# 2~10

" - 

# FP-P5-wJ

In: EA. 1978. Fourth National Workshop on 

## Entrainment and Impingement. December 5 , 1977. 

## Chicago 

## , IL. L. D. Johnson (Ed.



# A Practical Intake Screen which Substantially 

# Reduces the Entrainment and hnpingement of

Early Life Stages of Fish

Brian N. Hanson , William H. Bason Barry E. Beitz 

### , and Kevin E. Charles

Ichthyological Associates, Inc.

R. D. Box 

### 286 Middletown 

### , Delaware 19709



### INTRODUCTION

The objective of this study was to develop a surface 

### water intake compatible with power plant operation and capable of protecting the early life stages ' of fishes. Review 

### of existing technology indicated profIle wire screen (Fig

### ure I) possessed the greatest potential to meet the desired objectives. Screens were purchased from Johnson Division of Universal Oil Products 

### , and this report evaluates their 

### potential as a low- impact surface water intake screen. 

### Studies were initially directed toward the determination 

### of entrainment and impingement of striped bass eggs, 

### larvae, and young by a profile wire screen intake. Studies . were expanded to 

### include other fishes, egg mortality resulting from impingement, biological and detrital fouling 

### rates, in situ long-term testing, and cleaning techniques. 

### Because of the practical and applied nature of the work all experiments were designed to provide a go/no-go result. If the screen failed to meet any biological or engineering 

### requirement , experimentation would have ceased because 

### of the lack of improvement over existing technology.



### MATERIALS AND METHODS

Test Apparatus

Most experiments were conducted in a 30-X- 15- ft oval 

### flume (Figure 2). The aluminum and plywood channel

was 33 in. wide and 48 in. deep. A 4-X- 

### 4-ft sump 

### attached to the flume s inner wall served as the site for

!he model intake. Water was 

### pumped from the sump by a S-hp horizontal turbine pump, which initiated a gravity flow from the flume channel through the test screen. The maximum sustainable pump rate was 505 gpm. 

### Pump rate was measured with an Envirotech Sparling water meter 

### and controlled by butterfly valves. Discharge reentered 

### the flume opposite the sump box. Total volume of the facility at maximum depth (40 in. ) was 5, 472 gallons. 

### A single 83. in. 

### diameter paddle wheel with six
27- 

### 40-in. blades was used to generate flume currents. The wheel was driven by a 3- 

### hp electric motor tluough a variable speed hydraulic transmission coupled to a 

### 20 : I right angle gear reduction. Water velocity was 

### measured

with a Marsh- 

### McBimey Model 201 electromagnetic current


### " meter.

### Egg mortality studies were conducted in a IO-X

### oval flume. The channel was 12 in. wide and 17 in. deep.

A 36- 

### in. diameter paddle wheel with six 17- 

## Il- in. blades

was used to generate current. 

### The wheel was driven by a
1/2- 

### hp variable speed motor coupled to a variable speed hydraulic transmission. Total volume " of the 

### facility was 239. 1 gallons.. 

### A test cage (29. 22. 28. 

### 5 in. 

### ) was used to keep ~est specimens in the 

### proximity of the intake during

l ~xperimental runs 

### in static mode (channel velocity = 0).

--rIle front panel was plexiglass; 

### the sides and bottom were

500-micron mesh nytex fabric. The bottom was custom 

### fit to expose the specimens to only the top 

### half of the

screen (Figure 6). The 

### bottom portion of the screen was frequently covered to reduce the effective open area and 

### increase the maximum intake velocity. Since the exclusion of striped bass eggs and larvae was

the major objective, s-mriWtd.tm':of':o.~ 04Q: 

### in.andlesswere



## ;~~r 

# ,~~~)

AlI cylindrical screens viet~" lTih"':'lff' 

### diamet~r

393

### 394 Fourth National Workshop on Entrainment and Impingement



### Figure 1. Schematic diagram of a cylindrical Johnson

screen with detailed enlargement showing

profile shape of wire. The screen is con. structed wiLh a single continuous wrap of 

### wire (A = internal support rod, B = wire).

i \'('i'Im

Egg Mortality



### . Striped bass eggs were supplied from an onsite 

### hatchery.

All eggs were incubated in a solution of50, 

### 000 IU/I penicillin- 

### G and 50 mg/I streptomycin sulfate for at least 15 hours before testing. Each test consisted of a 30-, 60- 

## G -

Figure 2. 

### Schematic diagram of the large flume

(A = channel , B = sump, C = screen 

### D = intake pump, E = paddle wheel F = paddle wheel drive 

### , G = hydraulic 

### backwash pump, H = air compressor).

and 120-second impingement trial of live eggs with one 

### replicate and one control for each duration. Any given test 

### used eggs from a single brood. Natural dieoff rates were monitored with long- 

### term controls, which were accomplished by holding live eggs in a gallon jar of antiseptic solution. Eggs were aerated and held until the brood' 

### s testing 

### was completed. Total dead eggs were counted and recorded 

### every 30 minutes. Eggs were then preserved in a formalin

### rose bengal solution for microscopic examination.

### Impingement trials and replicates proceeded in the fol

### lowing manner. An unknown number oflive eggs were re

### leased a t ~ q"4~p, 

## !b.,jA!9f,~~rp~1(!i,i~~r~$if~~1bfthe test screen~ After impingement for the prescribed duration , Lhe current was stopped. Eggs were siphoned from 

### the screen into a gallon jar partially filled with antiseptic

solution. Samples were inspected for mortality at 5, 20,

### , and 60 minutes for the first two tests; thereafter inspec

### tion was made at 5, 30, and 60 minutes. Samples were

preserved after I hour.

### Trial controls were held in flume water for the appropriate

time period and then siphoned into a holding jar 

### filled with

the antiseptic solution. Mortality was 

### monitored for 1 hour

and the samples preserved. Preserved samples were exam

### ined With a Bausch & Lomb stereo zoom dissecting scope.

. Developmental 

### stage was determined and the live and dead 

### ratio detennined. Eggs were termed dead when they contained abnormal or disintegrating embryonic material , an 

### emulsified oil globule , or translucent perivitelline space. The smallest and largest eggs in each sample were measured.

