and growth rates, the most 

effective fouling control techniques tested were backwashing with heated seawater, daily chlorination, and anoxia. 

The mean run time was 260 hr to a head loss of 1.32 m. Filtration time 

The design filtration rate 

Six marine fouling control techniques were tested, including backwash with ambient seawater, 

The test data were utilized in the development of the engineering design concept, including 

siting and operational procedures. Additional on-site model testing over one annual cycle was 

recommended to provide operating experience prior to final design; however, such tests were not 

conducted due to cancellation of plans to build the proposed power plant. 

The concept of filter intake systems to prevent entrainment of aquatic organisms has been 

evaluated more frequently in river environments (DeVries 1773; Richards 1978). River water is 

characteristically loaded with large amounts of suspended particles which greatly reduce the 

performance and reliability of sand filter systems. Operation in other environments where the 

concentration of suspended sediment is usually less may be more promising (i.e. lakes, reservoirs, o'ffshore marine environments); however, biological fouling is an additional problem in 

marine environments. 

-\ 

Filter intake systems could be a very attractive and effective technology for the exclusion 

Extensive biological and engineering research 

of Pelagic eggs and larval fishes. 

developed to allow reliable design and operation. 

However, the present technology is not sufficiently 

13 
14 

and development programs designed to meet site-specific criteria are needed if this technology 

is to be feasible. 

short term. 

Application of alternate technologies may be more cost-effective in the 

REFERENCES 

DeVries, J. J., R. B. Krone, and J. Amorocho. 1973. Sand Filters for Screening at Water 

Diversions: A Feasibility Study. Water Science and Engineering Paper No. 1053. 

Department of Water Science and Engineering and Department of Civil Engineering, 

University of California, Davis. 48 pp. 

Richards, R. T. 1978. Engineering considerations in the use o f a r t i f i c i a l filter beds, 

pp. 5-12. In R. K. Sharma and J. B. Palmer (eds.), Larval Exclusion Systems for Power 

Plant Cooling Water Intakes, Proceedings of the Workshop held at Shelter Island Inn, San 

Diego, Calif., Feb. 7-8, 1978. 

Stober, Q. J., C. H. Hanson, and P. B. Swierkowski. 1974. A high capacity sand filter for 

thermal power plant cooling water intakes. Part I: Model studies and fouling control 

techniques, pp. 317-334. 

Intake Screening Workshop, The Johns Hopkins University, Baltimore, Md., Feb. 5-9, 1973. 

EPRI Publ. No. 74-049-00-5. Electric Power Research Institute, Palo Alto, Calif. 

Strandberg, H. V. 1974. A high capacity sand filter for thermal power plant cooling water 

NUREG/CP-002. Argonne National Laboratory, Argonne, Ill. 

L. D. Jensen (ed.), Proceedings of the Second Entrainment and 

intakes Part 11: Design concept, pp. 335-343. & L. D. Jensen (ed.), Proceedings of the 

Second Entrainment and Intake Screening Workshop, The Johns Hopkins University, Baltimore, 

Md., Feb. 5-9, 1973. EPRI Publ. No. 74-049-00-5. Electric Power Research Institute, Palo 

Alto, Calif. 
COOLING WATER INTAKES UTILIZING RANNEY 

COLLECTORS OR RANNEY INTAKES 

Frederick C. Mikels 

Ranney Method Western Corporation 

Kennewick, Washington 99336 

BOX 6387 

Truman W. Bennett 

The Ranney Company 

Box I45 

Westerville, Ohio 43081 

Abstract 

Minimization of the loss of aquatic biota is a major factor in the locaiion, 

design, construction, and capacity of cooling water intake structures. In a comprehensive report, the U. S. Environmental Protection Agency (1976) has reviewed the 

present methods and-technology available for minimizing adverse environmental impact 

of cooling wafer intakes. Two types of intakes, described in the report and classified as non-conventional intakes, are discussed in this paper: the Ranney Collector, 

which is a subsurface intake utilizing natural sand and gravel deposits to transmit 

water from a surface source, and the Ranney Surface Water intake, which is a submerged, 

horizontal perforated-pipe intake. 

I NTRODUCT I ON 

Where proper geological conditions exist, Ranney Collectors afford a means of screening 

large volumes of naturally filtered surface water by inducing infiltration through existing sand 

and gravel deposits. 

that neither impingement nor entrainment of larval fish or drifting river organisms occurs. The 

water filtered is free of turbidity, suspended matter, organic matter, and pathogenic bacteria 

and has a mineral quality very similar to that of the surface source. Water temperatures have 

a seasonal variation similar to that of the surface source, but significantly less in magnitude. 

Ranney Collector systems have been designed for capacities up to 340,000 m3/day. 

tor, is not dependent upon natural sand and gravel deposits and can be used in almost any surface source. The Ranney Intake consists of offshore horizontal perforated-pipe screens, connected to an onshore pumping station. Maintenance is minimal, since there are no moving parts 

and the screens are normally self-cleaning. 

to 650,000 m3/day. 

The screening and filtering characteristics of Ranney Collectors are such 

The Ranney Surface Water Intake, based upon the same design concepts as the Ranney CollecRanney Intakes have been designed for capacities up 

THE RANNEY COLLECTOR 

INDUCED INFILTRATION 

The valleys of most major streams and rivers of the United States are underlain by unconNormally, these aquifers are saturated with 

solidated alluvial deposits of sand, grave’l, clay, and silt. In most instances, these deposits are porous and permeable and are called aquifer-s. 

water to a level at or near the level of the surface stream or river. Under natural conditions 

of the hydrologic cycle, the water table in the aquifer slopes toward the river, and groundwater 

is slowly moving toward and discharging into the river. During periods of high river flow the 

15 
16 

hydraulic gradient may temporarily be reversed and water from the river will discharge into the 

aquifer. Thus, a free interchange of surface water and groundwater occurs continuously, on a natural, cyclic basis. 

If the water level in the aquifer is lowered by pumping below that of the river, a hydrauThe cone of depression created by the pumping will continue to expand until 

lic gradient will be created, causing water to flow from the river into the aquifer and to the 

source of pumping. 

a steady-state flow condition exists in which most of the water pumped will come from the surface source. This process is called induced recharge or induced infiltration. 

I The process of induced infiltration assures a permanent, dependable water supply, since it 

derives water from a known, definable surface source and is not dependent upon recharge from 

seasonal rainfall distribution. In effect, sand and gravel aquifers, as they exist in nature, 

perform as high'ly effective screening and filtering mechanisms, resulting in the production of a 

clean, potable water which far exceeds the requirements for cooling water supplies. 

HYDROGEOLOGICAL INVESTIGATIONS 

The principles and theory of induced infiltrat 

Kazmann (1 947, 1948, 1972), Rorabaugh (1 952, 1956), 

briefly discussed here. The prime requisite for an 

a permeable sand and gravel aquifer which is hydrau as a stream, river, or lake. 

on have been extensively documented by 

Walton (1970), and others and will be only 

infiltrated water supply is the existence of 

ically connected with a surface source such 

At any given site, the magnitude of the water supply that can be developed by induced 

infiltration is a function of the following independent variables: 

thickness of the aquifer, the permeability of the aquifer, the infiltration rate of the riverbed 

intake area, and the type of structure to be used to produce the water. A thorough hydrogeological investigation is necessary for evaluation of these variables and design of the structures prior to the actual construction of the water supply installation. Initially, such an 

investigation consists of the drilling and sampling of a series of exploratory test holes along 

the riverbank to determine the depth, zharacter, saturated thickness, and areal extent of the 

aquifer. These test holes are drilled until the base of the aquifer is reached, generally 

represented by a layer of impermeable material such as clay or bedrock. At sites selected from 

the results of the exploratory test drilling, detailed pumping tests are conducted. 

the depth and saturated 

The pumping test requires the construction of a pumping well and a series of properly 

spaced observation wells. The pumping well is pumped continuously, at a constant rate, until 

water levels become stable and a steady-state condition exists. 

levels in the observation wells and changes in river stage are continuously recorded. Experi- ence shows that the duration of such a pumping test should be not less than 48 hours and, in 

some instances, as long as 96 hours. The data from the pumping test are used to determine the 

permeability of the aquifer and the infiltration rate of the riverbed. With this information, 

the quantity and quality of water that can be produced by induced infiltration can be accurately 

predicted. 

During the test pumping, water 

Over the past 35 years, our companies have carried out more than 300 such hydrogeological 

investigations. A comparison of predicted results with actual results shows that pumping test 

methods are extremely reliable in predicting water supply developments by induced infiltration. 

According to Mikels and Klaer (1956), an accuracy of estimates of 10 to 15 percent can be normally expected when applying these methods. Thus, infiltrated water supplies can be designed 

with the same degree of predictability as any other type of water supply development. 

METHODS OF DEVELOPMENT 

The principal methods of developing infiltrated water supplies are vertical wells, infiltration galleries, and Ranney Collectors. 

of initial cost, operation, maintenance, and reliability. 

Each method has advantages and disadvantages in terms 

Vertical wells can penetrate the entire depth of the aquifer and have been used successfully to induce infiltration in many localities in the United States, particularly along major 

rivers and streams. When water requirements are small, the initial cost of a vertical well 

system is often lower than other methods. However, a major disadvantage of a vertical well 

system is that insufficient screen area is exposed to the aquifer, due to vertical limitations 

of the aquifer. 

high frictional or well losses. 

amount of induced infiltration possible. 

ated well loss may create clogging or incrustation of the well screen, materially reducing the 

life of the well. 

This lack of screen area results in high entrance velocities and, consequently, 

These losses'reduce the amount of usable drawdown and limit the 

Furthermore, the high entrance velocities and associ- 
17 

Since the depth of the alluvial aquifers along most rivers of the United States is generally less than 20 m, the capacity of a single vertical well can be expected to be on the order 

of 6,000 m3 per day. Thus, for a typical nuclear power plant, consisting of two 1300-MWe units 

and having a cooling water makeup requirement of 200,000 m3/day, over 30 vertical wells would be 

required. 

pipelines would render such a system economically impractical, not only in terms of initial 

construction costs but also in terms of operation and maintenance costs. 

well systems have been proven practical for smaller water supplies, it is doubtful that they 

represent a viab’le alternative for most large cooling water supplies. 

from the ancient times of Persia and the days of early Greece. 

zontal, permeable conduits or pipes constructed in unconsolidated materials below the water 

table. Because of the large area of screen exposed to the aquifer, infiltration galleries are 

more efficient and generally collect more water than vertical wells. 

results in low entrance velocities and minimal well losses, resulting in a structure relatively 

free from clogging and with a long life. 

Los Angeles, California, and Des Moines, Iowa, which have been used for over 40 years without 

reported reduction in collection rates. Stone (1954) also reports yields of up to 50,000 rn3/day 

for a single infiltration gallery. 

because construction is by open excavation below the water table, its application is*limited to 

very shallow depths, generally not in excess of 6 m. 

The multiplicity of pumps, pumphouses, electrical connections, and interconnecting 

Thus, while vertical 

Infiltration galleries are among the oldest known means of inducing infiltration, dating 

Infiltration galleries are horiThis large screen area 

Stone (1954) cites examples of galleries at 

The chief disadvantage of an infiltration gallery is that, 

A relatively new method of developing water supplies by induced infiltration is the Ranney 

Collector, developed by Leo Ranney of Northwestern University in the early 1930’s. The Ranney 

Collector combines the major advantages of both vertical wells and infiltration galleries, since 

it permits utilizing the entire depth of the aquifer and allows virtually unlimited amounts of 

screen to be exposed to the aquifer. 

RANNEY COLLECTOR DESCRIPTION 

Figure 1 is a sketch of a typical Ranney Collector. A large-diameter reinforced concrete 

caisson is sunk, by open excavation, to the base of a sand and gravel aquifer adjacent to a surface source. The bottom of the caisson is sealed with a concrete plug and, near the base of the 

caisson, horizontal screen pipes are projected radially, much like the spokes of a wheel. These 

horizontal screens are projected by a combination washing and jacking process, resulting in the 

removal of large volumes of fine material and the development of a natural gravel zone surrounding the entire length of each horizontal screen lateral. Silitch (1948) states that from 0.3 to 

0.6 m3 of fine materials are removed for each meter of screen pipe projected, resulting in a natural gravel bed of more than 1.2 rn in diameter surrounding the screen pipe. 

extended above flood level to form a base for a pumphouse and pumps, resulting in a complete 

water-producing system contained in one unit. 

The Ranney Collector is in reality a special type of infiltration gallery that can be 

economically constructed to depths of up to 60 m. large area of horizontal screen, surrounded by highly permeable gravel, to the aquifer. 

results in very high yields, while maintaining extremely low entrance velocities. 

entrance velocities virtually eliminate well loss, clogging, and incrustation, thus assuring a 

reliable and long-lived installation. 

thicknesses of 450 to 600 rnm. The horizontal screen laterals are fabricated from heavy steel 

plate or pipe, with longitudinal keystone slots, and may range from 200 to 600 mm in diameter. 

As much as 600 m of horizontal screen pipe have been projected in some Ranney Collectors, with 

individual laterals ranging up to 135 m in length. 

At the present time, there are more than 300 Ranney Collectors in operation in the United 

The yields.of Ranney Collectors range up’ to as 

Some of the larger Ranney Collector systems 

The caisson is 

The basic principle consists of exposing a 

This 

These low 

The size of the reinforced concrete caissons ranges from 4 to 6 m in diameter with wall 

States and Europe. 

industrial process and cooling water supplies. 

high as 80,000 m3/day from a single installation. 

are the Grand Gulf Nuclear Station (120,000 m3/day), the Indiana Ordnance Works (250,000 m3/day), 

the Wabash River Ordnance Works (340,000 m3/day), the Sonoma County, California, Water Agency 

(250,000 m3/day), and Belgrade, Yugoslavia (300,000 m3/day). 

yield capability required for large power plant cooling water supplies. 

About 55:, of these are municipal water supplies, while the remaining 45% are 

Thus, Ranney Collectors have the 

SCREENING AND FILTERING CHARACTERISTICS 

Klaer (1953) states that experience has shown that turbidity, suspended matter, organic 

matter, and pathogenic bacteria are removed from water by induced infiltration, especially in 
Fig. 1. Sketch of Typical Ranney Collector 

the use of Ranney Collectors. 

river, which is comparable in many ways to a very large slow sand filter, but larger and thicker 

than any made by man. 

have been computed using the methods of Walton (1970) and are given in Table 1. These riverbed 

infiltration rates are very low, averaging only 0.0023 cm/s, and the filter bed thicknesses (or 

aquifers) are very large, ranging from 4.4 to 22.0 m. 

man-ma.de rapid sand filter has an infiltration rate of 0.27 cmfs, or over 100 times faster than 

the riverbed infiltration rates, and a filter bed thickness of only about 1 m. 

Velocities through the riverbed are also- given in Table 1; the average is only 0.0078 cm/s. 

These velocities are extremely low and are only about one-two thousandth of the intake velocity 

of 15 cm/s, generally considered adequate to prevent impingement of adult and most juvenile fish 

(Schreiber et al. 1973). As a matter of fact, the riverbed velocities are so low, being in the 

range of natural seepage, that even impingement of larval fish or free-floating river organisms 

would not be expected to occur. 

pathogenic bacteria, which vary in size from 1 to 4 U, it is likely that no entrainment of larval 

fish or free-floating river organisms will occur. 

The filtering ability of the riverbed is further shown by the low turbidity measurements 

(Table 1). 

than 1.0 JTU and most show a turbidity of less than 0.5 JTU. 

sing a proposed Ranney Collector system for a nuc?ear power plant in western Washington, state 

that the utilization of a subsurface intake system will prevent any damage to the river's 

aquatic life and have little impact upon the land surface at the intake area along the riverbank. 

This screening and filtration takes place on the bed of the 

Riverbed infiltration rates for a number of existing Ranney Collectors 

As a matter of comparison, a conventional 

Furthermore, since riverbed infiltration is known to filter 

Turbidity removal is virtua1ly.complete; all installations show a turbidity of less 

Kenny and Wise (19751, in discusWATER QUALITY AND TEMPERATURE 

The water from Ranney Collectors, being naturally filtered, is clear and free of turbidity, 

suspended matter, organic matter, and pathogenic bacteria. After a relatively short period of 
19 

Table 1 - Screening and Filtering Characteristics of Ranney Collectors 

Velocity 

Ranney Collector Below River Ra nney River Inf i 1 trati on Riverbed 

Riverbed Through Turbidity (JTU) Aqilifer Depth 

Site Level (m)a Collector Maximum Rate (un/s.)b (cm/s) 

Boardman, Oreg. 71.5 0.40 29 8.7 10-4 

Carmichael, Calif. 6.6 0.10 55 1.6 10-3 

Charleston, Ind. 15.2 - - 1.6 10-4 

Crescent City, Calif. 4.4 0.35 200 9.3 10-3 

Gladstone, Oreg. 8.0 0.45 - 1.4 10-3 

Kalama, Wash. 8.0 0.40 100 4.3 x 10-4 

Collectors 1, 2, 3 9.1 0.40 29 2.2 10-4 

Kennewick, Wash. 

Collector 4 10.4 0.11 29 - 

Collector 5 8.5 0.03 29 - 

Marysvi 11 e, Wash. 10.0 0.80 29 5.6 10-3 

Port Angeles, Wash. 15.5 0.50 35 7.6 10-4 

Sacramento, Calif. 22.0 0.11 170 2.6 10-3 

St. Helens, Oreg. 10.5 0.33 29 1.1 10-4 

Collectors 1 & 2 21.0 0.10 1520 2.3 x,10-3 

Collectors 3 & 4 20.1 0.23 1520 2.3 10-3 

Woodland, Wash. 6.0 0.11 5.0 10-3 

Sonoma Co., Calif. 

aTo convert meters to feet, multiply by 3.2808. 

bTo convert centimeters per second to feet per minute, multiply by 1.9685. 

2.9 10-3 

5.4 10-3 

5.4 10-4 

4.7 10-3 

1.4 10-3 

3.1 10-2 

7.2 10-4 

- 

- 

1.9 10-2 

2.5 10-3 

8.7 10-3 

3.6 x 10-4 

7.9 10-3 

7.9 10-3 

1.7 x lob2 

pumping, the mineral quality of the water will approach the average mineral quality of the surface source, but will generally be slightly more mineralized due to small water contributions 

from groundwater - 

Theis (1941) has developed equations for determining the percentage of pumped water being 

diverted from a surface source of recharge. For a well or Ranney Collector located on the 

river's edge near the source of recharge, computations from these equations indicate that over 

90% of the water pumped is diverted from the river after a relatively snort period of pumping. 

As a confirmation of this, river water percentages have been determined for a number of existing 

Ranney Collectors, based upon water quality data, and are given in Table 2. 

selected as the mineral parameter for these determinations because of its stability in solution. 

The percentage of river water was determined from the observed total hardness of the groundwater, the river water, and the Ranney Collector water, assuming proportional mixing. 

The river water percentages vary from 74.4 to 112.5% and average about 92'L. 

percentages exceed 100% and such anomalies can be expected, since the water analyses are spot 

determinations rather than average water analyses over an extended period of time. Nonetheless, 

it is significant to note that virtually all of the Ranney Collector sites show that in excess of 90% of the water pumped is diverted from the river, thus confirming the theoretical equations 

of Theis (1941). 

The water produced by Ranney Collectors has a seasonal temperature variation similar to 

that of the surface source, except that it is substantially less in magnitude. A time lag will 

also exist between the surface water temperature and that of the water pumped. The water temperature characteristics at a number of existing Ranney Collector sites are shown in Table 3. 

These data show that, for aquifers deeper than 13 m, the seasonal temperature range of the water 

produced is 20 to 30% of the temperature range of the river, and time lags of 2 to 3 months occur. For the shallower aquifers (less than 10 m in depth), the temperature range of the water 

filtered is 45 to 70% of the temperature range of the river and time lags are only 1 month. 

Because cooler water is available during the summer months and warmer water during the winter 

months, this dampening of the river water temperature cycle is an obvious advantage for cooling 

water suppl ies. 

Total hardness was 

A few of the 
20 

Table 2. Percentage of Pumped Water Diverted from a River, 

Based upon Water Quality Data 

Total Hardness as CaCO;, (mq/L) 

Ranney 

Ranney Coll ector Sampl i ng Collector River . River Water 

Site Date Groundwater Water Water Percentage 

Anacortes, Wash. 

Carmichael, Calif. 

Charleston, Ind. 

Crescent City, Calif. 

Gladstone, Oreg. 

Kalama, Wash. 

Marysvi 1 1 e, Wash . Port Angeles, Wash. 

Quincy, Ill. 

Sacramento, Calif. 

Skagit County, Wash. 

Sonoma County, t a l i f . 

Woodland, Wash. 

1968 (avg.) 

Aug. 1959 

Jul. 1943 

Aug. 1943 

Sep. 1943 

Oct. 1943 

Nov. 1943 

Dec. 1943 

Aug. 1958 

Aug. 1959 

Mar. 1975 

Jan. 1978 

Oct. 1977 

1951 (avg.) 

1952 (avg.) 

1953 (avg.) 

1954 (avg.) 

Aug. 1967 

Nov. 1954 

Dec. 1954 

Jan. 1955 

Jul. 1959 

Aug. 1959 

May 1959 

Nov. 1960 

Mar. 1961 

Aug. 1963 

Aug. 1966 

Nov. 1970 

Apr. 1972 

Sep. 1968 

55 

62 

280 

28 0 

280 

280 

280 

280 

- 

41 

34 

41.4 

50 

94 5 

945 

945 

945 

76 

49 

46 

49 

48 

46 

190 

190 

190 

190 

190 

190 

190 

31.7 

24 

21 

173 

178 

177 

186 

21 0 

221 

64 

34.7 

25 

40 

45 

225 

209 

23 1 

21 8 

58 

22 

25 

26 

20 

21 

147 

129 

141 

142 

129 

132 

119 

13.6 

22 

19 

154 

152 

160 

179 

210 

21 0 

64 

34 

26 

40 

45 

146 

158 

176 

163 

56 

20 

24 

26 

15 

19 

133 

108 

127 

143 

125 

123 

119 

12 

94 .O 

95.3 

84.9 

79.7 

85.8 

93.1 

100.0 

84.3 

100.0 

90.0 

112.5 

100.0 

100.0 

90.1 

93.5 

92.8 

93.0 

90 .o 

93.1 

95.5 

100.0 

84.4 

92.6 

75.4 

74.4 

77 -8 

102.1 

93.8 

86.6 

87.3 

91 -9 

Table 3. Water Temperature Characteristics of Ranney Collectors 

Ranney Collector 

Site 

Water Temperature ("C) 

Ranney 

Time Lag 

Level (m) Max. Min. Max. Min. (months) 

River Water Col 1 ector Aquifer Depth 

Below River 

Anacortes, Wash. 

Carmichael, Calif. 

Charleston, Ind. 

Clinton, Ind. 

Kennewick, Wash. 

Louisville, Ky. 

Sacramento, Calif. 

Sacramento, Calif. 

Skagit Co., Wash. 

9.5 

6.6 

15.2 

16.5 

10.7 

13.7 

27.4 

22.0 

7.9 

16.7 

21.1 

31.1 

28.3 

20.0 

28.3 

23.3 

23.3 

16.7 

2.8 

7.2 

3.3 

2.8 

5.0 

7.7 

5.6 

5.6 

2.8 

14.7 

20.0 

20.0 

16.7 

16.7 

16.7 

16.7 

17.8 

12.2 

5.8 

10.0 

12.8 

8.9 

10.0 

11.7 

12.2 

13.3 

5.6 

1 

1 

2.5 

2 

1 

2.5 

3 

3 

1 
21 

COSTS. 

Within the capacity range of large nuclear power plant makeup cooling water supplies, the 

costs of Ranney Collector systems, in 1978 dollars, range from $700,000 to $2,200,000 per m3/s 

developed capacity, depending upon geological conditions and site location. These costs are for 

the basic Ranney Collector units and do not include the cost of pumping equipment, electrical 

controls, and discharge piping. 

50.78 to $1.54 per kilowatt. 

In terms of unit cost per kilowatt, these costs range from 

As a matter of comparison, the U. S. Environmental Protection Agency ('1976) gives costs for 

conventional makeup water shoreline intakes ranging from $1,000,000 to $2,300,000 per m3/s, 

adjusted to 1978 dollars. In terms of unit cost per kilowatt, these costs range from $1.10 to 

$4.30 per kilowatt. Kenny and Wise (1975), in discussing a proposed Ranney Collector system for 

F nuclear power plant in western Washington, state that the cost of a specially designed surface 

intake structure could cost on the order of twice the cost of a subsurface intake system. 

ENVIRONMENTAL ADVANTAGES 

Ranney Collectors offer the best available technology for minimal environmental impact. 

Having no direct contact with the waterway, they have no effect upon the aquatic ecosystem. 

Furthermore, since all construction takes place onshore, no disturbance or roiling of the river 

occurs during the construction period. 

The chief limitation on the use of Ranney Collectors for cooling water intakes is that of 

hydrogeology. Ranney Collectors can be successfully installed only in areas where there are permeable sand and gravel aquifers connected hydraulically with a surface source. 

course, limits the sites at which this method can be applied. 

This, of 

THE RANNEY SURFACE WATER INTAKE 

RANNEY INTAKE DESCRIPTION 

The Ranney Surface Water Intake is based on the same design concepts as the Ranney Collector. 

water supply that is provided by the intake system. 

the lower portion of the caisson at an appropriate, pre-selected elevation and extend to the 

portion of the channel that has been previously selected to provide the intake water supply. 

minimize adverse environmental effects during construction, these lines are usually projected 

from the caisson, beneath the bank of the lake or stream, and may be designed to intercept the 

bank or shore at a chosen elevation, or may be extended completely beneath the stream or lake 

bottom and be connected by a vertical riser to the intake screens. The intake screens are 

located directly within the body of water serving as the water supply source. type is illustrated in Figure 2, with an alternate arrangement shown in Figure 3. 

the intake system; thus it is completely redundant. 

open. 

The onshore caisson, or pumping station, is gravity-fed through the intake lines. 

turn have the intake screens located in the appropriate portion of the mainstream channel. 

proper location of the intake screens within the stream channel and the specific design of the screens is determined only after careful evaluation of both the hydrology and aquatic biology of 

the stream. 

A large-diameter caisson is installed onshore and serves as the pumping station for the 

Two or more intake lines are installed from 

To 

A system of this 

In most installations, each intake line and screen is designed to carry the entire load of 

In normal operation both intake lines are 

These in 

The 

The intake screens and critical portions of the intake lines where they join the screens are usually pile-supported. 

steel, everdur metal, or other appropriate material. 

parallel to the predominant direction of current flow. 

entrance velocities (in most cases lower than the natural velocity of the stream current), there 

is no tendency for suspended stream debris to impede the intake, and the screens are selfcleaning in normal operation. 

been installed in both large, navigable rivers, and in smaller streams where only minimal 

hydraulic head is available. 

The screens are perforated cylinders of carbon steel, stainless 

The long axes of the screens are aligned 

By maintaining extremely low screen 

Backwash facilities are provided for extraordinary conditions. 

Intakes of this design are applicable to either small or large demand requirements and have 
22 

Fig. 2. Ranney Surface Water Intake 

SCREEN 

\ __ -- ...__ ~ ~ ~ 

PILINGS DRlV 

TO STABILITY 

Fig. 3. Typical Ranney Intake 
23 

OPERATIONAL FEATURES 

Except for the onshore pumping facilities, which are gravity-supplied through the intake 

lines, this complete intake system has no moving parts; hence, there is very little to maintain 

except the pumps. 

located at sufficient depth to avoid most floating debris. 

bottom of the stream to minimize the effect of the abrasive products associated with sedimentation, siltation (sand and pebbles bouncing along the bottom of the stream bed), and genera7 bedload migration. 

move into direct contact with the surface of the screen and float tangentially into the screen 

will enter the intake lines and make its way into the pumping station. Thus, pump maincenance 

is minimal, while actual intake maintenance is practically eliminated. 

The pumping facilities are located onshore, above maximum flood stage, and are easily 

The instream intake screens, which are easily replaceable should the need .ever arise, are 

They are sufficiently far off the 

Only that small portion of the suspended load of the stream that is able to 

accessible for power supply or general maintenance requirements under all conditions. 

installing a standby power unit within the pumphouse, water supply can be maintained even during 

total general power failure. 

By 

ENVIRONMENTAL ADVANTAGES 

Openings in the intake screens may be of any size or shape that is considered to be enviThe openings should be small enough that only the smallest of organisms 

Inlet velocities through the screen openings are designed at 15 cm/s or 

At these inlet velocities, the smallest of fish fry can actually swim into, through, and 

Natural stream current velocities often actually exceed the 

Only by swimming directly into the screen and down the intake line to 

ronmentally suitable. 

can enter the intake. 

less. 

out of the screens without injury. 

screen inlet velocities. 

the pumps can fry or larvae be injured. 

approach is almost 360". 

have substantially no effect on bottom-dwelling organisms. In addition, the screens are located 

in or near the mid-channel area, in most instances, away from the near-shore, shallow-water 

zones where aquatic life is most abundant, and where most of the aquatic reproduction occurs and 

larval forms are most prevalent. 

during the short interval required for construction. Good construction procedures can minimize 

even this short-term, adverse effect. 

The potential angle of safety or escape from the screen 

The screens are located sufficiently far above the bottom of the stream or lake so as to 

The only significant adverse environmental effect occurs 

When specialized construction techniques are utilized whereby the intake lines are hydraulically projected from the bottom of the caisson to either near or beneath the stream itself, 

the natural banks of the stream are not disturbed during construction, or at the very worst 

disturbance is minimal. 

minimum or are eliminated entirely. 

Coffer dams and major stream excavation and disturbances are kept to a 

Prior to the development of detailed plans and subsequent construction, site evaluation is 

necessary. This requires a comprehensive soil investigation both onshore and offshore, to determine construction difficulties and bearing capacities for both the caisson pumping station and 

the supporting piling. 

