Eel passes – improving design and performance
This project reviewed eel passes in England and considers how to improve them.
Documents
Summary
Project overview
This project reviewed how different designs of eel passes in England are working. The aim was to identify any problems with installed passes and consider how to improve the design and performance of existing and future passes.
Background
In response to the severe decline in numbers of European eels in England, eel passes were installed at more than 500 Environment Agency river structures such as dams, weirs, and tide gates. These passes aim to make it easier for juvenile eels to migrate upstream to help restore eel populations in freshwater habitats. As some passes were installed several years ago, this gave us the opportunity to learn lessons to improve eel passage.
Method
This project had 2 phases. The first was a literature review on eel pass performance and seasonal eel migration patterns. The second part was a detailed case studies of 2 facilities that have been operating and monitored for more than 10 years: Judas Gap Weir (Essex) and Greylake Sluice (Somerset).
Findings
The final report draws together the phase 1 literature review findings with the phase 2 data on how eel passes have worked. It can be used as a resource to:
- identify any issues with passes that may have been installed for several years
- make sure existing and new eel passes work as efficiently as possible with lessons learned and current guidance
- develop a research programme to improve design and performance of eel passes for all upstream migrating life stages of the European eel
Design considerations
The report’s design considerations for eel passes are for the Environment Agency and other structure owners, such as water companies and private individuals. They use lessons learnt from existing passes to help make sure future ones are designed to protect and secure the survival of the nation’s eel population.
The design considerations cover all aspects of pass installation and design, such as:
- choosing the appropriate type of pass
- selecting the right construction materials
- the operating schedule and maintenance considerations
The report also includes a summary of the characteristics of upstream eel migration that are important when designing and operating passage facilities, for example:
- differences in the physical capabilities of eels at their various migratory life stages, to ensure all sizes of upstream migrating eels can use the passes
- eel migration patterns are strongly seasonal, affected by factors such a temperature, river flow, moon phase and tidal cycle
Next steps
The project identified areas for future research to further improve eel pass design and performance. These are based on a better understanding of the behaviour and requirements of different life stages of eel and lessons learned. This report was written in 2019 and the future research is underway.
Project Information
Project managers: Juliet de Little, Zora van Leeuwen and Sarah Twohig (FCERM research), Ros Wright (National Monitoring, Fisheries and Ecology)
This project was commissioned by the Environment Agency’s FCRM Directorate, as part of the joint Flood and Coastal Erosion Risk Management Research and Development Programme.