Egg-Screen Interaction
Egg impingement studies were conducted in the large 

### flume. Tests were designed to evaluate egg-screen inter

### actions at various channe e.ocitie 

### Approximately 300 preserved 

# t!RGG!! . :1, ~~. C;W"" 

### " "

lfi~~~ !;',

~r~ ,0 

### release4JQJt..upstr~~ th~ ' _,,

1I1., s1oU~~~t\ri 

### opet- "'"

",.h,"r" ",,"..!Ij;j:, ~ ,." ~."" ._" ,,-,,

"h"* ~"'- .

atedatameanintii.k~:yeH5cityof'O;5:Jp,-. 'T4ree 

### experi

### ments of one trial eac 

### ~~re ron at\::hamiei' 

### v~i&Hiesof io:$d;:9. 

### 75tand 

## r'2$'~~ Interactions were fli;:;' e-Jc ;;nd'; 1.,



### per cen tage1~pffi'ge:(ffi~fed. 1D.Ei:O. 04O-in.::Slot'sdeeriil . ' ., 

# ' '

~..""" ", ,



### functioningjatO. s. fp~Was exposed to 15, 

### 000 preserve



### e~;;. 

## ~acl=~ili€Wffect of various channel velocities 

### (0. 

### 6 fps) on impingement. Changes oflocation and 

### number of impinged eggs were monitored for each of the 

### four test velocities. The value of an air bubble curtain as an impingement preventative and cleaning mechanism was investigated at 

### channel velocities of 0.5 and 2. 0 ips. 

### Compressed air was 

### released through a 12- in. long perforated nozzle at 10 psi. 

### The nozzle was positioned to allow the bubble curtain to 

### strike tl-J.e 

### leading side of tlJ.e screen. 

### Approximately 500 ml of preserved eggs (2- 3 mm 

### diameter) were dispersed in the large flume at a channel
velocity 0 , 

### e.nt. Intake was 

### initiated throu~ a 

# 12-m. ; s~~iAd hole at 500 gpm for 10 minutes. Entrained eggs were collected 

### in the sump with a SOD-micron mesh net, and 

### their
volume was measured.

The O. 

### 04O-in. slot screen was installed and the above procedure repeated. In addition, 

### eggs still in the flume

### were removed; those impinged on the screen were re

### covered in a 32- 60-in. 

### , 500-micron mesh net. The volume ofimpinged eggs was measured and 

### used to determine the percentage impinged.

Striped Bass Larvae 

### Swimming ability and avoidance behavior of striped 

### bass larvae exposed to a functioning screen were studied in a static mode. 

### Specimens were obtained from the

onsi te ha tchery \. 

### T.~g:j1~kSof ~sli, "1and 5 days old, were
held in separate 20-gaIIon aquaria and fed brine shrimp. 

### Daily tests of each stock were made for 16 days. 

### Hanson etal. : A Practical Intake Screen 

### 395

Fish in groups of 50 or less were acclimated to flume 

### temperatures for up to 3 hours and released into the test 

### area formed by the screen and test cage. Mter a 2- minute

acclimation to !l!e e~. ~~osure 

### , a 

### ~~~~:



### ~~f,~~jty:1

~: ~~f~ :?O , fPJl)'cw~1Jlijtj, ~~~;h~l,~ 

# ~. ":i 9:4Wgi'~t1

'scr~~'i!hJ~ Swimming ability and behavior oflarvae were 

### . noted until all specimens were entrained (usually less

than 5 minutes). Specimens were recovered in a 500- 

### micron mesh net placed over the screen discharge pipe. 

### Total length of the largest and smallest specimens and of all dead fish was recorded. Survivors of each test were held in a separate 20. 

### gallon aquarium for later experiments.

M~~r ~~"



## s!~~$.~~ste;.., ~;;:imens was depleted 

### ,allStiJYlvo~(f~~1t~2y,~1~141\were' transferred to a 500-
ga1rori' 

### lanksupplied with unf1ltered pond water and used in subsequent tests. These fish exhibited greater 

### resistance 

### to entrainment , and consequently tests were terminated after 30 minutes. Inta:ke\,eJocitie~range(J.frOII1, ();5;tQ-, ffiJlJ~, Impingeme



### ~t&thr1~a~~~~flsh- ~in impinged , '

number entrained, behavior 

### , and swimming ability were
recorded. Fish- min denotes t.i.e sum of t.i.e products 

### the number of fish and the time exposed to any event. 

# ~ry~~w.e.:.J; ~fSCO~ x g;!,~e1js p~(;!J1ieriS' i~athe di. ' ., ,

. Y.soK~ge':'(llPj!.~J1Jnl1,l., 

### !.L).

Fish Impingement

Fish were collected by seine from the Bohemia River, 

### Chesapeake and Delaware (C&D) Canal , Delaware River 

### and nearby freshwater ponds. Striped bass were also supplied by the onsite hatchery. Test specimens were transported in insulated, aerated containers and held in two 6- 

### ft deep plywood boxes continuously supplied with flume water. Water was 

### pumpedthrougb. a sand filter to the holding boxes and

drained throu 

### standpipes back to the flume. Some 

# \~~m~ ~:..s!lf~~~1t) were held in a 500- gallon tank and 42S- gallon swimming pool. These facilities were supplied with water from a nearby pond. 

### Except for striped bass, specimens were not fed prior testing. 

### Specimens acquired from brackish waters were 

### acclimated (4-16 hours depending on salinity) to flume 

### water in insulated 

### , aerated containers prior to testing. Flume salinity was raised to 4 ppt during the summer to

minimize holding and acclimation mortality. This limited 

### the osmotic stress on wea:.lcer and 

### more sensitive species as 

### well as on migrant marine fishes. Before testing, specimens 

### held in flume water were allowed to adjust to the test cage

for 5- 20 minutes; fish held in other facilities were accli

### mated for as long as 60 minutes. 

# Tw~ differen re' used~~rif1g 

### iiiipift~mli1 , ' 

# .' .

pr~ ~ 

### - " 

### -=-- 

# ~ "

' , , ','""",,,

, , .."'"

ce: d ure ~'

, 1. 'Ie, , p 1JWPN~ 'as st 1Ii;!~9; a,t l~, pt~ ~! ;~~t~ ,. iiPd , tbg;;.~ lf~.c is

### 396 

### Fourth National Workshop on Entrainment and Impingement



### ~ noted. Intake velocity was t.~en increased approximately 

## 6 0. 2 fps at lO-minute intervals until the maximum rate was reached. Starting intake velocity ranged between 0. 

### 0 and

i;; 

### 1.3 fps. The second procedure was similar except the pump 

# ~;

rate was held constant for 30 minutes. Three intake 

# ~"

velocities (0. 