In addition, a hydrologic evaluation of the stream is necessary. This includes making 

cross-sectional and longitudinal profiles of the stream in the vicinity of the proposed construction,, and making both horizontal and vertical measurements of stream velocities in order to 

adequately describe the streamflow regime in the vicinity of the screens. 

preliminary planning is frequently neglected, but is important from both the environmental and 

operational point of view. 

Consideration should be given to the aquatic environment to be sure that the screens are 

properly placed with respect to creating the minimum impact upon the aquatic environment. In 

general, nearshore and shallow-water zones should be avoided, where possible, and the screens 

should be placed where the most effective currents are available to maximize the self-cleaning 

effect and minimize any prospective future requirement for backwashing. It should be determined 

which portions of the stream are most likely to become debris-laden or heavy with sediment 

during varying stage conditions, and this should be considered along with other factors, such as 

economics, navigation channels, dock areas, etc., in determining the proper placement of the 

screens - 

This aspect of 

The greatest potential danger to the effective and efficient long-term operation of this 

intake is the improper placement of the screens within the streambed. 

of the operational function of the system, it is very easy to overlook the sophistication 

Because of the simplicity 
24 

required in determining the proper location and orientation of the screens. ating both the hydrology and the aquatic environment, the system will have minimum adverse 

impact, low capital and operating costs, maximum dependability and security, and ease and convenience of operation. 

By properly evaluDEPENDABILITY 

The instream intake screens are designed to withstand shocks and impacts to which they may 

be subjected. 

bility or adverse effect on either commercial river traffic or the environment. 

The intake lines themselves are buried and/or otherwise fully supported and protected. 

Backwash facilities are provided in case the screens become blocked by any unusual event. 'The 

dual intake lines permit the use of either or both screens when necessary or desirable. 

design is such that either intake line is capable of carrying the full supply load without 

exceeding the design entrance velocities through the screens; thus the actual capacity of all 

units is double that which is considered to be the rated design capacity, and in normal operation actual entrance v.elocities through the screens are only fifty percent of the design value. 

Carefully designed soldier pilings can be employed where necessary, without visiThe 

The design of the pumping station, and its great stability due to the depth and construction of the caisson-type foundation, permits full access to the pump house and to all facilities, even during maximum floods. 

Direct access to the interior of the shaft of the caisson makes inspection easy and permits any 

repair work that might be required. 

All operating machinery is protected inside the unit. 

TYPICAL INSTALLATIONS AND COSTS 

Shown in Table 4 are installation and operation data for five typical Ranney Surface Water 

Intakes, ranging in capacity from 55,000 to 650,000 m3/day and in age from four to seventeen 

years. 

small pleasure boats; two are in the Ohio River; and one is in the Mississippi River just below 

its confluence with the Ohio River. Two of the units are instalTed in firm to hard shale; one is installed in metamorphic, schistose rock; and two are installed in unconsolidated materials-- 

alluvial sediments in river floodplains. Comments solicited from the operators of each of these 

units in January of 1978 are included in the table. 

application and operational effectiveness after many years of utilization. 

Two of these are installed in relatively small, shallow streams frequented by canoes and 

Clearly indicated is the diversity of 

Table 4. Installation and Operation Data for Five Typical Ranney Surface Water Intakes 

Caisson Diameter Rated 

'tear Depth of Diameter of Intake Capacity 

Owner Installeo Water (m) (m) Line (mn) (PI /day) River Operational Comnents 

Detroit Steei Corp. 1961 

Portsmouth, Ohio 

Ariuco Rolling Mill 1962 

Ashland, hy. 

Westvaco 1970 

Wickliffe, Ky. 

American Mater Works 1973 

Service Co. 

Clarion, Penn. 

9.1 6.1 Two 1200 490,000 Ohio EJo problems, yearly 

pull R paint screens, 

weekly air-hydraul ic 

backflush. 

5.5 Two 4.9 Two 120G 545,000 Ohio bo problen6, very 

satisfactory, daily 

hydraulic backflush. 

19.3 9.1 Two I200 650,000 Kississippi 

7.9 4.4 Two 400 55,000 Clarion No oroblems, very 

satisfactory, weeh 1 y 

hydraulic backflush. 

Pennsylvania Power 8 1975 2.4 9.1 Two 1100 272.500 Susquehanna No problenis. 

Light Company Watsontown. Penn. 

To arrive at approximations of 1978 costs for comparative purposes, all of these units were re-estimated in terms of what the current costs of the basic units would be, i.e., exclusive of 

pumping equipment, electrical controls, instrumentation, and mechanical piping. The cost range, 

in 1978 dollars, would be from $158,000 to $396,000 per m3/s developed capacity, with the mean being about 6190,000 per m3/s developed capacity. As might be expected, the unit price is highest 

for low-capacity intakes and goes down substantially with the larger structures. Soils, water 

depth, current velocities, and related factors all contribute to variations in the priCF. Depth 

of the waters in the rivers shown vary from 2.4 m to over 18.3 m at the site of the installations 

indicated. 
25 

REFERENCES 

Kazmann, R. G. 1947. River infiltration as a source of ground water supply. Proc. Am. SOC. 

Civ. Eng. 73(6):837-853. 

. 1948. The induced infiltration of river water to wells. Trans. Am. Geophys 

Union 29( 1 ) :85-89. 

____c___ - 1972. Modern Hydrology, 2nd ed. Harper & Row, New York. 365 pp. 

Kenny, J. H., and K. R. Wise. 1975. Underground Water Intake for Nuclear Plant Will Protect 

the Environment. Paper presented at the Association of Engineering Geologists Annual 

Convention, South Lake Tahoe, Calif.,.Nov. 5-6, 1975. 

Klaer, F. H. 1953. Providing large industrial water supplies by induced infiltration. Min. 

Eng. London 5:620624. 

Mikels, F. C., and F. H. Klaer. 1956. Application of ground water hydraulics to the development of water supplies by induced infiltration, pp- 232-242. 

of Scientific Hydrology Symposium. Darcy, Dijon. Publ. 41. 

& International Association 

Rorabaugh, M. I. 1952. Stream-bed percolation in the development of water supplies. International Association of Scientific Hydrology, General Assembly, Bruxelles. Vol. 2, 

pp. 165-174. 

. 1956. Ground-water resources of the northeastern part of the Louisville area, 

Kentucky. U. S. Geol. Surv. Water-Supply Pap. 1360-8. 

Schreiber, D. L., C. 0. Becker and 3. 3. Fuguay. 1973. Appraisal of Water Intakes on the 

Columbia River. Battelle Memorial Institute, Pacific Northwest Laboratories. 69 pp. 

Silitch, E. W. 1948. The place of Ranney collectors in the water supply industry. 3. New 

Hampshire Water Works Assoc., Oct. 1948. 

Stone, R. 1954. Infiltration galleries. Proc. Am. SOC. Civ. Eng., Vol. 80, Separa,te No. 472, 

Theis, C. V. 1941. The Effect of a Well on the Flow of a Nearby Stream. Trans, Am. Geophys. 

U. S. Environmental Protection Agency. Development Document for Best Technology AvailAugust 1954. 12 pp. 

Union. 

1976. 

able for the Location, Design, Construction and Capacity of Cooling Water Intake Structures for Minimizing Adverse Environmental Impact. EPA 440/7-76/015-a. Washington, 0. C. 

Walton, R. C. 1970. Groundwater Resource Evaluation. McGraw-Hill, New York. 664 pp. 
HYDROLOGIC ENGINEERING CONSIDERATIONS FOR 

RANNEY COLLECTOR WELL INTAKE SYSTEMS 

Nicholas J. Beskid 

Division of Environmental Impact Studies 

Argonne Nationa I Laboratory 

9700 S. Cass Avenue 

Argonne, I I I inois 60439 

Abst ract 

The basic hydrologic aspects affecting the location, design, and operation of 

Ranney Collector Well intake structures are presented. 

erations are discussed and the types of problems that require site-specific design 

considerations are outlined. The fundamental concepts of hydrology related to 

collector well design, such as surface water flow regime and the more complex grounciwater hydraulics, are briefly discussed. Emphasis is placed on the application of the 

results of field pumping tests to the estimation of aquifer properties, groundwater 

flow, and infiltration rates and the utilization of these parameters as input to 

Ranney Collector Well system design. 

Siting and design considINTRODUCTION 

The Ranney Collector Well is a groundwater well--a hydraulic structure which, when properly 

designed and constructed, permits economic withdrawal of water from an aquifer. 

years, the Ranney Collector Well intake has become increasingly popular at power plants in areas where favorable hydrologic conditions exist. or entrainment; pose no threat to navigation because they are emplaced horizontally at depths 

below the streambed; and, due. to the contribution from groundwater storage, remove less water 

from streams during low flow than do conventional stream intakes. The Ranney Collector Well 

supplies groundwater by the process of induced infiltration. Simply, induced infiltration, or 

induced recharge, is the process by which the cone of depression (or zone of influence) formed 

by a pumping well induces water to infiltrate through the bed of a nearby stream or lake. 

lector Well and the factors that limit its installation and use, we will look at a typical 

i ns tal 1 a ti on. 

In recent 

Such intakes incur virtually no fish impingement 

In order to discuss the hydrologic parameters which govern the operation of a Ranney ColA TYPICAL RANNEY COLLECTOR WELL INSTALLATION 

Typically, a Ranney Collector Me11 is located in a highly permeable alluvial aquifer where 

The collector well (Fig. 1) is constructed by lowering a cylindrical concrete caisson 

The construction features of collector wells installed in 

the water table is high, and in direct hydraulic contact with a surface stream or lake (recharge 

source). 

into unconsolidated deposits, sealing the bottom with a concrete plug, and jacking perforated 

pipes horizontally into the aquifer. 

the United States were described by Spiridonoff (1964). The caisson is a reinforced-concrete 

vertical shaft, 2-1/2 to 4 m (8 to 13 ft) in diameter, poured in place. The wall thickness of 

the caisson is 45 or 60 cm -(18 or 24 in.), depending upon whether the caisson is shallow or 

deep. The bottom of the caisson is a reinforced-concrete slab. 

One or more tiers of horizontal perforated steel pipe (laterals) are connected to valved 

The laterals usually have an outside diameter of 20 cm (8 in.) and a l-cmThe 

ports in the caisson wall 1.3 m from the bottom of the caisson. 

than 22.5" apart. 

thick wall of special copper-alloy steel. The slots in the pipe are cut with a saw, and are 

1 cm wide and 4 cm long; the perforated area equals about 20% of the total surface area. total lengths of individual laterals range from about 35 to 85 rn, generally made up of 2.4-m 

The ports are usually no less 

27 
28 

I 

Fig. 1. Ranney Collector Well Intake. From Todd (1967) 

(with permission). 

lengths of pipe. 

in a wheel. 

The laterals may fan out in a semicircle or in a full circle like the .spokes 

Under equilibrium (steady-state) conditions, the yield of a Ranney Collector Well is dependent 

on aquifer thickness and permeability (transmissibility), infiltration rate through the bed of 

the recharge source, water temperature, effective radius of the collector, and distance to the 

control discharge boundary. 

The withdrawal efficiency of any well depends on the storage and conveyance capacities of 

the aquifer and on the hydraulic principles governing flow toward a pumping well. 

efficiency of a Ranney Collector Well depends in addition upon well location and the nature of 

the stream connected to the aquifer. 

The withdrawal 
29 

AQUIFER STORAGE AND CONVEYANCE 

An aquifer is a water-saturated geologic formation that will yield water to wells at a 

sufficient rate that the wells can serve as a practical source of water. The upper zone of 

saturation, just below the earth's surface, is called the water table. The water table is used 

primarily in the development of Ranney Collector Wells and most shallow wells. 

location is the area of a water table that is hydraulically connected to a nearby surface stream. 

A favored well 

An aquifer has two major functions--storage and conveyance. It stores water, as a reservoir, 

and conveys water like a pipeline. 

areas of recharge to areas of discharge. 

The groundwater in the aquifer is constantly moving from 

The storage capacity of an aquifer is determined by its porosity and specific yield or 

coefficient of storage (S). 

released from storage, or taken into storage, per unit of surface area of the aquifer per unit 

change in head. 

yield. 

The coefficient of storage of an aquifer is the volume of water 

Generally, for water-table aquifers, S is essentially the same as the specific 

The ability of the aquifer to convey water is determined by its permeability. Permeability 

is the capacity of a porous medium to transmit water. 

by Darcy's Law, which states that the flow of water through a porous medium is proportional to 

the difference in hydraulic head between ends and inversely proportional to the length traversed. 

As in most mathematical expressions of natural phenomena, there is a constant term in the Darcy 

equation. The coefficient or Permeability (more appropriately, hydraulic conductivity), K, is 

dependent on the physical character of the geologic formation (porosity, particle size, etc.), 

expressed in units of gallons per day per square foot (gpd/ft*). 

term coefficient of transmissibility (T) to represent the water-transmitting capability of the 

full thickness of an aquifer (i.e., the product of permeability and aquifer thickness). 

missibility can be determined from aquifer pump tests. 

laboratory values of permeability, which usually include inaccuracies due to nonrepresentative 

sampling. 

sites, aquifer transmissibility is one of the most important factors considered. Values range 

from 1000 to over 1,000,000 gpd/ft of aquifer. For large-yield intake facilities for industrial 

uses and generating stations, T's on the order of tens of thousands to over 1,000,000 gpd/ft are 

required. 

The flow of water in an aquifer is described 

Theis, in 1935, introduced the 

TransThis is an improvement over using the 

In determinations of Ranney Collector Me11 feasibility and yield estimates for specific 

The coefficients of transmissibility and storage are particularly important because they 

define the essential hydraulic properties of an aquifer. Where these two coefficients can be 

determined for an aquifer, significant predictions of storage are possible, including the specific 

capacity of wells of different diameters, the drawdown in the aquifer at various distances from 

a pumped well, and the drawdown in a well at any time after pumping commences. 

HYDRAULICS OF FLOW TOWARD A PUMPING WELL 

According to Darcy's Law, the velocity of flow through porous media varies directly with 

the hydraulic gradient. With increasing hydraulic gradient the velocity increases as flow 

converges toward a pumping well, resulting in a continually steeper slope toward the well. 

shape of this surface resembles a cone-shaped depression and thus is known as the cone of depression. All pumping wells have a cone of depression, each differing in size and shape depending on pump rate, aquifer characteristics, water table slope, and recharge sources within the zone 

of influence of the well. 

When water is pumped from a well, the discharge is initially derived from aquifer storage 

The 

immediately surrounding the well. As pumping continues, more water must be derived from storage 

at increasingly greater distances from the well. This means that the circular-shaped cone of 

depression must expand so that water can be drawn from greater The radius of influ- ence of the well increases as the cone continues to expand. Drawdown also increases as the cone deepends to provide the additional head required to move the distant water. The cone expands 

and deepens at a decreasing rate with time, however, because with each unit of horizontal expansion a larger volume of stored water is available. 

condition of equilibrium exists. There is no further increase in drawdown with increase in time 

of pumping. 

others, it may be years. 

Division 1975). 

water-table conditions. 

formula for the water-table well is 

distances. 

When the cone has stopped expanding; a 

In some wells, equilibrium occurs within a few hours after pumping begins; in 

Well discharge formulae for equilibrium conditions were derived many years ago (Johnson 

There are two basic formulae--one for artesian conditions and the other for 

Both assume recharge at the periphery of the cone of depression. The 

P ( H2-h2 ) ' = 1055 log R/r ' 
30 

where Q = well yield or pumping rate (gpm), 

P = permeability of the water-bearing sand (gpd/ft?), 

H = saturated thickness of the aquifer before pumping (ft), 

h = depth to water while pumping (ft). 

R = radius of the cone of depression (ft), and 

r = radius of the well (ft). 

Theis developed the non-equilibrium well formula in 1935. This formula was the first to 

take into account the effect of pumping time on well yield. Its derivation was a major advance 

in the field of groundwater hydraulics. 

time after pumping begins. 

the early stages of a pumping test rather than after equilibrium is reached. 

cients can be determined from the time-drawdown measurements of only a single observation well. 

By use of the formula, drawdown can be predicted at any 

The transmissibility and average permeability can be determined from 

The aquifer coeffiINDUCED IN FI LTRATI ON 

When a well is pumped near a stream (recharge boundary) that is hydraulically connected to an aquifer, water is first withdrawn from aquifer storage in the immediate vicinity of the well. 

The cone of depression then spreads, drawing water from within an increasing area of influence. 

Water levels in the vicinity of the stream are lowered, and more and more of the water which 

normally would have discharged into the stream is diverted toward the pumped well. Ultimately, 

water levels are lowered below the surface of the stream in the immediate vicinity of the well, 

and the aquifer is recharged by the induced infiltration of surface water. 

stream cannot keep pace with discharge, the cone of depression spreads up- and downstream. 

continues to expand until it intercepts sufficient area of the streambed that induced infiltration 

balances discharge. 

Recharge boundaries can be analyzed by the image-well theory. Consider an aquifer bounded 

on one side by a stream as shown in Figure 2a. The cone of depression cannot spread beyond the 

stream. 

effective line of recharge somewhere offshore. The imaginary hydraulic system of a discharging 

well and its image recharge well in an infinite aquifer (Fig. 2b) simulate the boundary condition 

shown in Figure 2a. An imaginary recharge well has been placed directly opposite and at the same distance from the boundary line as the real well. The recharge image well operates simultaneously and at the same rate as the real well. 

arithmetic summation of the components of the real-well cone of depression and the image-well 

cone of impression. The resultant profile of the actual cone of depression is steeper on the 

river side of the real well and flatter on the land side of the real well than it would be if no 

boundary were present, thus indicating induction of river water into the groundwater aquifer. 

of events after pumping which cause the capture of groundwater flow to an effluent river. 

sequence applies only to a single cross section; upstream and downstream hydraulic effects would 

be in earlier stages of development. 

stream. The positive differential head (+Ah) forces groundwater up through the streambed. As 

pumping begins (Fig. 3b), the water table is lowered below the river surface on the right side 

of the stream; thus a negative differential head (-Ah) pushes water from the river down through 

the streambed. On the left side of 

the stream a positive differential head (+Ah) still pushes water into the stream. In Figure 3c 

it is shown that under heavy pumping the water table is Towered completely below the streambed, 

and infiltration proceeds at full potential rate. At this point infiltration is constant sand 

maximum. It will vary only with head conditions across the area subject to head loss, and will 

not increase with additional drawdown (Rahn f968). 

When recharge by the induced infiltration of surface water from the affected reach of the 

It 

In this case, the condition is established that there can be no drawdown along an 

The resultant actual cone of depression is the 

The concept of induced infiltration is shown in Figure 3, which depicts the ideal sequence 

This 

Figure 3 represents natural conditions for an effluent 

Underflow is captured and induced infiltration has begun. 

The amount of water induced into an aquifer depends on the rate of pumping, infiltration 

rate of the streambed, distance from surface source, nature of the surface source, and natural 

groundwater movement. 

The nature of the surface stream is important because streams can be of several different 

types. 

of a stretch of stream that contributes water to the zone of saturation is termed influent 

(Fig. 4a) with respect to the groundwater. 

channel from the zone of saturation because the water table is higher, the stream is termed 

effluent (Fig. 4b) with respect to groundwater. Some sections of a stream may be influent, 

whereas other stretches of the same stream may be effluent. 

fore provides the greatest recharge capability and is preferred over an influent reach for 

optimum induced infiltration. 

Two types, influent and effluent are the most amenable to induced infiltration. A stream 

On the other hand, if water seeps into the stream 

An effluent reach of a stream there- 
31 

Ground surface 

Zero drawdown 

boundary -i Q 

Recharging 

Aquifer thickness should be 

very large compared to resultant 

drawdown near real well. 

Fig. 2. Representation of Image-Well Theory Applied to a 

Recharge Boundary (Perennial Stream). Sectional 

views of (a) a discharging well near a perennial 

stream and (b) the equivalent hydraulic system 

in an aquifer of infinite areal extent. From 

Todd (1967) (with permission). 
32 

Fig. 3. Idealized Sequence of Hydraulic Events Resulting in 

Induced Infiltration. From Rahn (1968). 
33 

Fig. 4. Relationship of Influent and Effluent Streams to Aquifer. (a) An 

influent stream loses water to an aquifer; (b) an effluent stream 

gains water from the aquifer because the water table is above the 

streambed. From Johnson Division, UOP Inc. (1975) (with permission). 

It is also important that the velocity of the surface stream be sufficient to prevent silt 

deposition from sealing the streambed. In river reaches where currents are low, or where flood 

flows no longer provide periodic scouring of the bed, silting can gradually reduce infiltration. 

CONSIDERATIONS IN THE DETERMINATION OF INSTALLATION SIZE 

The determination of the capacity of a Ranney Collector Well intake system requires an 

analysis of t.he hydraulic factors involved and a characterization of the proposed installation 

site. Such a characterization includes well drawdown and collector yield, and can best be 

determined by field pumping tests. 

RANNEY COLLECTOR WELL DRAWDOWN 

The flow pattern around Ranney Collector Wells is extremely complex. The thickness of the 

aquifer and the length, location, and number of laterals are important factors in determining the 

drawdown distribution around such wells. 

laid pipes of small diameter compared to aquifer thickness. Consequently, solutions for problems 

of flow toward collector wells can be obtained by treating the laterals as line sinks (Hantush 1964). 

Analytical solutions that describe the flow toward collector wells have been obtained and some of 

the results are presented in Figure 5. 

face of a lateral depends on the geometry of the collector well. In the case of a single lateral, 

this point occurs at the middle of the lateral. Computations in the drawdown equations show that 

this point approaches the face of the caisson of the collector well as the number of the laterals 

is increased (Fig. 5). For a well of four or more symmetrically located laterals, this point can be taken along one of the laterals at the face of the caisson. If the number of laterals in such a well is six or more, the same approximation can be made (Hantush 1964). 

Collector wells are partially penetrating horizontally 

The location of the point of maximum drawdown along the 

RANNEY COLLECTOR YIELD 

Under equilibrium conditions, collector yield is dependent on the following: aquifer 

thickness and transmissibility, infiltration rate of the streambed, water temperature, effective 

radius of the collector, and distance to the recharge boundary. 

by actual measurements or indirectly by field pump tests. 

discharge formula and an experimentally derived equivalent-well radius. The suggested value for 

the equivalent-well radius is approximately 75:: of the average lateral length in the collector 

well system (Hantush 1964). 

15 MGD, of which approximately 80-90;; is derived from surface water through induced infiltration. 

All can be determined directly 

The yield of a collector well is generally estimated by using the Dupuit-Forchheimer wellYields of Ranney Collector Wells are estimated to range up to 
34 

fc = rl 

rl= 011 

4.f = l0OI2 

b‘=41 

___Vertical well of depth = 41 

Fig. 5. Distance-Drawdown Variation in the Plane of 

Maximum Drawdown Due to the Collectors Shown 

in a Thick Aquifer. 

(with permission). 

From Hantush (1964) 

FIELD PUMPING TESTS 

Knowledge of the physical conditions of aquifers and of their hydraulic properties is 

essential in quantitative studies on collector yield. Determination of numerical values of the 

coefficients of storage and transmissibility permits evaluation of an aquifer as a source of 

water. 

through it. 

qualitatively significant only for hydrologic purposes. 

be obtained from aquifer tests by which the water-bearing materials are tested under natural 

conditions. 

These coefficients depend on factors characteristic of the aquifer and the water flowing 

Although various laboratory techniques are available, the numberical values obtained are 

More re1 iable (integrated) values can 

There are no specific rules that apply to all types of pumping tests. 

ducted under certain prevailing conditions which are seldom identical in any two tests. 

of the range of the variable factors involved, there is no substitute for the experience and 

judgement of qualified persons to conduct these tests. 

The analysis of data collected during a pumping test depends largely on the selection of 

the well-flow equation applicable to the flow system under investigation and on the degree to 

which the basic assumptions governing the applicability of the flow equation are in accord with 

the geologic characteristics of the aquifer being studied. Observed drawdown variations with 

time and distance from the pumped well may be interpreted in several ways if other supporting 

data, such as stream stage and water temperature, are not available. 

Analysis of stream flow data is necessary when low-flow periods may result in reduced 

infiltration recharge. Streams considered for a large-capacity Ranney Well intake should have a 

flow regime such that the withdrawal rate is no more than 15% of the 7-day-10-year low flow. It 

must be determined from low-flow duration and frequency evaluation whether there is sufficient 

storage available to supply the required withdrawal through the deficient period. 

be established that recharge is sufficient during high-flow periods to restore the water removed 

from storage. Otherwise the yield of the collector will steadily decline.. The most important 

aspect of collector design is basic understanding of the direct interaction of surface and 

subsurface conditions. 

Each test is conBecause 

It must also 

In collector design the most difficult factor to evaluate is whether the infiltration rate 

measured during the pump test is characteristic of average stream conditions or of some extreme. 

stream conditions, and the results compared before any production unit based upon induced infiltration is designed. 

Ideally, pump tests should be repeated during different seasons representing a variety of 

Because this is usually impractical, the pump test should be run during 
35 

- 

z 

* m 

the season when the surface stream is at lowest flow. During this period channel sedimentation 

and organic accumulation are at a maximum and infiltration is usually at a minimum. If it is 

not possible to run the pump test under known minimal conditions, then the reliability of the 

projection to minimal conditions is dependent solely upon the experience and reliability of the 

person performing the analysis. The collector installed will yield only in accordance with 

natural conditions. 

is expensive or otherwise particularly important. 

Since the pump test data are of such significance, it is generally necessary to use several 

observation holes, both onshore and offshore, in making the determinations. 

tions, driven well points are often most convenient and economical, although it may be necessary 

to correct observed drawdowns for partial penetration. The pumping well should be of sufficient 

size to accommodate the available pumping equipment. During pumping it is advisable to maintain 

the highest constant pumping rate possible under existing conditions. 

tinued at a constant rate until drawdown has stabilized in all observation holes. 

induced infiltration conditions are present, stability will usually be attained in less than 72 

hours of pumping. 

test repeated. 

recharged area. and time lags for high efficiency are short. 

Hence, detailed pump testing is necessary if the anticipated construction 

In shallow formaPumping should be conWhere good 

If stability cannot be attained, the pumping rate should be reduced and the 

In determining stability, adjustments must be made for changes in stage of the 

Where induced infiltration is good, the river efficiency of the wells is high 

A typical test pattern often used for obtaining the necessary data is illustrated in 

Figure 6. The two lines of wells, one perpendicular to the prospective recharge boundary and 

one parallel to it, will prove the existence of induced infiltration, if present, and will 

supply data for the determination of formation characteristics. 

points are screened approximately one foot beneath the soil-water interface to give direct 

information on the infiltration conditions through the streambed. 

Within the streambed, well 

A 

V 

RIVER0 PUMPING WELL 

0 OBSERVATION WELL 

V WELL POINT 

NOTE: Spacing of well 

points is optional. 

V 

'd m 

Fig. 6. Typical Pump Test Pattern. From Bennett (1970). 

Other factors that must be considered in analyses of pump test data include those listed 

below: 

- The average depth of water in the stream will decrease as the result of induced 

infiltration; this is the estimation of potential recharge. 

Provided the water table remains below the streambed, the least amounts of induced 

infiltration occur during extended dry periods when stream-flow and the temperature 

of the surface water are low. 

the average depth of water in the stream and the average width of the streambed for 

different stages of the stream during these periods. 

- 

Profiles of the stream channel can be used to determine 
36 

- An aquifer test usually is made at a pumping rate that is only a fraction of 

the planned capacity of a proposed well. 

Where the streambed is narrow, the depth of water in the stream small, and the 

infiltration rate low, the aquifer test at a low pumping rate may indicate a certain 

position of the recharge boundary which may be invalid for a higher pumping rate. 

At higher pumping rates, water may be withdrawn at a rate in excess of the ability 

of the streambed to transmit it; as a result, the water tab1.e may decline below 

portions of the streambed. 

pumped well as maximum infiltration occurs in the reach of the stream in the immediate 

vicinity of the pumped well, and the cone of depression spreads further up- and downs treani . 

- 

- 

In such a case the recharge boundary moves away from the 

REFERENCES 

Bennett, T. W. 1970. On the design and construction of infiltration galleries. Ground Water 

8( 3) 16-24. 

Johnson Division, UOP Inc. 1975. Ground Water and Wells. Saint Paul, Minn. 440 pp. 

Hantush, M. S. 1964. Hydraulics of Wells, pp. 281-432. In Ven Te Chow (ed.), Advances in 

Hydroscience, Vol. 1. Academic Press, New York. 

Rahn, P. ti. 1968. The hydrogeology of an induced streambed infiltration area. Ground Water 

6(3)21:32. 

Spiridinoff, S. V. 1964. Design and use of radial collector wells. Paper presented at the 

California Section Meeting, Sanitary Engineering Association, San Francisco, Calif., 

Sept. 26, 1963. 

Theis, C. V. 1935. The relation between the lowering of the piezometric surface and the rate 

and duration of discharge of a well using ground water storage. Trans. Am. Geophys. Union 

16:519-524. (As cited in Johnson Division, UOP Inc. [1975].) 

Todd, D. K. 1967. Ground Water Hydrology. John Wiley & Sons, inc. New York. 336 pp- 
AN ENGINEERING EVALUATION OF POROUS-DIKE 

INTAKE SCREENING SYSTEMS 

John C. Roberge 

h I den F'esearch Lebcraic.r.: 

torcester "0 I ztechn ic I rs: i tute 

3G Ehrewsbury Street 

ho I den, I:'assachuseits 'j l52C 

Abstract 

As one of many concepts currently under investigation for use in screenin9 fish 

and larvae from power plant intakes, the corous-dike sysier. presents unicue chat lenses 

to the designer and constructor. A complete understanding of the hydraulic losses . 

through such a struciure is necessary tc properly size and locaie the intake ar:d tc 

ensure proper pump selection and oerformance. 

In the study described in this report, an analogy iqith frictional losses ir. COPduits was employed, and empirical data on losses were determined for three sizes ef 

filter stone typical of the types used ir? the construc+ion of a porous-dib,e inTake 

system. -hese empirical data were corncared with additional information from the 

literature. The dependence of hydraulic losses throuah large-diameter media on stone 

shape and porosity were demonstrztec although no enpirical expression of this dependence 

was develcped. A hypothetical porous-dike intake installation was developed, demonstrating the fundamentai design considerations which must be made for such a structure. 

