MEMORANDUM

October 17, 2008

Marla Smith, Work Assignment Manager

Bob Lordo, Battelle Work Assignment Leader

Chris Sroka, Battelle Statistician

EPA Contract No. EP-C-05-030, Work Assignment No. 3-13: 

316b: Laboratory Test Data Related to Entrainment 

This memorandum presents entrainment data from studies that assessed the performance of fine 

mesh screens in reducing impingement mortality and entrainment under controlled laboratory

conditions. These entrainment data originated from documents which we have been reviewing 

on this work assignment and its predecessor in support of the Section 316(b) rulemaking effort. 

This memorandum also summarizes the results of statistical analyses to evaluate whether slot 

width and slot velocity have a significant impact on the percentage of organisms that are 

entrained through the screens. 

Measure of Performance Considered in the Laboratory Studies

Ideally, we would use the laboratory study data to derive the same performance measure as that 

used in the field studies: percentage reduction in entrainment. Recall that this measure requires 

measurements from paired density samples taken in front of and behind a screened intake. 

However, none of the encountered laboratory studies performed this type of sampling. Instead, 

the laboratory studies measured the extent of entrainment (and impingement mortality) 

associated with the installed screens within the test flume. Therefore, the percentage of 

organisms that were entrained through the screen (i.e., percent entrainment) is the performance 

measure used in the summaries and analyses of laboratory data in this memorandum. Note that 

because field and laboratory studies are utilizing different entrainment performance measures, it 

is not possible to make direct comparisons in the values of the performance measures between 

field and laboratory studies. 

Sources of Entrainment Data from Laboratory Studies

The summarized entrainment data used in this evaluation are documented in Tables 1 through 3. 

Table 1 summarizes entrainment for all organisms (i.e., all life stages), while Table 2 considers 

entrainment data for eggs only, and Table 3 documents entrainment for larvae (non-eggs) only. 

These data represent summaries calculated across species of the data presented within the source 

specified in the first column. The summaries are presented by slot size and, when specified, slot 

velocity and screen orientation (parallel or perpendicular to water flow). The Study ID is 

assigned to the given data within Battelle’s performance evaluation database. (The data from 

EPRI [2003] currently exist in separate Excel worksheets, as they were captured in electronic 

form from a PDF version of the study report.)

Date

To

From

Subject
October 17, 2008

316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

Page 2

Table 1. Percent Entrainment of All Organism Types by Screen Orientation, Slot Size, and Slot Velocity, as Reported from 

Controlled Laboratory Studies

Data Source Study ID

# 

Species

Screen 

Orientation*

Slot 

Size 

(mm)

Slot 

Velocity 

(m/s)