### , 1.0, and 1.5 fps) were tested. Specimens

(i. 

### were continually monitored for impingement, entrainment, and behavior. Upon test termination all 

### specimens were

" measured 

### (FL).



### ~ Far- field effects of the screen on seven species were 

### ~ investigated by increasing the size of the test area to 6 ft ~, of flume channel centered around the O. OIO-in. slot screen.

### ~; Intake velocity was held at 1.0 fps for 10 minutes then inf. creased to 1.25 fps for IS minutes. After 25 minutes , par- 

### ~ titions were removed and fish were allowed to swim freely ~: about the flume for 13 minutes. A 1. 00fps channel current 

### ~ was then initiated and maintained for 20 minutes. Velocity ~ was increased to 1.35 fps for an additional 8 minutes , after 

## , which the test was t~lminated. 

# Irt;.!l~amiCIJ:r , fIsh were acclimated for 15- 

### minut~fif":" 

# ""

plastic bag suspended in the 

### channel 10 ft upstream of the intake. Current of a selected velocity was generated in the flume and the pump 

### started. Specimens were released and their behavior noted, 

### especially on the first pass b)' t.lJ.e 

### intake. . ~uifi., 

## i~\y~~9 (, 

# ~~/~,

~ ~4~ row ~~~



# J~~, J:!~ J:il;x ~1 Q(; tM t~J, ~h ~~~i?

'J",'.j; 

# ~?'

oo.J ~1;;ID taf((b:ve Q.ci 

## ~"L~c qI1~JI!!lJzt;:tfte r 10. 

## minute .

exposure at 2. 

### 00 ips , current in the flume was reduced to

zero. Fish were exposed to Lite functioning inta.1ce for 

### additional 5 minutes.An index was devised to compare the relative suscepti

### bility of each species to a functioning Johnson screen and is given by the formula: 

# Su bili t In 

### fIO- r FM 

# seep y 

# ex - L 10

LTFM



### where

1:1 

### 10 is the number of impingement occurrences

ES is LlJ.e 

### number of escapes

FM is fish-min impinged

TFM is total fish- 

### min exposed.



### The index can range from 0 to 2 and is sensitive to dif

### ferences in behavior and swimming ability.



### Detrital Fouling

Detrital fouling studies have been conducted in the large 

### flume from October 1976 through the present. Effects and interrelationships of channel current, intake velocity, detrital load, and screen slot size have been examined. Effectiveness of hydraulic backwash , compressed air 

### (1) 

### backwash, and continuous cleaning with bubbles also have 

### been investigated. Two types of detrital material , peat


### moss and detritus from C&D Canal ichthyoplankton 

### samples, have been used. Detritus has been renewed periodically because particle size was eventually reduced 

### by pumps and cleaning activities.

### All tests have been run at flume levels of 30-35 in. Insofar as possible, flume volume has been held constant for 

### each series of experiments. Th~fflcfs- gf' 

### firt1llCe~vel~ \ '

(();41j7f( ~~IWfiie1&~10C1~~Oi2S~1i7 S' fi ' s Y" aff(file tri t81 " "



### I~~dn~5'~~3'7~'3' I!!;:l3;'



### l~r!t3)~f)~1l~

s~r~~~i p~r-r;)1ifi' 

### fuce

have been evaluated. 

### A selected wet volume of test material was dispersed inthe flume before testing began. Channel current was main

### tained at a predetermined velocity. The screen was cleaned 

### by backwashing and/or brushing immediately prior to the test. Time- 

### to-clog (TIC), head differential versus time , and



### visual observations have been recorded for each run. head differential of 12 in. in the sump has been considered

the endpoint of each test. Tests have usually 

### terminated

in 4 hours if substantial head differential has not been 

### generated. When the volume of detritus required to clog the screen has equaled a substantial part of the test load, an additional 16 oz of material has been added 10 minutes 

### after initiation of the test.

An air bubble curtain identical to thatused in egg im### pingement studies has been evaluated as a fouling preventa

### tive. The nozzle is placed so that air bubbles sweep up

across the leading surface of the screen. 

### TIC and fouling pattems have been compared to tests conducted under the

same parameters but without the bubbler system. 

### Hydraulic backwash normally has been used to clean 

### the screen prior to testing. A 610-gpmHomelite trash pump supplies a reverse flow of 500 gpm through th. 

### e test

screen (Figure 2). A1t.~oug.~ not 

### strictly documented, hydraulic backwash efficiency has been observed and noted. Oeaning effectiveness of air/hydraulic backwash has been investigated. Each test consisted of a comparison of TTC

### after thorough manual cleaning and after air/hydraulic back

### wash. Manual cleaning has been performed with a stiffbristled brush and is considered the basic cleaning technique. Compressed 

### air was accum'ulated in a 2- fe vessel 

### equipped with a 4-in. butterfly valve. Backwash has been accomplished by closing the 12- 

### in. intake butterfly valve and instantaneously releasing air into the screen through a 6- length of 4- 

### in. PVC pipe. Two concentrations of detritus


### were used in the tests.



### RESULTS AND DISCUSSION

Dynamics The initial phase of thestudy consisted of refining the 

### experimental apparatus and determining the hydrodynamics$"I'IP c h4Md

Sc,...", 

# " .



# , . , , ' .



### """ ........ c" ...

t Ve/ocl t.'J

UrTOCe.S



### Figure 3. 

### Schematic diagram of flow patterns



### associated with a Johnson screen 

### (provided by Lee Cook , Universal Oil Products).

of the test screens. Information provided by Johnson 

### Division of Universal Oil Products , Inc. (personal commun

### ication , lee Cook) indicated angle and velocity of 

### approach should decrease from the proximal to the distal

end of the cylindrical screen (Figure 3). Current measurement and behavior of test specimens confirmed this. As expected , measured approach velocity was always 

### less than calculated intake velocity. Actual intake velocity could not be measured for comparison with calculated values since the available current meters could not operate at the screen surface. Theoretica!1y, approach velocity 

### at one wire width from the screen surface is equal to the 

### product of intake velocity and the open area ratio. Approach velocity then decreases as a function of the 

### square of the radius. Approach velocity 3 in. from the screen surface at 455 gpm was 0. 25, 0. 27, and 0.34 fps 

### measured equidistant from the distal to the proximal end. The calculated mean intake velocity for this rate was 

### 1.5 fps. The presence of higher approach velocity at theproximal end was verified by egg and detrital impinge

### ment patterns. Visual observation in the dynanrl,c mode indicated the



### screen 

### s influence was restricted to that portion of the water column that would have passed through or within 2 in. of the screen. Impingement or entrainment of small suspended particles was most common along the leading 

### edge of t.lIe screen. This phenomenon was caused by channel current and enhanced by pump rate. Particles that approached the screen more obliquely were generally Hanson et ai. 