Finaily, a cursory economic cornparisor! of various intake screening systems derons-trated 

that the porous-dike intake concept was economically competitive with all others. 

INTRODUCTION 

The hydraulics of flow through porous media has been extensively studied in disciplines 

ranging from groundwater hydrology to coastal engineering. Of particular interest in the past 

decade has been the use of porous gravel structures in water intake screening systems. Conteptually, porous gravel dikes would allow a high intake flow rate through the structure at a low 

approach velocity, while blocking the passage of fish and other waterborne organisms into the 

intake. Knowledge of the energy loss through porous gravel structures is required for their 

design and construction, for both pump selection and dike stability. 

energy losses for various dike materials and flow conditions are presented in this paper and are 

compared with those in available literature. 

losses to indicate which parameters need further clarification and standardization. 

tion, an economic evaluation of a typical porous-dike intake facility is projected and a compari- son of this concept with other intake screening devices is presented. 

Experimental data on 

Analysis is made of factors governing energy 

In addiFLOW CONDITIONS THROUGH POROUS MEDIA 

Flow through porous media, using an analogy with flow in conduits, has been expressed as a 

relationship between a friction factor and a Reynolds number. 

dimensionless number expressing the ratio of inertial to viscous forces. 

through porous media, the Reynolds number is defined as 

The Reynolds number, IR, is a 

In analyzing flow 

IR = v d/v , (1) 

where v is the superficial average velocity determined from the volume flow rate per unit cross- sectional area perpendicular to the flow, d is the mean grain diameter (dS0) of the material, 

37 
38 

and >J is the kinematic viscosity of the fluid. 

Fanning,' is expressed as 

The dimensionless friction factor, as defined by 

(2) 

where Ah is the piezometric head difference over the flow length L, d is the characteristic 

diameter of the media (ds0), g is the gravitational acceleration, and v is the average flow 

velocity as defined above. 

The design of a porous gravel structure requires the preliminary selection of a nominal 

gravel diameter and average approach velocity, yielding the expected Reynolds number and thus 

characterizing the state of flow. A friction factor could be obtained from an empirical plot of 

friction factor versus Reynolds number for the chosen material, and a head loss could be c3lculated according to Equation 2, for a selected dike length. In case the effective dike length is 

related to the energy loss, an iterative solution is required. If the energy loss is excessive, 

a different material, approach velocity, and/or dike length may be selected. 

/ 

Investigations to date2-' have demonstrated a dependency of f on IR in the laminar flow 

range, while at higher Reynolds -numbers, the value of f tends toward a constant asymptotic 

value, independent of IR. While little agreement of the available data can be noted, generally 

these investigations have demonstrated the relative importance of media grading (porosity) and 

gravel shape in describing the resistance to flow. 

reflecting the dependence of the friction factor on the porosity of the media as well as on the 

Reynolds number. 

stone shape. 

flow resistance through porous media at high Reynolds numbers. 

Empirical expressions have been proposed6 

More recent investigations5 have recognized the less clearly defined effect of 

No universally accepted expression currently exists which completely describes 

QUARRY STONE MATERIAL PROPERTIES 

To supplement existing data on energy losses through porous media, and to evaluate such 

information for specific porous-structure materials, three quarry stone samples with nominal 

sizes of 8 cm, 20 cm, and 60 cm were evaluated. 

granite quarry blast, yielding rough and highly angular stones similar to those commonly used in 

small dike and filter bed construction. 

The samples were graded by standard screen sieve analyses, yielding the size gradations and 

The graded samples were taken from a typical 

distributions indicated in Figure 1. Porosity, e (defined as the ratio of the volume of voids 

to the gross volume of the sample), was evaluated for each sample by randomly dumping the test 

stone into a tank with a volume of 12 m3; weighing the tank and stone; filling the tank with 

water; weighing the tank, stone, and water; arithmetically determining the volume of water, 

which was equivalent to the volume of voids; and determining the ratio of the volume of voids to 

WEIGHT 1, PERCENTAGE, CUMULATIVE PASSED 

2? I 40 , 6? , 8p , 1y124 

0.33 

0.47 a 

0.67 ," 

0.95 - 

-1.35 

-1.91 + 

8 cm STONE, d50 = 4.55 cm -2.69 5 

-3.75 " 

I -60.35 cn 

Fig. 1. 

Quarry Stone Gradation (1 cm = 0.3937 in.) 

120.70 

100 80 60 40 20 0 

WE 1G HT PERCENTAGE, CUMULATIVE R ETA I NED 
39 

the known volume of the tank. 

Table 1. It should be noted that the porosity of such stone samples is dependent upon the 

placement of the stones as well as on the size distribution of the sample material. All samples 

were randomly dumped and allowed to settle naturally, both in the volume tank during evaluation 

of the porosities and in the test flume, approximately duplicating the typical placement of such 

material in the field. 

which resulted in denser packing of the stones after natural settling. 

The physical properties of the three samples are summarized in 

The quarry run sample contained a broader distribution of stone sizes, 

Table 7. Quarry Stone Properties 

Sampl e Nominal Diameter Mean Diameter, d5,, Standard Deviation Porosity, e 

8 cm 8 cm 

20 cm 20 cm 

Quarry run 60 cm 

4.55 cm 

12.45 cm 

25.65 cm 

1.32 cm 

2.95 cm 

14.17 cm 

0.49 

0.50 

0.44 

EXPERIMENTAL FACILITIES 

Tests were conducted in a rectangular steel channel approximately 18 m long, 2.4 m wide, 

and 1.8 m deep (Fig. 2), sized such that boundary effects were minimized through the test sec- tion. 

vertical pumps. Flow rates were metered by an orifice meter in the supply line and controlled 

by valves. The inflow water was discharged into one end of the channel, where it passed through 

a baffle screen flow straightener, which damped turbulence and swirl and generated approximately 

uniform flow through the channel. 

through a withdrawal line situated at the flume bottom at each end of the channel. 

flow rate and channel water depths could be controlled by valves located in the withdrawal 

lines. 

flow through the porous test section. 

piezometers located along the channel centerline at 30-cm intervals. 

Water flow through the channel was supplied from a water storage sump by a network of 

Water could be withdrawn from the test channel by gravity 

Withdrawal 

Windows were situated in the side of the channel to permit direct observation of water 

Head differentials and water depths were measured by 

Fig. 2. Test Facility 
40 

INSTRUMENTATION 

Total inflow rates were monitored by a calibrated orifice meter, 6 = 0.875. 

differential through the orifice meter was displayed by an air-water differential manometer and 

measured visually on a linear scale. The visual interpretation of the differential pressure 

display contributed to a variation and error in inflow rate measurements of up to 27.2%. These 

errors reflected additional errors of up to _+2.0% in the calculation of the superficial average 

velocity. 

meter (Fig. 3). 

centerline and across the channel, and approximately perpendicular to the flow direction. 

revolution of the propeller was sensed by a photo-electric cell and digitally displayed by a low-frequency analog counter. 

either continuous, instantaneous velocities or long-term, time-averaged velocities could be 

measured. 

The pressure 

Velocity profiles in the test channel were determined with a miniature laboratory propeller 

The meter was positioned at fixed intervals in the water column, along the 

The 

The period of the analog signal could be selected such that 

Fig. 3. Velocity Meter 

The meter and analog counter were calibrated before use in the laboratory tow tank. 

The accuracy of the velocity measurements was approximately ~4.0%. 

The 

results of each calibration yielded a plot of pulse counts (directly proportional to revolutions) 

per time period versus known speed. course of the study. 

These meter calibrations varied by less than 2.0% over the 

EXPERIMENTAL PROCEDURE 

The quarry stone samples were tested in two basic configurations: a trapezoidal section 

with upstream and downstream slopes of S = 1:1.5 and a rectangular section contained in a wire 

mesh gabion with vertical upstream and downstream faces (Fig. 4). The trapezoidal section was 
41 

Fig. 4. 

Test Configurations 

SLOPED DIKE CONFIGURATION 

L= AR EAabcd 

RECTANGULAR RECTANGULAR GAB ION CON F IG UR AT ION 

constructed by randomly dumping the test stone into the channel and hand-placing the face stone 

such that a 1:1.5 slope was achieved. An additional trapezoidal section of 20-cm stone with 

upstream and downstream slopes of 1:l was constructed and tested to determine the effects of 

variations in material volume on the friction factor for various inflow rates and approach 

velocities. A wire gabion with 3.8-cm mesh was used to contain the rectangular section, as 

depicted in Figure 5. 

Fig. 5. Rectangular Gabion 
42 

Velocity traverses (Fig. 6) of the channel were conducted to verify that the approach flow 

was uniform across the flume for both unobstructed flume flow and for flow approaching a porous 

dike. In a typical traverse using the miniature laboratory propeller meter, flow velocities 

were sampled at 30-cm increments across the flume width and below the water surface. The maximum variation of velocity with respect to the mean channel velocity was generally less than 25% 

for traverses at the upstream face of the rectangular dike test section and less than 5% for 

flow in the unobstructed channel. 

.--- 

GAB ION CON FIG URATl ON 

Fig. 6. 

Velocity Profiles 

DIKE CONFIGURATION 

The water inflow rates and the upstream approach depths were selected in a manner that 

would insure a broad range of approach velocities and Reynolds numbers for flow through each 

material tested. Approach velocity and Re nolds number limits ranged from approximately 1.5 to 

adjusting a control valve in the flume supply line at the beginning of each series of tests. 

Water flow rates were monitored on a conventional air-water differential manometer. Upstream 

approach depths were varied by adjusting the flume discharge valve, yielding several different 

approach velocities for each inflow rate. A period of time, typically one hour, was required 

for establishment of water depth equilibrium. Approach and withdrawal depths did not vary by 

more than 0.03 cm for the duration of any single test. 

piezometers located along the channel centerline were read and water depths were recorded. 

water temperatures were recorded for each test, affording the means for proper determination of 

kinematic viscosity and Reynolds number. 

stream face, Va, and the effective flow length of dike test section, L. 

of data for the trapezoidal test sections, an equivalent test length was calculated based on a wetted area defined by the trapezoid abcd shown in Figure 5. 

be defined in terms of the dike crest width, the dike height, the dike face slope, and the depth 

of ffow at the upstream face of the dike. 

The equivalent test length is reduced to the crest width as the dike face slope becomes 

steeper (S -f 0), resulting in a rectangular section equal to that of the experimental rectangular gabions. 

75 cm per second and 1.5 x lo3 to 3.0 x 10 i , respectively. A flow rate was established by 

Once equilibrium was established, 

Sump 

Friction factor calculations were based on the average approach velocity at the dike upTo ensure compatibility 

The geometry of the trapezoid can 

EXPERIMENTAL RESULTS AND EVALUATION 

HEAD LOSS RESULTS 

Figures 7 and 8 depict typical hydraulic gradelines produced by flow through the quarry 

stone test sections. Data on head losses through the various dike configurations and quarry 

stone sizes are presented as a plot of friction factor, f, versus Reynolds number, IR, in Fig- ure 9. The gradations of the quarry stone test samples and the flow velocity range over which 

the tests were conducted resulted in Reynolds numbers that extend from the transition phase Of 

laminar to turbulent flow into the range of fully turbulent flow. 

from IR for increasing values of IR is graphically demonstrated by the asymptotic curves, which 

approach f values of 12 for the 8- and 20-cm stone sizes, and 60 for the quarry run test stone. 

The greater independence of f 
43 

The relative positions of the data curves correspond to the decrease in porosity, or increase in 

size distribution, of the stone samp'les. 

. ., -..- 

Fig. 7. Hydrdulic Gradeline through Sloping Dike 

Data from the present test series are compared to published data in Figure 10. The rubble 

data4 were for rough, angular stones with a porosity of approximately 0.4, with diameters ranging from 1 to 3.4 cm. 

porosity with diameters ranging from 0.18 to 1.6 cm. are located in the lower range of f values defined by these two rough, angular samples. 

stream gravel tests2 were for smooth washed gravel with a porosity of 0.38 and dS0 = 4.32 cm, 

yielding a limiting value of the friction factor of approximately 3.0. The 8-cm quarry stone 

tests (e = 0.49) yielded a considerably higher friction factor than the 8-cm stream gravel 

(e = 0.38), indicating that the effect of stone shape in flow resistance is considerably more important, and can even overshadow the effect of porosity. These tests empirically verified the 

dependence of f on stone shape. It was, therefore, evident that stone shape and porosity affect 

the value of the friction factor. If the relative degrees of roughness of various stone samples 

were identical, plots of f versus IR would be sensitive only to porosity. 

the porosities were identical, f versus 1R would be sensitive only to stone shape. 

average stone diameter changes only the Reynolds number. Therefore, if both stone roughness and 

porosity are constant, a plot of f versus IR should be a single line, irrespective of stone size. 

This was verified by the data shown in Figure 9 for the 8- and 20-cm stones, and probably for 

the three stream gravel samples] shown in Figure 10. 

Figure 10 for the various investigations can, therefore, be attributed to variations in porosity 

and stone roughness. Future investigators should take sufficient measurements to quantify these 

controlling parameters. 

the 20-cm test stone were not significantly affected by variations in volume of dike material. 

The friction factors for the same Reynolds numbers for the three dike configurations were in 

The gravel and coal data7 represent rough angular material of unknown 

The 8- and 20-cm quarry stone test results 

The 8-cm 

On the other hand, if 

A change in 

The scatter of the data presented in 

Test results for the rectangular and sloped (S = 1:1, S = 1:1.5) dike configurations for 
44 

Fig. 8. Hydraulic Gradeline through Rectangular Dike 

10 20 cm STONE, D50 = 12.45 crnm 

Fig. 9. 

Results of Experiment (7 cm = 0.3937 in.) 
45 

agreement with one another; therefore no distinction or consideration of test section shape was 

required. 

I I 1 r2- 

f Fig. 10. 

Energy Loss for Flow through Porous 

Media (1 in. = 2.54 cm) 

VELOCITY OBSERVATIONS 

Upstream velocity traverses verified that approach velocities remained uniform immediately 

downstream of the flow-straightening baffles to within 15 cm of the upstream dike face. Velocity traverses approximately 15 cm downstream of the back face of a rectangular test section and 

the sloped dike test section indicated regions of jet-like flow. Jet formation, caused by local 

variations in porosity of the dike material, resulted in velocity gradients with variations of 

up to 600% greater than the average downstream channel velocity for all stone sizes. 

porous dikes. Excessive flow velocities and head drop through the 8-cm stone dike resulted in 

scouring of the downstream dike face and subsequent failure of the entire structure (Fig. 11). 

The 20-cm and quarry run dike structures demonstrated relatively greater stability at the higher 

velocities; no slope failure was observed. 

Jetting discharge from the downstream dike face should be a consideration in the design of 

SUMMARY OF LABORATORY STUDIES 

Experiments were conducted to measure energy loss through various porous dike materials that 

may be used in field applications for screening water intakes. 

out with stone sizes and flow rates which produced higher Reynolds numbers than in previous 

investigations, and demonstrated the independence of the friction factor from the Reynolds 

number in the fully turbulent flow range. The following conclusions may be drawn from this 

These experiments were carried 

study. 

1. 

2. 

3. 

4. 

5. 

For turbulent flow, the friction factor is affected primarily by stone angularity and 

secondarily by the porosity (related to size distribution) of the sample. 

The characteristic stone size is not an important parameter by itself, if the- shape 

and porosity are constant, and affects only the Reynolds number. 

The shape of the dike is not important, if the effective flow length can be adequately 

described. 

Stability of the downstream dike face is an important design parameter. 

head drop or flow velocity can cause slumping of the dike material. 

Velocity distribution of flow at the downstream face can be highly irregular due to 

local variations in porosity. 

Excessive 
46 

Fig. 11. Slope Failure of 8-cm- (3-in.-) Stone Dike 

HYPOTHETICAL POROUS-DIKE INTAKE SCREENING SYSTEM 

For a full appreciation of the scope of engineering required for the installation of a 

porous-dike intake screening system, a hypothetical installation was evaluated. Typically, 

large modern power stations maintain relatively high cooling water demands--on the order of 

60 m3/s. 

thus present a potentially detrimental effect to that water system either in the vicinity of the 

cooling water intake or at the discharge location. 

water. For the purpose of this example, several site assumptions were made, including those 

listed in Table 2. 

is inherent in this screening system. 

as the principal filter bed materia?. 

Such facilities are therefore comnonly constructed near large sources of water and 

Figure 12 depicts a typical power plant installation situated on a semiprotected body of 

The assumption that the porous-dike system is an effective biological filter 

In addition, the 20-cm stone (dS0 = 12.45 cm) was chosen 

Table 2. Hypothetical Plant Site Conditions 

Water depth at the intake 7m 

Tidal range lm 

Storm surge lm 

Significant wave height 1.5 m 

Cooling water demand 60 m3/s 
47 

_--- - *-- 

NTAKE STRUCTUR 

17 

/ 

, DIFFUSER , 

Fig. 12. Typical Power Plant Installation 

The foremost concern of the design engineer is the stability of the porous dike structure 

under expected tidal and surface wave effects. Structural stability can be assured by properly 

armoring the dike face. Hudson specifies design guidelines for flexible coastal structures. 

Employing Hudson's empirical design for the stated parameters results in a multi-layered breakwater design which employs the 20-cm filter stone as the core and base of the structure. 

Figure 13 depicts a dike section typical of that which would be required at the hypothetical 

location. However, loss through the underlayers is significant, and can be determined for various flow conditions from the empirical data 

devel oped above. 

Energy loss through the 500-kg stone is negligible. 

i 

1 OM 

30M 

Fig. 13. Section of Typical Porous Dike 
48 

For this example, the minimum allowable depth at the intake port was established at 5.0 m. 

At mean low water, the water depth at the intake site is 7.0 m, therefore permitting a maximum 

loss of 2 m through the proposed dike section. 

for the stated conditions can be directly determined from Equation 2. 

depth of 7.0 m on the upstream face of the dike, a maximum approach velocity of 6 cm/s, and ai 

required intake flow rate of 60 m3/s, the required circumference of the dike was determined to 

be 150 m. To minimize the volume of stone material required, the dike was arranged in a circle 

with a radius of 25 m. 

A maximum achievable approach velocity of 6 cm/s 

Thus, with a minimum 

The proposed intake installation is depicted in Figure 14. 

Fig. 14. 

Layout of Proposed Porous Dike 

Intake Facility 

l---*O METERS 

c 

The placing of any structure in the aquatic environment is a formidable and expensive task. 

A porous-dike intake system, such as that proposed above, would require a large source of quarry 

material in addition to extensive capabilities for waterborne placement of these materials, 

includine ocean-going barges, cranes, and service boats. While the cost of installing such a structure is highly dependent upon local labor and material supplies, this proposed installation, based upon current rates in the New England area, would require approximately $200,000 for 

the purchase and delivery of filter material and armor stone'and approximately $1,000,000 for 

machinery and labor to construct the porous dike structure. 

porous-dike intake screening system is, therefore, approximately $1 -2 million. This estimate 

does not include the cost of pipe, pumps, tunnels, etc., and therefore reflects only those costs 

which would be required for an effective biological screening system. 

The total cost of the hypothetical 

In those installations requiring Class 1 safety-related features, additional construction 

costs undoubtedly would be incurred. 

automatically in the event that the dike failed due to fouling or clogging, would be installed 

in the structure and would require an additional outlay of up to $1.5 million. 

For instance, emergency gates, which could be opened 

The porous-dike screening concept is proposed as an a1 ternative to currently accepted 

methods of biological screening for industrial water intakes. Richardsll describes several of 

the screening techniques now employed, including placement of velocity caps over vertical offshore water intakes to induce horizontal approach flow to the intake; flush-mounted and angled 

screens to dissuade fish from approaching an inlet; perforated-pipe inlets which eliminate the 

need for screens and trash bars; and a radial well intake which employs a porous aquifer as the 
49 

filter. All such screening systems require extensive structural works and sizable financial 

outlays. For example, a typical intake water system for a power station situated in the coastal 

zone would include three offshore submerged intakes with velocity cap structures affixed and a 

screenwell structure housing a series of traveling vertical screens. The projected cost of the 

velocity caps and the screenwell would be in excess of $4 million. Somewhat less elaborate and 

like the porous-dike concept, yet to be proven in the field, is the angled screen concept with a 

bypass flow which carries fish and waterborne organisms away from the intake. . Including fish 

handling facilities, such an installation would cost approximately $3 million. 

The biological performance of any one of the above systems is not completely defined. However, cursory economic analysis of the various systems does indicate that the porous-dike screening concept is economically competitive. 

structure at the New England Power Company's Brayton Point Station will not only demonstrate the 

biological effectiveness of the concept, but will lend significant insight into the long-term 

costs of operation and maintenance. Field installation, under typically and carefully monitored 

conditions, of all practical screening concepts will contribute significantly to an understanding of the biological, hydraulic, and economic performance of the various systems. This understanding will enable the design engineer to make competent and justifiable decisions for the 

installation of any 'screening device. 

A proposed field installation of the porous-dike 

CONCLUSIONS 

The porous-dike intake screening system is one of many concepts currently being evaluated 

for use as a fish and larval exclusion system. 

through porous structures were conducted in preparation for the field evaluation for the porousdike concept at the Brayton Point Station. 

Preliminary hydraulic investigations of flow 

A hypothetical porous-dike installation was described 

and 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

several general conclusions can be drawn from this discourse. 

1. Empirical design techniques for the design of large porous structures are available 

and are currently being refined. 

The porous-dike screening concept is economically competitive with other exclusion 

sys terns. 

A comparison of the various screening concepts operating under carefully monitored 

field conditions is required to gain a more complete understanding of their relative 

engineering feasibility, biological performance, and cost effectiveness. 

2. 

3. 

REFERENCES 

Bear, J. 1972. Dynamics of Fluids in Porous Media. 

Inc., New York. p. 604. 

Bell, M. C., R. E. Nece, and R. G. Porter. 1974. A 

of a Permeable Dike as a Fish Barrier. Prepared for 

Michigan. 30 pp. 

Kamel, A. M. 1969. Water Wave Transmission Through 

Structures. U.S. Army Engineer b!aterways Experiment 

Mississippi. 27 pp. 

American Elsevier Publishing Company, 

Report on the Laboratory Examination 

Consumers Power Company, Jackson, 

and Reflection by Previous Coastal 

Station, Corps of Engineers, Vicksburg, 

Kondo, H., and S. Toma. 1972. Reflection and Transmission for a Porous Structure, 

pp. 1847-1865. In Proceedings of the Thirteenth International Conference on Coastal 

Engineering, Vancouver, Canada, July 1972. 

Nece, R. E., E. M. Wilson, and D. C. Millns. 1970. Head Losses in Gravel Packs. Civ. 

Eng. Public Works Rev. 65(773):1466-1467. 

Rose, H. E. 

lar materials. Proc. Inst. Mech. Eng. 153:141-148. 

Ward, J. C. 1964. Turbulent flow in porous media. Proc. Am. SOC. Civ. Eng. 3. Hydraul. 

Div. No. HY9. pp. 1-12. 

Richardson, J. G. 1945. Flow Through Porous Media. in V. L. Streeter (ed.), Handbook of 

Fluid Dynamics. McGraw-Hill, New York. p- 1614. 

1945. An investigation into the laws of flow of fluids through beds of granu- 
50 

9. Nece, R. E., and M. C. Bell. 1973. Hydraulics of a gravel core fish screen, pp- 31-39. 

- InProc. 21st Annual Hydraulics Division Specialty Conference. 

Engineers. 

American Society of Civil 

10. Shore Protection Manual, U.S. Army Coastal Engineering Research Center, Fort Belvoir, 

Virginia, 1973. 955 pp. 

11- Richards, R. T. 1977. Fish Screening - The State of the Practical Art, pp.'296-303. &I 

Hydraulics in the Coastal Zone. 25th Annual Hydraulics Division Specialty Conference, 

Texas A&M University, Aolerican Society of Civil Engineers, College Station, Texas, August 

1977. 
BIOLOGICAL ASPECTS OF POROUS-DIKE INTAKE STRUCTURES 

Bradley P. Schrader and Barry A. Ketschke 

New England Power Service Co. 

20 Turnpike Road 

Westborough, Massachusetts '01581 

Abstract 

Current knowledge is reviewed on the potential for both adult and larval exclusion with a porous dike. It is shown that exclusion is possible, given small enough 

filter material. In addition, limited observations show that some adult and larval 

fish wilt avoid a porous-dike intake, thereby suggesting that dikes can also act as 

behavioral barriers. Information on fouling and clogging of porous dikes is reviewed, 

and proposed anti-fouling techniques are discussed. Data are too limited for prediction of flow restrictions due to fouling; however, it is shown that fouling is not 

a problem when large filter material is used in the dike. 

To determine the feasibility of a porous-dike intake, a pilot-scale field experiment is proposed. The proposed in-situ test facility, to be installed in Mount Hope 

Bay, Mass., is described. Plans to assess the exclusion capability and fouling rates 

of several dike materials are presented. A parallet laboratory program of larval 

behavioral studies is described. Results of this study are expected in 1981. 

INTRODUCTION 

The porous dike is being considered as one possible means of larval exclusion at power 

plant cooling water intakes. It' resembles a breakwater surrounding a cooling water intake. 

Unlike a breakwater, however, a porous dike would have a cobble or gravel core to allow relatively free passage of water while presenting a physical and behavioral barrier to aquatic 

organisms. Figure 1 is a conceptual view of a porous-dike intake system, showing a dike cross section and a conceptual layout for an onshore intake. 

surrounding an offshore intake is also possible. 

achieve any desired approach velocity, simply by adjusting its exposed surface area. 

approach velocities. 

Intermediate filter material, probably in the gravel-to-cobble size range, may be small enough 

to effect larval avoidance without quickly fouling and clogging. 

A porous dike application completely 

A porous-dike intake is easily sized to 

.The porous dike concept is attractive because it may achieve larval avoidance at low 

This would obviate the need for larval collection and return systems. 

FILTERING AND FOULING IN POROUS DIKES: CURRENT KNOWLEDGE 

POTENTIAL FOR FISH AND LARVAL EXCLUSION 

Two exciusionary mechanisms are expected to operate in a porous-dike intake. Physical 

exclusion will occur because nothing larger than the pores in the dike will be able to pass 

through. 

through the pores may choose to avoid the dike. 

Behavioral exclusion is also likely to occur, as'some organisms which could fit 

Several formulae are available for predicting physical exclusion of fish by a porous barrier. 

f rom Bel 1 (undated) : 

The following equations for screen-mesh sizing are quoted by Sonnichsen et al. (1973) 

M = 0.04 (L - 1.35)F if 5 5 F 5 6.5, and 

M = 0.03 (L - 0.85)F if 6.5 I F 5.8.0, 

51 
52 

SECTION OF POROUS DIKE 

-.~r.. INTAKE CANAL ~ C., 

Fig. 1. Porous Dike Intake Screening Structure. By permission 

of the Alden Research Laboratory. 

where M = maximum screen mesh opening in inches, 

L = length of fish in inches, 

D = fish body depth in inches, and 

F = L/D = fineness ratio. 

Because these equations are derived from a small data base, they should be used only as rough 

guides. 

slightly larger openings than permitted by Bell's equations may be adequate. 

For comparison, Sonnichsen et al. also present data by Kerr (1953) which suggest that 

Fisher et al. (1977) found that a screen opening 2-3 m smaller than the mean body depth of 

juvenile king salmon (hcorhynchus tshmJytscha) was required for physical exclusion. 

design rule could be combined with available body depth-fork length relations to provide a basis 

for assuring physical exclusion of various species and age classes. 

was ascertained by Nece and Bell (1973), who cite Yalin and Franke (1961): 

This 

The range of pore sizes present in a porous dike, for a bed of uniform-diameter spheres, 

d = 0.1550 (assuming tightest possible packing), and 

.d = 0.414D (assuming the loosest packing), 

d = the maximum diameter circle which can be inscribed in a pore and 

D = the diameter of bed particles. 

where 

In practice, a porous dike will incorporate a distribution of rock sizes, resulting in lower 

porosities than predicted above for uniform rock size. Nevertheless, by using the median rock 

size (D50) in the above equations, one can estimate the range of pore sizes in a dike. 

exclusion of larvae would require a fine filter material. 

larvae 25 mm long would require a maximum pore size of about 4 mm, necessitating a filter material 

with a median diameter of about 3 an. filter stone (DS0 = 4.5 cm) could be expected to physically exclude any larvae and juveniles 

larger than 7 mm body depth (approximately 35-45 mm long). 

Based on the above relations, a porous dike designed to operate entirely via physical 

For example, exclusion of king salmon 

Conversely, a dike constructed of standard 7.6-cm (3-in.) 
53 

In addition to the physical obstruction presented by a porous dike, there is a small amount 

of theory and experience to suggest that avoidance of a porous dike may also occur. Such behavioral exclusion would enhance larval and post-larval exclusion beyond the levels predicted on 

the basis of physical exclusion alone. 

substrate (thigmotropism), and velocity gradients (rheotaxism) (Vernberg and Vernberg 1972). 

These behavioral responses are expected to cause some species to avoid the dark, rocky interstices of a porous dike; however, this avoidance reaction is predictable only in isolated instances 

Fisher et al. (1977) show that shad (AZosa sapidissirnu) and striped bass (.'.?:>Fsjzc sazutil~s) will 

avoid a screen mesh large enough to permit passage; on the other hand, king salmon (0izcorhyi:chus 

tsbytscha) aggressively attempt penetration. 

In any case, to allow juvenile and adult fish avoidance where it is attempted, the proposed 

approach velocities at the porous dike face (7.5-15 cm/s) are lower than the swimming speeds 

of most species (18-110 cm/s) (New England Power Company 1976). 

Avoidance by larval fish may be possible at the lowest proposed approach velocity (1.5 cm/s). 

Barker et al. (1977) measured the swimming endurance of larval American shad (-ilnsa sap~dissiira) 

in a swim speed chamber. 

of 2.4 cm/s (0.1 fps) for approximately 1 min and against a current of 6.6 cm/s (0.2 fps) for 

21 sec. These are average endurance values; the individual observations show considerable 

scatter. 

increases its swim speed capability. Differences of 1 or 2 mm in length may have dramatic 

effects on swimming response. 

tive locomotive ability early in its larval period. on a species-by-species basis the necessary approach velocity to allow larval fish to perceive 

and avoid an intake current. 

