Screening Assessments

Abstractions – an introduction

Fish population impact

Water is removed from watercourses for a variety of reasons, however the most common are for consumption by humans (whether directly as ‘potable’ water, or for agriculture) and for use in hydropower schemes to generate electricity. This water is typically abstracted from a river or stream via a conduit like a pipe or canal. Where water is removed from a watercourse, there is the potential for aquatic fauna, including fish, to be ‘entrained’ and removed along with this water. This can have a detrimental impact on the fish population within that watercourse at both a local and catchment level.

We have significant experience in assessments of abstractions and the range of options that may be required to mitigate against a potential impact from an abstraction. The first stage of the assessment of an abstraction is often to look at the degree to which fish may be entrained by an abstraction. This can be theoretical and based around the size of abstraction relative to the watercourse, location of the abstraction point and species of fish present and their behaviour.

Where an empirical entrainment assessment is required, this can take the form of investigation into the number and species of fish being entrained through an offtake over time. Such work is useful to quantify the degree of entrainment occurring, if any, and subsequent mitigation and screening measures that may be required to reduce this.

Abstractions and eels

Eels regulations screening assessments

In addition to determining the risk of entrainment and / or impingement of fish at an abstraction, the Eels (England and Wales) Regulations 2009 (the ‘Eels Regulations’) are implemented by the Environment Agency, which requires any abstraction to be ‘Eels Regulations’ compliant to protect the critically endangered European Eel.

Fishtek has undertaken numerous Eels Regulations screening assessments, which include determination of current compliance with the Eels Regulations, and if not compliant the identification of the best practice screening solution at the abstraction in question and the undertaking of a cost benefit analysis (CBA) in support of this assessment. Where a best practice screening solution is deemed not cost beneficial then alternative measures are subsequently investigated, including additional CBA’s as necessary.

Assessment Examples

Our previous work includes:

• The identification and design (and ultimately installation) of a fish exclusion screen as part of a biomanipulation plan to improve a SSSI and SAC currently in unfavourable condition. The temporary screens are designed to be robust, but easily removable to enable access for emergency services to the SSSI and enable manual cleaning
• Eels regulations assessments (including screens and, where necessary, eel passage) at numerous sites within Devon and Cornwall for a water utilities company. This included the identification of some screens that were already compliant, exemptions where entrainment risk to eels and fish was identified as low, the identification of best practice screen solutions where sites currently do not meet the screening requirements, and the undertaking of CBA’s. Fishtek have subsequently been requested to design some screens and have designed, fabricated and installed (in house) a number of eel passes
• Assessment of screening requirements at a number of hydropower facilities
• Entrainment monitoring of a water utilities abstraction to determine if it poses a risk to fish and eels and ascertain an exemption under the Eels Regulations

Fishtek also undertake design of screen systems using our highly experienced in-house engineers. Designs can be at the level of concept or outline design (RIBA Stages 2 and 3 respectively), all the way up to complete construction-ready and fabrication drawings (RIBA Stage 4).