### : A Practical Intake Screen 

### 397

deflected by a boundary current. Deflection was augmented by the cylindrical shape of the screen. The buildup of impinged material was greatest on the proximal 

### t'Iird of tfJ.e upstream edge 

### where intake velocity was hig.hest. Materia! impinged elsewhere on t.lIe screen was

### not held as tightly and tended to move to the down

### stream side. Eddy and channel currents in this area produced a washing effect, which increased with increasing

c.hannel velocity.

Egg-Screen Interaction

Egg-screen interaction tests revealed 

### two distinct areas of impingement on the screen. Screen orientation 

### to flow exposed eggs to direct impact and possible impingement 

### on the leading edge of the screen; eddy currents 

### resulted. in a secondary area of impingement in t.l-J.e proximal onethird of the trailing edge. 

### Impingement on the leading edge was a function of channel velocity but was self- 

### limiting above 2. 

### 0 fps. At velocities greater than 2. 0 fps 

### , all available surface area was rapidly occupied; thereafter, a slow rate of interchange,

### approximately 1% per minute, accounted for all new impingement. A very low percentage of the eggs exposed

impinged on the leading edge. This portion of 

### the screen was the only area where entrainment and wedging in the slots occurred. Entrainment and wedging in slots is 

### apparently caused by pressure generated by channel velocity rather than intake current. . 

### Impingement on the trailing edge was maximum when 

### channel velocity was equal to or less than intake velocity. Eggs in this area were loosely held as evidenced by 

### their movements on the screen surface. As much as 20% of the passing eggs impinged on the 

### leading edge, but most (95%) rolled over the screen and gathered in the 

### proximal portion of tfJ.e 

### trailing edge. . At higher channel velocities 

### the number of eggs present in this area approached zero. Entrainment or wedging in the slots was never observed in this region.

### Incorporation of a bubble curtain was effective in reducing egg impingement. Eggs did 

### not impinge on areas 

### of the screen that were struck by bubbles. The bubble curtain also removed previously impinged eggs. Entrained 

### bubbles were vented in the sump and prevented pump 

### cavitation. Results indicate impingement of eggs can be virtually eliminated by a bubble curtain. Reorienting the 

### screen so that the long axis was parallel to the current would also have virtually eliminated impingement and entrainment. In addition 

### , hydraulic problems associated with the leading and trailing edges would be eliminated and the screen should effectively exclude particles as small

as one- 

### half the slot size because of the coanda effect. Entrainment was primarily associated with the upstream 

### side of the screen. Less than 0. 1 % of all eggs 

### exposed..-..- --. --.-Table 1Summary of Striped BassEgg Mortality Resulting from Impingement on a 0.020-in.Slot Johnson Screen at a 0.fps Approach VelocityAgeDiameterTemperatureDevelopmental Stage(hr)(mm).(C)s::...sr.Late gastrula-early embryo (LG-EE)18.0-31.1.8-15.22.Tailbud.free (TBF)21.5-22.22.F1,1l1ydeveloped embryo (FDE)36.38.20.21.Total18.38.1.8-15.22.:::toDevel.30-Second60-Second120.SecondTotalsLong.termStageTestControlDiffer.TestControlDiffer.TestControlDiffer.ControlTestControlDiffer.All;::sLa- EETrials;;!Dead n123202...% Dead4.31.6c:oTotal n8134787634986694312962451,407948't;jTBFTrials---;;!Dead n...% Dead1.11.1Total n188131116118435226779FDETrials---Dead n.--% Dead0.40.10.4Total n283376254127225302651762805218TotalsTrials.--Dead n129---212% Deadl,30.11.4Total n284930148713010795065442438.--945(a)These eggs were held from 2.0 to 6.5 hours; percentages are on a per hour basis for comparison.(bJT'I~M. :- -1" -'In 1 nn~+Q~ nnnhn'""'



### -"

:7"\ 4.0 ..g,

c:

2.0

5 I 

### LG - EE 

### c Test

Con 

## tro



## TBF FDE oS



### Tota

Figure 4. 

### Mean mortalities of striped bass eggs



### impinged on a 0. 020-in. slotJohnson 

### screen for 0. 

### , 1.0 , and 2. 0 minutes.



### entrained in 2 hours of testing. In tests run without the screen (pumping through the 12- in. mounting orifice), 40% of all eggs were entrained during each of two IO-minute trials. Only 1% entrained and 11 

### % impinged during two similar 

### trials with the screen in place, yielding a 97. 5% reduction 

### in entrainment.

Egg Mortality



### A total of 26 tests was conducted with 6 945 striped

bass eggs of six different stocks. Eggs ranged from 18 to 

### 38 hours old with diameters of 1.8 to 3. 2 rom (after preservation). Developmental stages tested were late gastrula (LG), early embryo (EE), tail bud free (TBF), and 

### fully developed embryo (FDE). Mean mortalities of tests Hanson et al. 

### " A Pr(Ji:tical Intake Screen 

### 399

and controls at three different impingement durations are summarized in Table 1 and Figure 4. Statistical analyses for differences in percentage mortality (student s t- 

### test after arcsine transformation; Sokal and Rohlf 1969) yielded significant (p"::::: 0. 

### 05) differences between test andcontrol for 30-second impingement duration (stages com

### bined), lG- EE stages (durations combined), and all data 

### combined. In general , LG. 

### EE eggs suffered greater 

### mortality than other stages in both tests and controls. Higher mortality of the earliest stages tested may reflect the greater fragility of these stages. Mortality resulting from impingement (test.control 

### difference) ranged from 0. 

### 0% to 11.9%. Mean mortality of developmental stages versus impingement 

### duration ranged

from 0. 

