Energy and Climate Change CommitteeWritten evidence submitted by HR Wallingford (SEV 20)
Executive Summary
1. This submission has been prepared by HR Wallingford, one of the UK’s leading research and consultancy organisations in engineering in the water environment. We have had a long-standing engagement with the Severn Barrage, including many of the studies undertaken for the Severn Barrage Committee in the late 1970’s and published in 1981 and more recently for the 2008–10 DECC studies of tidal power on the Severn. As a result of more recent research, we believe that the evidence has improved in the following areas:
Far field effects on water levels;
Effects of infrastructure projects on estuary morphology; and
The modelling of noise and other disturbance effects, and the response of migratory fish to these.
2. We believe that recent research and experience elsewhere, provide an improved basis for considering the impacts of a barrage and the options to minimise the habitat losses from tidal range schemes in relation to energy yield, so reducing the scale of challenge posed by habitats compensation under the Habitats Directive.
3. We also recommend the following as priority areas to improve the evidence base:
Bathymetry and morphology survey of the estuary;
Sedimentology and benthic communities, especially on the intertidal areas; and
Fish behaviour/mortality and turbine design.
About HR Wallingford
4. HR Wallingford carries out advanced research, consultancy and software development relating to civil engineering hydraulics and the water environment. Established in 1947 as a Government research centre, it is now an independent research and technology organisation (RTO). We operate on a non-profit-distributing basis and employ over 200 engineers, scientists, mathematicians and support staff. Our research and specialist consultancy advice is backed by state of the art computational and physical models. We have techniques available to establish wave and current climate, and to examine issues associated with sediment transport, water quality and aspects of ecology. We also investigate dredging and navigational concerns, structural aspects, and the environmental and coastal impact of maritime projects.
5. HR Wallingford made a substantial contribution to the Severn Tidal Power Feasibility Study, commissioned by Department of Energy and Climate Change (DECC) in 2008–10. We undertook computational modelling and advice to predict the effects of barrage schemes on estuary tidal water levels, the redistribution of estuary sediments, and morphological change of the estuary. Thus we used the tools and data available at the time to predict how the Severn estuary would respond to the introduction of a tidal power scheme.
6. In this submission of evidence we provide a summary of key new areas of evidence that we are aware of, and also highlight major areas of uncertainty that we recommend are considered priority research areas.
Far-field effect on water levels
7. The DECC study found that the Cardiff to Weston Barrage could lead to impacts on high and low water levels along the Devon and Cornwall coasts, the coast of Wales, the east coast of the Republic of Ireland, and potentially further north. Since that time, the Energy Technologies Institute (ETI), with expertise from HR Wallingford, Black and Veatch, and the University of Edinburgh, has developed a continental shelf computer model. This included an assessment of schemes in the Severn Estuary, and further demonstrates the potential for interaction of tidal range energy schemes at this scale. It is expected that the model will be available for wider use in early 2013.
Morphological changes in the estuary
8. An ebb-tide generating scheme of the scale of a Cardiff to Weston Barrage would lead to the loss of more than 12,000 hectares of intertidal habitat, through the effects on tide levels alone. An area of uncertainty at the time of the DECC studies was whether there would be further longer-term loss of intertidal through processes such as wave erosion. This is a pivotal issue because of the implications for compliance with European Directives on wildlife habitat conservation.
9. The morphology/bathymetry of an estuary, and how this develops under different environmental conditions has and continues to be a highly active area of research within the international science community. Globally, this is driven by the need to better predict long-term change, especially in response to climate change. Within Europe, this research has also been given a particular focus by the Habitats and Water Framework Directives. As a result, there is now a better understanding of some of the complex feedbacks that exist within the geo- and eco-morphological systems, which has improved the predictive capability of the models that are now available. With further data (see below), this offers the potential for improved predictions of longer term change, coupled with a better appreciation of the level of uncertainty associated with such estimates. .
10. Investigation of both the morphological and ecological aspects of intertidal areas has been greatly aided by the many habitat restoration and habitat creation schemes that have been implemented over recent years. Notable in this regard are the managed re-alignment schemes in the UK and the across Europe (see list of online resources in Townend et. al. 2010) and the post-barrage learning in the Netherlands (de Vriend, 2004; Eelkema et. al., 2012). More recent work has seen the introduction of several large-scale pilot studies to test a number of innovative restoration techniques (http://www.ecoshape.nl/).
11. There is therefore the potential to re-visit the likely impacts of the scheme on the habitats within the Severn estuary and the opportunities to mitigate or compensate, for at least some of these, using a number of techniques in a suitably integrated manner. This would help inform the debate and guide considerations in respect of the various legislative constraints, not least the Habitats Directive.