# 

Entrained**

# 

Released

Avg. % 

Entrained**

Avg. % 

Retained

Appendix C of 

EPRI, 2003

2001 WW lab study 1 0 0.50 0.15 39.70 2,000 1.99

2001 WW lab study 1 0 0.50 0.30 249.50 1,900 13.13

2001 WW lab study 1 0 1.00 0.15 255.20 1,800 14.18

2001 WW lab study 1 0 1.00 0.30 357.60 1,800 19.87

2001 WW lab study 1 0 2.00 0.15 504.60 1,800 28.03

2001 WW lab study 1 90 0.50 0.15 2.20 1,800 0.12

2001 WW lab study 1 90 0.50 0.30 2.20 1,800 0.12

2001 WW lab study 1 90 1.00 0.30 304.10 1,050 28.96

2001 WW lab study 1 90 2.00 0.15 893.70 1,800 49.65

Appendix D of 

EPRI, 2003

2002 WW lab study 4 NS 0.50 0.15 649.60 5,688 11.42

2002 WW lab study 5 NS 0.50 0.30 471.70 4,285 11.01

2002 WW lab study 3 NS 1.00 0.15 1477.40 2,525 58.51

2002 WW lab study 3 NS 1.00 0.30 1859.70 2,773 67.06

2002 WW lab study 1 NS 2.00 0.15 900.40 1,125 80.04

2002 WW lab study 2 NS 2.00 0.30 427.60 1,874 22.82

Table 2-4 of 

EPRI, 2008

116 1 90 0.50 NS 9.00 120 7.50 92.50

116 4 90 0.50 NS 57.89 1,250 4.63 95.37

116 5 90 0.50 NS 36.54 1,695 2.16 97.84

Table 1 of 

Tomljanovich 

et al., 1978

248 5 90 0.50 NS 0.36 99.64

249 6 90 1.00 NS 19.97 80.03

250 9 90 1.30 NS 35.67 64.33

251 4 90 1.80 NS 20.20 79.80

252 4 90 2.50 NS 32.60 67.40

Page 401 of 

Hanson et al., 

1977

253 1 NS 1.01 NS 16.00 100 16.00

* 0=parallel to flow; 90=perpendicular to flow.

** Adjusted for collection efficiency (CE) for WW lab studies.

NS = Not specified
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Table 2. Percent Entrainment of Eggs by Screen Orientation, Slot Size, and Slot Velocity, as Reported from Controlled 

Laboratory Studies

Data Source Study ID

# 

Species

Screen 

Orientation

Slot 

Size 

(mm)

Slot 

Velocity 

(m/s)

# 

Entrained*

# 

Released

Avg. % 

Entrained*

Appendix C of 

EPRI, 2003

2001 WW lab study 1 0 0.50 0.15 0.00 900 0.00

2001 WW lab study 1 0 0.50 0.30 0.00 900 0.00

2001 WW lab study 1 0 1.00 0.15 0.00 900 0.00

2001 WW lab study 1 0 1.00 0.30 0.00 900 0.00

2001 WW lab study 1 0 2.00 0.15 0.00 900 0.00

2001 WW lab study 1 90 0.50 0.15 0.00 900 0.00

2001 WW lab study 1 90 0.50 0.30 0.00 900 0.00

2001 WW lab study 1 90 1.00 0.30 0.00 600 0.00

2001 WW lab study 1 90 2.00 0.15 21.00 900 2.33

Appendix D of 

EPRI, 2003

2002 WW lab study 1 NS 0.50 0.15 0.00 1,122 0.00

2002 WW lab study 2 NS 0.50 0.30 100.20 1,737 5.77

2002 WW lab study 1 NS 2.00 0.30 407.60 1,125 36.23

* Adjusted for collection efficiency (CE)

NS = Not specified
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Table 3. Percent Entrainment of Larvae (non-eggs) by Screen Orientation, Slot Size, and Slot Velocity, as Reported from 

Controlled Laboratory Studies

Data Source Study ID

# 

Species

Screen 

Orientation*

Slot 

Size 

(mm)

Slot 

Velocity 

(m/s)