### 0% to 2. 0%. Overall 

### , mean mortality owing to impingement was 1.4% (Table 1). The low average 

### mortality oflong- term controls probably resulted from less handling stress. Visual inspection of eggs during the 60- 

### minute postimpingement holding time revealed most

mortality occurred in t.he 

### first 30 minutes. 

### Skinner (1974) reported mortality of striped bass eggs 

### impinged on 16 mesh/inch screen (0. 044- in. 

### ) was generally 

### less than 10% at approach velocities less than 0. 

### 9 fps and 

### less than 30% at 1.0 fps. At 0. 

### 5 fps approach velocity, immediate mortality was approximately 8% and 12% at 

### I and 2 minutes 

### , respectively. In our study, comparable mean mortality (test only) was 3. 7% and 2. 

### 9% for 1- and minute impingement durations 

### , respectively. Thedifferences between studies may be due to screen construc

### tion , slot size (0. 044- 

### in. versus 0. 

### 020- in. 

### ), procedural

variation , egg stage 

### , or egg origin (wild versuS hatchery

### reared in our study).

Striped Bass Larvae

A total of 42 tests were conducted with more than 1, 

### 000 hatchery-reared striped bass larvae. Larvae 4-33 days old (5. 20. 0 rom FL) were exposed to mean intake velocities

of 0. 13- 

### 1.50 fps at temperatures that ranged from 13 to

24 C. During one set of experiments, more than 930 larvae 

### (aquaria- 

### held) were tested daily from age 4 to 20 days (5. 

### 2 rom TL) at mean intake velocities of 0. 13-
fps and temperatures of 13- 

### 19 C. Ability to resist entrainment was rated subjectively on a group and individual basis (Table 2). Performance was rated 

### on general swimming 

### ability, resistance efforts, and burst ability 

### compared with
the previous day 

### s testing. 

### Avoidance behavior was observed in all 

### experiments

with aquaria- 

### held larvae. Although most specimens entrained within 1 minute, many exhibited positive rheotaxis and actively resisted entrainment 

### upon contact with the screen; those that did not touch the screen were en

### trained more or less passively.-------c=~=~-=~...::. -~~?C: ~~==::=? - .Table2Performance of Hatchery-Reared Striped Bass Larvae Exposed.;."to a 0.040-in. Slot Johnson ScreenMin toRelative Resistanceto Intake;::Agex IntakeEst. % Ent.100%...TL(mm)(days)Vel. (fps)inlminEntrainedGroupfudividualc::to1.431.330-6.0'11000.13D'T1.256.335 ,6.3-0.35 .35 .;::0.351.506.435 .6.40.3520.;::0-6.0.3510....I:.;::6.4. 100.355.3-6.30.35'\:s6.40-6.0.35;::...0.350.3510.0.356.4.0.3550 ,I'J1.505- 7.30.35 .15.0- 7.50 .10,7.36.3-1001.007.41001.000.5022.0012.fa)Ambient water temperature ranged from 13 to 19b)p= Poor; F = Fair; G = Good; E = Excellent.(c)Rating of 10% of total.

### Most larvae were en trained in the proximal half of the



### screen where intake velocity was greatest. The percentage that actively resisted entrainment increased with age , but 

### 100% still were entrained (Table 2). Mean intake velocity 

### was increased to 0. 5 fps after 11 tests because of improve

### ment in swimming ability; results were similar to tests at 0.35 fps (Table 2). 

### The extent of escape resulting from a washing current

### or movement away from the screen could not be ascer

### tained since all tests were in the static mode with a test cage. However 

### , in a situation with current , a " 

### burst " fromt.he screen after contact should greatly decrease the poten

### tial of impingement or entrainment. Tests were originally designed to monitor the increase 

### in avoidance capability as larvae increased in age and size. 

### However 

### , by test day 10 t..lJ.e 

### performance of the aquaria

### held larvae was more or less constant. Comparison with specimens of the same age that were fed natural food and 

### held in larger tanks or rearing ponds revealed substantial 

### differences in size and swimming ability. Mansueti (1958) noted stunting may result from factors 

### such as overcrowding, 

### lack of proper nutrients , variable effects of metabolites in the aquaria, and hormonal imbalances owing to an 

### artificial

environment. These 

### factors may explain the rapid change in growth rate '!Ild swimming ability oflarvae transferred to larger tanks supplied with natural food. 

### In another set of tests , 100 larvae held in a SOD-gallon

tank and a 425- 

### gallon pool were tested at mean intake 

### velocities of 0.35- 1.50 ips. Ages and 

### totallengt.'1s ranged 

### from 10 to 33 days and 8 to 17 rom. Water temperature 

### ranged from 19 to 24 C. Many of these specimens were survivors of earlier experiments. Larger size and greater 

### ability enabled testing at higher intake velocities and re

### sulted in frequent but usually temporary 

### impingements. 

### The oldest specimens tested (13- 17 rom TL) were easilyable to resist intake velocities up to 1.5 fps. Most tempo

### rary impingements occurred near the top of the screen
where intake currents were vertical. 

### Overall, there were 93 impingement occurrences , 75 

### escapes 

### , and 16 entrainments (Table 3). Mortality resulting from impingement was not investigated. Most prolonged impingements were wedged tail first between the wires and 

### held by their opercles; the damage incurred was probably 

## fatal. Avoidance (no entrainment or prolonged impingement) ranged from 40% to 

### 100% for 30-minute tests. ill tests with currents ' of 1.0-1.5 frs , 92. 7% of the larvae (9. 17. 

### 0 mm) swam for 30 minutes wiQ1out entrainment or prolonged impingement.

,C'". FISb. 

### Impingement

A total of 1 

### 387 specimens of20species were tested

(Table 4). Relative 

### susceptibility indices for species tested 

### in numbers of 50 or more are presented in Figure 5, :;Q1;t Hanson et al. 

### : A Practical Intake &reen 401

,,~, 4""c" ,,:?,~?,

V(' :Y~'l!, :r:~:1r'?~" '~?""i"'Y' i"'. .,,"'

,.,., , 

## '. ,.

O:04O-iIh' s!()fScreen waHested 

### at mean intake velocities \
1."" 

# , " ' '

" .
, ...



