Why do we need Eel Screening?

Why do we need Eel Screening?

In the UK in England and Wales, the Environment Agency regulates the abstraction of raw water. Licences for drawing water from lakes, rivers, estuaries, are now granted or renewed subject to compliance with regulations in force to protect eels.  

The regulations set criteria for the use of raw water and screening and pumping equipment. In simple terms, the regulations seek to ensure that Eels at all stages of life are protected, but particularly glass eels and elvers - eels live in fresh water at this young stage of their lifecycle. 

Eels populations are a vital component of their habitat and the ecosystems that support them; although they are actually fish, they can live in freshwater, the marine environment, and can travel considerable distances on land if conditions are wet enough.

The salient about European eels is that today their population has collapsed down to 5% of its total 40 years ago. The Wildlife and Wetlands trust has this excellent summary of the plight of eels.

Eels migrate to the Sargasso Sea to breed, and the young return to European shores, where they grow to adulthood. The Eel regulations are concerned, in part, with preventing young glass eels and elvers becoming trapped or killed as water is abstracted, pumped and screened for domestic and industrial uses.

Why Eel Screening Helps

The European Eel population is at an all-time low, and eel populations are not recovering. Many factors contribute to this - on their journey to Europe from the Sargasso Sea eel fry are affected by climate change altering the ocean currents, marine pollution and overfishing at sea.  

European river water quality is often poor or even deadly for eels as they make their way upstream, and eels are fished throughout the UK and Europe for sport and food. 

Huge volumes of water are removed daily from rivers ponds and lakes for irrigation, industry, drinking water and much else. The equipment needed to divert, pump and process water is fatal for glass eels, elvers and fish fry. At the least, eel screening can reduce this impact and is one of several measures aimed at protecting eels and aquatic life more generally.

Entrapment and Entrainment

The aims of the eel regulations - as far as water abstraction is concerned - are to avoid the entrapment and entrainment of young eels as raw water is being drawn for other uses.

The use of screens at raw water intakes and outfalls can successfully prevent the loss of young eels if used following Environment Agency rules. For eel screening, the angle of approach, intake velocity and the size of mesh aperture are the determining factors.  

Entrainment. A mesh barrier at the point of abstraction is necessary to prevent glass eels and elvers becoming entrained in a water flow system beyond their natural environment. For example, inside a cooling water system, or a water treatment works.  For Eel Screening, the maximum mesh size is a 2 mm aperture to prevent young eels entering systems.

Entrapment. So far so good, but young eels are small and once drawn towards a screen at an intake may not be able to escape from the mesh inf the intake flow is too strong. The eel regulations constrain the intake velocity at intakes, the minimum flow rate being set at 0.1 metres a second, sufficient to allow most young eels to escape entrapment on the mesh.

Rotorflush Filters Ltd's innovative self-cleaning intake screens are ideal for eel and fish screening. Their 2 mm and 1 mm mesh, low intake velocities, and all stainless steel construction are ideal for eel and fish protection at raw water intakes.