# 

Entrained**

# 

Released

Avg, % 

Entrained**

Avg. % 

Retained

Appendix C of 

EPRI, 2003

2001 WW lab study 1 0 0.50 0.15 39.70 1,100 3.61

2001 WW lab study 1 0 0.50 0.30 249.50 1,000 24.95

2001 WW lab study 1 0 1.00 0.15 255.20 900 28.36

2001 WW lab study 1 0 1.00 0.30 357.60 900 39.73

2001 WW lab study 1 0 2.00 0.15 504.60 900 56.07

2001 WW lab study 1 90 0.50 0.15 2.20 900 0.24

2001 WW lab study 1 90 0.50 0.30 2.20 900 0.24

2001 WW lab study 1 90 1.00 0.30 304.10 450 67.58

2001 WW lab study 1 90 2.00 0.15 872.70 900 96.97

Appendix D of 

EPRI, 2003

2002 WW lab study 4 NS 0.50 0.15 649.60 4,566 14.23

2002 WW lab study 3 NS 0.50 0.30 371.50 2,548 14.58

2002 WW lab study 3 NS 1.00 0.15 1477.40 2,525 58.51

2002 WW lab study 3 NS 1.00 0.30 1859.70 2,773 67.06

2002 WW lab study 1 NS 2.00 0.15 900.40 1,125 80.04

2002 WW lab study 1 NS 2.00 0.30 20.00 749 2.67

Table 2-4 of 

EPRI, 2008

116 1 90 0.50 NS 9.00 120 7.50 92.50

116 4 90 0.50 NS 57.89 1,250 4.63 95.37

116 5 90 0.50 NS 36.54 1,695 2.16 97.84

Table 1 of 

Tomljanovich et 

al., 1978

248 5 90 0.50 NS 0.36 99.64

249 6 90 1.00 NS 19.97 80.03

250 9 90 1.30 NS 35.67 64.33

251 4 90 1.80 NS 20.20 79.80

252 4 90 2.50 NS 32.60 67.40

Page 401 of 

Hanson et al., 

1977

253 1 NS 1.01 NS 16.00 100 16.00

* 0=parallel to flow; 90=perpendicular to flow.

** Adjusted for collection efficiency (CE) for WW lab studies.

NS = Not specified
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316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

Page 5

The data in Tables 1 through 3 originate from the following four documents:

 EPRI (2003) is a biological evaluation of cylindrical wedgewire screens performed at 

Alden Research Laboratory’s Fish Testing Facility. Two distinct sets of tests were 

performed that involved releasing a specified number of larvae/eggs into a test flume. 

One test was conducted in 2001, with striped bass larvae (length range: 3.5 to 10.6 mm; 

width range: 0.1 to 2.0 mm) and a surrogate egg type (diameter range: 3.6 to 6.3 mm), 

whose objective was to determine if the test facility and procedures could be used to 

evaluate effectiveness of the various screen types. After necessary modifications were 

made to the procedures based on 2001 testing, more comprehensive testing was done in 

2002 that considered additional species that exist within a wide range of water body types 

and that represent a greater range of swimming capabilities. Eggs used in the 2002 study

represented alewife (diameter range: 0.5 to 0.9 mm) and white sucker (diameter range: 

2.8 to 3.5 mm), while larvae represented bluegill, carp, rainbow smelt, winter flounder, 

white sucker, and yellow perch. Mean lengths of these larvae ranged from 6.1 mm 

(winter flounder) to 18.5 mm (bluegill), while mean widths ranged from 0.8 mm (yellow 

perch) to 5.4 mm (bluegill). Both of the 2001 and 2002 studies controlled for the 

following:

o Slot size (0.5, 1.0, 2.0 mm)

o Slot velocity (0.15, 0.30 m/s)

o Channel (or approach) velocity (0.08, 0.15, 0.30 m/s).

(Not all species of larvae were tested at all slot size/velocity combinations in the 2002 

study.) In addition, the 2001 study collected data for two different screen orientations: 

parallel (radial slots) and perpendicular (axial slots) to the water flow. In 2001, three test 

replicates were performed for each set of test conditions, while up to five replicates were 

performed in 2002 testing. The test flume channel in 2001 testing was 1.5 m wide, and 

water depth was 1.3 m. In 2002 testing, flume width and water depth were both 1.8 m.

The 2001 and 2002 data are summarized separately. In both tests, entrainment data were 

reported after being adjusted for net collection efficiency (as determined from releasing 

known amounts of fish or eggs directly into the entrainment collection tank).

 EPRI (2008) is a two-year biological evaluation of fine mesh traveling screens whose 

main objective was to determine retention and post-impingement survival of larval fish 

on the screens. These tests were performed in a closed-loop testing facility at Alden 

Research Laboratory. The test flumes were 30.5 cm wide and contained water 30.5 cm 

deep, and fine-mesh screens were mounted perpendicular to the flow. Fish larvae were 

introduced to the system, then the study evaluated the length of time at which the larvae

could be impinged on the screens before being rinsed off the screens and bypassed to 

holding tanks. The data presented in this memorandum originate from an investigation of 

the ability of 0.5 mm mesh screens to prevent the entrainment of larval fish that occurred 

within impingement survival testing in Phase I (in 2006). When using 0.5 mm mesh 

screens, survival testing involved performing four replicates for selected combinations of 

the following: 

o Larval species (blue catfish, channel catfish, emerald shiner, fathead minnow, and 

smallmouth bass)
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316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

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o Approach velocity (0.152, 0.35, and 0.61 m/s)

o Duration of impingement on the screens (4, 8, 16 min.).

