Assessing the influence of low head weirs and low head ‘on weir’ hydropower on the phytobenthic biofilm

O'Keefe, Laura (2017) Assessing the influence of low head weirs and low head ‘on weir’ hydropower on the phytobenthic biofilm. PhD thesis, UNSPECIFIED.

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In recent years there has increased interest in low head ‘on weir’ hydro across the UK. This directly corresponds to carbon reduction targets, renewable energy targets and financial incentives directed at renewable energy generating schemes. Despite increased interests, current understandings of the aquatic implications of low head ‘on weir’ hydro are unclear and not one in field investigation has been carried out at an existing scheme. Yet with important environmental legislation preventing the deterioration of ecological river quality, mainly the Water Framework Directive (WFD), there is an urgent need to improve current understandings. Fundamentally low head ‘on weir’ hydropower is a human activity that could potentially alter the aquatic environment, change natural biotic communities and cause failure to comply with WFD targets. On the other hand, as low head ‘on weir’ schemes are fitted on existing weirs which have already potentially altered the aquatic environment, there is the chance that adding a hydro scheme to a weir could in fact improve the aquatic environment and provide benefits for ecology whilst also providing meaningful amounts of electricity (EA, 2010). The overarching aim of this project was to advance the understanding of how low head ‘on weir’ hydropower can influence physical and chemical habitat condition and the phytobenthic biofilm. In order to achieve the aim, this thesis also investigated how weirs themselves change physical and chemical riverine conditions and the phytobenthic biofilm. To investigate the influence of an existing low head weir on the phytobenthic biofilm comparisons were made between the tail riffle below an existing obsolete weir and riffles upstream and downstream of the weir over time. This design was also replicated for a low head ‘on weir’ hydro scheme. Large scale and small scale spatial surveys were also conducted to explore finer scale spatial patterns below the scheme. There was evidence across this study to suggest that low head ‘on weir’ hydropower is having minimal effects of phytobenthic biomass and community composition. Moreover changes in biomass and community composition were more obvious over time than spatially across sampling locations. There was also evidence to suggest that low head ‘on weir’ hydro schemes can mask the effects of weirs by reducing the proportion of flow over the weir.

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Thesis (PhD)
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24 Nov 2017 10:58
Last Modified:
22 Sep 2023 00:55