### iiiSm~'aSm5 ,. S'; t aJ.er:te,mp~rClt\1r~, 

### 1:3Jlgedfrom3 to

"~~hTj~~i11' . e 

## ~ete



# ~=~;~

tf6~ji~~~~d~.

caiire'$fftlie:COns1anfex" 

### osu~"' an(tTh:cf 

### " . ri'" ' 

### 0 ' 

# cu e~

t ;, ' i ~~ ~jf~ nti futi #fe 

### fit

7~?1 ~ Pl!i &~ 

# d;~

p~;; n . pr6ve YV: !IIi ~ih

~~' 

# ~: ,

J~en interaction was virtually n ~m- 

### ,ilit~nfinthe 

### ayJ cIrtOde.

illtake velocity, fish size 

### , and behavior were the major

factors that influenced1 

### impingement. Effect of low temperature on performance was not investigated thoroughly. Bibko et aI. (1974) noted tllat long- term swimming endurance decreased with decreasing temperature. 

### Although some impingement occurred among the 70 striped bass (105- 141 mm FL) tested at temperatures below 10 C,

### the data were inadequate to determine effects of temperature on performance. Observations indicated specimens
were under no stress. 

### Frequency of impingement varied between species and

in some cases was a function of behavior. 

### Mummichog and banded killifish occasionally' rested on the screen surface 

### and left at will regardless of intake velocity. Some species 

### appeared to play with the functioning screen while others exhibited feeding behavior on and around the screen. 

### direct relationship between intake velocit 

### andim 

## ing;

ment was assumed but was not clearly exhibited. 

### In at

least two cases the inverse was true. 

### Atlantic menhad and spot sustained hig.lJ.er 

### impingement rates at lowe 

# velocities,

A total of 1, 

### 318 specimens of 19 species were tested in the static mode. Only 20% of the 261 impingement occurrences failed to escape. The majority of screen 

### interactions occurred at intake velocities in excess of I fps 

### or after more than 10 minutes of exposure. Both values exceed the expected velocity (0. 5 fps) and exposure time

(1 minute) for an intake. Mortality usually resulted after 

### prolonged impingement and was primarily associated with weaker or more sensitive fishes. Handling stress was 

### probably the most important factor in causing prolonged 

### impingement. A total of 34 specimens died as a result of testing; most were in poor condition before 

### the tests began. 

### Although impingement- 

### induced mortality should be investigated, it is expected to be a minor factor in 

### impact assessment for fish larger than 20 mm FL. 

### Little or no loss of sca.ies or other physical damage was incurred by

specimeriS impinged for long durations. 

### The only instances
of screen- 

### induced injury occurred during runs of striped bass larvae when specimens were wedged in the slot to the 

### level of the opercles. 

### A total of 69 specimens of seven species (Atlantic menhaden, banded killifish , mummichog, tidewater silver

### side, Atlantic silverside, bluefish 

### , and spot) were tested in the dynamic mode, Channel and mean intake velocity._--. H...Table 3Performance of Hatchery-Reared Striped Bass Larvae Exposed to04O-in. Slot Johnson Screensx IntakeEst. %Relative Resistanceto IntakeAgeVelocityEntrainedImpingement...TL (mm)(days)(fps)in First MinEntrainedOccurrencesEscapesFish-minGroupIndividual:::to10.10-141O0d10.24.11.21.0107.;:s8.3-12.41.0160.;:-;:s13.0-15.419-53....10.10.'1::38.3-12.Ji'---...13.29.14.1.012.16.1.545.13.0-17.1.013.0-17.32-1.5(a)Ambient water temperature ranged from 19 to 24 C. Fish were held in a 500-gallon Bishop tank~d a 425-gallon pool and fed freshwater invertebrates.Test duration was 30 minutes.(b)p= Poor; F = Fair; G = Good; E = Excellent.(c)Rated 10% of total.(d)Entrained in 25 minutes.~~~;'~;;;rii\~;;"e" ".......,-.............~~..",.Table 4Summary of Performance of Fishes Exposed to Johnson Screensin Static and Dynamic ModesSpecies. AlewifeJAtl~tic menhaden.....' Bay. anchovyCarpSilvery minnowGolden shinerSpottail shinerBanded killifish- M~g~~TIdewater silversideAtlantic silversideThreespine sticklebackFL (mm)Temp. (C)X IntakeVelocity(fps)50-1.5050-1.5050,1.5000-50-1.5021-1.4250-1.5096-1.4298-1.420.41.50-1.501.00I. O.White perch96 21-41 17.24.0 0.50-1.50- griRedf)!iSs";' .6488-151:6,;;; .,;: "3.0-25.h~0.3H.50 .Pumpkinseed70-91 23.1.50Bluegill30 25-98 11.0-23.0 0.20-1.50Yellow perch1834-40 17.0 0.50-1.50~~Ii~'&4~);~J~+'1.1i~~ ~.~~~~;2'(~r~~;~",t::f:Yi". .-- .Spot64 20.23.5 0.50.1.50Total37-17.24.'7738.145j):":~22.Oc24.Q,,~6$25. 7L~1t,i';22~0.27.17-19.23.30-3117.21.035-12.23-17.24.34-8922.24.~,Z; ';;:L:,~?:I?YfJl..;.1ii&;;i~Ltt;~L'44 27-81 20.0-24.13634-9522.26.24.00-1.$0, 263MeanImpingementSuscept.EscapesFish-rninDur. (min)Index000034.. 0.0l6~21453" ",OX202~26.011800000000186.D137.29890000'.c,.QQQO000100130017::!996.96,12.g~3.~'l,:.,:;c:!,;"""".,,,C\\...000000000000:::t.qPjJ:: W'0004i:t, '71.653.120427212535.0250.;:.,3871510-27.(all.00 = Impingement Occurrence.(blT.c00005.

### 404 Fourth National Workshop on Entrainment and Impingement ,.... .....



### r-1 01'



# 0"1 5/,0 1 ~N~ ~.....I,c alh, 

# ft ~I,

.I1th",/"
//AJ(!/,ovy &rss '-~.!.J 

# -'bv, .5;~dc 25- 71""" '&'-98 8-1S1 .J9-lfIs .Z'-~""" .31-'l:1 31'- .u=68 AI=?,! AJ=t'/B,d= 

# 77
"'=S'd: AJ=o$.3 11.1=/;5' \ "('

Figure 5. Relative 

### susceptibility indices for

species tested (n ? 50).