The lengths of the larvae ranged from 6.9 to 23.4 mm (Table 2-3 of EPRI, 2008).

 The study in Tomljanovich et al. (1978) was performed in a fine-mesh screening test 

flume (2.4 m wide x 1.2 m deep) at the Tennessee Valley Authority (TVA) to evaluate 

the extent to which post-impingement survival of fish larvae were related to impingement 

duration, fish species and size, approach water velocity, and screen mesh size. The study

measured percent retainment of the larvae within various numbers of tests for selected 

combinations of the following:

o Species (jewelfish cichlid, threadfin shad, golden shiner/fathead minnow, white 

sucker, channel catfish, striped bass, bluegill, smallmouth bass, largemouth bass, 

walleye)

o Mesh size (0.5, 1.0, 1.3, 1.8, 2.5 mm) of screens oriented perpendicular to flow.

According to Table 1 of Tomljanovich et al. (1978), approach velocities ranged from 

0.152 to 0.46 m/s among the tests, and test duration ranged from 0.5 to 16 minutes. Mean 

larval lengths ranged from 6.2 (striped bass) to 39.5 mm (threadfin shad), while mean 

widths ranged from 0.7 (striped bass) to 4.2 mm (threadfin shad). Exact numbers of fish 

in each test were unknown but ranged from 10 to over 200. 

 The study in Hanson et al. (1977) was performed in an oval test flume (0.84 m wide and 

1.22 m deep) at the Delmarva Power and Light test laboratories. While this reference 

documents several phases of testing to evaluate entrainment and impingement of eggs 

and larvae by a profile wire screen with 1 mm slot width, only a set of tests involving the 

introduction of 100 striped bass larvae into the test flume appeared to measure 

entrainment through the screen, and therefore, was relevant for this memorandum. These 

tests were performed at an intake velocity ranging from 0.152 to 0.46 m/s, and duration 

of 30 minutes. Larval lengths ranged from 8 to 17 mm.

Note that only EPRI (2003) controlled for slot velocity in its tests; no other document reported 

slot velocity. Furthermore, EPRI (2008) and Tomljanovich et al. (1978) reported “percent 

retention” data, rather than percent entrained data. EPRI (2008) also reported the number of 

organisms that were released in the test flume. As noted below, we assumed that any fish not 

“retained” was entrained, and therefore, we calculated the numbers of organisms entrained as the 

number released minus the number retained. Hanson et al. (1977) did not report the number of 

organisms released, and therefore, we calculated percent entrainment as 100% minus percent 

retention for this study.

When numbers of entrained (or retained) organisms were reported in these references, they were 

summed across species and test replicates. Likewise, when numbers of organisms released into 

the test flume were reported, they were summed in the same manner. Both sets of sums appear 

in Tables 1 through 3. Percent entrainment was then calculated as the total number of entrained 

organisms divided by the total number released, and the tables include this result. If a reference 

only reported percent entrainment, with no accompanying numbers of organisms entrained or 
October 17, 2008

316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

Page 7

released, we calculated the average of these percentages across species and test replicates and 

presented them in Tables 1 through 3.

Data Acceptance Criteria 

In order to be included in Tables 1 through 3 (and accepted for statistical analysis), entrainment 

data needed to achieve the following criteria:

 The data must originate from a study performed at a test laboratory under controlled 

conditions (e.g., not in a test barge placed in a natural water body).

 The test screens in this study must be categorized as “fine mesh” screens, where the mesh 

size is clearly specified.