Juvenile and adult fish are known to orient in response to light intensity (phototropism), 

They found that 11-mm shad could maintain their position in a current 

Barker et al. also confirm that as a fish develops from an egg to an adult, it quickly 

These results strongly suggest that a fish may acquire an effecHowever, at present we are unable to predict 

These results also point out the limited endurance of larval shad. The porous dike may 

In this way, a larval fish exposed to a porous dike will have 

offer a solution to the limited swimming endurance of the larvae by providing a matrix of 

exposure and sanctuary areas. 

many opportunities to rest between swimming episodes. 

expectation of larval avoidance behavior. These include casual observation of 1 arval winter 

flounder (PseudopZeuronectes mericanus) in rearing tanks, and the difficulty in sampling larval 

fish with a pump. 

observed in the laboratory on several occasions. Newly hatched larvae exhibit little, if any, 

swimming ability, but as yolk-sac absorption proceeds, swimming ability increases. 

flounder at this stage often swim in the vertical plane. Following yolk sac absorption and the 

beginning of exogeneous feeding, swimning ability is quite pronounced as the animals frequently 

dart after food. 

capture many individuals even when large numbers of larvae are present. This perhaps is due to 

the avoidance by larvae of the velocity field induced by the pump suction. 

on exclusion performance. 

at the Wisconsin Electric Service Company's Lakeside Plant on Lake Michigan. 

penetrated the large void spaces of the dike; nevertheless, a recent assessment of the dike 

suggests that it "effectively limits accessibility of fish to the Lakeside intake" (Wisconsin 

Electric Power Company 1976). 

entrainment. 

and juvenile pink salmon (hcorkynchus gorbusehu) from a rapid sand filter of 4-mm-diameter 

particles. Marine Research, Inc., (1975) reports partial success in filtering zooplankton with 

a full-scale gravel-core dike. In two separate samplings one month apart, they found 95 and 

997; reductions in bivalve larvae, 74 and 100% reductions in gastropod larvae, and 67 and 901.' 

reductions in copepod nauplii. However, other taxa showed unexplained density increases on the 

downstream side of the dike. 

In addition to the above-cited work on larval shad, our personal observations support the 

Winter flounder reared from gametes stripped from mature fish have been 

Larval 

Additionally, attempts to sample fish larvae with a small pump often fail to 

Laboratory and field experiments on porous dikes generally support the above speculations 

A full-scale porous dike of large (0.2-0.5 m) rubble stone is operating 

Numerous fish have 

Fine sand and gravel filters have proven to be'effective in reducing larval and zooplankton 

Stober et al. (1974) report 700:;. success in excluding mysids (komgsis awatzc;zcizts) 

Nece and Bell (1973) report the performance of an intermediate filter material, 7.6-cm 

(3-in.) gravel (D50 = 4.3 cm). Using a section of gravel 30 cm (1 ft) long inserted into a narrow (30-cm) laboratory flume, penetration tests were done with juvenile rainbow trout (2.5- 

3 cm) and juvenile chinook salmon (5-8.5 cm). After a 20-hour exposure to a 5.8-cm/s (0.2-fps) 

approach velocity, 60% of the exposed rainbow trout remained upstream of the filter. Since the 

mean body depth of the fish was less than the calculated pore size, this result strongly suggests 

behavioral exclusion. A half-hour exposure to roughly the same conditions showed 922 retention 

of exposed fish. 

intake and suggests that a full-scale porous dike might achieve an acceptable exclusion rate in 

the field. 

This shorter exposure time is more characteristic of an unconfined, open-water 
54 

In summary, the limited data on fish behavior and on rock filters suggest that a porousdike intake may achieve a useful combination of physical and behavioral exclusion of fish. 

However, there are very limited data on porous dike performance under field conditions, and no 

data yet on larval exclusion capabilities. 

POTENTIAL FOR FOULING 

In any locale, a porous dike will present a fresh, bare substrate for settlement by the 

typical rocky intertidal and sub-tidal communities of the area. Colonization, growth, and 

ecological succession will occur until eventually a stable community develops. The growth of 

this fouling community will result in increased flow resistance (head loss) through the dike, 

which must be accounted for in the initial design. 

The analytic basis for predicting fouling levels is provided by theories and experiments 

on colonization and succession in rocky intertidal and subtidal environments. These results 

suggest that the fouling community may begin to stabilize within two years 3f dike construction 

(Connell 1972; Brown and Moore 1977). 

structure within a dike (where light and algae are absent), nor have they addressed the special 

condition of continuous slow unidirectional flow present in a porous dike. Furthermore, it 

would be extremely difficult to relate a species abundance prediction to a hydraulic head loss, 

were such a prediction available. 

However, these studies have not addressed the community 

In the absence of quantitative fouling predictions, a few speculations about the fouling 

process seem justified. These hypotheses, derived from basic littoral ecology combined with 

experience in power plant cooling systems, are offered as a starting point for analyzing and 

combatting the fouling process. Fouling is likely to be most severe on the dike face in the 

photic region of the subtidal zone, where attached algae growth will be most dense. In the dike 

interior, flow resistance will be caused primarily by a seasonal bryozoan (e-g., TLlhlEu~ia sp. ) 

or by attached bivalves, both commonly observed in power plant cooling systems. Predation is 

not expected to exert significant control on the fouling community, nor are flow velocities 

through the dike expected to be high enough to retard settlement of fouling organisms, nor is 

food expected to limit growth. 

Actual experience with rock filters in nature confirms that, given a large enough filter 

material, fouling growth can establish a stable level without causing an intolerable resistance 

to flow. Large rubble-stone breakwaters in Florida and Rhode Island show complete permeability 

after many years of operation (Roberge 1978; Anderson 1977). The rubble-stone porous dike at 

the Lakeside generating plant, mentioned previously, has shown no increase in flow resistance in 

over fifty years of operation (Wahtola 1977). 

Merced River did not foul in three years of operation (Menchen 1975). 

A porous dike of large cobble on California's 

In contrast, filters using sand or other fine media have experienced significant fouling 

problems. Stober et al. (1974) report serious fouling of filters, in the absence of corrective 

action. Ray et al. (1976) report that the Pennsylvania Power Ccmpany has encountered similar 

fouling problems with an infiltration system at the Montour power plant. 

Based on these results, one approach to the fouling problem is to design a porous dike with 

large enough filter material to avoid possible flow restrictions. 

fouling levels are not yet accurate enough for design purposes; however, proposed research 

(described below) will improve this predictive capability. 

rock filters; however, several possible techniques are under consideration: 

Present methods to predict 

Fouling control may also be effective. No research has been done on fouling control in 

- Backwashing with ambient water 

Backwashing with heated water 

- Backwashing with chlorinated water 

- Continuous low-level chlorination of inflowing water 

- Mechanical rejuvenation of the gravel core by overturning it 

- Replacement of isolated core sections 

Each scheme has its own disadvantages. 

avoid channeling all flow through one clear area. 

regulatory restrictions. , 

expensive and complicated. The most relevant results to date on this subjec are the experiments by Stober et al. (1974), who evaluated the first four options in this list on a model 

rapid sand filter and found that backwashing with heated water was the most effective method. 

than clogging by attached growth. Chronic, low-level accumulations of debris are expected to 

concentrate in the intertidal region, causing minimal head loss. Siltation can be prevented by 

Any backwashing must carefully equal ze backwash flow to 

Rejuvenation or replacement of core sections would be relatively 

Discharges of heat and ch orine entail special 

Clogging of the dike by suspended debris appears to present a less serious cleaning problem 
55 

proper siting and engineering of the dike. 

weed, may or may not be a problem; because approach velocities will approximately equa: ambient 

current velocities, natura7 flushing may prevent serious clogging. If necessary, it wculd be 

possible to sequentially isolate and backflush invididual subsections of the dike, if such provisions are made in the dike design. 

Acute seasonal clogging, e.g., by jellyfisi and seaA PROFOSED RESEARCH PRGGRAM TO DEVELOP AND EVALUATE THE POROUS DIKE INTAKE 

The feasibility of the porous dike intake depends on two basic considerations: exclusion 

The two objectives of a proposed three-year program to develop and evaluate the porous 

of a significant proportion of larvae and reliabifity in supplying cooling water to the power 

plant. 

dike intake are: 

- To quantify under natural conditions the effectiveness of porous dikes of various ED%- 

positions in excluding zooplankton, fish larvae, and post-larval to adult fish. 1r.herent 

in this evaluation is a measurement of potential organism attrition in the dike itself. 

- To quantify the level and composition of fouling and/or clogging of the dike on a seasonal 

basis. 

To achieve these objectives, a field-testing facility would be constructed and used for sit^. 

experiments. A parallel set of laboratory experiments on larval behavior and swimming a;ility 

is also planned. 

DESIGN OF FIELD-TEST FACILITY AND FOULING STUDIES 

A field-test facility would be installed at Brayton Point Station, a 15OO-P.lWe fossi7-fueled 

steam-electric power plant owned by the New England Power Company (a New England Power Service 

Company affiliate). 

Narragansett Bay (see Fig. 2). 

discharge channel dike (see Fig. 3). 

dike test facility. 

The station is located on Mt. Hope Bay, an estuary comprising an ami of 

The field test facility would replace a section of the existing 

Figure 4 is an artist's conception of the proposed porous 

Fig. 2. General Location of Brayton Point Generating Station 
56 

c1 

u) 

W 

IW 

Y 

.r 

n 

L 

0 

YS 

03 

7 

n 

aJ 

c1 

v) 

V 

W 

u) 

0 

0 

L 

.r 

n 

a 

m 

0, 

U- 

.r 
57 

Fig. 4. Artist's Conception of Proposed Test Facility 

The interior of the test facility would allow flexibility in experimental arrangements. 

The plans in Figure 5 show the proposed initial experimental setup, which would employ test 

chambers separated by impermeable dividers. Two test chambers would contain rock filters of 

7.6- and 20-cm (3- and 8-in.) stone, respectively; the center chamber would act as an unfiltered 

control section (required for the field tests of screening performance). Size distributions for 

these and one other test material are shown in Figure 6. Water would flow from Mount Hope Bay 

through each chamber and would be pumped by a single pump into the existing discharge channel. 

Flow rates through each chamber would be controllable by separate weirs at their downstream 

onds, providing the flexibility to test approach velocities between 1.5 and 15 cm/s (0.05 and 

3.5 fps). 

The rock filters would be constructed using easily removable gabions (large wire-mesh cages 

filled with rock); this would allow convenient exchange of filter rock, if tests on other filter 

naterials are desired. 

)f each rock-filled chamber, sampling slots would be built into the rock fill (typically between 

jabions). 

lets required for impoundment tests. 

To allow sampling at intermediate 'locations along the longitudinal axis 

Iron framework would be provided at the upstream end of the facility to support the 

Work in this phase of the study would quantify the growth rate of fouling organisms as a 'unction of time of year, depth, species, and rock type, and would relate fouling levels to flow 

.esi stance. 
58 

8.7 I 

8 HOIST 

PORTS 

N 

\ 

EXISTINO 

CHANWEL 

BOTTOY 

CL77.0 

_. 4- 

I 

1.900'1 TO END 

OF DISCHARGE 

CHANNEL, 

\ 

I 

I 

I 

f 

SCALE OF FEET 

nl 2- 10 20 

Fig. 5. Porous Dike Test Facility for Brayton Point Generating Station 

Water from Mount Hope Bay would be pumped through the test chambers at 0.03 m/s (0.1 fps) 

continuously for two years, to stimulate maximum fouling growth. 

filter rock suspended in coarse net) would be hung on the upstream and downstream interfaces. 

Eight fouling bags would be set out initially at each end; one would be removed from each end 

every three months, representing the total accumulated growth since startup. 

of the samples would include identification of the organisms, the biomass accrual, and an estimate 

of the percentage decrease in the interstitial void space. 

Fouling bags (small samples of 

Laboratory analysis 

Head loss measurements would be taken regularly throughout the study for each filter 

material. 

be computed and correlated with observed biological growth. 

filter section appeared to be severely clogged, it would be removed and replaced with an alternate 

test material. 

of the fouling community. 

From these data, changes in the hydraulic friction factor (f) for each material would 

If from head loss measurements a 

A portion of removed material would be carefully disassembled to allow analysis 
59 

SIEVE OPENING, INCHES 

0 

10 

20 

30 W 

2 

L 

k 40 

50 

60 

70 

80 

90 

1 00 

Fig. 6. Gradations of Quarry Stone (1 in. = 2.54 cm). By permission of the Alden 

Research Laboratory. 

LARVAL CULTURE AND BEHAVIORAL STUDIES 

In preparation for larval exclusion studies under field conditions, information on the 

behavior and escape capabilities of larval fish relative to a porous dike structure would be 

gathered under laboratory conditions. Different species of larval fish would be reared in a 

laboratory facility, and their escape capabilities in relation to such parameters as size, water 

speeds, and temperature would be evaluated. 

An indoor larval culture facility would be established at the Canal Electric Plant (New 

England Gas and Electric Association, Sandwich, Mass. ). 

holding tanks, heating systems, and food necessary for larval culture. 

from their gametes. 

would be given to the species for which information on larval culture is available and which 

appear to be particularly vulnerable to entrainment; e.g., winter flounder, menhaden, stickleback, tautog, cunner, anchovy, and windowpane. 

Larvae would be placed in a specially designed laboratory flow system through which water 

speeds may be accurately regulated (Barker et al. 1977). Test runs in the laboratory would measure the maximum escape velocities of the larvae and the rapidity with which fatigue may 

reduce escape velocities to zero. These experiments would isolate those stages of particular 

species for which escape capabilities are so low as to preclude their successful avoidance of 

any screening structure. (It is recognized that larvae reared in a hatchery facility may not, 

for dietary or other reasons, be as healthy and vigorous as their: counterparts in the wild. 

Therefore, these laboratory swimming/behavior tests would be viewed as worst-case experiments. ) 

Larval behavior in the presence of rock filters with and without sanctuary areas also would be 

observed. These observations would provide information on possible avoidance or sanctuaryseeking behavior, and would suggest possible areas along the dike where larvae may congregate. 

The results would factor in the design of subsequent field tests on naturally occurring or impounded larval fish. 

The facility would include pumps, 

Ripe specimens of selected species would be collected and fertilized eggs would be obtained 

Larval cultures would be maintained for as long as possible. Priority 
60 

FIELD EXPERIMENTS ON BIGLOGICAL SCREENING PERFORMANCE 

Fish Studies 

Known numbers of small fish would be impounded in a mesh enclosure on the upstream side of 

the dike, and impingement avoidance would be evaluated as a function of various parameters. The 

enclosure would be constructed so that the impounded fish could position themselves directly in 

the line of flow through the dike, or in a sanctuary area not exposed to the flow-stream into 

the dike. At the end of the chosen exposure period, counts would be made of fish remaining on 

the upstream exposed side of the dike, of fish in the sanctuary area, and of any fish which have 

passed through the dike. (These would He retained by a mesh barrier in a chamber on the downstream side.) Pumping would be stopped briefly at this time, and all fish in sight would be 

removed from the impoundment. Both the upstream and downstream chambers would be observed for 

several hours to determine whether any live fish had emerged from the crevices within the dike 

itself. 

of the fish remaining alive on the upstream side of the dike to the number of fish initially 

impounded. 

the impingement barrier would be conducted in the open cell. Also, fish behavior at the face of 

the dike would be studied through the use of viewing buckets from surface positions or by SCUBA 

observations. 

The measure of the performance for impingement avoidance would be defined as the ratio 

For comparison with a rock filter, several parallel tests using a fixed wire-mesh screen as 

Key parameters which may influence fish avoidance of a porous dike or movement to a sanctuary area are listed in Table 1. To quantify the influence of these variables, thirty-six 

experiments would extend over the range of conditions listed in Table 1. Fish species would be 

selected for testing because they are locally available and historically vulnerable to impingement on the Brayton Point traveling screens. 

tested by Alden Research Laboratories in a previous phase of research (Roberge et al. 1976). 

The proposed filter materials are similar to those 

Table 1. Parameters that may Influence Fish Avoidance of a Porous Dike 

Parameter 

Fish species 

Fish length 

Exposure density 

Exposure time 

Ambient water temperature 

Lighting conditions 

Approach velocity 

Rock shape 

Rock size 

Porosity 

Range of Conditions 

Winter flounder (PseudopZeuronectes amerieanus) 

Si1 verside (Menidia rnenidia) 

Three- s pi ne s ti c kl e bac k ( Gasteros teus aeu Zeatus ) 

Mummichog (Fundulus heteroczitus) 

Windowpane (ScophthaZmus aquosus) 

Cunner (Tautogolabpus udspersus) 

Men haden (Brevoortia tyrannus ) 

Alewife (Alosa pseudoharengtrs) 

Si 1 ver hake (Ideerluccius bizinearis) 

Tautog (Tautoga onitis) 

Bluefish (Pornatomus saZtatrZx) 

2-15 cm 

25-500 fish per enclosure 

1 /2-24 hr 

0-25°C 

Bright sun-dark 

.01-.1 m/s (0.05-0.5 fps) 

Angular 

7.6- and 20-cm (3- and 8-in.) stone 

.5 

Naturally Occurring Ichthyoplankton 

Entrainment avoidance by naturally occurring larvae would be determined by comparing filtered and unfiltered (control) chambers. 

is expected to provide an estimate of the population exposed to entrainment in. an adjacent 

filtered chamber. 

the upstream population would be sampled by installing a plankton net across the unfiltered 

The larval population entering the unfiltered chamber 

(This assumption would be confirmed at the start of experiments.) Accordingly, 
61 

chamber. 

at intermediate locations within the filter. Periodically, all larvae passing a certain point 

would be collected and analyzed for species and abundance data. 

occur simultaneously. 

larvae which pass through the filter or are collected within it. 

In each filtered chamber, plankton nets would be mounted downstream of the filter and 

Sampling at all locations xould 

Analysis of these measurements would quantify the proportions of exposed 

In those cases where larval densities at interior and downstream sampling .points were 

minimal, the fate of the larvae would be determined by sampling larval densities at the upstream 

interface using a vertical lift net or other technique developed during the laboratory phase. 

Larval sampling at the field test facility would begin when the company's regular ichthyoplankton monitoring at Brayton Point indicated the presence of larvae in sufficient numbers for 

a meaningful study. 

calendar year. 

sampling day, eight 100-m3 samples would be taken at one-hour intervals. 

Typically, the period of such study would be June 15-September 15 for any 

Sampling would be done one .day per week during this 13-week period. On each 

. . 

Naturally Occurring Zooplankton 

Entrainment avoidance by naturally cccurring zooplankton would be quantified in the same 

way as for fish larvae, comparing filtered and unfiltered chambers. 

zooplankton which pass through the filter or are collected with it would be determined. 

The proportions of exposed 

Zooplankton sampling would be done at the same locations as the larval fish samplicg 

described above. Dctylight sampling would be done hourly during an eight-hour period one day 

per week for at least one year. In addition, on a monthly basis, sampling would be undertaken 

every hour over a 48-hour period to evaluate the stratification of zooplankters in the water 

column and the occurrence of certain noc,turnal zooplankters. 

RESEARCH SCHEDULE AND LONG-RANGE PLANS 

Present plans call for completing installation of the test facility by February 1979. 

'Immediately thereafter, the two-year program of in-situ experiments on fouling and exclusion 

performance would begin. During 1978, laboratory studies of larval behavior and swimming capability will be performed. At the conclusion of this research, data will be available to determine whether the porous dike offers a realistic prospect as a larval exclusion device for power 

plant intakes. If the technology still looks attractive, a full-scale demonstration of a porous 

dike would then be required as the next step. 

SUMNARY AN5 CONCLUSIONS 

A porous-dike filter would resemble a gravel-core breakwater surrounding a power plant 

cooling water intake. 

large to pass through it. 

barrier, achieving larval exclusion by avoidance. 

larval exclusion from power plant cooling water intakes. 

porous dike internal geometry can be used as a crude design basis to achieve physical exclusion. 

Laboratory results and field observations suggest that avoidance by both larvae and post-larvae 

is likely, but design methods to maximize avoidance are not yet available. 

and on a porous dike is potentially a problem, but this problem has been avoided at several 

existing porous dikes and breakwaters by the use of large filter materials. 

available to predict flow restriction due to fouling. Several anti-fouling techniques have 

promise, but need to be tested. 

It is not certain at this time whether a porous dike can successfully exclude fish and 

The porous dike would present a physical barrier t o a l l organisms too 

However, its principal promise lies i n i t s potential as a behavioral 

Current information suggests that the porous dike offers promise as a means of fish and 

Information on fish dimensions and 

Fouling growth in 

Methods are not yet 

larvae while continuing to reliably supply cooling water to a power plant. 

of field experiments on a pilot-scale porous dike is proposed. 

exclusion capabilities and fouling rates under natural conditions. 

behavior will be conducted. This research will determine the feasibility of the porous-dike 

intake, and determine whether further development of this technology is warranted. 

sibility tests show promise, a full-scale demonstration of the porous dike would follow, leading 

to availability of a new technology for larval exclusion from power plant cooling water intakes. 

A three-year program 

Laboratory studies of larval 

Experiments would quantiVy 

If the fea- 
62 

ACKNOWLEDGEMENTS 

The authors wish to thank George Mathiessen, Alexander Beichek, Donald Bourne, and Richard 

Toner of Marine Research, Inc., for their major contributions in the planning of the proposed 

porous dike testing program. 

REFERENCES 

Anderson, M. R. 1976. New England Power Service Company, Westborough, Mass., personal communication. 

Barker, A. J., S. Partain, and F. J. Germano, Jr. 1977. The collecting, culturing, and swimming ability of larval american shad, .:;OSO sapiai,-simc. 

Boston, Mass. 23 pp. 

New England Aquarium Report, 

Bell, M. C. Undated. Handbook of Design Criteria for Fish Facilities. U. S. Army Corps of 

Engineers, North Pacific Division. 

Brown, R. T., and S. F. Moore. 1977. An Analysis of Exposure Panel Data Collected at Millstone 

Point, Connecticut. MIT-EL 77-015, Energy Laboratory, Massachusetts Institute of Technology, Cambridge. 158 pp. 

(Prepublication draft.) 

Connell, J. H. 1972. Community interactions on marine rocky intertidal shores. Annu. Rev. 

Fisher, F. W., D. 6. Odenweller, and J. E. Skinner. 1977. Recent progress in fish facility 

research for California water diversion projects, pp. 381-403. In L. D. Jensen (ed.), 

Third National Workshop on Entrainment and Impingement, EcologicTi Analysts, Inc., 

Melville, N. Y. 

Ecol. Syst. 4~169-192. 

Kerr, J. E. 1953. Studies on fish preservation at the Contra Costa steam plant of the Pacific 

Gas and Electric Company. Calif. Dep. Fish and Game Fish Bull. 92. 

Marine Research, Inc. 1975. Technical Proposal - Leaky Dam Evaluation. Marine Research, Inc., 

Fa7mouth, Mass. 

Mayo, R. D. 1974. Conventional fish screening methods and some promising alternatives, 

pp. 277-280. In Proceedings of Second Workshop on Entrainment and Intake Screening, 

EPRI 74-049-0015, Electric Power Research Institute, Palo Alto, Calif. 

Menchen, R. S. 1975. Perforated pipe used to screen and trap juvenile salmonids. Prog. Fish 

Cult. 37~85-89. 

Nece, R. E., and M. C. Bell. 1973. Hydraulics of a gravel core fish screen, pp. 31-41. In 

Proceedings of the 21st Annual Hydraulics Division Speciality Conference, American Sozety 

of Civil Engineers, New York. 

New England Power Company. 1976. Environmental Report - New England Power Units No. 1 and 2. 

New England Power Company, Westborough, Mass. 

1976. A State-of-the-Art Report on Intake 

Technologies. EPA-600/7-76-020, Industrial Environmental Research Laboratory, Office of 

Energy, Minerals and Industry, U. S. Environmental Protection Agency. 83 ppRoberge, J. C. 1977. Alden Research Laboratory, Holden, Mass., personal communication. 

Roberge, J. C., D. C. Gramer, and W. E. Lee. Hydraulics of Flow through Porous Gravel 

Sonnichsen, J. C., Jr., B. W. Bentley, G. F. Bailey, and R. E. Nakatani. 1973. A Review of 

Ray, S. S., R. L. Snipes, and D. A. Tomljanovich. 

1976. 

Structures. 119-76/M14JF. Alden Research Laboratories, Holden, Mass. 24 pp. 

Thermal Power Plant Intake Structure Design and Related Environmental Considerations. 

HEDL-TME 73-24, Hanford Engineering Development Laboratory. 

Stober, Q. J., C. H. Hanson, and P. B. Swierkowski. 1974. A high-capacity sand filter for 

thermal power plant cooling water intakes. Part I: Model studies and fouling control 

techniques, pp. 317-334. 

Screening 

92 ppIn Proceedings of the Second Workshop on Entrainment and Intake 

EPRI 74-049-00-5, Electric Power Research Institute, Palo A1 to, Cal if. 
63 

U. S. Environmental Protection Agency. 1976. Development Document for Best Technology Available 

for the Location, Design, Construction and Capacity of Cooling Water Intake Structures for 

Minimizing Adverse Environmental Impact. EPA 440/1-76/015-a, Washington, D. C. 

Vernberg, W. B., and F. J. Vernberg. 1972. Environmental Physiology of Marine Animals. 

Springer-Verlag, New York. 346 ppWahtola, C. H., Jr. 1977. Wisconsin Electric Power Company, Milwaukee, personal communication. 

Wisconsin Electric Power Company. 1976. Lakeside Power Plant - Final Report on Intake Monitoring Studies. Wisconsin Electric Power Company, Milwaukee. 49 pp. 

Yalin, S., and L. Franke. 1961. Experimental investigation of the laws of filter flow, 

pp. 324-331. 111 Proceedings of the Ninth Convention of the International Association for 

Hydraulic Research, Dubrovnik, Yugoslavia. 
ENGINEERING ASPECTS OF PASSAVANT SCREENING 

Kenneth R. Siddle 

Solids Disposal Division 

Passavant Corporation 

P. 0. Box 2503 

Birmingham, Alabama 35201 

Rajendra K. Sharma 

Division of Environmental Impact Studies 

Argonne National Laboratory 

Argonne, Illinois 60439 

Abstract 

The Passavant screen was developed in Europe almost 30 years ago. The Passavant 

screen is a vertical traveling screen; however, the basic difference between the conventional vertical traveling screen and the Passavant screen is that in the conventional screen water passes through the front screen belt and then the back screen belt, 

whereas in the Passavant screen the water enters in between the two belts and passes 

laterally through either of the belts. 

the Passavant screen is doubled as compared to the same size conventional vertical traveling screen. Various design and operational modifications of the Passavant screen are 

possible to yield optimum design and performance chara.cteristics which make it amenable 

to installation at power plants for safe removal of not only fish but also smaller 

organisms such as fish eggs and larvae. In this paper, details of the screen design 

and operational characteristics are discussed with notes on how these features can be 

modified to suit site- and organism-specific requirements. 

Thus, theoreticaliy, the screening surface of 

DESIGN AND OPERATION 

The Passavant screen is a series of screening baskets connected to two strands of endless 

chain suspended on drive sprockets supported at the operating floor. screen is held in position by two steel guides which eliminate the need for underwater sprockets, 

shafting, and bearings. As the water flows through the screening baskets, debris is retained 

within the baskets, allowing the clean water to flow through the screen. 

The Passavant center-flow traveling screen operates according to the internal flow system, 

whereby the water passes through the screen from the inside to the outside. Because this principle is used, the entire submerged screening area is used in the screening procedure. 

screening elements. These patented baskets increase the screening area approximately 60% compared to the base area of the basket frames. This special basket and a shovel-type retaining 

plate results in optimum efficiency of the unit. 

mulates on the internal screen surface from dropping back into the screening unit. This also causes dewatering of the trash, which results in an increased solids concentration. 

waste trough inside the screen. 

header with flat spray nozzles and a cleaning device for the pipe and nozzles. 

water discharge drain must be provided on the operating floor and linked to the waste trough. 

TO prevent the trash from matting the screen cloth, a special electric control combined with a 

timer system is used. 

shower header. 

The bottom portion of the 

A design feature of the Passavant screen is the application of the semicircular type of 

The retaining plates prevent debris that accuAll screened particles are removed by a spray from the outside and are collected in-the 

Debris is removed from the baskets by a special screen shower 

A special spray 

This delays the shutdown of the screen rotation and the operation of the 

The time delay is adjustable. 

65 
66 

The semicircular screening baskets are exchangeable and have special retaining shovels. 

The baskets are attached to traveling non-lubricated chains that have plastic rollers and are 

guided in cast iron or steel guides. 

Scaling of the rotating screen against the channel walls is provided by oil-resistant sealing 

strips. 

and linked to a torque tube. 

take-up device. 

in Table 1. 

The lower circular guide rows are made of cast iron. 

Above the operating floor the screening baskets are driven by two sprockets made of steel 

The number of baskets necessary for given submergence of the screen are shown 

The whole unit is disc-spring-suspended and equipped with a chain 

Table 1. Number of'Baskets Utilized 

at Various Submerged Depths 

I TOTAL NUMBER OF 1 

1 I' I I I I I 
67 

MODIFICATIONS IN DESIGN AND OPERATION 

The lower portion of the screen can be adjusted to various widths to accomodate given flow 

conditions ("pear-shaped design," Fig. 1). 

normal rotating speed is 3 fpm; tests have indicated that a rate of 14 fpm is more appropriate 

for low-speed operation and 28 fpm for high-speed operation. Operating experience and testing 

with various screening materials indicates that a polyester or nylon screen media, usually with 

4 mm or 1 mm openings, is preferable for safe screening of fish larvae. 

The screen can be rotated at various speeds. The 

~ ~~ 

Fig. 1. Design of Lower Portion of Passavant Screen 
68 

As the screen is rotated, debris and fish are washed off as each basket makes the turn at 

the upper end; the washing spray, which is designed for maximum coverage, washes the matter into 

a trough located under the torque tube and is shaped to direct flow to the effluent channel. 