### ranged from 0. 0 to 2. 0 fps and 0.41 to 1.25 fps, respec

### tively. Only three impingements occurred; the total time impinged was 5. 0 seconds. Results and observations indi

### cate impingement oflonger than 5 seconds is not expected

to Occur.

Striped bass was the most extensively studied fish. The following discussion is based on its performance. Results 

### of the other 18 species tested are also presented in Table 4. A total of 648 specimens (8- 

### 151 rom FL) were exposed to mean intake velocities of 0. 

### 31- 1.50 fps in the static 

### mode. The 77 impingement 

### occurrences resulted in a relatively low susceptibility index of 0. 0335. In 1976 

### 533 specimens (8- 

### 151 mm FL) were exposed

to intake velocities of 0.3 1- 1.43 fps. Of the 58 impinge

### ments , 30 escaped. Most impingements (72.4%) occurred 

### in three of the 22 tests at intake velocities greater than 90 fps. Two of these tests used specimens of 8- 17 mm 

## TL All impingements of specimens greater than 17 mm FL occurred after 7 minutes of exposure time. 

### Refinement of procedure and technique during 1977 studies yielded more realistic results. 

### Of the 115 speci

### mens (14-46 rom FL) tested 

### , 60 were hatchery-reared 

### and had undergone earlier testing. Exposure 

### to mean intake velocities of 0. 

### 1.5 fps resulted in a total of 19 impingement occurrences with 19 escapes. Most impinge

### ments lasted less than I second; the longest duration was 4 seconds (0. 07 minutes). Hatchery-reared specimens 

### suffered impingement at all velocities tested; however 

### most (69%) occurred at 1.0 fps. All impingements of wild specimens occurred at an intake velocity of 1.5 fps 

### after 6 minutes of exposure. Performance of test specimens was consisten t with published swimming speed data. 

### Skinner (1974) found 90% of the 40-50 mm striped bass tested could swim 

### as long as 6 minutes in a current of 0. 

### 8 fps. Tatham (1970) reported 0. 9 fps was the maximum swimming speed for 30- 

### 41 rom bass , 0. 

### 1.3 fps the maximum for 43- 50 mm fish , and 1.1- 

### 1.2 fps the maximum for 50- 

### 63 mm fish. Tests by Bibko et aI. (1974) indicated a sustained swim speed of 0. 0 fps for 88. 

### 137. 5 mm striped bass and 1. 7- 

### 5 fps for 150. 212. mill fish. 

### Exposure to the screen elicited a distinct and consistent behavior pattern. Upon introduction to the test cage, one or two schools formed and milled about the lower half of the enclosure. When the pump started 

### , specimens quickly fanned out along the midsection of the screen. Most remained 

### 3 in. off the screen surface and oriented into the approach

vector. As intake velocity was increased, specimens tended 

### to move toward the distal end and farther from the screensurface (Figure 6). Observation of fish activity and measurement of approach velocity indicated striped bass appeared

to prefer velocities of 0. 15- 25 fps. 

### Most bass appeared unstressed during tests, as evidenced by feeding behavior. Avoidance behavior consisted of rapid

### movement to areas of reduced current; some specimens even

### tually returned to the school , others remained in areas of re

### duced current. Impingement occurred when physical control was lost; impact usually occurred in the proximal half of the screen. Most impinged individuals escaped the screen at least

### once. Some specimens escaped the screen on the first at

### tempt; others moved to the distal end and escaped. Less
than 3. 

### 0% of the impinged bass suffered immediate mortality or equilibrium loss. 

### Tests in the dynamic mode indicated young striped bass were essentially invulnerable to screen interactions because of strong orientation to the bottom.5 fps 

## -..

0 fps \ "

Jo-.

5 fps

Figure 6. General location and 

### orientation of

striped bass at three intake velocities.



### Detrital Fouling



### A total of29 trials were conducted with three concentrations of C&D Canal detritus and peat moss. A O. 04O-in. 

### slot , O. 

### 120-in. wire screen was operated at a mean intake 

### velocity of 0. 4 fps; channel velocity ranged from 0. 

### 25 to 1. 7 5 fps. 

### Table 5 gives the mean TIC of the three concentrations tested at various channel currents. Values 

### preceded by the symbol), indicate only 0. 75- 

### 1.25 in. head loss at the time of termination. 

### Hanson et al: A Practical Intake Screen 

### 405

Screens clogged relatively quickly in tests at 77 times

normal Canal concentration. 

### TIC generally increased as channel velocity increased owing to washing by the 

### current. The greater TIC for tests at a 0. 25- 

### fps current compared to tests at 0. 

### 50 fps probably resulted from 

### detritus settling to the bottom at the lower channel velocity. 

### Screen clogging patterns were similar at all 

### channelvelocities. The leading or upstream side of the screen im

### pinged a 3-4 in. band of detritus along the length of the

screen 

### . because of channel current. As the test progressed 

### detritus built up and the band spread in the proximal high intake velocity areas. At the same time , a 1- 

### 2 in. band formed on the trailing edge. Both bands continued to


### widen 

### , particularly in proximal areas 

### , until they met on the

top and bottom of the screen. Spreading continued on the

### distal portion until the entire surface was covered. Although tests were terminated at a 12- 

### in. head differential the screen was still passing from 60% to 90% of its initial 

### capacity. Incorporation of a bubble curtain positioned to sweep the leading side of the screen increased TTC up to 000%. Many tests were terminated with essentially no 

### increase in head. 

### As detrital concentration decreased , TTC generally 

### increased. The suspended detrital concentration normally found in the C&D Canal is 9.46 cm 3 /m . This load is 

### not expected to clog a screen of this type under actual 

### operating conditions. A model intake with a30- in. diameter, 24-in. Iong screen (O. 04O-in. slot and 0. 1 58- 

### in. 

### wire) installed in the Canal in March 1977 has operated 

### continuously at a 0. 

### fps intake velocity with no head loss resulting from detrital clogging and fouling. The

screen did clog (12- 

### in. head loss) on several occasions 

### during the summer months as a result of heavy biofouling. Clogged screens were hydraulically backwashed as a 

### matter of course before a fouling test was initiated. Water was pumped through the screen in a reverse flow at 

### rates of 200-400 gpm. All flow rates tested were equally effective in removing material from the screen. This screenwas generally free of debris after 15 seconds of back

### washing. 

### . Air/hydraulic backwash was investigated in greater de~ail. Six experiments were conducted with a mean intake 

### velocity of 0. 5 fps and three channel velocities (0. 5, 1.0, and 1.5 fps). Air pressures of 10 

### , 25 , and 50 psi were

tested. Comparisons of TIC for 

### manual and air backwash are presented in Table 6. 

### Approximately 23 gallons of water were contained in parts of the air backwash system below water level. Release 

### of compressed air flushed this water through the screen slot 

### at a velocity of approximately 2 fps. The air blast reached

the slots at 36. 

