The deterioration of river environments and increased risk of flooding has led to a rise in river restoration and flood alleviation projects across the UK. Projects aiming to reduce flooding have shifted away from traditional methods to using more natural approaches that involve working with and/or restoring a river’s natural processes. Natural Flood Management (NFM) projects often include the installation of Leaky Woody Dams (LWDs) into streams to slow the flow and minimise flooding downstream. Although, prior research has shown how the channels geomorphology and hydrology changes, and that macroinvertebrate communities often benefit from the installation of wood structures, there has been limited research highlighting how LWD with different designs affect macroinvertebrate communities. In 2018, LWDs were installed across multiple streams at Hardcastle Crags, in West Yorkshire, in the UK, to mitigate flood risk. This thesis aims to understand how these LWD structures influenced the geomorphology, hydrology, and macroinvertebrate communities in sites directly upstream and downstream and whether LWDs with a particular design (e.g., length, width, and height, the number of logs, and its height from the streambed) effect macroinvertebrate communities differently. Environmental conditions and macroinvertebrate communities were sampled from upstream and downstream of LWDs, and LWD characteristics were noted for each structure. Although pools failed to form, habitat heterogeneity increased with the presence of wood with changes to fine sediment, organic matter, and flows. Macroinvertebrate communities were significantly different between streams with and without wood, likely due to increased habitat heterogeneity. Macroinvertebrate community composition was affected by the LWDs design, with its length and width driving compositional changes. The LWDs height also influenced macroinvertebrate communities upstream of LWDs, however, the reasons for these changes require further research. Overall, this research highlights that wood increases habitat heterogeneity, and that the size of wood may be important in influencing macroinvertebrate communities. Therefore, wood structures should be carefully designed before their implementation. Future research should examine the changes to macroinvertebrate communities over a long temporal scale, use baseline data whenever possible, sample the wood surface and habitats between LWD structures, and measure vegetation and microbial activities on and around the wood.
Date of Award | 3 May 2024 |
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Original language | English |
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Supervisor | Ryan Wilson (Main Supervisor) |
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