 From the reported data, it must be possible to determine the percent of organisms that 

were entrained through the test screens. 

o Data sources reporting only numbers of entrained fish were not accepted if the 

total number of fish released was not also reported.

o Data were not accepted if numbers of entrained organisms could not be 

determined with sufficient confidence from them. For example, if a data source 

reported a number or percentage of fish that avoided either impingement or 

entrainment and no other data, then these data were not accepted for use because 

it would not be possible to determine only those fish that were entrained from the 

reported data. 

While data were reported specifically on entrainment in EPRI (2008) and Hanson et al. (1977), 

the studies in EPRI (2003) and Tomljanovich et al. (1978) measured “retainment” rather than 

entrainment. Organisms are “retained” when they do not pass through the intake screens, 

meaning that they are either impinged on the screens, are able to keep swimming in front of the 

screens, etc. Thus, one may be able to assume that all organisms that are not retained are 

entrained through the screens. In order to accept data for studies that reported only retention 

data, it was necessary to make this assumption. Therefore, when utilizing data from EPRI (2003) 

and Tomljanovich et al. (1978) to characterize entrainment in this memorandum, this assumption 

should be noted.

Plots of Percent Entrainment Data

Figures 1 through 6 contain plots of the percent entrainment data, with Figures 1 and 2 

presenting data for larvae, Figures 3 and 4 for eggs, and Figures 5 and 6 for all organisms. Oddnumbered figures plot the data versus screen slot width, with slot velocity noted by the plotting 

symbol. Even-numbered figures include data only for EPRI (2003), with slot velocity specified 

along the horizontal axis and screen slot width given by the plotting symbol. The values plotted 

in these figures represent both parallel and perpendicular screen orientations (relative to flow).
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Figure 1. Percent of Larvae Entrained by Slot Velocity and Screen Size, with Screen Size on 

the Horizontal Axis

Figure 2. Percent of Larvae Entrained by Slot Velocity and Screen Size, with Slot Velocity on 

the Horizontal Axis

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3

Screen Size (mm)

Precent Entrainment of Larvae

Slot Velocity = 0.15

Slot Velocity = 0.3

No slot velocity given

0

20

40

60

80

100

120

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Slot Velocity

Percent Entrainment of Larvae

Screen Size = 0.5

Screen Size = 1.0

Screen Size = 2.0
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Figure 3. Percent of Eggs Entrained by Slot Velocity and Screen Size, with Screen Size on the 

Horizontal Axis

Figure 4. Percent of Eggs Entrained by Slot Velocity and Screen Size, with Slot Velocity on 

the Horizontal Axis

0

5

10

15

20

25

30

35

40

0 0.5 1 1.5 2 2.5

Screen Size (mm)

Precent Entrainment of Eggs

Slot Velocity = 0.15

Slot Velocity = 0.3

0

5

10

15

20

25

30

35

40

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Slot Velocity

Percent Entrainment of Eggs

Screen Size = 0.5

Screen Size = 1.0

Screen Size = 2.0
October 17, 2008

316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

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Figure 5. Percent of Total Organisms Entrained by Slot Velocity and Screen Size, with Screen 

Size on the Horizontal Axis

Figure 6. Percent of Total Organisms Entrained by Slot Velocity and Screen Size, with Slot 

Velocity on the Horizontal Axis

0

10

20

30

40

50

60

70

80

90

0 0.5 1 1.5 2 2.5 3

Screen Size (mm)

Percent Entrainment of Total Organisms

Slot Velocity = 0.15

Slot Velocity = 0.3

No slot velocity given

0

10

20

30

40

50

60

70

80

90

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Slot Velocity

Percent Entrainment of Total Organisms

Screen Size = 0.5

Screen Size = 1.0

Screen Size = 2.0
October 17, 2008

316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

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Note that because a large portion of the percent entrainment data values for eggs are zero (from 

the EPRI 2001 study), Figures 3 and 4 appear to have fewer plotting points compared to the other 

plots. As noted in Table 2, no surrogate eggs were entrained in the EPRI 2001 study except 

when the 2.0 mm screens were oriented perpendicular to flow. In addition, no entrainment of 

white sucker eggs occurred in the EPRI 2002 study (although alewife eggs were entrained at 

high percentages). In both studies, the lack of entrainment was due to the large egg diameters 

related to the slot widths and the eggs’ “ability to maintain their shape and not be forced through 

the screens” (EPRI, 2003).

