Good for fish

It is not scientifically possible to prove a negative. Anyone who asks for proof that hydro schemes have no impact on fish populations misunderstands the scientific process. Anyone who asserts they have any such proof does the same.

Good practice is to weigh all available evidence to reach an informed opinion on the most likely impact of an individual hydro scheme on the fish populations in the relevant river system, alongside the level of residual risk that the most likely outcome is not realised and what mitigating measures may be implemented.

The available evidence strongly indicates that the Hexham River Hydro design will have a positive impact on the fish populations of the River Tyne – and hence also a positive impact on the economic interest of all the individuals, organisations and businesses in our region with fisheries interests.

Set out below are 17 reasons why the Hexham River Hydro design will be good for the fish populations in the River Tyne river system.

(1) There is widespread agreement that fish passage at Hexham Bridge must be improved and the Hexham River Hydro design would achieve this. Following extensive sand and gravel extraction over the years, the river Tyne at Hexham does not currently comply with the European Water Framework Directive. The weir is continuously being undercut due to readjustments of water levels and work is required to address this and so improve the quality of the river. The Hexham River Hydro design provides new fish passage facilities for game fish, coarse fish and eel through the installation of a ‘multi-species’ Larinier fish pass with steel plates enabling lamprey to move upstream through the same pass, and with a bespoke eel pass positioned alongside the outer wall of the Larinier pass. The Hexham River Hydro design would enable the quality of fish passage at Hexham to comply with the European Water Framework Directive.

See section 10.1.1 of the design report for more information

(2) Expert design consultants have concluded that the Hexham River Hydro design, with fish pass facilities co-located with an Archimedes screw for hydropower generation, would be better for upstream fish passage than if a new fish pass were to be built at this site on its own using the design drawn up for Tyne Rivers Trust. This is because:

  • installing a fish pass next to a hydro turbine produces a much greater attraction flow to ensure fish can find the fish pass;
  • there is much less variation in flow in the fish pass associated with the hydro system over the whole range of river flows;
  • in all flow conditions, the hydro design enables fish to move upstream underneath Hexham Bridge through the deeper third arch, rather than only through the much shallower first and second arches (from the south bank); and
  • the hydro design provides more water to the fish pass element of the design, improving its performance in different flow conditions.For a more technical explanation of the first three points above please read this paper: Benefits of the fish pass associated with the Hexham Hydro Scheme

See sections 10.1.1 and 10.3 of the design report for more information

(3) The structures relating to fish passage have first priority in the operation of the scheme. Electricity will only be generated (by enabling water to pass through the turbine) when there is sufficient water passing through the southern three arches of Hexham Bridge to feed both the hydro turbine and the fish pass. At times of the year when there isn’t sufficient water for both, the fish pass has priority and water would not be taken through the hydro turbine, only through the fish pass.

See sections 2.2.3 and 9 of the design report for more information

(4) The Angling Trust Position Statement on Run-of-River Hydropower recommends three tests before permission to develop a scheme should be granted and Hexham River Hydro passes all of these tests.The Angling Trust Position Statement states:“we believe that permission to develop run-of-river hydropower should only be granted if the scheme can meet the sustainable hydropower three stage test:

1. if the development can be proved to have a very low impact on the ecology and other functions of the rivers both individually and cumulatively with other schemes and;
2. if it is installed on an existing weir and;
3. if that weir cannot be removed or eased for technical reasons or because it has some other legitimate and long standing function (such as navigation on heavily used rivers).”

Hexham River Hydro would have a low impact on the ecology and other function of the river and would be the first run-of-river hydropower scheme on the River Tyne, so there is no cumulative impact (test 1). The weir at the foot of Hexham Bridge is the site for Hexham River Hydro (test 2) and provides structural support for Hexham Bridge (test 3). For more information on the low impact of Hexham River Hydro on the river ecology, see ‘Benefits – Good for local ecology’ and the design report

The Angling Trust Position Statement can be downloaded from the bottom of this page:!

The above linked page and the front page of the Angling Trust Position Statement include a picture of “dead perch killed in hydro turbine” and the same picture has been used by individuals objecting to hydropower schemes on the energyshare website and elsewhere.
The Hexham River Hydro team enquired of the Angling Trust which hydro scheme had caused such damage, as we wished to understand the nature of that scheme (what type of turbine used, what design, how old etc) in order to avoid any such situation arising at Hexham. We were told by the Angling Trust: “the perch were from a Dutch hydropower installation, but it is unclear specifically what type it was”.

Other community groups have further questioned the veracity of the photograph, hypothesising that a remarkable degree of luck and effort must have been required to retrieve matching halves of the same seven fish from a live river environment.

(5) The chosen turbine for Hexham River Hydro is the Archimedes screw turbine, selected because it is widely acknowledged to be fish friendly. Other types of turbine, such as the Kaplan, might be lower cost to install and/or produce a greater energy return (and hence greater revenue) but were ruled out by the Hexham team because of the over-riding importance of safeguarding fish.The most important reason why the Archimedes screw turbine is fish friendly is because fish travel safely through this design of turbine as they migrate downstream. Studies have shown minimal effects on both salmonids (salmon smolts, kelts, trout) passing through this type of turbine (Fishtek Consulting, 2007; Fishtek Consulting, 2008) and also on coarse fish species, including chub, roach, eels, pike, barbel, perch and lamprey (Spah, 2001, Vis Advies 2007, Fishtek Consulting, 2009).The Hexham River Hydro design report contains findings from tests with >1,000 fish of different species, taken from trials on the River Dart and River Derwent with schemes directly applicable to the Hexham River Hydro scheme design. The data clearly demonstrates minimal impact on fish of all species.See the video footage in the section on hydro power research on the Fishtek website, showing fish passing safely through an Archimedes screw turbine

Fishtek are the leading consultancy in the UK in assessing the interaction between hydropower and fisheries.

