Evaluating the role of land use management on sediment transfers within Northern Irish river systems

Abstract

Intensive land use accelerates transfers of fine sediment (<2mm) to the drainage network. This can have negative impacts on ecosystem functions and the ecological integrity of streams. This research in Northern Irish River catchments aimed to investigate 1) temporal and spatial variation of sediment delivery and the influence of land management practices, 2) cattle access to rivers and its effects on bank erosion and destabilisation, and 3) a novel digital assessment method for colmation in fluvial systems. Sediment delivery was investigated using temporal and spatial land management maps and physical catchment characteristics. Analysis identified a moderate/strong correlation (P < 0.01) between streamflow (both direct and total) and sediment delivery. Results also showed that the percentage of field parcels grazed by livestock and fields with bare earth had a positive correlation with sediment delivery (P < 0.05). Streambank geomorphic modifications caused by cattle access was investigated using Terrestrial Laser Scanning (TLS) and motion-capture cameras. TLS results indicated a loss of 0.141 m3 to 1.035 m3 stream bank material, which equates to 0.067 m3 m-2 to 0.092 m3 m-2 of stream bank area (between 27 % and 41 % in the <2 mm fraction). The geomorphic volume loss had the potential to impact 29 m2 to 197 m2 of stream bed with fine sediment (<2 mm) from the study sites. Cattle stream access was associated with elevated turbidity signals downstream at low flow. However, it was not possible to distinguish between local erosion and upstream sediment transfers when elevated turbidity coincided with high flow events. Streambed colmation was investigated using Digital Image Analysis (DIA). Data analysis identified three levels of streambed colmation (High, Medium and Low). There was a moderate/positive and significant correlation (r = 0.489; p < 0.05) between DIA and resuspendable sediment quantified by the Quorer method.

Date of Award	Sept 2021
Original language	English
Sponsors	Department of Agriculture, Environment and Rural Affairs Northern Ireland
Supervisor	Phil Jordan (Supervisor), Colm Lowery (Supervisor), James Dooley (Supervisor), Joerg Arnscheidt (Supervisor) & Rachel Cassidy (Supervisor)