The trough can be designed with a split arrangement, whereby the fish can be gently dropped in 

one section and the debris in an adjoining section. 

is used (0.5 bass) and for the second section a higher-pressure shower is used (2 to 5 bass). 

This arrangement allows fish to exit in one channel while the debris exits separately. 

In the first section a low-pressure shower 

SCREENING OF FISH EGGS AND LARVAE 

The screen is suitable for screening of fish, fish eggs, and larvae. The following design 

and operational features of the screen are conducive to such a use: 

1. 

2. 

3. 

4. 

5. 

6. 

The mesh size of the screening material for the baskets can be selected on the basis of 

screening requirements. 

The screened organisms are retained in the retaining lip and are not exposed to air as the 

basket rotates end is washed as it makes the pass at the upper end of the screen structure. 

The screened organisms are gently washed into a trough from which they can be returned to 

the source water body as appropriate. 

The screen can be rotated at high speed (28 fpm) to accommodate increased influx of organisms and/or debris and thus organisms from the screen well can be removed without much 

delay. 

The baskets are easily removed and the screening material can be replaced. This results in 

better maintenance, and various screening materials can be used during different seasons as 

dictated by the screening requirements. 

Further changes in design and operation are possible if the screening requirements dictate 

such a change. 

Mesh of 4 mm size has been used satisfactorily. 

Currently, engineering and biological experimentation is underway at the Central Power and 

Light facility and the Tennessee Valley Authority research laboratory to explore further the 

engineering and biological aspects of using Passavant screens for protection of ichthyoplankton. 

The reader is referred to the papers of Magliente et al. and Murray and Jinnette in this proceedings. 
INVESTIGATIONS ON THE PROTECTION OF FISH LARVAE AT WATER INTAKES USING FINE-MESH SCREENING 

IMPINGEMENT-RELEASE CONCEPT: LABORATORY STUDY OF A SINGLE-ENTRANCE, 

DOUBLE-EXIT, VERTICAL TRAVELING SCREEN CONCEPT 

Salvatore H. Magliente 

Tennessee Valley Authority 

Energy Research 

1320 Commerce Union Bank Building 

Chattanooga, Tennessee 37401 

David A. Tomljanovich and John H. Heuer 

Tennessee Valley Authority 

Division of Forestry, Fisheries and Wildlife Development 

Norris, Tennessee 37828 

Svein Uigander and Marvin N. Smith 

Tennessee Vat ley Authority 

Division of Water Management 

P.O. Drawer E 

Norris, Tennessee 37828 

Abstract 

The Tennessee Valley Authority (TVA) is investigating the concept of protecting 

larval fish at power plant intakes using fine-mesh screening. The larvae can be 

safely impinged on the screens, washed off the screens, and returned to the source 

water body (impinge-release concept). Initial studies by TVA have indicated that 

such a concept of screening larval fish is feasible. 

A single-entry, double-exit vertical traveling screen was selected for the 

experimental test facility. Such a screen has desirable characteristics for safe 

handling of fish and is amenable to design modifications if warranted. Testing is 

designed to evaluate larval fish survival using the impinge-release concept for commercially available modified and unmodified screens. The importance of various 

stresses critical to survival of larvae will be examined under laboratory conditions 

INTRODUCTION 

The protection of fish at water intake structures has a long history in the United States, 

In 

but the enactment of recent legislation has resulted in an intensified nationwide examination of 

entrainment and impingement effects at power plant cooling water intakes (Ray et al. 1976). 

the past, efforts have been focused on ways to reduce impingement, while entrainment has been 

largely neglected. In recent years, however, the Tennessee Valley Authority (TVA) has been 

directing research efforts toward identifying and solving problems involved in reducing impingement and entrainment by utilizing various screen concepts. One of the concepts that TVA is 

investigating to protect larval fish at power plant intakes uses fine-mesh screening to safely 

impinge rtnd return the fish to the source water body (the impinge-release concept). The basic 

questions of this concept were considered in the initial TVA studies on the impinge-release concept (Tomljanovich et al. 1977). In the laboratory phase of the initial studies, TVA investigated the retention of fish as a function of (I) size of screen opening, (2) approach water 

velocity, (3) fish size and species, and (4f length of time the organisms were impinged against 

the screen. The survival percentage of the retained fish as a function of the variables listed 

69 
70 

above also was investigated. The laboratory study clearly demonstrated that (1) a relationship 

exists between fish retention and screen opening size, (2) impingement duration is the predominant variable affecting survival and shows a strong inverse relationship to survival for all 

taxa which responded to the test conditions, and (3) low current velocities through screens 

provide the best survival rates. A field study was performed to provide a comparison with the 

laboratory screening results. Several fine-mesh screen samples (0.5- to 7.0-mm square mesh 

openings) were superimposed on a conventional vertical traveling screen of a TVA steam plant. 

Results of this initial study indicated that the concept of screening larval fish is feasible. 

Since the initial studies indicated the biological feasibility of the concept, additional 

studies were directed at developing a feasible prototype screen. To perform satisfactorily, a 

prototype fine-mesh screen system must (1) limit impingement time for larvae to several minutes 

or less, (2) transport the fish from the impinged position back to the source water, and 

(3) insure high post-impingement and transport survival of the larvae which are returned to the 

source water. The characteristics which would permit a prototype screen to perform satisfactorily are (1) an endless belt arrangement of screen panels, (2) vertical orientation of screen 

such that fish and debris are lifted out of the water, (3) continuous rotation, (4) a lowpressure spray to assist in transferring fish from the screen panel to the return channel, (5) a high-pressure spray to remove any remaining debris after the fish are transferred, and (6) a 

"fish slide" for organisms to ride into a return channel after being spilled from the screen panel. 

technology to determine the screens possessing the majority of desired fish handling characteristics. 

fish. These five types are: (1) a conventional vertical traveling screen equipped with fish 

troughs and continuous rotation, (2) a single-entry, double-exit (center-flow) vertical traveling screen with semicircular-shaped screen panels, (3) low-velocity infiltration beds, (4) a 

low-velocity slotted or perforated conduit, and (5) a horizontal traveling screen. TVA chose to 

test and modify a dual-flow, single-entry, double-exit vertical traveling screen system because 

it has many good fish-handling characteristics, its present design can be improved with minor 

modifications, it has a good record of reliability and performance on intake structures, and it 

is available on the market in standardized designs. 

In the single-entry, double-exit vertical traveling screen system (Fig. 1 ), the water 

enters the center of the screen and passes from the inside to the outside of the screening surface. The screening material and mesh size selected for a particular site will vary according 

to the fish to be protected and the type and size of debris to be screened. 

in an endless belt, and can be rotated continuously for extended periods of time. 

debris are retained inside the screen; therefore, the possibility for fish and debris carryover 

to the condenser is eliminated. 

gravity and a spray wash into an overhead sluice trough. 

This screening system can utilize various shapes of screen panels. 

mounted into the system. Another option is a European-designed panel (Fig. 2) in vJhich semicircular screen mesh baskets provide increased screening area and facilitate the removal of fish. 

These basket panels have a vertical lip along the bottom to retain debris and fish in the 

basket until it rotates directly over the sluice trough. 

After preparing the above list of screen characteristics, we reviewed currently available 

We identified five types of screen systems which may provide protection for larval 

Screens are arranged 

Fish and 

The accumulated fish and debris are cleaned off the screen by 

Flat panels can be 

Present industry designs do not adequately handle impinged fish, and no studies have been 

The study will (1) estimate fish surperformed to assess the potential of this screening system to reduce entrainment. We will conduct studies in 1978 focusing on the cumulative stresses associated with impingement and transport of the fish from the screen to the return channel. 

vival associated with each aspect of fish impingement on and transfer from a mode7 screen 

designed to safely return them to the water body, and (2) optimize survivaT of fish by modifying 

those screen components which adversely affect the organism. 

plished through structural and/or operating modifications--for example, modification to structural components such as the debris lip or to operational features such as screen speed.) 

laboratory test facility will be used to evaluate the stresses associated with those components 

of the prototype screen which are critical to the handling of the larvae. 

(This optimization will be accomA 

SCOPE OF INVESTIGATION 

The four areas of the screening-transfer process and the stresses most likely to affect fish 

survival are (1) impingement of larval fish on the test screen panel, (2) emergence of the test 

panel from the water, (3) movement of the panel from the position of emergence to a position of 

spilling into the trough, and (4) spilling of the panel into the return trough. 

ing aspects of investigation are (1) survival of fish larvae as a function of length of time 

The correspond- 
71 

_Jt 

SCREEN 

. . . . . . . 

tCIRC. WATER PUMPS 

-.. v 

.. 

.. 

- EMERGENCY 

BYPASS GATE 

-EMERGENCY SCREEN 

BYPASS GATE 

t 

INFLOW 'A J t t 

HORIZONTAL CROSS SECTION 

OF INTAKE 

Fig. 1. Schematic of Single-entry, Double-exit 

Vertical Traveling Screen 

impinged, (2) survival of larvae transported on the screen panel, (3) survival of the fish 

transferred from the screen panel to the return trough, and (4) adhesion of the fish to the screen material. 

Biological testing is designed to compare larval fish survival on an unmodified, commer- cially available screen (presumably a worst case) with survival on a modified screen. procedure for investigating larval fish survival is sequential. Initial tests are limited to 

impingement only. 

from the water to a position of spilling into the return trough, follows the initial tests. 

Finally, tests will include all cumulative stresses (on both the modified and the unmodified screen panel f . 

The 

The next level of stress, exposing the fish to air as the screen panel travels 
72 

HIGH-PRESSURE 

~&~~i?kBRlS 

SPROCKET 

WHEEL 

DEBRIS TROUGH 

- SEMICYLINDRICAL 

SCREEN PANEL 

Fig. 2. European Design of Single-entry, Double-exit 

Vertical Traveling Screen 

MATERIAL AND METHODS 

TEST 4PPARATUS 

-TVA's Water Systems Development Branch is responsible for the construction of the test 

facility. 

plies the water flow and a portion of a vertical traveling endless screen belt. 

designed to simulate the important fish handling components of a commercially available singleentry, double-exit vertical traveling screen with 0.5-mm openings. The components of the laboratory facility are constructed to prototype dimensions and traveling screen kinematics. 

Thereby, the stresses to which larval fish are subjected can be reproduced for a wide range of 

postulated prototype intake desiqns. Areas of hiqh fish stress will be identified and screen 

The test apparatus (Figs. 3 and 4) consists primarily of a wooden flume which supThe facility is 

modifications can-be made to obtain higher degree; of fish survival. 

A rail-hoist system is used to raise and lower the screen panels out 

One to 

The screen panels are raised and lowered 

Panels 

This action duplicates the kinematics of prototype screen motion. 

be mounted on the hoist system. 

system which is powered by a variable-speed, reversible DC motor. 

speed from about 0.02 m/s to about 0.15 m/s. 

The wooden flume is 15.2 m lona and 1.2 m deeD. A constant-head box 

of and into the flow. 

four screen panels can 

by a drive mechanism are raised at any 

supplies the water. 

Flow comes to the head box through 

trol. 

51-cm pipe equipped with a Howell-Bunger' valve for flow conA slide gate at the downstream end of the flume controls water depth. 

A 0.3-m section of gravel, two 0.2-m sections of hog-hair packing at the head-box outlet, 

The actual test section begins roughly 2.6 m downstream from the head box and is 1.0 m 

wide. 

and a gradually contracting approach section assure relatively uniform water velocity in the 

flume test area. Nominal velocity approaching the screen panels is 0.31 m/s and is measured 

with a miniature Ott-type current meter. Maximum flow capacity is about 0.42 m3/s. 

The screen panels currently installed (Fig. 5) were purchased from the Passavant Corporation. Each consists of a 

metal frame covered with woven polyester screening material having 0.5-mm square openings and 

50% open area. plate at the lower edge to help retain the screened material until the basket is nearly inverted. 

For testing purposes, the panels are equipped with an axial division baffle which splits the 

screens into two 0.6-m sections. 

screen panel, thereby permitting the investigator to more easily retrieve test fish for survival 

studies and counting. 

The panels are semicylindrical, 53 cm in diameter, and 1.2 m wide. 

As indicated in Figure 5, each panel is equipped with a baffle or retaining 

This division makes it possible to use one-half the area of a 
-TO 

r- I 5.2 IT-~ 0.2 m 

SLIDE J 

PLAN SECTION GATE 

YEADBOX 

SPRAY HEADER 

FlSH RETURN TROUGH 

SCREEN WELS 

f 

ELEVATION 

73 

TRACKS TO IMPART SIMULATED PROTOTYPE 

MOTION TO SCREEN BASKETS fFig. 4, Schematic of Test Apparatus (1 m = 3.2808 ft; 

1 em = 0.3937 in.) 
74 

Fig. 5. Sketch of Test Panel 

Two types of screens are used in the tests (Fig. 6). 

the fish are transported through air as all the water runs out of the screen basket. 

second, the wet screen, the fish stay submerged in a pool of water approximately 5 cm deep. 

Sealing the lower portion of the semicylindrical baskets screen openings with epoxy paint 

In the first type, the dry screen, 

In the 

allows retention of the pool of water at the bottom of the panel. 

essarily indicate the depth of water that would be adequate in an operational system.) 

(The 5-cm depth does not necTo remove impinged fish, water is sprayed through the screens from behind. For this purpose, the facility is equipped with a header holding six spray nozzles on 15-cm centers. This 

header is positioned anywhere from the water surface to the point where the baskets are inverted. 

Using this header or a hand-held hose, the impinged fish can be washed from the panels onto a fish slide and into a fish return trough. 

fish that have survived the impingement. 

rails represents the hub of the top prototype sprocket wheel for the projected endless screen 

belt (Fig. 4). 

During preliminary testing of the laboratory facility by TVA's Fisheries and Waterf.ow1 

Resources Branch, the lack of temperature control was a serious deficiency in the test facility. 

TVA's Water Systems Development Branch is now assembling a cooling system for the test facility's 

flume water; the system will reduce the flume water temperature approximately sixteen degrees 

Celsius in a 27-hour period, and maintain water temperature within one degree Celsius. 

Sufficient water is kept in the trough to sustain the 

The suspended cylinder below the arch of the steel 

TEST VARIABLES 

All tests will be conducted on a screen panel having square-mesh polyester screen with 

0.5-mm openings. 

percentage of the smallest fish larvae entrained (Tomljanovich et al. 1977). In earlier tests, 

This size screen opening was earlier shown to be required to retain a high 
75 

Fig. 6. Detail of Screen Panels 

ronment. 

1. 

2. 

- 3. 

4. 

5. 

6. 

7. 

differences in survival of impinged fish in waters with velocities between 0.15 and 0.31 m/s 

were minimal (Tomljanovich et al. 1977); therefore, an approach water velocity of 0.31 m/s will 

be used in all tests. The water temperature in the flume will correspond to the water temperature-to which the test species would be exposed at its present life stage in its natural enviThe following variables are to be evaluated in this study: 

Impingement duration (screen exposure time) - 0.5, 1.0, 2.0, and 4.0 min. 

Screen panel shapes - semicylindrical, flat, and others. 

Spray volume and velocity - varied increments from high-volume, low-velocity to 

low-volume, high-velocity. 

Species - dependent on availability during the test period. 

Fish developmental stage - prolarval, postlarval, and early juvenile (depending 

on availability during the test period). 

Length of time test panel is out of water prior to spilling of fish into return 

trough (air exposure time) - 0,5, 7.0, 2.0, and 3.0 min. 

Screen speed - 0.07, 0.11, and 0.14 m/s. 

TEST PROCEDURES 

The procedures for investigating larval fish survival will be conducted sequentially, as 

described in the section Scope of Investigation. 

detailed at the outset of the study, we may deviate somewhat from the schedule, depending on the 

Although a specific testing format will be 
76 

initial results for each species. 

following paragraphs. 

mately 0.31 m/s (measured just in front of the screen). 

carefully removed from the transfer-temperature adjustment container and placed in a Styrofoam 

cooler containing test flume water. This group will represent a control for mortality associated with the fine-mesh screening process. 

testing. Each replicate test will consist of 25-200 fish. 

The approach and basic test pattern is summarized in the 

Velocities Established, The water velocity in the flume will be established at approxiSurvival Control. Approximately 25-200 fish (depending on availability of species) will be 

Replication. Three replicates of each test will be performed throughout all phases of 

Impingement Only. A sample of fish will be removed from the transfer container and placed 

in a beaker. 

before testing. The remaining live fish will be charged directly onto a dry screen panel. via an L-shaped pipe (fish injector funnel, Fig. 4). 

with the screen for a specified duration (0.5-4 min). Next, the test screen panel will be 

raised to the surface of the water; the bottom portion of the screen will remain immersed. As 

the upper portion of the screen panel emerges from the water, the impinged fish will be gently 

splashed into the water at the bottom of the panel. 

into a Styrofoam cooler. 

be held in the containers for up to 24 hours to assess delayed mortality. 

portion of the testing will provide a control for determining the effect of the additional 

stresses associated with the transfer process on fish survival. 

These test fish will be carefully examined and any dead fish will be removed 

The fish will be allowed to remain in contact 

The impinged fish will then be siphoned 

Dead fish will be removed and counted and the remaining live fish will 

The impingement-only 

Impingement-Plus Air Exposure. In the next phase of testing the fish will be impinged on 

the dry screen for the same period of time as in the impingement-only tests. At the end of the 

impingement period, the screen containing the impinged fish will be raised completely out of the 

water and the impinged fish will be exposed to the air for 0.5-3 min. to simulate travel time of 

the prototype screen panel from the water surface to the top of the screen structure. Since the 

Screen panels on the prototype are designed to travel continuously at speeds of 0.07 to 0.14 m/s, a three-minute air exposure represents a range of total distance from water surface to the top 

of the screen structure of 12.8 to 25.6 m. screen panel will be lowered until the bottom portion of the curved screen panel is immersed in 

the flume water. The impinged fish will be gently splashed to the water at the bottom of the 

panel. This procedure will permit us to siphon the test fish from the panel into a Styrofoam 

container, thus imposing minimal additional stress on the fish. As in the previous test, the 

dead fish will be immediately removed and counted and the remaining live fish will be held in 

the container 24 hours for assessment of delayed mortality. 

subjected to stresses associated with impingement, air exposure, and spilling of the fish from 

the dry screen panel into the return trough. 

trough (Fig. 4) will terminate approximately 1 m below the spill position. The spill distance 

and angle of the slide wi7l approximate those dimensions in the prototype. As the screen panel 

reaches the spill position, a wash will be varied from a high-volume, low-velocity spray to a low-volume, high-velocity spray. 

will be recorded as dead fish. 

Styrofoam container. 

fish will be impinged on a wet screen, air-exposed, and sluiced. 

panel emerges from the water, a spray wash will be directed behind the screen to flush-the fish 

into the water pool of the wet screen. velocity spray to a low-volume, high-velocity spray. 

tical to the previous tests and the results will be compared to the results from the impingementair exposure-sluicing phase using the dry screen. 

Adhesion of Fish on a Wet Screen. In these tests, the fish will be impinged on a wet screen and transported out of the water. After the screen panel emerges from the water the fish remaining in the pool of water will be siphoned into a container and counted. 

screen surface will be flushed into the water pool of the wet screen. 

varied. 

Immediately following the air exposure time, the 

Impingement Plus Air Exposure Plus Sluicing. In this phase of testing the fish will be 

The sheet metal fish slide and shallow return 

The screen .panel will be checked for unremoved fish, which 

The remaining fish will be siphoned from the trough into a 

Fish will be treated as described for earlier tests. 

Impingement Plus Air Exposure Plus Sluicing on a Wet Screen Panel. In these tests, the 

Immediately after the screen 

The spray wash will be varied from a high-volume, lowThe fish will be treated in a manner idenThose fish left on the 

Again, spray wash wil7 be 

Both the fish in the water pool and the fish on the screen will be counted. 

DISCUSSION 

The TVA larval fish testing will progress from an evaluation of fish survival on a basic screen with few modifications (presumably a worst case) to an evaluation of fish survival on a 
77 

screen with several fish protection modifications. After all phases of testing have been completed on a species of fish, the survival of the fish exposed to the entire impingement and 

transfer process will be compared to the survival of the fish exposed only to impingement. If 

the survival in the former group is significantly less than that in the latter group, testing 

will be repeated with additional modifications until no significant differences in survival can 

be detected between the processes. Therefore, the amount of testing is dependent on the results 

of each phase. 

result in.optimum survival and justify an early termination of testing. 

testing may have to proceed through several phases to arrive at optimum survival. 

It is possible that high survival on the screen with few modifications could 

On the other hand, 

As test data are generated, numerical analyses will be performed. Data analyses obtained 

on the initial test species will provide information that will allow for the additional testing 

of those species and for modifications to the test procedures and facility. 

ACKNOWLEDGEMENTS 

This study is being funded by the U. S. Environmental Protection Agency (EPA) and conducted 

by the Tennessee Valley Authority (TVA) as part of the Federal Interagency EnergylEnvironment 

Research and Development Program. 

publication. 

policies of either agency, nor does mention of trade names or commercial products constitute 

endorsement or recommendation for use. 

The report has been prepared by TVA and EPA and approved for 

Approval does not signify that the contents necessarily reflect the views and 

REFERENCES 

Passavant Corporation. 1976. Passavant Screening Equipment Bulletin 1002, Birmingham, Alabama. 

Ray, 5. S., R. L. Snipes, and D. A. Tomljanovich. 1976. A State-of-the-Art Report on Intake 

Technologies. TVA-PRS-16, EPA-600/7-76-020, PB-246-874/AS- Tennessee Valley Authority, 

Chattanooga, Tenn.; and Environmental Protection Agency, Research Triangle, N. C. 

tion of Fish Larvae at Water Intakes Using Fine-Mesh Screening. 

Tennessee Valley Authority, Division of Forestry, Fisheries, and Wildlife Development, 

Norris, Tennessee. 

Tennessee Valley Authority, Division of Water Management, 1977. Vertical Traveling Screen Test 

Tomljanovich, D. A., J. H. Heuer, and C. W. Voigtlander. 1977. Investigations on the ProtecTechnical Note B22. 

Facility. Report No. 07467. Norris, Tennessee. 
SURVIVAL OF DOMINANT ESTUARINE ORGANISMS IMPINGED ON FINE-MESH 

TRAVELING SCREENS AT THE BARNEY M. DAVIS POWER STATION 

L. S. Murray and T. S. Jinnette 

Central Power and Light Company 

Corpus Christi , Texas 

Abstract 

One of the primary environmental impacts associated with electric generatino 

stations in the United States is the loss of aquatic organisms pessing through, or 

impinged on, various screening media at intake structures. 

Historically, many +raveling screens have been fitted with 3/8-inch mesh and 

designed primarily to screen out aquatic organisms and debris preven? cloggirg of 

pumps and condenser tubes (Stupka and Sharma 1977). Presently, comparatively new 

screening technologies are being evaluated by the power industry in an effort to 

alleviate impingement losses at power plant intakes. 

An impingement study was conducted at the Barney M. Davis Power Station, Corpus 

Christi, Texas. The study spanned twelve months, beginning in January, 1977, and 

ending in December, 1977. 

The primary purpose of this study was to accurately describe survival of marine 

organisms, principally dominant fishes and shrimps, impinged on Passavani fin€-mesh 

center-flow traveling screens. The influence of debris loading on the survive! of 

selected dominant soecies also was examined. 

SITE DESCRIPTION AND STUDY AREA 

The Barney M. Davis generating station is situated along the shoreline of the upper Laguna 

Madre near Corpus Christi, Texas (Fig; 1). The station is a fossil-fuel-fired, two-unit installation. It consists of one oil-fired unit and one gas-fired unit with a total generating capacity of 650 MWe. 

Madre via an intake channel 1173 m (3850 ft) long, 2.4 m (8 ft) deep, and 23.5 m (77 ft) wide. 

The heated water from the power plant discharges into a 457-hectare (1130-acre) perched saltwater cooling pond. 

Bay. 

It employs a once-through cooling system using water drawn from the Laguna 

From this pond, cooling water is discharged into the upper Cayo del Os0 

The Laguna Madre of Texas, as characterized by Hildebrand and King (7972), is a narrow 

coastal lagoon 209 km (130 mi) long, with an average depth of 0.8 m (2.5 ft). The vegetation is 

primarily marine spermatophytes and algae, with no marshes or intertidally emergent grasses. 

Although Hedgepeth (1947) describes this lagoon as a hypersaline body of water, it is noted that 

fluctuations in salinity occur as short-term oscillations. 

ally ranges from 30 to 50 parts per thousand. The Laguna serves as an important nursery for 

nany comercially and recreationally important marine organisms. 

stretches the entire length of the Laguna Madre and is one of its most remarkable man-made 

features. 

The salinity of this system generThe Intercoastal Waterway 

INTAKE OPERATIONAL PARAMETERS 

The Davis generating station intake structure is composed of four intake bays 4 m (13 ft) 

dide. 

in.) centers. 

:enter-flow traveling screens. jcreens and the circulating water pumps are 12.3 m (40.5 ft) behind the chlorinators. 

Each bay has a trash rack constructed of 73-mn of (0.5-in.) steel bars set on 89-m (3.5- 

The chlorinators are located 2.3 m (7.5 ft) behind the traveling 

The trash racks are located 7.0 rn (23 ft) in front of the Passavant fine-mesh 

79 
80 

Fig. 1. Overall Site and Study Area 

The maximum flow rate for each intake bay is 8.5 x lo4 gal/min, which creates an approach 

velocity of 0.23 m/s (0.75 fps) at the outermost trash rack. 

tinually over a 24-hour period. 

The screeps are qperated conDESCRIPTION OF PASSAVANT FINE-MESH 

CENTER-FLOW TRAVELING SCREEN 

The Passavant fine-mesh center-flow traveling screen is a single-entry, double-exit system 

that uses a set of continuous chains, fitted with 53 semicircular screening baskets (Fig. 2). 

The screens may be rotated at either 0.25 or 0.50 km/hr (14 or 28 ft/min). Each removable 

basket-or screen panel has a shovel-type lip to aid in the retention of screened material. . 

Using an inside-to-outside water flow, the enti,re submerged portion of screen functions as a 

screening surface. Additionally, with this type system there is no debris carry-over as there 

is with the conventional cross-flow designs. 

spray with a wash pressure of 40-60 psi at 230 gal./min. 

material into an internal spray wash trough that is linked to the peripheral fish-handling 

devices. 

Impinged organisms are removed by an overhead 

This outside spray washes the screened 

The mesh size of the screen in use during the course of the study was 0.5 mm. The velocities through the screen were 0.5 m/s (7.7 fps) at 100% efficiency and 0.9 m/s (3.7 fps) at 50% 

efficiency . 

SAMPLE METHODOLOGY 

Samples were taken over a diel period on a monthly basis extending from January, 1977, to 

December, 1977. 

months, sampling frequency was once every six hours for the 24-hour sample period. 

In January, six samples (one every four hours) were taken. For all other 

Samples were taken directly from the screen wash at each of the four traveling screens. The samples consisted of four individual 30-second replicates taken at each screen for a total 

sample time of eight minutes. Samples were collected with a 1/8-inch square mesh dip net that 

filtered the entire voTume of screen wash water. 

placed in Styrofoam ice chests containing ambient water. 

The replicate samples for each screen were 

Debris consisting primarily of marine 
81 

Fig. 2. 

Passavant Center-flow Traveling Screen 

spermatophytes, algae, ctenophores, and scyphozoans was removed by hand and retained for wet 

weight analysis. 

live and dead components. 

behavior was considered dead. 

returned to the laboratory for weighing, measuring, enumeration, and identification of species. 

The remaining organisms were observed for 10-15 minutes and then sorted into 

Any organism showing visible physical damage or exhibiting erratic 

The sorted components were placed in marked one-liter jars and 

RESULTS AND DISCUSSION 

During the 1977 impingement study, 15 species of invertebrates representing 7 families, and 

37 species of vertebrates representing 22 families were collected from the Passavant screens 

(Table 1). 

organisms were classified as alive and 1,654 were classified as dead (Table 1). The overall 

percent survival for all individuals collected during 1977 was 86.0"L. 

There was a total of 12,060 individuals collected during the study; 10,406 of these 

The dominant species by total numbers of individuals were Brevoortia patronus, Anehoa 

mitchilli, Mieropogon unduZatus, Penaeus azteeus, and Lucmia pma (Tables 1 through 3). 

Monthly comparisons of dominant species collected from the screen wash are shown in 

Table 2. Greatest numbers of individuals for these species were collected from January 1977 

through May 1977 (Table 2). Fewest numbers of individuals were taken from June 1977 through 

December 1977 (Table 2). Hildebrand and King (19771, in a similar study on this screening system, report that fall abundance in August and September, 1976, comprised only 12.1% of the total 

catch, with 66.7% of the total catch collected during January, February, March, and April of 

1 977. 

The lowest overall percent mortalities for the dominant species by month occurred during 

These menhaden averaged 21 mm (MSL) 

February (Table 2). Menhaden (Brevoortia patronus) were the most abundant fish collected during 

February, representing 33% of the total catch (Table 2): 

and mortality was 5% (Table 2). 

The second lowest overall percent mortalities by month occurred during April (Table 2). 

These 

The greatest total number of individuals collected for a single month was also during April 

(Table 2). 

menhaden averaged 25 mm (MSL) and suffered only a 4% mortality (Table 2). 