Fishtek were part of the consortium of specialist consultants (led by Cundall) who prepared the Hexham River Hydro design

See section 10.1.2 of the design report for more information

(6) The Archimedes screw selected for the design is 3.8m diameter with a rotational speed of 21 revolutions per minute. The screw’s leading edge is fitted with a protective bumper and allows the safe passage of fish (and debris). The chambers of water in which fish pass downstream are large, and fish pass through them safely. There is no ‘washing machine’ effect for the fish.

See section 10.1.2 of the design report for more information

(7) The detailed design has taken into account the need to ensure no pollutants enter the river either during the construction phase or once the scheme is constructed and operational.

See section 15.2.2 of the design report for more information

(8) The scheme is a very modest size for the capacity and size of the River Tyne at Hexham. The design flow for the hydro scheme is 7.75 cubic metres per second, compared with a long term average flow in the river at Hexham of about 42 cubic metres per second. For those familiar with the more technical aspects of hydro design, the level at which Hexham River Hydro would operate is between Q85 and Q90 i.e. well within the Environment Agency Good Practice Guideline of Q95.

See section 2.2.2 of the design report for more information

(9) A new ‘resting pool’ for fish will be created in the river just downstream of the southernmost three arches of Hexham Bridge. The water in this pool will be part of the river flows (i.e. far from still) and large rocks will be fixed into the base of the pool to provide refuges for fish.

See section 10.2 of the design report for more information

(10) The system is equipped with multiple sensors and failsafes enabling effective operation to its design parameters and remote operational monitoring, including the ability to start or stop its operation from anywhere with an internet connection. So, for example, should a level sensor fail (which, if it occurred at low flow conditions, might mean water is allowed into the turbine when it should be going through the fish pass)  effective and quick action can be taken to correct the problem.

See sections 7, 8.1 and 14 of the design report for more information

(11) For all of these other aspects the impact of the scheme on the river is neutral:

  • No water will be removed from the river. (And no water will be added to the river either)
  • The flow in the river channel will not be depleted (i.e. it will not be reduced). In technical terms, this means there is ‘no depleted reach’
  • Water levels upstream of the scheme will remain unchanged
  • Water levels downstream of the scheme will remain unchanged
  • There will be no change in the natural temperature of the water since an Archimedes screw turbine neither heats nor cools the water passing through it
  • There will be no change to the oxygenation, salinity, acidification or nutrient conditions within the river
  • The water level upstream of Hexham Bridge and as it flows underneath the Bridge itself will remain unchanged
  • The scheme will not affect: any Site of Special Scientific Interest (SSSI); any Special Area of Conservation (SAC); any Special Protected Area (SPA); any national nature reserve; any local nature reserve; any Area of Outstanding Natural Beauty (AONB); or any national park.

(12) There is no ‘allowable fish mortality level’. The scheme has been designed to enable all fish to pass safely upstream and downstream through the scheme structures.

(13) The Hexham River Hydro design incorporates fish monitoring of a type and extent not previously conducted on the River Tyne at this site. Monitoring plans incorporate underwater cameras, fyke nets and other in-river measures alongside external data analysis. The data and insight this would provide in to the movement of fish across the footings of Hexham Bridge would benefit all organisations working on the river’s ecology.

Note: In-life fish monitoring is not a requirement under Environment Agency good practice guidelines for small hydro schemes such as this.

See Appendix 19 of the design report for more information

(14) In the highly unlikely event that the scheme would need to be shut down (e.g. if monitoring demonstrates that fish are not passing upstream and downstream through the new structures as planned) the scheme can be decommissioned in a way that retains the improved fish passage facilities and maintains the structural integrity of Hexham Bridge.

See section 6.5 of the design report for more information

(15) The scheme design and operating assumptions require no changes to be made to the release regime from Kielder reservoir.

(16) ‘Future-proofing’ of the fish pass is built into the Hexham River Hydro design because the pass will be constructed in such a way that, should downstream water levels drop in the future due to shifts in the downstream bed, a further section of pass can be bolted onto the end of the constructed pass, extending the pass further downstream. This is a critical design parameter, as downstream water levels at Hexham Bridge have steadily reduced since the 1960s.

See section 10.3.2 of the design report for more information

(17) Climate change threatens all species of fish. Action is needed to reduce the UK’s carbon emissions, urgently.

Climate change is thought to have already had some effects upon Atlantic salmon and may be partly to blame for their decreasing numbers. There is evidence that the temperature of the sea’s surface may affect smolt survival. It is also thought that climate change may affect salmon growth rates or make their food less available. Predator numbers may also be affected by temperature.

See ‘Benefits – Good for the planet’ for the reduction in CO2 emissions that would arise from Hexham River Hydro

More information

See section 10.2 of the design report for responses to the specific questions and concerns raised by anglers and others with fishing interests during the course of feasibility and design work.

See our lessons learned for more information on consulting with organisations and individuals with fisheries interests.

See also:
Fishtek were part of the consortium of specialist consultants (led by Cundall) who prepared the Hexham River Hydro design

Hexham River Hydro, an energyshare project made possible by British Gas and supported by Carbon Leapfrog, Cooperative Enterprise Hub, Vattenfall and The Naturesave Trust