These plots suggest that percent entrainment tends to increase with increased screen slot width 

for both egg and larval life stages. In contrast, increased slot velocity was more highly 

associated with increased percent entrainment only for eggs. (This was observed primarily due 

to increased entrainment with alewife eggs at the 0.30 m/s slot velocity in the EPRI 2002 study.)

Conclusions on Slot Width and Slot Velocity as Noted by the Study Authors

The following types of conclusions were made by the authors of the above studies upon review 

and analysis of the entrainment data. Only EPRI (2003) based some of its conclusions on 

entrainment or retainment data on the outcome of a statistical analysis (ANOVA).

EPRI (2003)

 Entrainment increased with increases in slot size and slot velocity.

 Entrainment decreased with increases in channel velocity.

 The ability to characterize relationships in entrainment among the various test factors was 

hampered by interactions among the factors or data gaps.

 Most larvae and eggs were excluded from passing through 0.5 mm screens, but not larger 

mesh screens.

 In the 2001 study, under the parallel screen orientation, entrainment rates increased 

significantly with slot size (at the 0.05 level) and were higher at the 0.3 m/s slot velocity.

 In the 2002 study, statistical analysis was performed by species. Slot velocity effects 

were significant at the 0.05 level on percent entrainment for larvae of selected species 

(e.g., winter flounder, yellow perch, carp). While it was not statistically significant, the 

analysis on winter flounder data indicated that the impact of slot velocity was greatest at 

the smallest screen mesh size.

EPRI (2008)

 “The 0.5 mm screens used during survival testing were effective in retaining the majority 

of fish released.”

 “In general, retention increased as (approach) velocity and duration of impingement 

increased.”

Tomljanovich et al. (1978) 

 “Velocity and test duration contributed little to percent retention.”

 “Body length alone was not a good indicator of percent retention.”
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In addition, EPRI (2003) cites Hanson et al. (1977) in making the following statement: 

“Impingement and entrainment have been positively correlated with slot velocity and inversely 

related to ambient velocity.” Hanson et al. (1977) noted that over 90% of the tested larvae were 

able to swim for 30 minutes without entrainment when subject to currents of 1.0 to 1.5 fps.

Statistical Analysis of Percent Entrainment Data in Tables 1 through 3

We utilized analysis of variance (ANOVA) methods to investigate the possible effect of screen 

size and slot velocity on the percent of organisms entrained as reported in Tables 1 through 3 

above. We applied ANOVA separately to each table (i.e., organisms in the egg life stage, 

organisms in the larval (non-egg) life stage, and organisms in both life stages). We considered 

several ANOVA model forms that differed according to whether percent entrainment was 

transformed, whether slot velocity was included as a model predictor, and, if slot velocity was 

included, whether an interaction term between screen size and slot velocity should be included. 

Note that for eggs, percent entrainment was reported to be zero for most test conditions (Table 

2), in part due to the limited number of laboratory studies that considered eggs, and to limited 

variation in the different types of eggs that were considered in these studies (EPRI, 2003). Thus, 

conclusions from the statistical analyses performed only on eggs should be made with caution.

Two-way ANOVA. Slot velocity data were available only for the 2001 and 2002 EPRI

evaluations of wedgewire screens (EPRI, 2003). Thus, in the two-way ANOVA model that 

included both slot size and slot velocity as predictor variables, only data from EPRI (2003) were 

used to fit the model. The model that best fit these data took the following form:

Yijk =  + i + βj + (αβ)ij +ijk (1)

where Yijk is the “inverse arcsine”-transformed percent entrainment reported by the k

th study

under the i

th slot width and jth slot velocity conditions,  is an overall constant, i is the amount 

contributed by the i

th slot width, j is the amount contributed by the jth slot velocity, (αβ)ij is the 

amount contributed by the combination of the i

th slot width and the jth slot velocity, and ijk is 

random error left unexplained by the model. Because only two values (0.15 m/s and 0.30 m/s) 

for slot velocity were represented among the available data, we considered the variable to be 

categorical like the slot width variable. 