Menhaden represented 71% of the total sample for this month (Table 2). 
82 

Table 1. Total Number of Individuals Collected 

from Screen Wash During 1977 

Species A1 i ve Dead Total 

Invertebrates 

Penaeidae (shrimp) 

Penaeus aztecus 

Penaeus duoranan 

Penaeus setifems 

Palaemonidae (shrimp) 

Palaemonetes intermedius 

PaZaemonetes pugio 

Alpheus heterochaezis 

Tozewna carolinensis 

Hippo Zy te p leuracantha 

Portunus gibbesii 

Catlinectes sapidus 

Callinectes simi Zis 

Menippe mereenaria 

Neopanope texana 

Panopeus herbstii 

Loll inginidae (squids) 

LoZZiguncula brevis 

A1 pheidae (shrimp) 

Hippolytidae (shrimp) 

Portunidae (crabs) 

Xanthidae (crabs) 

962 

283 

52 

71 4 

7 

8 

16 

22 

1 

189 

0 

4 

16 

0 

19 

Vertebrates 

Elopidae (tarpons) 

EZops saws 

(LeptocephaZus Larvae) 

Ophichthidae (snake eels) 

Gphichthus gomesi 

Clupeidae (herrings) 

Brevoortia patronus 

HarenguZa pensacolae 

Engraul idae (anchovies) 

Anchoa hepsetus 

Anchoa zyozepis 

Anchoa rnitchilli 

Arius fezis 

0pshntds beta 

Urophycis floridanus 

Lepophidiwn brevibarbe 

Hyporhqhzis uni fasciatus 

Strongy Zura marina 

Cyprinodon variegatus 

Lucania parva 

Atherinidae (silversides) 

Menidia beryZlinia 

Arridae (sea catfishes) 

Batrachoi di dae (toadfishes) 

Gadidae (codf ishes ) 

Ophidiidae (cusk eels and brotulas) 

Exocoeti dae ( f 1 yingf i shes, ha1 f bea ks) 

Bel onidae (needle fishes) 

Cyprinodontidae (killifishes) 

4 

12 

43 

3,868 

3 

3 

1 

1,888 

14 

31 

0 

1 

6 

15 

5 

561 

256 

31 

4 

3 

2 

0 

0 

0 

0 

0 

3 

1 

0 

0 

2 

0 

0 

0 

0 

408 

0 

1 

0 

853 

0 

0 

'I 

0 

5 

2 

1 

247 

31 

993 

287 

55 

71 6 

7 

8 

16 

22 

1 

192 

1 

4 

16 

2 

19 

4 

12 

43 

4,276 

3 

4 

1 

2,741 

14 

31 

1 

1 

11 

17 

6 

808 

287 
83 

Tab1 e 1. Continued 

Species A1 i ve Dead 

~ 

Total 

Sygnathidae (seahorses, pipefishes) 

Hippocampus zosterae 

Sy,mthus Zouisianae 

Sygnathirs scovelli 

Chloroscombms chrysurus 

Oligoplites sums 

Archosargus probatocephalus 

Lagodon rhomboides 

Bardiel la chrysura 

Cynoscion aremius 

Cynoscion nebulosus 

Leiostomus xarzthurus 

Micropogon una'ulatus 

Sciaenops ocellata 

Mugi 11 idae (mu1 lets) 

%gi 1 cepk lus 

MugiZ curema 

Polynemidae (threadfins) 

Po lydacty lus octonemus 

Go b b i i d a e (gobi es ) 

Gobiosoma bcsci 

Gobiosoma robustwn 

Trichiurus lepturus 

Etropics crcssotus 

Sphoeroides parvus 

Carangidae (jacks and pompanos) 

Sparidae (porgies) 

Sciaenidae (drums) 

Trichiuridae (cutlass fish) 

Bothidae (lefteyed flounder) 

Tetraodonti dae (puffers ) 

Totals 

18 

38 

28 

0 

5 

18 

43 

5 33 

1 

2 

0 

0 

1 

2 

1 

26 

0 

0 

1 

26 

7 

1 

56 

21 0 

763 

2 

0 

0 

8 

10 

27 

0 

7 

1 

64 

220 

790 

2 

7 

183 

0 

2 

7 

185 

2 0 2 

39 

4 

0 

0 

39 

4 

1 G 1 

1 0 1 

12 

10,406 

2 

1,654 

14 

12,060 
Table 2. Monthly Composition of Dominant Species Collected from 

Screen Wash During 1977 

Mean 

Standard h Z Catch of 

Species Alive Dead Length (mm] Mortality Total Sample 

January, 1977 

Brevoorzic pczronus 

Anchoc ?litehiZZ-: 

i&a-opooci: urduictus 

.?encaus azteDs 

Luecnic ~CrVC 

February, 1977 

Srevoortia ptronus 

Ar.choa nitchill: 

?emeids (iiTezkc 

iuccnia pruc 

&<CPopGgO7 U?& ,a ;US 

March, 1 97 7 

Brmoorzic patronus 

Anckoc nitchilli 

Perdeuz CZ:EC:CS 

Lkcznic pcrvti 

.. i.4icroppm UECl! s.ctas 

April, 1977 (3 screens only) 

Brsvoort fa ::ctroniLs 

Anchca nitchiils' 

?.?icri;.oyoi: srLu Ictac 

Perceus czzecas 

Lucania parvc 

May, 1977 

Ersrtoorzic ?ctronus 

Anchpa nitchili- 

!+icrc.z o~cn Urdu lc :US 

F'enaeus CZZ~L-~B 

Luccr<c ;criic 

392 

506 

1 

274 

298 

539 

33 

12 

24 

2 

239 

24 

41 

20 

59 

ia 

8 

4 

20 

15 

25 

24 

0.14 

5 

67 

47 

27 21 

31 

0 

19 

?a 

5 

11 

4 

0 

2 

33 

16 1 

76 

0 

2 

3 

0 

4 

5 

0 

11 

330 

124 

268 

100 

12 

0 

20 

27 

23 

23 

4 

0 

0 

0 

42 

27 

12 

8 1 

0 

0 

0 

89 

0 0 

2,343 

240 

4 

100 

116 

0 

4 

4 

25 4 

33 

0 

2 

4 

71 

30 

21 

48 

10 

0.11 

1 a2 5 

a6 21 3 

262 

790 

680 

38 

a 

148 

328 

0 

0 

0 

29 

26 

36 

29 

0 

0 

0 

17 

46 

2 

28 

0.32 

70 

20 

a5 

0 

21 4 

0 

23 

0 

26 

53 

92 

0 

0 

98 

0 

74 

1 

46 17 

0 0 0 0 

0 

50 

0 

2 

0 

72 

26 

0 

51 

1 

66 

130 

108 

0 

0 

15 

0 

0 

12 

5 

16 

0 

0 

35 

160 

96 

0 

0 

43 

0 

32 

0 

0 

0 

8 

25 

0 

September, 1977 (Unit 2 down; two screens only) 

Brertccrls. !-otyn,:u: 0 

Anckoc *~izcktII< 1 

:.!icrc~Gp: ueza LJiUE 1 

Perseus az:icus 3 

LUCCr.C ForrtJ 0 

Breooortic ;zz rcns 0 

hnchoc rnt~c;IiIII I02 

<viern::ogon ul~d~zotus 1 

Penaeus aztecx 19 L .icazia pcrvz 9 

Erevoortic patronus 0 

Mici-o.zogoz ur& La tirs 0 

Luccnic ,7arva 0 

Srevoortia pctrcnss 1 

Anckc XftchiZii aa 

Kierojopor; urku is tus 5 

Perceus cztecx 9 

iuc,-r:tz :C?"m 4 

1. 

October, 1977 (Unit 2 down; two screens only) 

November, 1977 (Unit 2 down; two screens only) 

A?;choc nttchs'lii 24 

Penceus czte~as 6 

December, 1977 (Unit 2 down; two screens only) 

0 

16 

0 0 

94 

0 

0 

0 

0 

44 

3 

28 

200 

36 

0 

0 

0 

8 

0 0 

0 

14 

0 

29 

154 

59 

0 

0 

12 

0 

0 

0 

0 

59 

1 

10 

5 

0 

0 

0 

0 

11 

0 

0 

0 

0 0 

33 

0 

0 

0 

0 

53 

0 

9 

0 

32 

0 

77 

0 

0 

64 

0 

0 

0 

86 0 

42 

0 

0.19 

29 

1 

33 

77 

ao 0 

0 

2 

19 1 
85 

Table 3. 'Annual Composition of Dominant Species 

Collected from Screen Wash During 1977 

Species Alive Dead 

Anchoa mitchiZZi 1,888 853 

Ejrevoortia patronus 3,868 408 

Micropogor. unduZatus 763 27 

Lucania parva 561 247 

Fenaeus aztecus 962 31 

Total 8,042 1,566 

Mean Standard /: 7: of 

Total No. Length (mm) Mortality Total Catch 

2,741 30 31 23 

4,276 10 10 35 

790 78 3 7 

808 19 31 7 

993 69 3 8 

9,608 __ -- 80 

Highest percent mortalities of impinged organisms occurred during June (Table 2). The bay 

anchovy, /mhos nitchiZZi, represented 74% of the total sample during June, and mortality was 

98% (Table 2). 

head jellyfish (StomoZophus melecgris) mixed with the screen samples. 

lethal to fish as well as shrimp, and have a paralytic effect on most species encountered. 

Hildebrand and King (1977) report that during June, 1977, mortality rates of impinged organisms 

were probably high due to the presence of jellyfish. During September, the second overall 

highest percent mortality for the dominant species was recorded (Table 2). gmzhoa mitchiZZi 

represented 44?; of the total sample and suffered a 94% mortality (Table 2). Only 39 organisms 

were collected from the screens during this sample period and it is doubtful that this small 

number bears any statistical significance. 

in Table 3. 

during 1977: 

parva, 7%; and f.iicropogon unduliatus, 7% (Table 3). 

individuals collected. The fragile forms, Anchoa mitckiZZi and Brevoortia patronus, represented 

58% of the total number of impinged organisms collected during 1977. 

the dominant species ranged from 10 mm for Brevoortia pctronus to 78 mm for Micropogon unduZatus 

(Table 3). !.!icropogon urzduZatus and Penaeus aztecus incurred the lowest annual percent mortality (3%) (Table 3).. knckoa mi.tckiZZi and Lucania parva suffered the highest overall mortalities for the year (31E) (Table 3). The Atlantic menhaden, Brevoortia patronus, incurred 

only a 10% mortality during 1977 (Table 3). 

This high mortality was directly attributable to the large numbers of cabbageThese jellyfish are quite 

The annual composition of dominant species impinged on the traveling screens is illustrated 

The five dominant species represent the following percentages of the total catch 

Brevooi.tia patronus, 35%; Anchoa mitchilli, 232, Penaeus aztecus, 8%; Lucania 

These species compris'ed 80% of the total 

Mean standard lengths for 

It has been suspected that the amount of debris loading on the traveling screens has some 

effect en the survival of impinged organisms. Figure 3 illustrates combined monthly mortality 

for the dominant species versus debris weight. As indicated in Figure 3, when the debris 

weights during January, February, and March fluctuated, the percent mortality Tollowed relatively the same pattern. The low percent mortality during April (Fig. 3), when debris loading 

was at its peak, is somewhat puzzling; however, the composition of the debris may have been a 

factor. During spring, algal forms often dominated the debris load, displacing the generally 

more abundant endemic marine spermatophytes. These algal forms are more consolidated and 

resilient and can be picked from a biological sample much more rapidly than the loosely consolidated marine grasses. Similarly, it is believed that impinged organisms,do not become as 

entangled on the screen in this algae as they do in grasses. As stated previously, organisms 

collected in May and June (Fig. 3) suffered mortalities directly associated with the cabbagehead 

jelly fish, StomoZophus meieagris, and the stinging nettle jellyfish, Chrysaora quinquecirrha; 

therefore, any relationship between debris loading and mortality during these months is somewhat 

skewed. 

Debris weights were relatively high during July, as were percent mortalities; however, a 

rather uniform decline in debris weight and percent mortality was noted in August (Fig; 3). 

Only 21 individuals representing the dominant species were collected from the screens during the 

September sampling (Table 2). 

low for any significant correlation to debris, again jellyfish were probably the factor influencing mortality.. Hildebrand and King (1976) report that during September sampling the mortality for fish caught on the screens at the Davis Station was IOOX, due to the overwhelming 

number of stinging nettle jellyfish. 

(Fig. 3). 

(Fig. 3). 

December (Fig. 3). 

Although the numbers of organisms collected in September are too 

Percent mortality during October was 10.w as compared to relatively high debris weight 

Percent mortality was relatively high in November and increased somewhat in December 

Similarly, debris weights were relatively high in November and increased during 
86 

Xi0 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 

Fig. 3. Combined Monthly Mortality for the Five Dominant Species, Including 

Debris Weight. 

A. mitchiZZi, M. unduZatus, L. parva, and P. aztems. 

The five dominant species were B. patronis, 

CONCLUSIONS 

During the twelve-month impingement study at Central Power and Light Company's Barney M. 

Davis Power Station, 12,060 organisms were collected from the Passavant screens. The overall 

percent survival for all individuals collected during 1977 was 86%. 

Five species--Brevoortia patronus, Anchoa mitchiZZi, Micropogon unduZatus, Pmeus azteeus, 

and Lucania pama--represented 80% of the total number of individuals collected during 1977. 

The fragile forms, Anchoa mitchiZZi and Brevoortia patronus, represented 58% of the total 1977 

impingement catch. 

lected from February through May, and fewest collected from June through December. 

only a 3% mortality during the study. 

(Anchoa mitchiZZi) suffered the highest mortalities for the year (31%). 

Monthly catches were highly variable, with the greatest numbers of dominant species colThe Atlantic croaker (Micropogon unduktus) and brown shrimp (Penaeus azteeus) incurred 

The rainwater killifish (hernia parva) and bay anchovy 

Some correlation between debris loading and mortality was observed during seven months of 

the year. 

fish than any other factor during this impingement study. 

It is believed however, that survival was decreased more by the occurrence of jellyACKNOWLEDGEMENTS 

The authors are indebted to Dr. Henry Hildebrand for his comments concerning this study. 

Thanks also go to Alfred Hesse for drawing the figures included in this paper, and to Juan De 

Los Santos and Joe Guerra for the many hours of laboratory and field analyses performed-to make 

this study possible. 
87 

REFERENCES 

Hedgepeth, J. A. 1947. The Laguna Madre of Texas. Trans. North Am. Wildl. Conf. 12:364-380. 

Hildebrand, H. H., and D. King. 1972. A Preliminary Biological Study of the Cay0 del Os0 and 

the Pita Island Area of the Laguna Madre. Annual Report to Central Power and Light Company. 

333 pp. 

Laguna Madre. 

Laguna Madre. Annual Report to Central Power and Light Company. 297 pp. 

United States. Vol. 111. Estuaries and Coastal Waters. ANL/ES-56. Prepared for the U.S. 

Energy Research and Development Administration by Argonne National Laboratory, Argonne, 

Ill. 310 pp. 

. 1976. A Biological Study of the Cay0 del Os0 and the Pita Island Area of the 

257 pp. 

A Biological Study of the Cay0 del Os0 and the,Pita Island Area of the 

Annual Report to Central Power and Light Company. 

. 1977. 

Stupka, R. C., and R. K. Sharma. 1977. Survey of Fish Impingement at Power Plants in the 
LARVAL EXCLUSION WITH WOVEN-SLOT, FINE-MESH SCREENING 

William 0. Cheesman and R. Roy Cheesman 

Royce Equipment Company 

P. 0. Box 34543 

Houston, Texas 77034 

The woven-slot fine-mesh screen can be used for screening of fish larval forms and is 

adaptab’le to various screening mechanisms including the conventional vertical traveling screens 

and the single-entry, double-exit screen. 

screening have been investigated in a research program at Rice University. These investigations 

have focused on the dynamic and kinetic factors affecting survival of screened organisms. 

results of these findings the reader is encouraged to contact the authors. 

The hydraulic and mechanical factors of fine-mesh 

For 

89 
CURRENT TVA WORK ON THE FLUID MECHANICS OF SCREENS 

WITH VERY SMALL OPENINGS FOR THE EXCLUSION OF 

LARVA€ AT POWER PLANT COOLING-WATER INTAKES 

Svein Vigander 

Division of Water Managemeni 

Tennessee Valley Authority 

Norris, Tennessee 37828 

P.0, Drawer E . 

Abstract 

The potential use of screening media with very small openings to exclude larval 

fish at power plant cooling-water intakes opens several areas of possible fluid 

mechanic problems. In this paper, ongoing research is described which focuses on 

four specific areas: (1) the prediction of the pressure drop across a screen, given 

flow rate and screen properties; (2) the estimation of the pressure drop across partially plugged screens; (3) the rate of debris buildup on a site-specific stationary 

screen sample; and (4) methods for stationary screen cleaning and their effectiveness, 

Other areas are identified in which research is needed to aid in the design of 

intakes that will effectively exclude larvae. 

INTRODUCTION 

The typical power plant cooling-water intake in the Tennessee Valley area is equipped with 

vertical traveling screens covered with a woven steel mesh with 9.5-mm openings (3/8-in.-square 

mesh). These screens are intended to protect the cooling-water circulating pumps and condenser 

tubes from potential problems caused by debris entrained in the cooling water flow. 

are typically rotated once per shift to wash the accumulated debris mat off the screening medium. 

The medium may be protected from mechanical damage by vertical trash bars mounted 15 to 20 cm 

apart upstream from the screen. 

Except for occasional undesirable approach flow conditions, these standard intake screens 

have posed little challenge from the hydraulic point of view. However, larvae and small fish 

that are entrapped in the approach flow may be entrained and killed, and larger fish may be 

impinged on the screens for relatively long periods and may consequently suffer lethal stress 

levels. 

practicability of excluding larval fish using screens with openings so small that most entrapped 

larvae will not be entrained and in such a manner that most larvae will not suffer intolerable 

stress levels in the process of being excluded from the intake. -A host of new fluid mechanic 

problems are encountered with such an exclusion system. In this paper we discuss current work 

aimed at solving these problems, which are: (1) the flow rate-pressure drop relationship for 

screens with very small openings; (2) the plugging and fouling of such screens; and (3) the 

methods necessary to clean the screens. In addition, this work has led to the identification of 

areas in which research is needed to better design intakes that involve the interface of structures, fluid mechanics, and fish behavior. 

The screens 

Therefore, developmental work is currently underway to investigate the feasibility and 

FLOW RATE AND PRESSURE DROP 

SCREEN NOMENCLATURE 

Screens with small openings are manufactured and are available in many configurations. The 

nain variables governing flow through a screen are those that define the geometry of the screen: Mire cross-sectional shape, weave type or method of assembly, mesh size on both sirrfaces of the 

screen, and wire size. Based on these basic parameters, many other secondary screen properties 

have been formulated for the purpose of correlating pressure drop and forces on the screens. 

91 
92 

Figure 1 is a definition sketch for a square-mesh screen of simple weave with circular 

wires. The following secondary screen properties are a1 so useful : 

-d 

x Fig. 1. 

Nomenclature Definition for Square-mesh, 

Simple-weave, Round-wire Screen 

Wire diameter = d (mm) 

Opening size = P (mm) 

Mesh = m (wires per mm) 

Fractional open area L ct (or percent) 

Basic Rclationrhlps : 

Screen opening size. The size of the hole in the screen (x) is governed by the mesh (m) 

and the wire diameter (d): 

Open screen area. The percent or fractional open projected area (a) of the screen is a 

function of mesh, wire diameter, or hole size: 

a = (l-md)2 = (mi)* = (1 - $!d)’ 

The last expression is shown graphically in Figure 2. Values given by a screen manufacturer 

agree well. 

specify the open screen area. 

Note that only.two of the three parameters m, d, and k are needed to completely 

Screen thickness. The total thickness (9) of a simple-weave screen is 

B=2d. (3) 
93 

I 

v 

\ 

4: 

6 

a 

E' 

- 

tLz 

W 

tW 

I 

P 

"3 

E 

I 

W 

0 

tW 

v) 

W 

-J 

0 

2 

N 

I -' 

FRACTIONAL OPEN SCREEN AREA, a 

Fig. 2, Computed Relationship between Screen Properties. 

manufacturer are represented by dots in open circles. 

The values given by a screen 

Area/volume ratio. The ratio (a) of screen surface area to screen volume is given by the 

expression: 

a = 12 71 m2 xi , 

in which ei is the length of a crimped wire segment. 

xi = (d2 + m-2)4 . 

Void fraction. The volume void fraction (E) of the screen is given by 

E=l-' m2 d . 

Screen wire Reynolds number. The Reynolds number (R) of the screen is based on the wire 

diameter; the unobstructed, upstream flow velocity (V); and the kinematic viscosity (u) of the 

fluid: 

IR = Vd/v . 

The Reynolds number represents the ratio between the interial and viscous fluid forces that contribute to the pressure drop across the screen. 

expressed as a pressure drop coefficient (K), which is defined as: 

(7) 

Pressure drop coefficient. The pressure or head drop across the screen (Ah) is comnly 

Ah 

v2 

29 

IK=-. (8) - 

The above screen properties were computed and are listed in Tables 1 and 2 for ten simpleweave screen samples that were tested. 
94 

Table 1. Characteristics of Tested Screen Samples of 

Square-mesh, Simple-weave Screens 

Mesh per Diameter of Space Between Open Area, 

0 v. 

No. Mater i a 7 a Inchb (in.) (in.) (percent ) d Wires, (1 - Screen Lineal Wire, d 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