### 6% of initial pressure. 

### This system also cleaned the screen effectively. Cleaning 

### action appeared to result from the water pushed out aheadiil

il'i

::i

liil 

### 406 Fourth National Workshop on 

### Entrainment and Impingement

Table 5 Mean Time- to-Clog (minutes) of a O. 04O-in. Slot Johnson &reen

Exposed to Three Concentrations of 

### Detritus

Channel Mean Time- 

### to-Clog 

### Velocity (fps) II 

### 22X 77 X



### 30. 

### ).240. 48.41 26.33
200. 

### 43. 1.00 

### ),300. 82. 

### 74. 1.25 

### ),315. 310. 

### 315. 1.50 :::.420. 

### ).240. 1.75 

### ),110.

(a)Mean intake velocity was 0. 4 fps. (b) 

### Ratio of detrital concentration to normal C&D Canal levels.

Table 6 

### Comparison of Manual and Air Backwash

Cleaning. Efficiency



### Channel 

### Detrital Air Pressure 

### Number Mean 

### Velocity 

### Concentration of Backwash 

### TIC (fps) (cm 

### (psi) Trials 

### (min)

105. 

### Manual 28. 77 105. 

### 30.33 1.0 105. 

### Manual 25. 1.0 105. 

### 25.38

209. Manual 

### 16.33 1.5 

### 209. 

### 14.48 1.5 

### 209. 

### Manual 

### 14.47 1.5 

### 209. 13. 1.5 

### 209. Manual 16. 1.5 

### 209. 

### 14.32 1.5 

### 209. Manual 16. 1.5 

### 209. 15. 

### (a)Based on time-to-clog (ITC) at a mean intake velocity

of 0. 

### 5 fps for a 0. O40-in. slot Johnson Screen.of the pressurized air blast. Material was blown from all



### areas of the screen and although a small amount reimpinged on the leading edge 

### , most was carried away by the channel

current. Head 

### differential consistently returned to initial levels after backwash.



### CONCLUSIONS

Research has demonstrated profile wire screens have 

### great potential as surface water intakes. Impact on the aquatic environment is expected to be many times less 

### than that of a comparable intake protected by traveling 

### screens. The ability to reduce entrainment and impinge

### ment results from the infinite number of escape routes available; the flow dynamics 

### , which enable a fish to easily 

### determine the direction of escape; the rapid decline in

approach velocity as a fish leaves the screen; t.he sma!! slot size; and the ambient washing currents 

### , which assist 

### escape and avoidance. Impingement of fishes larger 

### than 20 rom FL is virtually eliminated. The small slotwid th transfonns most potential entrainment to impingement. Contrary to impingement on a 

### traveling screen, 

### fish never leave the water, are supported by a greater surface area, and can escape with less difficulty because of the low intake velocities and self- cleaning characteris

### tics of the screen. Planktonic organisms are offered greater 

### protection because of the small slot size and boundary currents. Detrital fouling is greatly 

### reduced and the screen . can be quickly and easily cleaned. This system also

eliminates the problem of disposing of impinged de bris. 

### Biofouling is a major operational problem in brackish

and marine situations. Fouling organisms 

### attach. to and 

### proliferate on the screen surface and ultimately require removal. The use of metals with antifouling properties to construct the screen should minimize this problem. 

### Prome wire screens are highly versatile and specialized 

### installations can be engineered for most locations and

conditions. Our studies were directed toward the pro

### tection of early life stages (eggs, 

### larvae, and young) of 

### striped bass in the C&D Canal. Results to date indicate Hanson et al. : A Practical Intake 

### Screen 

### 407

this protection can be accomplished with little or no 

### constraint on intake operation.



### ACKNOWLEDGMENTS

The aut.~ors would like to express appreciation to the

### entire staff of t.he Delmarva Ecological Study, Ichthyological Associates , Inc. 

### , for their contributions during construction of test apparatus and collections of test materials. Special thanks are extended to Steven E. Allison , who 

### directed early experimentation; Michael R Headrick and his hatchery crew, who supplied striped bass eggs 

### and larvae; and Ronnie J. Kernehan for editorial assistance. Research. was funded by Delmarva Power and light Company, Isc. The manuscript was 

### typed by Arlene H. Hanson and R Lynn Cox.



### BIBLIOGRAPHY

Bibko, P. N., L. Wirtenan, and P. E. Kueser. 1974. Pre

### liminary studies on the effects of air bubbles and intense illumination on the swimming behavior of the

striped bass (Morone saxatilis) 

### and the gizzard shad

(Dorosoma cepedianum). 

### Pages 293- 304 in 

### Jensen

L. D. 

### , ed. 

### , Second Workshop on Entrainment and 

### Intake Screening. Edison Electric Institute Report 15. Mansueti 

## , R J. 1958. Eggs 

### , larvae and young of the striped bass Roccus saxatilis. 

### Ches. BioI. Lab. Contr. No. 112. 35 pp. Skinner 

### , J. E. 1974. A functional evaluation of a large 

### louver screen installation and fish facilities research on California water diversion projects. Pages 225- 249 

### Jensen , L. D., ed. 

### , Second Workshop on Entrainment

### and Intake Screening. Edison Electric Institute Report 15. 

### Sokal , R. R. 

### , and F. J. Rohlf. 1969. Biometry. W. H. Free

### man & Co. 

### , San Francisco. 776 pp. Tatham, T. R. 1970. Swimming 

### speed of the white perch,

Morone americana, striped bass Mororze saxatilis 

### and other estuarine fishes. Final Report No. 0-26156 Con. Ed. Co. N. Y. ; Inc. Ichthyological Associates 

### , Ithaca 

### N. Y. 48 pp.