Weirs are impoundments and they obstruct or impede the natural flow of water in a river or stream but are often necessary to manage water for most hydropower abstractions. These structures can change the upstream and downstream nature of a watercourse, disconnecting reaches, habitats, species and natural processes. They can also change channel morphology and habitats and interfere with the natural movement of sediment and organisms along a river ecosystem.

We are unlikely to licence a new weir unless it is in a stable small, steep stream or river and it can be sensitively located and designed to be of low risk to the river environment.

Water Environment Regulations

An important piece of environmental law that governs how we licence impoundments are the Water Environment Regulations. The Water Environment (Water Framework Directive) (England and Wales) Regulations 2003 give us a statutory responsibility to implement measures to protect and improve the water environment.

For the purposes of the Water Environment Regulations, waters are divided into water bodies. Each river water body has a defined catchment. A range of biological and non-biological elements is sampled to determine the current ecological status of the water body. Objectives are set for each water body, based on the status we expect the elements to achieve by a given date. The principle aim of the Water Environment Regulations is to achieve environmental standards for good ecological status or good ecological potential by 2021 and 2027 by implementing a programme of catchment improvement measures.

This means that we must understand how a hydropower proposal affects the river environment and only issue licences for schemes where we know they won’t cause a deterioration in current ecological status or prevent a water body from achieving water body objectives in the future. In doing this we must consider how a hydropower scheme may affect water quality, river flows, geomorphology, and fish passagethe ecology. We must also consider not only impacts from single activities, but the cumulative effects with other developments and activities.

Existing weirs

Hydropower schemes that are proposed on existing weirs are more likely to be licensed where:

  • the existing weir is required for a current licensed and essential use
  • the weir is not within, or does not affect, a designated site for nature conservation
  • the objectives of the Water Environment Regulations are being achieved and future achievement is not compromised by the presence of the weir
  • there is no risk of deterioration to the ecological status of water bodies from the proposed works

We are unlikely to accept proposals for hydropower schemes that involve raising the height or increasing the footprint of an existing weir, or require significant rebuilding of a derelict weir. If an existing weir that does not have a current use, is causing or contributing to a failure in the achievement of water body objectives, then we may seek to remove it or modify it as part of a river restoration programme.

New weirs

We are unlikely to license new impoundments for hydropower in lowland catchment rivers and streams. River reaches in these areas tend to be more sensitive to changes in flow and geomorphology and are important in maintaining ecological connectivity with the rest of the upstream river system.

We recognise that steeper, upland watercourses can be less sensitive to changes in stream flow and, given their setting in small, headwater catchments, reaches may be less sensitive in terms of ecological connectivity as impacts of hydropower schemes are likely to be spatially limited. New hydropower weirs may be licensed in stable, steep, upland streams where they have been carefully sited and designed to minimise their impact on reach geomorphology and in-river ecology.

Our siting and design principles are set out in Siting an intake weir for hydropower and

further information can be found on Design principles for hydropower weirs.

We are also unlikely to grant licences for new impoundments in designated sites and their supporting habitats.

Water Environment Regulations assessments

For most small scale, low risk hydropower schemes that have been sited and designed in line with our guidance and where the proposed abstraction regime is consistent with our zoning approach for abstraction rates, then we are unlikely to require any special information to address the Water Environment Regulations. We should be able to assess compliance with the Regulations from basic hydrology data, a geomorphology photosurvey, location and engineering drawings in most cases.

We are likely to require additional information in support of an application for larger, complex schemes, schemes where the abstraction is not consistent with our zone flow standards and where structures have not been sited and designed in line with our guidance. In these cases we may ask for additional ecological, geomorphological and hydrological surveys with analysis to help us understand if a proposal presents any risk to water body objectives.

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