The Physical and Ecological Impacts of Low Head, Retrofit, ‘Run of River’ Micro Hydropower in the Peak District National Park

Over the past decade there has been a sudden resurgence in the installation of ‘Run of River’ (ROR) hydropower schemes. In England, this interest has focussed on low head schemes, retrofitted to existing weirs. Despite minimal evidence, ROR schemes are often suggested to have negligible impacts on riverine ecosystems with much of the existing research focussed purely on how such schemes affect fish populations/migration. However, ROR schemes have the potential to affect all trophic levels, through hydraulic alterations, changes to river geomorphology and manipulations to habitat availability/quality. This distinct lack of knowledge surrounding the broader impacts of ROR schemes, combined with the legislative requirements of the Water Framework Directive, for all waterbodies to reach ‘good ecological status’, make this a very pertinent research gap which must be addressed. As such, this study takes an interdisciplinary approach, assessing the hydraulic, geomorphological and ecological impacts of three diverse ROR micro hydropower schemes at both the reach and patch scale. The study initially focussed on the reach scale impacts of the three schemes on habitat quality/availability and attempted to separate the impacts of the schemes, from those of the pre-existing weirs. The findings suggested that at the reach scale habitat quality/availability is dominated by the pre-existing modifications and thus, in the absence of baseline data, assessing reach scale ecological impacts is particularly difficult. As such, the remainder of the study focussed on the patch scale impacts of the schemes. In each case the study design was unique focussing on the area most affected by each scheme. Specifically the study identified the ecohydraulic impacts of a diversion type scheme around the hydropower outlet, and assessed the geomorphological and hydraulic impacts of construction and operation of an in-weir type scheme.