12. Our understanding and evidence for the effects of tidal schemes is hampered by the absence of robust and long–term basic data for the estuary. For example, all studies of the estuary to date have relied upon a mosaic of bathymetric datasets. A comprehensive bathymetric survey of the entire estuary is needed, to cover the whole of the Estuary from the Bristol Channel, to at least Beachley. In addition, the long term record of intertidal morphological change, under current conditions, should be extended through further LiDAR (Light Detection And Ranging) monitoring at low tide every five years for the foreseeable future.
13. Estimating the likely changes of the morphology and ecology of estuary systems also requires robust data on the make-up of the sediments, a description of the benthic communities and knowledge of the fringing vegetation, notably the saltmarshes. These data are currently of variable quality. The age of much of the data also means that it is often not well matched to the data needs of the types of model that have been developed more recently. These shortcomings only serve to increase the level of uncertainty and make interpretation at an estuary scale difficult.
Habitat Compensation requirement
14. The habitat losses referred to above, trigger the need for compensation under the Habitats Directive; or failing that a derogation of the directive. Derogation was not favoured at the time of the DECC study, with compensation by replacement habitat of “equal value” being the preferred approach. Regardless, we believe there is much valuable work that could easily be done, by making use of the tools already developed for DECC, to optimise the loss of habitat in relation to energy yield. This would principally entail optimising operational modes, looking more closely at a flood-ebb generating scheme, and the more detailed investigation of the type and intrinsic biodiversity value of the habitat that could be lost. By this approach, substantial reductions could be achieved in the compensation/derogation requirement.
Construction risk
15. To our knowledge, the construction process for a tidal power scheme, and in particular during the latter phases where the degree of constriction is high, of a tidal power scheme of this scale has not been the subject of serious study in the last 20 years or more. The major hydraulic forces during this operation therefore remain a risk area for any developer of such a scheme. The means exist to reduce this risk by using a physical model of part or all of the Cardiff to Weston Barrage. This would allow the forces that may exist at closure to be better understood.
Modelling of biological effects
16. The biodiversity impacts assessment conducted on behalf of DECC highlighted anthropogenic noise during construction and operation as a potential threat to fish species in the estuary. The noise assessment was carried out via literature review. Since 2010, the scientific literature has expanded as more species are investigated for their ability to hear noise and their reactions to various noise sources. The ability to model underwater noise has also been improved by, and is now used more regularly to assess effects and plan effective mitigation for new marine development.
17. Techniques have also been further developed since the DECC studies, to predict how fish may move in response to underwater noise and other changes in the properties of the water column. Species behavioural traits can now be used as parameters in a numerical model and their movement in response to noise or other anthropogenic disturbance predicted. For example, many of the fish species in the Severn are migratory, and juveniles must leave the freshwater section of the river at a certain time. Barriers to their exit, whether physical or created by sound or heat, could delay their departure from the upper estuary. The modelling techniques now available, can provide an estimate of how much longer this journey would take and this information could then be used in an assessment of the impacts upon migratory fish.
18. That said, our understanding of the effects of tidal range generation on fish survival and movements would undoubtedly benefit from further primary research. This would improve the certainty level attached to modelling predictions. We are also aware that progress has been made in the development of turbine concepts with low rotational blade speed, that may reduce the risk of fish damage during passage through turbines (e.g. the Atkins/Rolls Royce “low head” turbine). This is also the subject of related research within the hydroelectric power community, supported by resurgent interest in this technology. Thus we recommend that integrated study of fish behaviour/mortality and turbine technology is given priority as a research area.
Conclusion
19. We have highlighted areas of evidence and research priorities for future study of the Severn barrage concept. We would welcome the opportunity to contribute further to informed debate on the effects and practicalities of developing tidal range power on the Severn Estuary.
20. Our archives include reports covering many of the studies undertaken in the 1970’s, as well as the more recent studies for DECC that we were involved in. Should there be specific information regarding previous studies that the Committee would like sight of, we would be willing to make such material available (subject to any client restrictions).
References
de Vriend HJ, 2004, The Eastern Scheldt barrier: Environmentally friendly engineering?, In: Territorio y Medio Ambiente, II Congreso Internacional de Ingeniería Civil, Colegio de Ingenieros de Caminos, Canales y Puertos, Madrid, pp. 1269–1281.
Eelkema M, Wang ZB, and Stive MJF (2012) Impact of Back-Barrier Dams on the Development of the Ebb-Tidal Delta of the Eastern Scheldt. Journal of Coastal Research: Volume 28, Issue 6: pp. 1591—1605.
Townend IH, Scott C, Dixon M, 2010, Managed Realignment: A Coastal Flood Management Strategy, Ch. 4 In: Flood Risk Science and Management. Edited by Gareth Pender, Colin Thorne, Ian Cluckie and Hazel Faulkner, Published in 2010 by Blackwell Publishing Ltd.
November 2012