The best free-standing eel screens available today

Best Protection for Fish and Eels, Brilliant Design

A few years before the regulations were drawn up, Rotorflush Filters had already developed an innovative and reliable self-cleaning suction intake screen.  The screens are cylindrical and designed to attach onto the suction pipe of pumps, like basket filters. They allow dirty water to be pumped without blocking the screen intake, the pump or any attached equipment such as irrigation nozzles. The screens are water powered, the design is simple and can be scaled to meet flow rates up to 250 litres / second.

2 mm Aperture Eel Screens

The Eel regulations require a maximum screen aperture of 2 mm when drawing water in order to protect glass eels and elvers. Preventing 2 mm mesh from blocking while screening 1000’s of cubic metres of water a day is a challenge.

The self-cleaning intake makes possible the use of suction side 2 mm aperture screens when pumping raw water.  Without the self-cleaning mechanism, the 2 mm screens would rapidly clog with weed and other water-borne particulate. Our 2 mm screens scored highly in an Environment Agency trial of commercial eel screens carried out in the Somerset Levels. The trial evaluated four types of screen for use with large mobile pumps, and resulted in the purchase of sixteen Rotorflush units.

Very Low Intake Velocities

Another challenge is that the Eels regulations stipulate intake velocities for screens.  The intake velocity for a particular installation of an eel screen is decided by the Environment Agency and is a condition of a water abstraction licence.  Typically, the intake velocity of eel screens for the protection of glass eels and elvers is 0.1 metres / second, although this can vary. In the US, fish screening for cooling water intakes requires a 0.5 ft per second intake velocity, which equates to 0.15 metres a second.

An intake velocity 0.1 metres / second is a very low for any pump intake.  The only way to lower the pump intake velocity for a given flow rate is to increase its open area. Increasing the open area of an intake screen increases its size. The available depth and space for installation for screening must be considered.

Construction projects on waterways requiring the removal or movement of water generally have to comply with Eel regulations. The cylindrical design of Rotorflush self-cleaning intake screens lends itself to meeting low intake velocities by making best use of the screen area for the space the screens take up.  The screens allow water to be pumped and screened without blinding, and protect wild life by keeping the intake velocity at 0.1 metres / second or less.

Smaller Screens – Bigger Flow Rates

For example, a cylindrical screen fitted with 2 mm aperture perforated mesh has approximately 33% open area. To ensure an intake velocity of 0.1 metres / second when pumping 100 litres / second, the screen would need to be 70 cm in diameter and 70 cm high. Woven stainless-steel mesh has a greater open area – approx. 60 %, but needs to be supported, so allowing for a supporting cage open area could be as high as 45% – reducing the screen size to 60 cm x 60 cm.

The completely submerged cylindrical Rotorflush screens take up less space for the same open area than travelling screens. To keep their self-cleaning eel screens as compact as possible while meeting Eels regulations, Rotorflush Filters Limited have introduced another innovation. The 2 mm mesh is tensioned to form the body of the screen, this maximises the open area of 2 mm mesh to as much as 60%. For 100 litres / second, the screen is reduced to around 50 x 50 cm.

Water companies have already invested significantly in addressing the requirements of the Eels Regulations and will continue to do so. Rotorflush screens have the benefit of being relatively easier to manoeuvre and deploy; less civil works and restructuring at intakes is needed, compared with the expense and upheaval of lateral or band screening. 

Companies that hire industrial pumps for temporary works, the RSPB, WWT at Slimbridge and many others have deiscovered the advantages of Rotorflush's innovative Self-Cleaning Eel screens.

By adopting innovative approaches, the environmental impact of meeting Eels Regulations can be reduced while providing efficient, low maintenance eel screening