ss 

ss 

ss 

P 

ss 

ss 

P 

ss 

ss 

a 

18.0 

10.0 

18.0 

35.3 

14.0 

12.0 

11.1 

8.0 

4.0 

17.0 

0.023 

0.035 

0.0173 

0.0087 

0.0204 

0.0181 

0.0197 

0.0258 

0.0475 

0.011 

0 -0326 

0.065 

0.0383 

0.0197 

0.051 

0.065 

0.0709 

0.099 

0.203 

0.048 

~~~~ 

34.4 

42.3 

47.4 

48.2 

51 -0 

61.2 

61.2 

63.0 

65.6 

66.1 

1.43 

1.85 

2.20 

2.27 

2.50 

3.59 

3.60 

3.80 

4.26 

4.36 

= Stainless steel 

P = Polyester 

a = Aluminum. 

bTo convert inches to millimeters, multiply by 25.4. 

Table 2. Computed Screen Propertiesa for Square-mesh, 

Simple-weave Screens 

Pressure Drop 

Void Opening Wire Segment Coefficient 

Screen Thickness, Ratio, Fraction, Size Length, for R=100, 

Screen Area/Vol ume 

No. B (ft)b a (per ft) E(-) (ftP .ti (in.)c K(-) 

1 0.0038 734.5 0.648 0.00271 0.0601 5.13 

2 0.0058 399.6 0.709 0.00542 0.1060 3.16 

3 0.0029 710.9 0.744 0.00319 0.0582 2.35 

4 0.0087 1390.5 0.748 0.00164 0.0296 2.27 

5 0.0034 549.0 0.767 0.00425 0.0743 1.92 

6 0 - 0030 463.1 0.825 0.00544 0.0853 1.09 

7 0.0033 428 - 3 0.824 0.00587 0.0922 1-11 

8 0.0043 307.9 0.835 0.00827 0.1276 0.99 

9 0.0079 153.2 0.848 0.01 690 0.2540 0.85 

io 0.0018 652.0 0.851 0.00400 0.0598 0.83 

Units according to Reference 8. 

To convert inches to millimeters, multiply by 25.4. 

a 

bTo convert feet to meters, multiply by 0.30480. 

C 
95 

Figure 3 is a definition sketch for a wedge-wire, welded screen. For this type of screen 

the important secondary properties are defined as follows: 

Open screen area. An equation for the percent or fractional open area (CY) of a wedge-wire 

screen material can be derived from the screen geometry and is: 

the symbols of which are defined in Figure 3. 

14 are included in Table 3. 

Computed values of CY for screen Nos. 11 through 

v$lr d 

DETAIL B 

4 See 

DETAIL A 

4 See detail 8 

detoil A 

Fig. 3. 

Nomenclature Definition for 

Welded, Wedge-wire Screen 

Table 3. Characteristics of Tested Screen Samples of Welded, Wedge-wire Screens 

Measured Screen Dimensions (in.Ib (see Fig. 3) Screen Manufacturer's Open Area, a 

a2 d hb hr sb st- (%) No. Oesignation Material a, 

11 4041 slot SSa 0.092 0.040 0.145 0.145 0.167 0.038 0.469 

12 60-mil slot ss 0.091 0.040 0.146 0.145 0.171 0.061 0.469 

13 100-mil slot 

14 80-mil slot ss 0.093 0.041 0.146 0.147 0.170 0.080 0.464 

'22.3 

30.1 

ss 0.093 0-039 0.148 0.145 0.168 0.099 0.467 39.5 

35.2 

aStainless steel. 

bTo convert inches to millimeters, multiply by 25.4. 
96 

Screen Reynolds number. The screen Reynolds number (IR) is based on the unobstructed upstream velocity (V), the top width of the trapezoidal screen bars (al), and the kinematic 

viscosity (u) of the fluid: 

Va 1 IR=---. 

Table 3 shows the screen properties for the four samples of welded wedge-wire screens that were 

tested. 

Pressure drop coefficient correlations. The literature contains results of many investigations of the pressure drop due to flow through fine-mesh screens (Refs. 1-15). The following 

summary of published pressure drop coefficient correlations is valid for flow normal to a squaremesh, simple-weave, screen made of circular wire. The pressure drop coefficient is a function 

of the screen wire Reynolds number and the fractional open area of the screen: 

Figures 4 and 5 show this relationship as expressed by several authors. The pressure drop 

coefficient is shown as a function of Reynolds number in Figure 4 for a screen with 47.4% open 

area (Screen No. 3). For Reynolds numbers larger than about 500, the effect of viscous forces 

is negligible, the pressure drop coefficient becomes independent of the Reynolds number and is a 

function of the open area only. 

is also shown. This range corresponds to intake approach velocities from 6 cm/s to 60 cm/s. It 

can be seen in Figure 4 that in this range both viscous and intertial forces have an effect on 

the pressure drop coefficient. The nine curves shown exhibit fair agreement. 

gives high values in comparison to the others. Reference 6 gives low values for high Reynolds 

numbers. 

The probable range of Reynolds numbers for steam plant intakes 

Reference 14 

V= 60 cm/r 

I I 

,--. I I 

I I 

%a I 

I1 I I I I ltll I I I I I fr Ill I I I I I Ill} ~ 

10 20 40 60 80 100 200 400 600 800 1000 2000 4000 60008000 

SCREEN WIRE REYNOLDS NUMBER,IR =Vd/u 

Fig. 4. Comparison of Pressure Drop Coefficients Computed from Various Sources in the Literature 

The probable range of Reynolds numbers to be applied at steam plant intakes 

for Screen No. 3 (47.4% open area). 

properties. 

with water at 60°F corresponds to intake velocities of 6-60 cm/s (shown between the 

broken 1 ines). 

See Tables 7 through 3 for data and screen . 
97 

4. c 

3.5 

- 

0 

? 3.0 

> 

0 

N 

- 

\ 

r 

II 

g 2.5 

I= 

w 

z 

u 

LL 

W 

0 

V 

CL 

2.0 

1.5 

n 

W 

(z 

3 

v, 

(z 

a 

2 1.0 

0.5 

0' 

FRACTIONAL OPEN SCREEN AREA, Q 

Fig. 5. Comparison of Pressure Drop Coefficients for High Reynolds 

Numbers as a Function of Open Screen Area. 

numbers refer to the reference list. 

The encircled 

References 1, 6, 7, and 8 seem to yield good mutual agreement. These correlations are: 

From Reference 1: 

with 

IR I 50 100 150 200 300 

f(R)11.44 1.24 1.13 1.08 1.08 e 

From Reference 6: 

-5 I 

K(6) = 6(1-a)a-3 iR3 . 

From Reference 7: 

IK(7) = - - 1 f(lR) , (.: ) 

with 

€2 I 50 79 100 126 158 200 316 

f(W) I -89 .76 .71 -67 .63 -60 -57 * 
98 

From Reference 8: 

in which all length dimensions are in inches. Note that the last correlation does not make use 

of the percent open area, but instead uses the screen void fraction (E) and surface area/volume 

ratio (a). 

The pressure drop coefficient is shown as a function of the fractional open screen area in 

Figure 5. 

Note that the pressure drop coefficient increases rapidly for screens with open areas less than 

50%. 

Again, results from References 1, 6, 7, and 8 seem to be in good mutual agreement. 

RESULTS OF PRESSURE DROP MEASUREMENTS 

The ten screen samples were mounted at the end of a flow nozzle through which measured 

rates of air were blown for the measurement of pressure drop across the screen. 

tribution across the 40-cm-diameter (16-in.-diameter) nozzle throat was measured and found to be 

sufficiently uniform that no measurably large error existed in the pressure drop due to flow 

maldistribution. The air density was calculated for each test on the basis of wet-bulb, drybulb, static-pressure and atmospheric-pressure measurements. The airflow was metered with a 

sharp-edged orifice installed in a straight section of pipe between the fan and the nozzle. 

pressure drop across the screen was measured with a differential micromanometer down to the 

nearest 0.05 mm of water column. 

The flow disThe 

As an example of the results, the measured pressure drop-Reynolds number correlation for 

Also shown in Figure 6 are the head losses to be expected at each end of the' 

screen No. 5 is shown in Figure 6 and compared to the results from Reference 8. There is good 

agreement. The pressure drop measurements for all ten screen samples are similar, but are not 

presented here. 

velocity range from 6 cm/s to 60 cm/s. 

to 76 mm, and at the lower velocities the head drop ranged from 0.3 mm to 2 mm of water for all 

ten screen samples tested. 

errors in screen properties. Screen No. 2 was a nominal 10-mesh screen, according to the manufacturer. Using this value, a nearly 50% underestimate of the head drop resulted. A close 

inspection of the screen sample revealed that the actual mesh was higher than 10 and not square, 

namely 11 x 12. Using an average value, a much better pressure drop prediction resulted. 

Therefore, pressure drop is very sensitive to small changes in screen geometry. For accurate 

estimates, actual measured dimensions should be used in pressure drop calculations. 

At the higher velocities the head drop ranged from 13 mm 

Note in Figure 7, however, the strong effect on pressure drop of 

The measured pressure drop coefficients for the four samples of welded, wedge-wire screens 

The plots show that 

as functions of the Reynolds number based on the top width of the wedge-wire are shown in 

Figure 8. 

as the Reynolds number is increased to a critical value (Rc) of about 500 and 600 for screen 

Nos. 14 and 13, respectively, the pressure drop coefficient is increased. As JR is increased 

beyond this critical value, IK remains constant, indicating independence of the pressure drop 

coefficient with respect to Reynolds numbers larger than Rc. 

'apparently were all conducted at Reynolds numbers larger than IRc for these screens. Also shown 

in Figure 8 is the probable range of Reynolds numbers to be applied at steam plant intakes with 

water at 60°F. At 60 cm/s 

the pressure drops calculated from the pressure drop coefficients in Figure 8 are 180, 104, 53, 

and 71 mm of water for screen Nos. 11, 12, 13, and 14, respectively. 

The results indicate two distinct regions of IK dependence on IR. 

The tests on screen Nos. 11 and 12 

These numbers correspond to intake velocities from 6 cm/s to 60 cm/s. 

Given a constant screen geometry, independence of the pressure drop coefficient with 

respect to Reynolds numbers larger than IRc implies that IK is a function only of the open fractional area (a) of the screen in this region: 

K = f(a) . 

The functional relationship between M and CY for welded wedge-wire screens with Reynolds numbers 

larger ttian RC is indicated in Figure 5. 

boundary conditions (IK = 0 at a = 1, iK -f - as a -f 0) is expressed by the equation 

A curve fit through the data points and satisfying the 

K=- 0 044 0-511 + - - 0.555 for IR t IRc - 

a2 a 
99 

5 

h 

0, 

aJ 

\ 

> 

N 

'74 

a 

r 

II 

Y 

tLJ 

- 

. 

23 

Y 

LL 

LL 

W 

0 v2 

n 

- 

0 

of 

0 

W 

3 

v) 

cn 

w 

of 

off 

a 

0 

0 50 IO0 I50 200 2 50 300 

SCREEN WIRE REYNOLDS NUMBER, lFt =Vd/u 

Measured Pressure Drop Coefficient for Screen No. 5 (51.0% open 

area). See Tables 1 through 3 for data and screen properties. 

The probable range of Reynolds numbers to be applied at steam 

plant intakes with water at 60°F corresponds to intake velocities 

of 6-60 cm/s (shown between the broken lines). 

Fig. 6. 

I I I 

SCREEN WIRE REYNOLDSNUMBER, TR =Vd/v 

Fig. 7. Measured Pressure Drop Coefficient for Screen No. 2 (42.3% open area). 

through 3 for data and screen properties. 

to be applied at steam plant intakes with water at 60°F corresponds to intake 

velocities of 6-60 cm/s (shown between the broken lines). 

See Tables 7 

The probable range of Reynolds numbers 
100 

- . 

Screen NO. 12. a.30.1 % 

I 

100 200 300 400 500 600 700 800 900 

SCREEN REYNOLDS NUMBER, R=Va,/V 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

i 

I 

I 

I 

I 

-I 

Fig. 8. Measured Pressure Drop Coefficients for Welded Wedge-wire Screens. 

through 3 for data and screen properties. 

numbers to be applied at steam plant intakes with water at 60°F corresponds 

to intake velocities of 6-60 cm/s (shown between the broken lines). 

See Tables 1 

The probable range of Reynolds 

PRESSURE DROP FOR OBLIQUE FLOWS 

The pressure drop resulting from flow at an angle to simple-weave, square-mesh screens is 

studied in References 2, 3, 9, 11, and 12. Data show that if the flow approaches the screen at 

an angle (e) normal to the screen, the pressure drop can be estimated correctly using the normal 

or cosine component of the velocity in the pressure drop-Reynolds number correlation. In other 

words : 

K(e) = IK(o) cos2 e , 

in which IK(8) is the pressure drop coefficient for flow at an angle e normal to the screen and 

IK(o) is the coefficient for e = 0, i.e., IK for flow normal to the screen. 

different angle. 

screen, there will be a tangential force on the screen. 

drop coefficient, a tangential force coefficient (IF) can be defined: 

Note that if flow enters the screen obliquely it also leaves the screen obliquely but at a 

Also, in addition to the pressure drop which results in a normal force on the 

In a manner similar to the pressure 

F=- F 

@* 1' 

in which F is the tangential force on the screen and p is the density of the fluid. 

flow angles between 0 (normal) and 45", the following tangential force coefficient correlation 

is given in Reference 3: 

For approach 

in which the angle e is expressed in radians. 

agreement with a limited set of data. 

our own experiments on pressure drop due to oblique approach flows. 

This correlation is shown to yield numbers in 

We have not found any better correlations, nor performed 
101 

PRESSURE DROP THROUGH PARTIALLY, ARTIFICIALLY PLUGGED SCREENS 

The main problem encountered in calculating the pressure drop through screev which are 

partially plugged by accumulation of various kinds of debris and trash is the quantification of 

hydraulic properties of the debris. 

of possible debris sizes and shapes render the problem quite intractable. 

simplified approach was taken to gain at least a measure of insight into possible pressure drop 

magnitudes for partially plugged screens. 

It was postulated that the pressure drop could be estimated based solely on the fractional 

open area of the debris plugging the screen. 

drop across a screen which was plugged to various degrees by uniformly spaced circular rods. 

The measured pressure drops were correlated with the computed fractional open area of the partially plugged screen. 

Kpp = Ks -t Kd(a), in which Kpp 's the pressure drop coefficient for a partially plugged screen, 

Ks is the pressure drop coefficient for the clean screen itself, and Kd(a) is the pressure drop 

coefficient for the debris, based on the estimated fractionally open area (a) at the partially 

plugged screen, The latter, Kd(CL), is computed from the same screen pressure drop formula as 

the former (KS). For example, using screen No. 2 with a = 0.357 at a flow corresponding to a 

Reynolds number of 200 and the pressure drop equations from References 1 and 7, the following 

results were obtained: 

The randomness of the plugging process and the vast variety 

Therefore, a very 

This postulate was tested by measuring the pressure 

According to postulate, the pressure drop coefficient should be 

sf d - m 1 .ooo 0.500 0.250 0.125 

IK 4.3 6.2 10 21 47 

Me as u red 

IK (Ref. 7) 4.1 5.8 8.9 18 54 

IK (Ref. 1) 4.4 6.0 9 22 78 

The agreement between the measured and estimated values is reasonably good, indicating that the 

postulate for pressure drop across partially plugged screen can be used to obtain reasonably 

accurate numerical estimates. Note, however, that trash geometries deviating substantially from 

the circular cylinder shape can be expected to yield different values. 

A better approach might be to compute the "effective" fractional open area of the screen, 

based on the open area remaining after plugging, as ae = a(l-P), in which ae is the effective 

fractional open area, a is the fractional open area of the clean screen, and P is the fraction 

of the clean screen open area that is plugged. The pressure drop coefficient for the partially 

plugged screen can be estimated from the screen pressure drop formula for the clean screen with ae substituted for a. 

tially plugged wedge-wire screen is presented in Figure 9. Screen No. 14, with an approach 

velocity of 30 cm/s, was used for the pressure drop coefficient computations. 

debris" method is denoted by the solid curve and the "effective a'' method is denoted by the 

dotted curve on the plates. In Figure 9 it is indicated that the "effective a'' method predicts 

larger pressure drop coefficients than the "separate debris" method throughout the range of 

plugging. Also indicated in Figure 9 are the nearly vertical slopes of the curves for plugging 

percentages larger than 90%. 

P, comparison of these two methods for computing the pressure drop coefficient for a parThe "separate 

SCREEN PLUGGING AND FOULING 

One of the most often-raised questions regarding the use of screens with very small openings 

is: with such small openings will not the screen plug up and the flow of cooling water stop? 

In addressing that question, we will divide the screen plugging mechanisms into two distinct 

categories: (1) mechanical plugging due to the impingement of entrapped debris (organic or 

inorganic) and the formation of a filter mat, and (2) biological fouling due to the growth of 

live organisms that may colonize the screening medium. In addition, there is the problem of 

protecting the screening medium from the impact of large debris that may tear or damage the 

screens. 

Currently, we have tests underway to shed some light on aspects of the mechanical plugging 

There was a continuous flow of water approaching, flowing over, and bypassing the screen 

The results are necessarily site-specific and seasonal. 

of a flat, wedge-wire screen sample with 1-mi slot width. The approach flow was parallel to the 

horizontal surface of the 46-cm square screen sample and the sluts were arranged parallel to the 

flow. 

sample. Measurements were made of the flow-rate through the screen and the pressure drop across 

the screen. Most of the testing was performed in December 1977 in a river-like environment with 

rapidly varying stage. 

the debris collected consisted mostly of silt and fragments of aquatic vegetation. 

In this case, 

Pumping 
102 

3.6 

a 

W 

tU 

3 3.0 

0 

E 

? 2.4 2 

W 

W 

a 

0 

v) 

I 1.8 0 

J3 

0 

a 

I 

ILL 

c 

% 1.2 

a 

W 

a 

3 2 0.6 W 

U 

a 

n 

0 

Fig. 9. 

Comparison of Pressure Drop Estimates 

for Partial ly P1 ugged Screens 

0 20 40 60 BO IO0 

PERCENT OF SCREEN OPEN AREA PLUGGED, P 

CLEAN SCREEN, Q = 0.352 OR 35.2%. SCREEN No. 14 

TR > IR, 

V = 30cm/s 

t 

through the screen with an average, superficial slot velocity of about 15 cm/s continued until 

an arbitrary head drop-of 1.25 m occurred across the screen. 

backwashed and the test was repeated. Typical results are shown in Figure 10. 

At that point the screen was 

The average pumping time between backwashes was about three hours, a1 though times varied 

from as short as one-half hour to as long as eight hours, depending mostly upon the river stage. 

High stages promoted rapid plugging. 

river stage or whether the river was rising or falling. 

The first method was to stop pumping and let 

the bypassing river flow clean the screen for varying durations. 

from 0.3 to 1.0 m/s. The cleaning efficiency 

(c.e.) was based upon the residual head drop (AhR) after cleaning as compared to the head drop 

across a completely clean screen (Ahc): 

No trends were found relative to the rate of change of 

Backwashing was accomplished in three ways. 

The river velocities ranged 

Washing times of 30, 60, and 300 sec were used. 

AhR - Ahc 

c.e. = nh 

C ut4 

A value of zero would denote a perfectly clean screen. 

the longer washing times, but were not good (20-200) using this method. 

reversed pumping through the screen was tried, with slot velocities of about 0.4 m/s and 3- 

minute duration. 

compressed air was used to force water in the suction pipe back through the screen with slot 

velocities of about 1 m/s for about 3 seconds. 

These preliminary tests showed that the most efficient cleaning or backwashing method was the 

use of compressed air to force water out through the slot with a velocity an order of magnitude 

greater than the suction velocity, and that.this backwashing is essentially accomplished in a 

matter of a few seconds. 

Another concern is the possibility of a slowly increasing res-idual pressure drop accumuThe cleaning efficiencies improved with 

In the third method, 40-psi 

As a second method, 

Cleaning efficiencies of about 20 were obtained. 

Cleaning efficiencies from 2 to 15 were obtained. 

lated after repeated backwashing cycles. 

terms of cleaning efficiency in Figure 71. 

a trend towards an equilibrium condition of about 20. 

most applications. 

The accumulated residual pressure drop is expressed in 

The data are still'incomplete, but there seems to be 

This value should be sufficiently low for 
103 

336.1 

336.2 

335.s 

1.5 

1.0 

0.5 

I 

I 

-I 

I 

-+ 1 

0 

4P 6P 

DECEMBER 19, 1977 

Fig. 10. Typical Results of Plugging Tests in the Field (welded wedge-wire screen, 

1-mm slot, 15 cm/s slot velocity) 

1 I I I I I I I I I 0 2 4 6 8 IO 12 14 16 18 20 22 24 I 

. __ .. .- -- ~ ~~ NUMBER OF BACKWASHING CYCLES, AIR 

Fig. 11. Accumulating Residual Pressure Drop After Backwashing 
104 

Observation of screen surfaces after a period of use generally reveals dirty-looking screen 

wires that to the inexperienced eye may seem like a well-plugged screen, while in fact measurements show that the screen is still quite open and passing water readily with a tolerable 

pressure drop; It should also be noted that long, thin, elongated debris shapes like fibers, 

grasses, and seaweeds may be relatively easy to keep off a screen with openings so small that 

the debris is not partially entrained. 

and this mat must be frequently removed by moving the screen or by backwashing. The tests so 

far indicate no major problem in accomplishing this task with regard to mechanicdl plugging. 

tests have yet been made on biological fouling. 

A filter mat will form on the screen with small openings, 

No 

AREAS OF ADDITIONAL RESEARCH NEEDS 

More data are needed on the rate of mat.formation on screens with very small openings. 

These data will probably be both site-specific and seasonal and will depend on the flow field 

near the intake. 

by living organisms. 

There is a specific need for data on the possible colonization of the screens 

More field data are needed on long-term screen washing methods. Such tests must go hand in 

hand with the plugging and fouling tests. Data are also needed on the separation of larvae from 

the debris mat on the screen. 

The approach flow into large intakes should be considered carefully to prevent suction of 

undesirable water partials, to prevent separation, eddying, and other undesirable flow conditions, 

and to obtain the specific flow field needed to avoid entrapment of larvae. 

model tests may be necessary to insure the proper flow field. 

Physical scade 

There also seems to be a lack of knowledge on the response of larvae of various species to 

the measurable characteristics of a flow field such as (1) mean velocities, (2) velocity gradients 

in all three spatial directions, (3) turbulence intensity, and (4) turbulence scale. If we knew 

the response of fish to these flow parameters, we could design intakes to obtain specific desirable flow conditions and predictable fish response. 

REFERENCES 

1. 

2. 

3. 

4. 

5. 

7. 

8. 

9. 

10. 

Idel'chik, I. E. 1966. Handbook of Hydraulic Resistance--Coefficients of Locat Resistance 

and of Friction. AEC-tr-6630. Translated from Russian. Prepared by the Israel Program 

for Scientific Translations, Jerusalem, for the U. S. Atomic Energy Commission and the 

National Science Foundation. 

Schubauer,' G. B., W. G. Spangenberg, and P. S. Klebanoff. 1950. Aerodynamic Characteristics of Damping Screens. Technical Note 2001. National Advisory Committee for Aeronautics. 

Carrothers, P. J. G., and W. D. Baines. 1973. Forces on Screens of Small Solidity lnclined 

to a Fluid Flow. Am. SOC. Mech. Eng. Pap. No. 73-WA/FE-20. 

Cornel!, W. G. 1958. Losses in flow normal to plane screens. Trans. Am. SOC. Mech. Eng 

80: 791 -799. 

Collar, A. R. 1939. The Effect of Gauze on the Velocity Distribution in a Uniform Duct. 

Nat. Phys. Lab. U.K. Rep. & Mem. No. 1867. 

Wieghardt, K. E. G. 1953. On the resistance of screens. Aeronaut. Q. 4:186-192. 

Annand, ,W. J. D. 1953. The resistance to air flow of wire gauzes. J. R. Aeronaut. SOC. 

57: 141 -146. 

Armour, J. C., and J. N. Cannon. 

Chem. Eng. 14(3):415-420. 

Carrothers, P. J. G., and W. 0. Baines. 1965. Forces on screens inclined to a fluid flow. 

J. Fluids Eng. Trans. Am. SOC. Mech. Eng. 87:116-117. 

Baines, W. D., and E. G. Peterson. 1951. An investigation of flow through screens. 

Trans. Am. SOC. Mech. Eng. 73:467-480. 

Taylor, G. I., and G. K. Batchelor. 1949. The effect of wire gauze on ma71 disturbances 

in a uniform stream. Q. J. Mech. Appl. Math. 2(1):1-29. 

1968. Fluid flow through woven screens. J. Am. Inst. 

11. 
105 

12. Alsaffar, A. M. 1974. Hydrodynamic effects on flow through screens at intakes. Water 

13. Ingmanson, W. L., S. T. Han, H. D. Wilder, and W. T. Myers, Jr. 1961. Resistance of wire 

14: Hoerner, S. F. 1965. Fluid-Dynamic Drag. Practical Information on Aerodynamic Drag and 

15. Padman-abhan, M., and S. Vigander. 1978. Pressure drop due to flow through fine mesh 

Res. 8:617-622. 

screens to flow of water. Tappi 44(1):57-54. 

Hydrodynamic Resistance. Published by the author. Libr. Congr. Cat. card No. 64-19666. 

screens. J- Hydraul. Div. Proc. Am. SOC. Civ. Eng. (In press..) 
BIOLOGICAL AND ENGINEERING CONSIDERATIONS 

FROM COOLING WATER INTAKES 

IN THE FINE-SCREENING OF SMALL ORGANISMS 

Yusuf G. Mussalli, Edward P. Taft, and Peter Hofmann 

Stone 8 Webster Engineering Corporation 

P..O. Box 2325 

Boston, Massachusetts 02107 

Abstract 

Fine-screening of small organisms can be grouped into two concepts: impingement 

and deterrent. Impingement concepts involve the collection and removal of organisms 

with through-flow, center-flow, and dual-flow traveling screens. In evaluating the 

biological effectiveness of these screens, consideration should be given to species, 

approach and through-mesh vetocities, mesh opening, impingement duration, debris loading, and type of organism wash system, Engineering considerations include potential 

for clogging, need for continuous operation of the screen, and screening material. 

Furthermore, each type of traveling screen has advantages and disadvantages relating 

to the potential for debris and organism carryover, screening area, screenwell layout, 

velocity distribution along screen face, and potential effect on pump performance. 

Impingement and diversion systems require that collected organisms be returned to the source water body. 

units. The impingement concept appears to be the most practicable solution for once- through cooling systems. 

Deterrent concepts, in which the organisms passively drift by a screening device, 

Transport systems can utilize either gravity flow or pumping 

include infiltration systems such as radial wells, porous dikes, and wedge-wire 

screens. Biologically, the radial wells and wedge-wire screens will cause little 

impact to small organisms. The porous dike has not been employed for the protection 

of small organisms to date. Engineering considerations presently limit the use of 

wedge-wire screens and radial wells to makeup water intakes with small withdrawals. 

INTRODUCTION 

Extensive research and development efforts have led to the design of fish protection systems which are now being utilized to prevent losses of juvenile and adult fishes at power plant 

cooling water intakes. 

developing new technologies, for the protection of egg and larval stages which are normally 

subject to entrainment in circulating water systems. Due to the small size of such organisms, 

all protection systems investigated or proposed to date utilize collection or deterrent media 

with fine openings such that egg and larval forms are physically prevented from entering intakes. 

Such fine-screening can greatly increase the potential for engineering problems relative to 

reliable operation of the cooling water system. 

Biological and engineering criteria which should be considered when selecting design parameters for an intake utilizing fine screening are discussed. 

type of screen for a specific site, screenwell layout, screen mesh size, mesh material, wash 

systems and special features for protecting organisms are presented. 

Recently, attention has been given to extending available technology, or 

Criteria for selecting the proper 

BACKGROUND 

The entrainment of small organisms into cooling water systems has been a critical and controversial subject relative to the licensing of power plants. As a result, extensive research 

107 
loa 

has been conducted to quantify entrainment mortality and to determine the impact of such mortality on the ecology of the source water body. Large study programs have also been carried out to 

identify sources of mortality (thermal stress, mechanical injury, biofoul ing control agents, 

pressure) with the goal of developing power plant design and operating criteria which might act 

to improve the survival of organisms passing through a cooling water system. 

vent small organisms from entering the cooling water system altogether. While the concept of 

fine screening for the protection of organisms at power plant intakes is relatively new, finemesh screens and microscreens have been used extensively in the past for industrial purposes. 

Of particular interest is the fact that fine-mesh traveling screens of the center-flow (singleentry, double-exit) and dual flow (double-entry, single-exit) type and drum screens have been 

utilized for many years at power plants in Europe. 

operation of fine-mesh screens is available. 

the effectiveness of these European installations in excluding fish eggs and larvae. 

nary biological data on fine-screening have been obtained from recent studies in the U.S. These 

studies are the subject of other papers in this proceedings. 

broad overview of research efforts to date such that common engineering and biological considerations can be identified, and a basis for future studies can be developed. 

into two categories based on their mode of action: impingement concepts, in which organisms are 

physically impinged and removed from a screening medium, and deterrent concepts, in which the 

velocity through the screening medium is designed to be low and the screening device is oriented 

in a natural current such that organisms drift passively by the device. 

latter category would appear to offer a better solution to entrainment problems, application is 

presently limited to makeup flow rates of closed-loop cooling systems, and relies on the presence 

of specific hydrographic and environmental conditions. Their practicability is, therefore, sitespecific. Impingement concepts, on the other hand, utilize more conventional equipment which 

may be practicable at many sites, particularly for once-through cooling, provided that the 

organisms of concern can withstand the impingement and removal process. Therefore, it is evident 

that both concepts have engineering and biological advantages and disadvantages. 

is a discussion of these concepts, their present stage of development, and the research needed 

to resolve inherent design problems such that they may be applied to power plant intakes with an 

acceptable degree of reliability. 

Recently, preliminary studies have been initiated to develop intake designs which will preTherefore, information on the design a_nd 

However, no information is available relative to 

PrelimiTkerefore, this paper presents a 

The various fine-screening devices or systems investigated to date can be broadly grouped 

While concepts in the 

The following 

IMPINGEMENT CONCEPTS 

The impingement-concept category presently includes through-flow traveling screens, centerflow (single-entry, double-exit) screens, dual-flow (double-entry, single-exit) screens, and 

various modifications of these offered by different screen manufacturers. All screens incorporate a screening medium with sufficiently small openings to retain the smallest organism of 

interest - 

BIOLOGICAL CONSIDERATIONS 

To date, there is only one operating fine-screening installation in the United States from 

These operate continuously at a speed of 4.3 m/min (14 fpm) and screen 

which biological data have been obtained. 

pany's Barney Davis Station in Corpus Christi, Texas, which utilizes four center-flow screens 

with 1.0-mm nylon mesh. 

a total flow of 22 m3/s (757 cfs). 

corresponding to a through-mesh velocity of 0.52 m/s (1.7 fps). 

report that initial survival of fragile fishes such as Gulf menhaden (Brevoorti~ patronus) and 

Bay anchovy (Anchoa mitchiZZi) measuring 18 to 86 mm in length is high after they are washed 

from the screens. While latent mortality studies have not been conducted, these preliminary 

results indicate that impingement devices may offer a viable method for preventing entrainment 

of small organisms. 

This installation is Central Power and Light ComThe gross velocity at the screen face is 0.24 m/s (0.78 fps) 

Murray and Jinnette (1978) 

Several laboratory and field studies also demonstrate the potential for high survival of 

ichthyoplankton following impingement. 

sored an evaluation of a fine-mesh through-flow traveling screen at the Indian Point Generating 

Station Unit 1 on the Hudson River (Ecological Analysts, Inc., 1977). One traveling water screen 

was backfitted with 2.5-mm nylon mesh and modified with fish buckets, a low-pressure spray header 

and a collection trough on the rear side-of the screen. Collection efficiency studies were conducted with 72- and 14-day-old post-yo1 k-sac hatchery striped bass (Morone smitilis) with mean 

standard lengths of 7 to 9 mm. Survival estimates were obtained with wild fish, primarily late 

post-yolk-sac (15 mm MSL) and early juvenile (19 mm MSL) striped bass. 

approach velocity was approximately 0.12 m/s (0.4 fps) and the screen travel speed was 3 m/min 

(10 fpm). 

retained by the 2.5-mm mesh. 

In 1977, Consolidated fdison Company of New York sponIn all tests, the screen 

The results of these studies showed that 7- to 9-mm larvae were not effectively 

It was concluded that 10- to 18-mm larvae may be the smallest Size 
that can be collected on mesh of this size. 

post-yolk-sac larvae washed from the screen were 68 and 47 percent, respectively.' Initial and 

latent survival estimates of early juveniles were 100 and 88 percent, respectively (Ecological 

Analysts, Inc., 1977). 

The Indian Point study results are relatively consistent with those obtained in laboratory 

and field studies conducted by the Tennessee Valley Authority (Tomljanovich et al. 1977). 

of eleven fish species were tested in a flume containing various screen panels to determine the 

mesh size needed to retain the larvae and the mortality associated with impingement. 

ranging from 0.5 to 2.5 m were evaluated at water velocities of 15, 31, and 46 cm/s (0.5, 1.0, 

and 1.5 fps). 

from 0.5 to 16 minutes to determine the effect of impingement duration on retention and mortality. 

Tomljanovich et al. (1978) has presented an excellent sumnary of the results of these studies. 

Several conclusions reached from the research have important implications relative to the development of fine-screening design criteria for power plant application. First, it was found that the 

0.5-m mesh was the only screen size that retained nearly 100 percent of the smallest fish tested 

(average body depth 1.0 to 1.4 mm) and that with mesh sizes larger than 0.5 mm, retention was 

directly related to body depth. 

may be necessary to utilize a mesh size of 0.5 mm to adequately protect larvae despite the fact 

that they may have body lengths as long as 7.0 mm. The effects of screening to such a fine level 

must be carefully considered relative to increased debris clogging potential. In addition to the 

engineering problems which clogging causes, debris loading on a screen could result in conditions 

which would decrease the survival potential of impinged organisms. 

area decreases and through-mesh velocity increases. Therefore, at sites where debris loading is 

medium or heavy, actual through-mesh velocities will exceed the design velocity, possibly causing 

reduced retention and increased mortality, as shown by Tomljanovich et al. (1978) for several 

species. This problem can be minimized by designing the screen to operate at higher travel 

speeds when necessary to reduce the degree of clogging per unit area of mesh over time. Further, 

organisms may become entrapped by, or entangled in, the debris itself. This could lead to direct 

injury, but also implies that debris should be returned to the source water body along with 

separated organisms (assuming a dual-spray system is being used) if it is found that a substantial 

portion of the organisms reside in the debris and cannot be effectively separated from it. 

Initial and latent (96-hr) survival estimates of late 

Larvae 

Mesh sizes 

Test fish were impinged on the different screen meshes for varying lengths of time 

Therefore, depending on the species present at a specific site it 

As a screen clogs, the open 

ation 

among 

limit 

Tom1 janovich et al. (1978) also found a strong inverse relationship between impingement durAgain, such a requirement could necesand survival. While the duration which resulted in high latent mortalities varied widely 

the different test species, immediate survival data indicated that it may be desirable to 

the impingement time to approximately four minutes. 

sitate high-speed, continuous screen operation. 

larval survival cannot be made on the basis of the preliminary fine-screening experiments conducted to date. However, it is likely that continuous operation of fine-mesh screens will be 

required during periods of peak larval abundance, and the engineering implications of such operation must be considered. 

Naturally, generic design criteria for maximizing 

In conclusion, from a bi.ologica1 viewpoint, it would appear that the concept of impinging and 

removing larvae from fine-mesh traveling screens with relatively high survival is a viable one 

hdhich warrants further investigation. However, utilization of fine-screens may create engineering 

problems which must be identified and resolved to ensure reliable operation, as discussed below. 

Since the preceding discussion addresses the biological aspects of impingement concepts in a 

generat manner, additional biological considerations pertaining to specific screen designs will be 

brought forward in the following discussions. 

ZNGINEERING CONSIDERATIONS 

