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# Reductions in Impingement Mortality Resulting from Enhancements to Ristroph Traveling Screens at an Estuarine Cooling

Water Intake Structure Kenneth A. Strait, John H. Balletto, L. Raymond Tuttle, Shawn L. Shotzberger A Symposium on Cooling Water Intake Technologies to

Protect Aquatic Organisms May 6 - 7, 20032 

# Salem Generating Station

• Delaware Estuary Steam Electric Plant • Approx. 30 miles SW of Philadelphia • Each unit rated at 1,162 Mwe . • Commercial Operation

– Unit 1: 1977

– Unit 2: 1981 

## • Delaware Estuary Steam Electric Plant • Approx. 30 miles SW of Philadelphia • Each unit rated at 1,162 Mwe . • Commercial Operation

– Unit 1: 1977

– Unit 2: 19813 

# Cooling Water Intake Structure (CWIS)

• 12 Intake Bays • Monthly Average Flow of 3,024 MGD • Approach Velocity

– 1.0 ft/s at low tide

– 0.87 ft/s at high tide 

## • 12 Intake Bays • Monthly Average Flow of 3,024 MGD • Approach Velocity

– 1.0 ft/s at low tide

– 0.87 ft/s at high tide4 

# CWIS Traveling Screens

• 12 screens (one per intake bay) • Continuously rotating to remove detritus and marine life • Modified in 1996 to improve efficacy:

– Enhanced bucket profile

– Lighter construction

– Finer Smooth - Tex TM Mesh (0.25” x 0.5” vs. 0.375” x 0.375” with old screens)

– Modified spray wash configuration 

### • 12 screens (one per intake bay) • Continuously rotating to remove detritus and marine life • Modified in 1996 to improve efficacy:

– Enhanced bucket profile

– Lighter construction

– Finer Smooth - Tex TM Mesh (0.25” x 0.5” vs. 0.375” x 0.375” with old screens)

– Modified spray wash configuration5

FLOW



## Original Screens Bucket Profile & Screen Mesh 

## Modified Screens Bucket Profile & Screen Mesh6 

## Salem CWIS Fish Return System Top Right: Fish spray and flap seals Below: Fish and debris return troughs Bottom Right: Fish return trough terminus7 

# Salem CWIS Fish Collection & Holding Facilities

Impingement Abundance Sampling in North Fish Counting Pool Impingement Abundance Sampling in North Fish Temporary Latent Impingement Mortality (LIM) Holding Tank Temporary Latent Impingement Mortality8 

# 1995 Impingement Mortality Direct Comparison Study - Methods

• Unit 2 modified with improved Ristroph screens, Unit 1 retained original screens • Discharge split to north (U1) and south (U2) pools in 4 to 6 minute samples for comparison • LIM Samples collected on 19 dates between June 20 and August 24, 1995 • Sampled entire tidal cycle • Weakfish, bay anchovy and spot targeted for study • Fish held in six 100 gallon tanks • Survival fraction observed after 12, 24, and 48 hours9 Original Screens Modified Screens MONTH Number of

fish examined Impingement

Mortality Rate Number of

fish examined Impingement

Mortality Rate June 111 33% 366 17% July 367 31% 473 18% August 553 51% 623 25% TOTAL 1031 38% 1462 20% 

# Summary of Results from the 1995 Direct Comparison Study - Weakfish Original Screens versus Modified Screens10 

# 1997 – 2000 Impingement Mortality Study - Methods

• Modified Ristroph screen improvements completed for both units • Discharge combined and directed in the direction of the tide • Sampled entire tidal cycle • Study targeted weakfish, bay anchovy, spot, alewife, blueback herring, American shad, striped bass, white perch and Atlantic croaker • Fish held in six 100 gallon tanks • Survival fraction observed after 12, 24, and 48 hours11

RANK SPECIES ANNUAL MORTALITY * (%) MINIMUM

(%) MAXIMUM

(%) TOTAL

NUMBER SAMPLED 1 Striped Bass 4.66 2.10 6.87 1,505 2 White Perch 6.29 0.95 33.63 25,757 3 Spot 6.67 -- -- 132 4 Atlantic Croaker 22.64 3.86 44.86 35,186 5 American Shad 23.95 -- -- 40 6 Blueback Herring 27.39 14.11 43.38 4,150 7 Alewife 39.15 17.41 43.01 551 8 Weakfish 47.77 10.28 65.25 26,400 9 Bay Anchovy 58.02 27.48 83.97 10,235 * Calculated from abundance - weighted monthly mortality estimates. 

## Mortality Rate Ranking (Lowest to Highest) for RIS Species Based on 1997 through 2000 Data12 BLUEBACK HERRING AND ALEWIFE

MonthPercent MortalityRelative Impingement Abundance

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1978 - 1982 (old screens) 1995 - 2000 (new screens) Relative abundance13 ATLANTIC CROAKER

MonthPercent MortalityRelative Impingement Abundance

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1978 - 1982 (old screens) 1995 - 2000 (new screens) Relative abundance14 BAY ANCHOVY

MonthPercent MortalityRelative Impingement Abundance

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCY NOV DEC 1978 - 1982 (old screens) 1995 - 2000 (new screens) Relative abundance17 WHITE PERCH

MonthPercent mortalityRelative Impingement Abundance

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1978 - 1982 (old screens) 1995 - 2000 (new screens) Relative abundance18 

# Fish Collection Pool and “End - of - Pipe” Evaluation Methods

• Fish collection pool and “End - of - Pipe” models constructed off - site • Tests conducted with alewife and weakfish • Testing performed in both models as well as in the Salem fish collection pools • Marked control fish included in each replicate • Survival fraction enumerated after 12, 24 and 48 hours19 

# “End - of - Pipe” Model 6 - foot drop configuration20



## Treatment Immediate 48 Hours Existing Configuration 0.9965

(0.0035) 0.9964

(0.0059) 1.3 - ft Freefall 1.0 (N/A) 1.0140 (0.0098) 6 - ft Freefall 1.0 (N/A) 1.0034 (0.0034) 

# Estimates of survival (standard error) from pooled replicates by treatment with alewife for the end of - pipe experiment

Note: Values > 1 indicate higher control mortality21 

# Fish Collection Pool Model22 

# Estimates of survival (standard error) from pooled replicates by treatment for the fish collection pool experiment (Model) Treat ment Immediate 48 Hours 3 cfs / 25 c m o f cushion water 1.0 ( N/A) 1.16434 (0.0058) 3 cfs / 50 c m o f cushion water 1.0 ( N/A) 1.0315 (0.0379) Note: Values > 1 indicate higher control mortality23



## Treat ment Immediate 48 Hou rs 3 cfs / 25 c m o

f cush ion water 1.0034

(0.0058) 1.0034

(0.0058) 3 cfs / 50 c m o

f cush ion water 1.0067

(0.0047) 1.0067

(0.0047) 13 cfs / 25 c m o

f cush ion water 0.9966

(0.0034) 0.9966

(0.0034) 

# Estimates of survival (standard error) from pooled replicates by treatment for the fish collection pool experiment (Station)

Note: Values higher > 1 indicate higher control mortality24 

# Summary

• Properly designed traveling water screen/fish return systems can effectively reduce impingement mortality rates • Impingement mortality is variable & can be affected by fish distribution, condition factor, temperature and salinity • Properly designed fish collection, counting and return systems do not contribute to reported impingement mortality rates