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Product Abstract

Hydrolox Traveling Water Screen Fish Impingement and Survival Case Study: Plant Barry Generating Station

Product ID:3002005832
Date Published:28-May-2015
Sector Name:Environment
Document Type:Technical Results

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Price:$ 15,000 (US Dollars)

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This report presents the results of a 12-month field study at Alabama Power Company’s Plant Barry Generating Station to evaluate the survival of fish exposed to a Hydrolox traveling water screen specifically designed to protect juvenile and adult fish. Information in this report enhances the performance database for this fish protection technology. The data presented provides a basis for estimating the potential for these screens to meet the compliance requirements for impingement mortality of the final Clean Water Act’s §316(b) Cooling Water Intake Structure Existing Facilities Rule (the Rule) published August 15, 2014.


Hydrolox screens with fish protection features coupled with a fish return system are one option for meeting the impingement mortality reduction standard in the final Rule. In general, there is limited biological performance data available for demonstrating their similarity to other modified-Ristroph traveling screens. A 12-month field evaluation was performed to develop a substantial quantity of new data under various conditions for two purposes: to assess the modified screen’s comparative performance to conventional traveling band screens, and to support the identification of a suitable compliance approach.


  • To evaluate the operational and debris removal efficiency of Hydrolox screens in a high debris load environment.
  • To examine fish impingement rates.
  • To investigate the 24 and 48-hour latent impingement mortality (LIM) of wild fish, and
    latent mortality (LM) of hatchery-reared fish from Hydrolox screens.


The entire cooling water intake structure (CWIS) for Plant Barry Units 4 and 5 (five screens) was retrofitted with Hydrolox screens with fish protection features. The screens were fit with “fish-friendly” buckets that collect fish and debris that become impinged on the rotating screens. These buckets transport the fish to low-pressure spraywash nozzles that wash the fish and debris into a fish trough. Then, high-pressure spraywash nozzles are used to remove any remaining debris from the screens into a debris trough. The performance level of the fish return system was determined by evaluating the latent impingement mortality (LIM) of wild impinged fish, and the latent mortality (LM) of hatchery-reared fish that were placed directly in the fish return buckets affixed to the screen (but not exposed to the impingement process).


The following are key results from this project:

  • Hydrolox screens are operationally effective in removing fish and debris from the cooling water and preventing carryover into the condenser.
  • Approximately 90% of all fish and debris were collected from the fish trough. Therefore, most of the debris was not collected in the debris trough as designed.
  • Fifty-five percent of the species evaluated for LIM during the study had an average annual survival <30%. This is the criteria used by EPA to separate fragile from non-fragile fish and shellfish species in their Rule development analyses that explicitly identified 14 species of fish, including Gizzard shad and Bay anchovy collected in this study, as fragile.
  • The majority (76%) of the fish collected during this study were Threadfin shad and Bay anchovy, both considered fragile.
  • Comparable LIM and LM rates were observed at 24 and 48-hour intervals, demonstrating that a 24-hour monitoring period would be a sufficient and cost-effective approach to monitoring latent mortality.
  • The use of hatchery-reared fish may be a good approach when evaluating the traveling screen in order to optimize fish return systems. Using commercially available hatchery-reared fish as surrogates for impinged wild fish eliminates the impingement variability associated with fish size, and reduces the effort required to conduct a LIM study.
  • In contrast to wild fish where monthly mortality rates typically exceeded the 24% mortality limit, mortality of hatchery-reared fish was less than 24%, except during August and September (warmest months).
  • Monthly hatchery-reared fish survival rates were similar at each insertion location, suggesting mortality is not related to screen components.
  • Seasonality and water temperatures need to be carefully considered in latent mortality studies due to induced stress associated with water temperature.

Applications, Values, and Use

This report provides power generators with data on the ability of Hydrolox traveling water screens to maximize impingement survival of adult and juvenile freshwater fish. Power generators, resource managers, and permitting agencies can use these results to more accurately and easily predict the potential effectiveness of modified traveling water screens in reducing impingement mortality, and therefore achieving compliance under the final 316(b) Rule.

2015 Program 54   Fish Protection at Electric Generating Facilities
  • Cooling water intake structures
  • Clean Water Act Section 316(b)
  • Modified Traveling Screens
  • Fish protection technologies

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