The “inverse arcsine” transformation used in model (1), which EPRI (2003) also considered in 

its statistical analysis, is defined as follows:

  Yijk X ijk

1

sin  ,

where Xijk is the percent entrained associated with the k

th study that utilized the ith slot width and 

the j

th slot velocity. We transformed the percent entrainment measure because plots of residuals 

from the ANOVA model fitting suggested that, for all three subsets of data, the errors were more 

likely to be independent and normally distributed with a constant variance upon taking this 
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316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

Page 13

transformation. We also considered a logarithmic transformation, which appeared to perform 

similarly to the inverse arcsine transformation. 

Upon fitting model (1) to data in Tables 1 through 3, we noted the following:

 The interaction effect between screen size and slot velocity was significant for percent of 

larvae entrained (p-value = 0.0134) and percent of eggs entrained (p-value = 0.0198). Since 

there is an interaction effect, the effect of slot velocity varies by screen size. For example, 

percent entrainment of larvae appears to increase at the lower slot velocity at 2.0 mm mesh 

size. The least squares estimates of the mean percent entrainment for each combination of 

screen size and slot velocity are shown in Table 4.

 Only screen width was significant for percent of all organisms entrained (p-value = 0.0263). 

The smallest screen width (0.5 mm) had the smallest percent entrainment, while the largest 

screen width had among the largest percent entrainment values. 

Table 4. Least Squares Means and 95% Confidence Limits for Percent Entrainment

Measured in EPRI (2003), by Screen Width and Slot Velocity, As Estimated 

from a Two-Way ANOVA Model 

Data Set

Screen 

Width 

(mm)

Slot 

Velocity 

(m/s)

Least 

Squares 

Means

95% Confidence 

Limits for Least 

Squares Means

Larvae Only

0.5 0.15 4.3% (0.6, 22.5)

0.5 0.30 10.0% (0.1, 32.4)

1.0 0.15 43.1% (12.9, 76.5)

1.0 0.30 58.3% (30.4, 83.6)

2.0 0.15 80.8% (54.7, 97.1)

2.0 0.30 2.7% (10.4, 37.4)

Eggs Only

0.5 0.15 0.0% (0.0, 1.7)

0.5 0.30 0.7% (0.2, 4.4)

1.0 0.15 0.0% (0.0, 5.0)

1.0 0.30 0.0% (0.5, 2.5)

2.0 0.15 0.6% (0.7, 5.5)

2.0 0.30 36.2% (16.6, 58.5)

All Organisms

0.5 0.15 3.0% (2.0, 22.1)

0.5 0.30 6.0% (0.5, 28.6)

1.0 0.15 34.5% (5.7, 72.2)

1.0 0.30 37.9% (11.6, 68.9)

2.0 0.15 53.1% (23.0, 82.0)

2.0 0.30 22.8% (0.2, 74.8)

One-way ANOVA. In order to apply more data from the above four documents into the 

ANOVA, we also fit a second model that included only screen mesh width as a predictor 

variable. Thus, this model could assess only the effect of screen mesh width. The form of this 

model is:

 Yjk =  + i + jk (2)
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316b: Laboratory Test Data Related to Entrainment (EP-C-05-030; WA 3-13)

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where the notation is the same as for model (1). We again investigated the residuals for this 

model and concluded that the assumptions of the ANOVA method were satisfied. Based on the 

results of the three runs of the model, we noted the following:

 Screen width had a significant effect on average percent of larvae entrained (p-value = 0.002) 

and the average percent of total organisms entrained (p-value = 0.0109). This appears to be 

due to low percent entrainment outcomes associated with the 0.5 mm mesh size. Greater 

percentages of entrainment were associated with larger mesh sizes.