The available biological data on fine-mesh screening indicate that the concept of impinging 

ind removing small organisms through the use of traveling screens appears to warrant further 

investigation. 

if traveling screen is superior to others relative to potential stress and mortality incurred by 

rganisms. 

lisadvantages of specific screen types can be identified, as well as inherent features of each 

rhich might act to enhance survival of impinged organisms. 

Sufficient experimentation has not been conducted to determine whether one type 

However, generic engineering considerations in fine- screening and advantages and 

!enera1 Considerations 

The use of fine screens has many engineering implications relative to clogging, continuous 

,peration, type of spray wash system, and type of screening material. Due to the small openings 

as small as 0.5 mm) of fine-screening medium,.these screens will clog much faster than the con- 

-entional 9-mm (3/8-in.) screens currently in use at power plant intakes. A solution to this 

ncreased clogging potential is the use of one or more sets of trash racks upstream of the fine 

creens. These racks would have clear openings ranging from 3.8 cm (1.5 in.) to 12 m (0.5 in.) 
110 

depending on the type and loading of the debris. 

present, a traveling bar or coarse screen, (which is mechanically similar to a through-flow 

screen) utilizing bar spacings or mesh openings as small as 12 mm (0.5 in.) could be installed 

between the fine-screen and the coarse trash rack to reduce the debris loading on the fine-mesh 

screen. 

(1 in.) to 38 mm (1.5 in.), equipped with automatic raking equipment, could be utilized. 

should be capable of operating continuously at a low speed of about 0.3 m/min (1.0 fpm). 

on European experience with fine-screening, the following screen speeds are recommended: 

differential head across the screen of 10 cm (4 in.), a screen should be capable of operating at 

a speed of 3 to 4 m/min (10 to 14 fpm). 

screen should operate at a speed of 6 to 8 m/min (20 to 28 fpm). 

Because clogging is related to the type and loading of debris at specific sites and because 

little experience exists in the United States, prototype evaluations should be conducted to 

determine the degree of coarse screening required upstream of the fine-screen, rack spacings, and 

screen travel speeds which would ensure reliable operation. Bench tests and mathematical models 

(Saffran and Kormanick 1976) can be used to determine the hydraulic capacity of a fine-mesh 

screen. Also, full-scale tests could be conducted at a specific s i t e u t i l i z i n g a screen 0.3- to 

0.6-m (1.0- to 2.0-ft) wide prior to installation of a complete screening system, to evaluate the 

ability of the system to handle the debris loading present at that site. 

Continuous screen operation can result in substantial wear of the chain flex joints and the 

bearings and bushings. Therfore, since continuous operation is required with fine-mesh screeni?g, the traveling screen components should be upgraded to prevent excessive wear. The utilization of heavy-duty chains, roller bearings at the head shaft, "stoody" bushings at the foot 

shaft, light-weight components, and provisions for proper slack tensioning will all help to 

reduce operational problems and maintenance requirements (Mussalli et al. 1977). 

To reduce the clogging potential and the need for continuous operation throughout the year, 

traveling screens could be fitted with easily replaceable screen baskets of different mesh size. 

In this way, fine mesh could be utilized only during periods of larval abundance, while coarser, 

9-mm (3/8-in.) mesh could be used during the remainder of the year. 

are in the process of developing snap-on or insertable screen panels for this purpose. 

In cases where stringy debris such as grass is 

Similarly, for medium debris loading, a stationary rack with bar spacing of 25 mm 

Furthermore, to ensure that sudden clogging would not overload the drive motors, screens 

Based 

at a 

At a differential of 15 to 20 cm (6 to 8 in.), the 

Several screen manufacturers 

A final consideration in fine-screening is the type of screening material used. There are 

presently four types available: 

oblong (smooth-top), and wedge-wire oblong. The cost per 

square foot ranges from $1 for the synthetic and $5 for the smooth-top to $25 for the wedge-wire. 

Screen life ranges from 3 years for the synthetic to 10 to 20 years for the smooth-top and wedgewire. 

during washing. In larval protection designs to date, the synthetic square mesh has been used in 

once-through traveling screen applications, the wedge-wire in submerged, makeup water intakes, 

and the smooth-top in experimental flumes. In selecting a mesh type, consideration should be 

given to the different characteristics of the meshes. From an engineering viewpoint, ease of 

debris removal and the support bracing required behind the mesh are also factors to be considered. 

Biologically, the smoothness of the material, the shape of the mesh openings, and the percent 

open area are factors which will influence organism retention and survival. 

percent open area should be above 50 percent to provide adequate hydraulic efficiency for the 

fine mesh. 

supports, and fish and debris buckets or lips should be considered. 

screen area by 15 to 20 percent. 

woven metallic square, woven synthetic square, woven metallic 

Each has advantages and disadvantages. 

The synthetic mesh can puncture and is flammable, while the metallic square mesh fatigues 

Hydraulically, the 

Also, in computing through-mesh velocities, the area occupied by the basket frame, 

This could reduce the gross 

Screen manufacturers presently offer front-wash, back-wash, and overhead spray systems for 

In dealing with fish 

debris and organism remova7. 

there are varying advantages and disadvantages associated with each type. 

larvae, screens using any of the spray systems would have lifting buckets attached to each panel 

to contain the organisms in water during travel. 

sprays--one to rinse the screen mesh down into the bucket and a second to clear the bucket. 

Therefore, organisms could be exposed to two wash jets. 

the bucket are poured out onto the mesh as the screen basket passes over the head shaft; therefore, a gentle spray is required to wash organisms off of the mesh. The overhead spray design, 

used on the center-flow screen, is perhaps better than the others since there is a good chance 

that organisms contained in the lifting buckets will be spilled by gravity into the collection 

trough prior to encountering the spray wash. 

source water body. 

after it clears the water surface. 

likely that much of the impinged debris will be washed down along with the organisms. 

From an engineering viewpoint, they are similar. Biologically, 

The front-wash system requires two 7ow-pressure 

In the back-wash design, the contents of 

With all three spray systems, it may be desirable to return organisms and debris back to the 

Since larvae are very small, they can remain impinged on a traveling screen 

This necessitates cleaning the entire screen face. It is 

Therefore, 
111 

in the interest of protecting the organisms, the entire contents of the wash water should be 

returned to the source water body. 

Through-flow Screens 

The through-flow traveling water screen is the most commonly used screen in the United 

States. It should be pointed out, however, that there is a potential for debris carryover. 

Further, careful consideration has to be given to the potential for uneven velocity distribution 

along the screen face due to the influence of pumps, baffle walls, and intake configuration. 

The through-flow screen can be fitted with fine-mesh screen material and upgraded for continuous 

operation, as previously described, in order to handle both debris and organisms. For larval 

protection, the through-flow screens would be modified to incorporate lifting buckets on each 

screen basket to contain these organisms in water during screen rotation. 

the lifting buckets, low-pressure sprays would be added to wash organisms from either the front 

or the back of the screen (Mussalli et al. 1977), as disc-ussed previously. 

Another modification of the through-flow screen design which might be considered for larval 

In conjunction with 

protection is angling of the screen such that motile organisms can be guided to a bypass. 

Numerous studies with fish diversion devices such as louvers and angled screens have shown that 

these devices can be very effective in guiding juvenile and adult fishes to bypasses (Schuler 

and Larson 1974; Taft and Mussalli 1977; Taft et al. 1976). 

been evaluated to determine their potential for diverting fish larvae, the 100-percent guidance 

efficiencies observed with juveniles as small as 25 mn (Taft and Mussalli 1978) may indicate 

that earlier life stages could also be diverted by such screens with fine mesh. 

nonmotile eggs and early larvae would impinge on the screen, with the exception of those which 

happen to enter the diversion system on the bypass side. 

to collect these small organisms in the same manner discussed previously. All organisms capable 

of guiding on the fine-mesh screen would be diverted to a bypass. 

While angled screens have not yet 

Naturally, 

Therefore, the screens would be designed 

At this time, it is not possible to determine the age (size) at which larval fish might be 

diverted by an angled, fine-mesh screen. Naturally, the ability to guide along a screen will be 

influenced by environmental and hydraulic conditions and will vary between species. However, 

evidence that larval and early juvenile fish can guide along angled screens has been reported by 

Pavlov and Pakhorukov (1973) in a review of the fish protection research which has been conducted 

in the USSR. 

screens in laboratory and full-scale studies. 

leads to a fish bypass and utilizes a moving water jet device for cleaning. 

conical screen (Fig. 1) which leads to a central bypass and also has a water jet cleaning device 

which rotates around the periphery of the screen. 

water jets for cleaning screens may not be reliable for power plant applications. 

the fixed and conical screens with water-jet cleaning have been used for irrigation systems or 

large-scale test facilities. 

efficiencies can be achieved. In one study, mosquitofish (Gambusia sp.) 10 to 40 mm long were 

guided very effectively to a bypass over a range of hydraulic conditions. Through-mesh screen 

velocity varied from 0.15 to 0.40 m/s (0.50 to 1.3 fps) and the amount of water drawn into the 

bypass ranged from 1 to 10 percent of the total approach flow. With a through-mesh velocity of 

0.15 m/s (0.5 fps), 88.7 and 97.6 percent of the fish were diverted at bypass flows of 2 and 10 

percent, respectively. 

at 1 and 10 percent bypass flows, respectively. 

were diverted with a 10 percent bypass flow. Therefore, guidance efficiency was affected by 

approach velocity and bypass flow. However, under all conditions, the efficiencies were high 

(greater than 75 percent). Additional laboratory studies with roach (RutiZus mtiZus fZuviutiZis) 

showed similar results, with guidance efficiencies as high as 96 percent. 

ments, it was noted that the best guidance was achieved when the approach and bypass velocity 

were equal. 

One final investigation of the angled stationary screen design is reported by Pavlov and 

Pakhorukov (1973). 

16 degrees to the approach flow was evaluated at a fish hatchery in 1968 and 1969. 

showed that larval fish (species not given) less than 14 mm long were not effectively guided, but 

larger fish were a71 diverted to a bypass. 

Laboratory and large-scale studies of conical screens with internal bypasses have also shown 

high fish diversion efficiencies (Pavlov and Pakhorukov 1973). Experiments with several species measuring 9.5 to 50 mm in 7ength have shown very effective guidance along model and full-scale 

conical screens when the screen mesh (1 to 3 m> was angled 8 to 12 degrees to the approach flow 

with approach velocities as high as 0.9 m/s (2.95 fps). In one study, verkhovka, perch, and bitterling were held for a minimum of 48 hours following testing for determination of latent 

These studies investigated the effectiveness of two types of fine-mesh diversion 

One type is an angled, stationary screen which 

The second type is a 

It should be pointed out, however, that underIn the USSR, 

Results of studies with the angled stationary screen design have shown that high diversion 

At a velocity of 0.25 m/s (0.82 fps), 75.8 and 96.1 percent were diverted 

At 0.40 m/s (1.3 fps), 79.8 percent of the fish 

During these experiReducing the bypass velocity caused a drop in efficiency of up to 28 percent. 

A fine-mesh screen (1.0-mm mesh), 12.6 m (41.3 ft) long set at an angle of 

Results 
112 

mTmw 

CONICAL SCREEN 

Fig. 1. Conical Larval Diversion Screen. From Nikonorov and 

Me1 'ni kova (1 974). 

mortality. 

mortality. 

In conclusion, it would appear from the results of the Russian investigations that the 

potential for guiding larval and juvenile fish as small as 10 nun long with fine-mesh angled 

screens exists. Screen angle, approach velocity and approach-to-bypass velocity ratio appear to 

have the greatest influence on guidance efficiency. Since screen angle and flow velocity affect 

the overall size of a screen well at a given flow rate, future efforts should be concentrated on 

optimizing these parameters with consideration to both biological and engineerin A 

possible layout for a once-through larval diversion screenwell flow rate of 43 m /s (1500 cfs) 

is shown in Figure 2. 

Mortality among verkhovka averaged 8 percent while the other species displayed no 

! concernsCenter-f 1 ow Screens 

As shown in Figure 3, this screen is set parallel to the approach flow with water entering 

a central entrance port and exiting through both the ascending and descending screen faces. 

screen has an overhead spray system which washes debris into an internal trash trough. The 

screen baskets are elliptical and the overall screen assembly is oval. 

screen lengths (front to back) range from 1.2 to 4 m (4 to 13 ft), corresponding to approach 

channel widths from 2.5 to 5.0 m (8 to 16.5 ft). 

bel ow: 

1. 

The 

Commercially available 

The advantages of this screen are summarized 

Since all water is screened internally, there is no possibility of debris carryover, i-e., 

debris cannot enter the cooling water system without passing through the screen. 
113 

BYPASS AND 

TRANSITION 

SECTION 

SCREENWASH PUMPS 

TRASH BASKET (TYP) 

ICING DIFFUSER 

0 * 10 20 

SCALE (ft) 

SECONDARY BY PASS 

DRIVING PUMP (TYP) 

Fig. 2. Angled Screen Larval Diversion System 

FISH BUCKET ATTACHED 

TO SCREEN 

---____ 7-1 I !1 

,/ liD I ,- 

SECTION A 

.SH 

Fig. 3. Center-flow Screen. Courtesy of Passavant Corporation. 
114 

2. For a given screen width, a larger screening area is available than with a flat panel, 

through-flow screen. This is due to the fact that both the ascending and descending screening faces are used for initial debris removal and that the screen baskets are elliptical 

rather than flat. 

designs shown in Figure 4 provide approximately 60 and 110 percent more screening area, 

respectively, than a flat basket. 

screening water for the following reasons. 

circular baskets to each other (Fig. 31, the uppermost portion of the baskets is not very 

effective in screening water. This results in a reduction of screening area of approximately 10 percent. Second, for the protection of organisms, it would be desirable to fit 

each screen basket with a bucket as shown in Figure 3, to hold 5 cm (2 in.) of water. 

ing off the lower basket area in this way would reduce the screening area by 20 percent. 

Therefore, with a bucket added to each basket, the overall screening area of a semicircular 

basket may be only 12 percent greater than that of a flat basket. 

Various basket shapes are available; the semicircular and involute 

However, this additional area is not fully available for 

First, due to the close proximity of the semiBlock3. As 

gu 

4. As 

as 

5. Th 

. i.. 

Fig. 4. Comparison of Basket Types 

PANEL 

designed, the screen has adequate sealing between baskets and between the baskets and the 

des to minimize the passage of organizms without additional modification. 

designed, the screen can withstand frequent or continuous operation due to features such 

head shaft roller bearings and heavy-duty chains. 

increased screeninq area described above allows for a reduction in the width and/or 

depth of the screenweli structure. 

Additional design considerations of the center-flow screen are as follows: 

1. 

2. 

3. 

While it is possible to achieve low screen.face velocities by increasing the length and 

width of the screen, velocities at the entrance port would be higher than the approach 

velocities to through-flow screens. Thus, the advantage of increased screening area and 

the resultant increase in flow capacity may cause a higher entrance velocity which could 

increase entrapment of fish within the screen. For example, at the previously described 

Barney Davis Station, the approach channel and screen face velocities are only 0.23 and 

0.24 m/s (0.77 and 0.78 fps), respectively. However, the entrance port velocity is approximately 0.56 m/s (1.86 fps). In general, low entrance port velocities, such as 0.30 m/s 

(1.0 fps), could be achieved by using shorter screens (i.e., lower flow capacity per 

screen); however, reduction of the flow per screen would necessitate the use of more 

screens and, therefore, a wider intake structure for a given plant flow. 

It is doubtful whether the ascending side, which may be partially clogged, would screen 

water with equal efficiency as the cleaned, descending side. 

in the screen area of the ascending screen face should be assumed. 

ered when establishing design criteria for prototype installations. 

Due to the angle at which the approach flow streamlines enter the screen and to the presence of discharge ports on the downstream sides of the screen, the velocity distribution 

across the screen face is uneven. Therefore, from a fish protection viewpoint, average 

design velocity values should not be used. 

organisms will be subjected to through-mesh velocities in excess of the design velocityFurther, the additional influence of debris clogging on velocity distribution should be 

considered. Consideration should also be given to the fact that organisms impinged near 

A 25 to 50 percent reduction 

This should be considRather, it should be assumed that many 
115 

the surface of the descending face will be subjected to changing velocities as they travel 

around the baskets in the lower arch and up to the overhead spray wash. 

will experience the maximum impingement duration possible. 

Water exiting the screen faces discharges from the side ports as jets. 

patterns created in the pumpwell could affect pump performance. 

Research Laboratories 1974a) have been conducted to determine the effect of a center-flow 

screen 3.0-m (10 ft) long on a vertical wet-pit circulating water pump. 

considered for installation in a bay 5.2 m (17 ft) wide with a design capacity of 9 m3/s 

(320 cfs). 

center portion of the bay between the back wall of the screen and the pump (Fig. 5). 

was due to the jet action of the water exiting the screen faces along the walls of the 

intake bay. 

to occasionally pull air into the pump bellmouth. Further, the flow was not evenly distributed around the entrance to the bellmouth. The intensity of these flow characteristics 

was observed to increase as the screen assembly location was moved from 9.75 m (32 ft) to 

8.5 m (28 ft) to 5.5 m (18ft) from the pump center-line. To use the screen at a distance 

of 9.75 m (32 ft) or less from the pump would have required a special baffle (Fig. 6) to 

streamline the flow patterns to the pump bellmouth. 

tested; the final baffle design selected for this application is shorn in Figure 7. 

shown in Figure 5, a screen-to-pump distance of 14.6 m (48 ft) would have eliminated the 

need for the baffle. By comparison, utilizing a through-flow screen, with the same flow 

rate, would have required a distance of only 7.6 m (25 ft). 

screen-to-pump distance is to use horizontal or vertical dry-pit pumzi which, because of 

the design of the inlet to the pump suction, are less sensitive to fiow disturbances than 

vertical, wet-pit pumps. 

features which can affect screenwell layout and pump operation. 

These organisms 

4. The nonuniform flow 

Model studies (Alden 

The screen was 

Test results indicated that a zone of reverse flow was established in the 

This 

Eddies were active in the back corners of the pump bay and were strong enough 

Several baffles were designed and 

As was 

Another means of reducing the 

Therefore, it can be seen that the center-"low screen has design 

tP SURFACE FLOW PATTERNS 

/-CENTER FLOW SCREEN I IIt I I I I I I It J 

FEET 

85.6 80 70 60 50 40 30 20 10 6 0 

- V -- 

I 

IiI 

'i, ELEVATION -SECTION qC 

FEET 

6.5 

5 0 

a5 

-7.0 

-10.0 

-21.0 

Fig. 5. Pumpwell Model with Center-flow Screens (1 ft = 0.305 m). 

Courtesy of Alden Research Laboratory.. 
116 

CENTER FLOW SCREEN 

FEET SURFACE FLOW PATTEZNS GU,DE r WALL b 85 

5 .O 

0 

5.0 

8.5 

NIFORM 

I1 I I I I’ If I1 J 40 20 17 10 6 0 50 

BAFFLE 

FEET ’O )- 85.6 80 70 60 

1 

ahl=l.O’ 

CHANNEL 

‘p END WALL 

ELEVATION- SECT1 ON qc 

Fig. 6. Pumpwell Model with Center-flow Screen and Baffle (1 ft = 

0.305 m). Courtesy of Alden Research Laboratory. 

Fig. 7. Baffle Design (1 in. = 2.54 cm) 
117 

5. 

6. 

The entrance port of the center-flow screen is designed such that a contraction effect 

occurs which influences the distribution of flow (and velocity) across the screen. As 

shown in Figure 6, guidewalls can be added to minimize the contraction effect and increase 

the effective use of flow through the full surface of the screen. 

entrance port increases with depth, the guide walls should be tapered in the vertical plane 

to match the port. 

The potential impingement time on a center-flow screen is longer than on a through-flow 

screen at a given travel speed. 

the descending face at the water surface and is carried through the water column before 

being lifted to the overhead spray removal system. 

ment time has been identified for important species, the travel speed of a center-flow 

screen may have to be greater than that of a through-flow screen. 

Since the width of the 

Maximum travel time occurs when an organism impinges on 

Therefore, if a limitation on impingeDual-flow Screens 

center-flow screen and, accordingly, has similar advantages and disadvantages, as summarized 

briefly below: 

1- 

2. 

The dual-flow (double-entry, single-exit) screen (Fig. 8) is similar in concept to the 

Debris cannot carryover into the cooling water system. 

Because two faces are utilized in initial screening water, there is a greater screening 

area available for a given screen width than with through-flow screens. 

increase in screening capacity is not directly proportional to the increased area since the 

ascending side is not as efficient in screening water, as discussed previously for the 

center-flow screen. 

The flow distribution, and therefore the velocity distribution, along the screen face is 

not uniform. 

The flow patterns to the pump will be non-uniform. 

tories 1974b) for a 9-m3/s (320-cfs) vertical wet-pit pump, using a dual-flow screen 2.6 m 

(8.5 ft) wide, indicated that the screen should be located at a minimum distance of 11.6 m 

(38 ft) from the pump center-line when used in conjunction with a baffle, as shown in 

Figure 9. 

For the purpose of fine-screening at intakes there appears, at this time, to be no engineering advantages to using the dual-flow rather than the center-flow screen in a screenwell arrangement. 

design of the wash collection system is basically the same as with a through-flow screen, potential mortality associated with screen washing would be comparable. 

A variation of the dual-flow screen, known as the No-well arrangement, is shown in Figure 10. 

are.presently operating at power plants in Florida. 

struction advantages and may have biological benefits. 

to the screen via a transition and turning vanes, the need for a typical screenwell is eliminated. This results in cost savings related to excavation and concrete. 

however, has applications only in warm climates to avoid problems associated with icing. 

free passage of fish in the resulting low-velocity areas. Further, the through-mesh velocities 

could be kept low enough to allow larval avoidance. 

modifications would be required to permit utilization of fine-mesh. To ensure reliability 

during continuous operation, heavy-duty components would be required. Adequate sealing between 

screen baskets and between the baskets and guides would have to be incorporated to minimize the 

loss of organisms in these areas. Finally, a low-pressure spray system would be needed to 

gently remove organisms from the screen and lifting buckets, as previously discussed. 

However, the 

3. 

4. Model studies (Alden Research LaboraThe former has less screening area due to the flat panel design. Further, since the 

Several screening installations of the No-well design, utilizing 9-m (3/8-in.) mesh, 

This arrangement has obvious cost and conBy connecting the pump suction directly 

This arrangement, 

No-well screens could be installed with suitable distances between them to allow for the 

However, as with other screens, design 

. 

Organism Transport 

Organisms which are washed from all types of screens must be returned to the source water 

body in a carefully designed transport system. 

lifted, washed into a bucket, and therefore can be returned to the source water body by gravity 

transport systems. 

a lift basket or a non-clog pumping unit, such as a jet pump, to return the organisms (Mussalli 

and Taft 1977). 

For the impingement concepts, organisms are 

With the diversion schemes, the organisms enter a bypass and would require 
118 

I 

I 

I 

I 

STEEL FRONT PLATE / 

SEAL 

SCREENED WATER 

Fig. 8. Dual-flow Screen. Courtesy of Brackett. 

FEET SURFACE FLOW PATTERNS qP r DUAL-FLOW SCREEN 

8.5 

F, ~~ 

5.0 

8.5 

It I I I I I I II 1 856 BO 70 60 50 40 30 20 10 6 0 

FEET 

ELEVATION-SECTION Qc HLg 0.5' 

Fig. 9. Pumpwell Model with Dual-flow Screen and Baffles (1 ft = 

0.305 m)- Courtesy of Alden Research Laboratory. 
119 

SCREEN BRACE 

MLW EL. (3-0'' 

ELW EL. 5'-0' 

F EXCAVATION 

EL. 24"" 

Fig. 10. No-well Screen Intake 

In general, buckets and pipes should be smooth and sized to avoid high velocities. 

tions should be gradual and elbows should be long-radius to avoid undesirable velocity conditions. 

TransiFinally, valves and meters should not create obstructions in the flow. 

There is little experience in transporting larval fish, and therefore specific criteria 

cannot be identified. 

can be used as a guideline for further research. 

However, data from live-sampling gear, such as various types of pumps, 

DETERRENT CONCEPTS 

Fish deterrent systems have received attention due to the fact that they act to protect 

At present, two types of designs are being considered for larval exclusion: 

organisms with 1 ittle or no handling. Conceptually, these systems are designed and/or oriented 

in such a way that organisms with little or no motility can be passively deterred form entering 

an intake flow. 

infiltration systems, such as radial wells and porous dikes, and cylindrical, wedge-wire screens 

Biological and engineering considerations in utilizing such systems are discussed below. 

BIOLOGICAL CONSIDERATIONS 

The radial well is an available system which can be utilized where geological conditions 

are suitable. 

however, their use is limited to low-capacity intakes. 

power plant intakes. 

prevent the passage of fish eggs and larvae. 

motile, they drift passively in a current and would, therefore, be subject to entrainment into 

the dike unless a fine filtering medium is placed on the outer surface and an adequate ambient 

flushing flow existed to carry the organisms away from the structure. 

motile organisms must be screened at the outer surface boundary rather than within the dike, 

since any organism which penetrates this boundary will ultimately be lost regardless of the 

Operation of radial wells will result in little impact to small organisms; 

The porous-dike concept has never been employed for the protection of small organisms at 

The primary biological concern with the dike relates to its ability to 

Since these early life stages are essentially nonIt is believed that non- 
120 

screening capacity of the media located in the interior of dike. 

filtering media at the outer boundary could create engineering problems in terms of protecting 

the dike from wave forces. 

screen all of the life stages desired due to engineering design limitations. 

sented by Hanson et al. (1978). It would appear that such screens would be effective in preventing the entrainment of fish eggs and larvae provided that the screen slot size is small, the 

through-slot velocity is low, and a relatively high velocity cross-flow exists to carry organisms 

around and away from the screen. Accordingly, the biological effectiveness of wedge-wire screens 

may be site-specific in cases where they are intended to protect non-motile organisms. 

However, locating the fine 

Therefore, it may be found that the dike cannot be designed to 

The results of biological research on the use of cylindrical, wedge-wire screens are preENGINEERING CONSIDERATIONS 

Radial wells and wedge-wire screens are commercially available systems which, to date, have 

been successfully applied to makeup water intakes, while the porous dike is in the developmental 

stage and has not yet been utilized. 

Experience indicates that maximum capacity of a single radial well is limited to about 0.6 

to 1.25 m3/s (10,000 to 20,000 gpm). For a once-through application, given a suitable aquifer, 

about 30 to 45 km (20 to 30 mi) of shoreline could be required to supply 30 to 60 m3/s (500,000 

to 1,000,000 gpm) of cooling water. This consideration and the associated costs of pumps and a 

large piping network would rule out this principle as a practical solution for once-through 

cooling application. 

shows a conical screen designed to handle 1.0 m3/s (16,000 gpm). 

tions in wedge-wire screening are listed below: 

Wedge-wire screens also appear to be presently limited to relatively small flows. Figure 11 

General engineering considera7. 

2. 

3. 

4. 

5. 

6. 

7, 

Clogging. 

to establish suitable hydraulic conditions for self-cleaning and the removal of backflushed 

debris, thereby minimizing the clogging potential of the screen. An adequate backwash system is also required for periodic cleaning of the screen. Compressed air or water can be 

utilized. In order to assess backflushing requirements at a specific site and to determine 

the potential for interference between adjacent screens (Fig. 72), theoretical solutions, 

based on the potential flow theory, can be used. These solutions can determine the spacing 

and orientation of screens needed to minimize the amount of backflushed debris from one 

screen that may accumulate on an adjacent screen which is in a pumping mode. Parameters to 

be used in the analysis include backflushing velocity, pumping velocity, ambient current 

velocity and direction and distance between screens. (Colorado State University 1974). 

Velocity distribution. 

to minimize the probability of entrapment of motile organisms and to minimize the need for 

debris backflushing. 

One approach is to carefully select the screen length, screen diameter, and length of withdrawal pipe penetration into the wedge-wire screen. 

screen shape, such as the conical shape (Fig. 11) or a cylindrical shape with an internal 

diffuser. 

Navigation. The screens must be located such that they do not interfere with navigation. 

Large debris. 

screens or damage them. 

Frazil ice. In northern latitudes, provisions for the prevention of frazil ice formation 

on the screens must be considered. 

+ Biofoulin . Screen materials should be used which will minimize the degree of biofouling its effect on hydraulic efficiency. 

Access. The screens should be readily accessible for maintenance and performance monitoring. 

The screens should be located in an ambient current of at least 30 cm/s (1 fps) 

A uniform velocity distribution along the screen face is required 

Several approaches exist to achieve uniform velocity (Cook 1978) - 

Another approach is to select a 

In many areas, large debris (trees, etc.) and pack ice could block the 

To date, proven methods for adequately cleaning the screens by backflushing and preventing 

frazil ice formation have not been developed for once-through cooling systems that utilize a 

large number of wedge-wire screens. 

However, 

general engineering factors which should be considered during the developmental efforts are as 

f 01 1 ows : 

1- Resistance of the structure to erosion under prevailing current and wave conditions. 

As stated, porous dikes have not yet been developed for once-through intakes. 
121 

i 36" DIA. INTAKE PIPE 

SOLID PLATE END I rn 

Fig. 11. Conical Wedge-wire Screen (1 inch = 2.54 cm) 

a. U = 0.2FPS, a=ODEG BAC KFLUSH ING 

VELOCITY = 1.0FPS 

I- 10 ft. * 

b. U = 0.2FPS, a = 90DEG 

-5FPS 

Fig. 12. Streamlines Showing Movement of Backflushed Debris between Wedge-wire 

Screens .(l ft = 0.305 m). Courtesy of Colorado State University. 
122 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

Structural stability of dike and foundation. 

Hydraulic stability of the dike and foundation against internal erosion. 

The capacity to carry the design flow under biofouling and clogging conditions. 

Minimal effect on prevailing sedimentation or littoral drift patterns. 

Non-interference with boat traffic. 

Provisions for access, maintenance, and monitoring of performance. 

Provisions for backwashing the dike for removal of debris or the melting of frazil ice. 

Economic availability of construction materials. 

Viable and economical construction methods. 

- 

CONCLUSION 

Because the concept of physically preventing the passage of small organisms into power 

plant cooling water systems is relatively new, there exists an obvious need to expand research 

efforts in order to develop and refine the technology required to achieve this goal. 

be apparent that the biological requirements for protecting small organisms create engineering 

problems which have not been of concern in the past. 

developmental efforts be conducted with close interaction between engineers and biologists. 

being evaluated for the protection of small aquatic organisms. 

protection systems have been highlighted such that they can be maintained in future developmental efforts. 

direction to further research. 

It should 

Therefore, it is imperative that future 

This paper has addressed many of the problem areas which exist with the systems presently 

Positive features of specific 

Negative features have likewise been identified in the hope of supplying 

At this time, it appears that impinging concepts offer the most practicable solution to 

larval entrainment problems at once-through cooling sites while deterrent concepts are limited 

to closed-loop cooling systems. 

The-choice of a larval protection system for a prototype application depends on biological 

effectiveness and on engineering and cost considerations. 

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Circulating Water Pump Structure. Report No. 69-74/MlORF. Prepared for Long Island 

Lighting Company and Stone & Webster Engineering Corporation. 

Circulating Water Pump Structure. 

ing Company and Stone & Webster Engineering Corporation. 

Colorado State University. 

Gulf States Utilities Company. 

Cook, L. E. 1978. The Johnson Screen for Cooling Water Intakes, pp. 149-157. & R. K. Sharma 

and J. B. Palmer (eds.), Larval Exclusion Systems for Power Plant Cooling Water Intakes, 

Proceedings of the Workshop held at Shelter Island Inn, San Diego, Calif., Feb. 7-8, 1978. 

NUREG/CP-002. Argonne National Laboratory, Argonne, 111. 

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ting Fine-Mesh Traveling Screen to Reduce Ichthyoplankton Entrainment at Indian Point 

Generating Station. 

Hanson, B. N., W. H. Bason, B. E. Beitz, and K. E. Charles. 1978. Practicality of Profile-wire 

Screen in Reducing Entrainment and Impingement, pp. 195-234. In R. K. Sharma and J. B. 

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of the Workshop held at Shelter Island Inn, San Diego, Calif., Feb. 7-8, 1978. 

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Murray, L. S., and T. S. Jinnette. 1978. Survival of Dominant Estuarine Organisms Impinged on 

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Water Intake Structures. Ifl Pishchevaya Promyshlennost', 208 p. Translated by S. Pearson, 

National Marine Fisheries Service, Northwest Fisheries Center, May 1974. 

Saffran, E. P., and R. A. Kormanik. 1976. Designing Microscreens? Here's Some Help. Water & 

Schuler, V. J., and L. E. Larson. 1975. Improved Fish Protection at Intake Systems, Proc. Am. 

Taft, E. P., P. Hofmann, P. J. Eisele, and T. J. Horst. 1976. An Experimental Approach to the 

Wastes Engineering, April. 

SOC. Civ. Eng. Journal of EE6 101:897-910. 

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Intake Structures, pp. 343-365. 

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Taft, E. P., and Y. G. Mussalli. 1977. Biological and Engineering Investigation of Angled 

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Annual Hydraulics Division Specialty Conference. American Society of Civil Engineers, 

Texas A & M University, College Station, Texas, August 10-12, 1977, pp. 304-312. 

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