Evaluating environmental impacts of micro, mini and small hydropower plants in Norway

Small-scale hydropower plants with an installed capacity <10 MW are an important part of Norway's local and regional development. Small-scale facilities have been viewed as a relatively environmentally friendly form of energy production because they are assumed to have limited negative environmental impact. However, the plants potentially have environmental impacts related to land use changes from infrastructure installation and also instream effects such as barriers to fish migration or disturbed flow conditions within bypasses. We used a remote sensing and GIS approach to examine the relative environmental impacts of three different size classes of Norwegian small-scale plants - categorized as micro (<0.1 MW), mini (0.1-1 MW) and small (1-10 MW). We evaluated 148 small-scale hydropower projects in Trøndelag, central Norway, focusing on their footprint and potential environmental impacts. Our analysis showed a slight preference for siting in forested habitat and, in particular, forested gorges associated with high biodiversity. However, most hydropower plants were not sited in forested gorges, or in areas with high predicted intensities of threatened terrestrial species. Similarly, there was little overlap with known migratory paths of Atlantic salmon and sea trout, or with archived occurrence records of instream fishes: salmon, trout or European eel. A low degree of overlap was attributed to the limited number of projects compared to the extensive distribution of these fish populations. The footprint areas of the projects were small (<4 ha) but increased with the size of the hydropower plants. Individual micro plants likely had low impact within their footprint because they required the least infrastructure for installation, and lacked dams which may act as barriers to fish movements. However, small plants were more land-use efficient. Our findings suggest that all size classes of small-scale hydropower plant have a role in balancing Norway's goals of minimizing environmental impacts of energy production while contributing to local and regional development.