 Screen width alone did not have a significant effect on the average percent of eggs entrained.

The least squares estimates of the mean effect of screen width are reported in Table 5.

Table 5. Least Squares Means and 95% Confidence Limits for Percent Entrainment 

Measured in Controlled Laboratory Studies, by Screen Width, As Estimated 

from a One-Way ANOVA model with Screen Width as a Factor 

Data Set

Screen 

Width 

(mm)

Least 

Squares 

Means

95% Confidence 

Limits for Least 

Squares Means

Larvae Only

0.5 5.2% (0.2, 16.3)

1.0 41.7% (21.4, 63.6)

1.3 35.7% (0.3, 88.6)

1.8 20.2% (1.4, 75.4)

2.0 59.2% (30.6, 84.8)

2.5 32.6% (0.0, 86.4)

Eggs Only

0.5 0.2% (1.5, 4.0)

1.0 0.0% (0.0, 5.2)

2.0 6.9% (0.1, 22.6)

All Organisms

0.5 3.8% (0.4, 10.4)

1.0 30.7% (17.5, 46.1)

1.3 35.7% (4.9, 75.8)

1.8 20.2% (0.2, 59.6)

2.0 45.1% (25.4, 65.6)

2.5 32.6% (3.6, 73.0)

The outcome of the above statistical analyses were compared to that observed with percent 

reduction in entrainment from field studies, as reported in Battelle’s technical memorandum 

dated September 29, 2008. The above analysis on laboratory data noted significant slot velocity

effects (at the 0.05 level) separately for eggs and larvae (but not for all organisms) which varied 

according to the slot width size. However, as noted in the 9/29 memo, no significant slot 

velocity effects were observed in percent reduction in entrainment in field studies for any life 

stage, and the interaction of slot velocity and slot width was not significant. 
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In both lab and field studies, increased entrainment was observed to occur with increased mesh 

sizes. However, the outcome of the statistical analyses (involving the one-way ANOVA) 

differed between the two types of studies. While screen mesh size was observed to have a 

significant effect on percent reduction in entrainment within the field studies for eggs only (and 

not for larvae or total organisms), mesh size was a significant factor for percent entrainment in 

the lab studies for larvae and total organisms (but not for eggs). For eggs, greater entrainment 

levels were observed in the field studies compared to the lab studies documented in EPRI (2003). 

Again, caution should be made when comparing data outcomes between the field and lab studies 

due to differences in how the performance measure was defined and in the ANOVA models 

applied to the performance measure data.

References

EPRI (2008). Laboratory Evaluation of Fine-Mesh Traveling Water Screens for Protecting 

Early Life Stages of Fish at Cooling Water Intakes. Palo Alto, CA: Electric Power Research 

Institute, Inc. Technical Report No. 1014021. March 2008.

EPRI (2003). Laboratory Evaluation of Wedgewire Screens for Protecting Early Life Stages of 

Fish at Cooling Water Intakes. Palo Alto, CA: Electric Power Research Institute, Inc. 

Technical Report No. 1005339. May 2003.

Hanson, BN, Bason, WH, Beitz, BE, and Charles, KE. (1977). A practical intake screen which 

substantially reduces the entrainment and impingement of early life stages of fish. In: 

Fourth National Workshop on Entrainment and Impingement. LD Jenson, ed. Melville, NY: 

EA Communications (a division of Ecological Analysts, Inc.)

Tomljanovich, DA, Heuer, JH, and Voighlander, CW. (1978). Investigations on the protection 

of fish larvae at water intakes using fine-mesh screening. In: Larval Exclusion Systems for 

Power Plant Cooling Water Intakes: Proceedings of the Workshop Held at Shelter Island 

Inn, San Diego, CA, February 7-8, 1978. RK Sharma and JB Palmer, eds. Argonne, IL: 

Argonne National Laboratory.