Implications of small-scale run-of-river hydropower schemes on fish populations in Scottish streams

• Main Author: Robson, Andrea Lauren
• Format: Dissertation
• Language: English
• Published: University of Hull 2013
• Subjects: Biological sciences

In the past few years there has been a resurgence of interest in hydropower as a direct consequence of the UK government’s commitment to renewable energy and associated financial incentives. The majority of new schemes are run-of-river, which have no significant storage of water, the turbine only making use of the available flow at the site. Hydropower is often presented as a clean and renewable energy, and thus portrayed as having no negative impacts on the environment. However this description has been challenged by numerous authors who consider the impacts on fish and other biota as significant, particularly on salmonid fish populations in relation to migration. This study investigated the implications of small-scale run-of-river hydropower schemes on fish populations in Scottish streams. In these schemes, water is abstracted from an intake above a mall weir to drive a turbine before the water is returned to the watercourse at a downstream location. Abstracted water is channelled down a pipeline to the turbines in a powerhouse before release at the outfall position; this results in a depleted reach. The term “depleted reach” refers to the stretch of river between the intake and outfall of high-head run-of-river hydropower schemes that experiences reduced flow due to abstraction. The main impact in the depleted reach is a reduction in the amount of water, leading to associated changes in habitat including important spawning/nursery areas. The main impact upstream of the intake is reduced access because of the intake weir, which may be exacerbated by the reduction in the amount of water downstream. Therefore, impacts can be observed upstream of an intake (barrier effect), upstream and downstream of an intake (barrier and abstraction effect) and downstream of an intake (abstraction effect). In total, ten schemes were included within this study; five with extensive pre-and post-monitoring and a further five that were considered to have less extensive data. At Kinnaird Burn, Keltney Burn and Innerhadden Burn, salmonid populations varied over the study period. Densities of fish varied both within and outside the depleted reaches, therefore, the inter annual variations in salmonid densities made it difficult to detect any impacts, specifically in response to commissioning of the hydropower schemes, when comparing before/after and control/impact data, despite having extensive pre- and post-commissioning data. It was difficult to detect any impacts of the Ardvorlich Burn, Douglas Water, Camserney Burn and Allt Gleann Da-Eig hydropower schemes on fish densities due to the limitations of the data sets, including a lack of baseline and post-commissioning data and control sites to account for temporal and spatial variations in the fish populations. Consequently, confident conclusions could not be drawn. In the River Callop, 0+ salmonid densities declined at several sites in the depleted reach post hydropower commissioning. However, a lack of spatial and temporal data made it difficult to conclude whether the decline was in response to the hydropower scheme or natural variability. At Rottal Burn and Inverhaggernie Burn, a reduction in ≥1+ and 0+ salmon density respectively, was observed in the depleted reach, post hydropower commissioning. These declines were not reflected in the fish densities at the control site downstream of the depleted reach and thus suggest an impact of flow regulation. The meta-analysis of historical data and subsequent monitoring raised issues about the Environmental Impact Assessment strategies on some of the schemes. Therefore the concerns that existing sampling protocols and impact assessments are inadequate to provide robust, defensible information about the impact of small-scale run-of-river hydropower schemes on fisheries, was upheld. A proposed survey protocol was developed using Before After Control Impact analysis that is intended to answer this need and to be used in conjunction with appropriate guidance documents provided by the regulatory agencies, such as the Scottish Environment Protection Agency (2010) “Guidance for developers of run-of-river hydropower schemes” and the Environment Agency (2009a) “Good practice guidelines to the Environment Agency hydropower handbook”.