SPATIAL AND TEMPORAL DYNAMICS OF FINE FLUVIAL SEDIMENT TRANSFER: IMPLICATIONS FOR MONITORING AND MANAGEMENT OF UPLAND RIVER SYSTEMS

Abstract

Although the impacts of changing land use on the magnitude and timing of erosion in lowland catchments are well documented, much less is known about the transfer dynamics of fine sediment through the upland hydrological networks. Using a novel distributed monitoring approach, this thesis examines the magnitude, timing and physical characteristics of fluvial fine sediment in two adjacent upland rivers in North Yorkshire (UK). Annual suspended sediment yield (SSY) estimates range from 33.92 t km-2 in the 131 km2 Upper Derwent catchment to 57.91 t km-2 in the 96 km2 River Esk catchment. Infrequent events were found to be of greatest importance, transferring up to 38% of the annual load in under two days. Simple annual and seasonal rating curves were constructed and are effective in predicting SSC with relative errors of less than 15%. Analysis of within-storm fine sediment dynamics indicated the dominance of sources proximal to the channel in the Esk catchment, whereas sediment sources in the Upper Derwent were more variable. Distributed time-integrated fine sediment sampling identified high SSYs in the headwaters of the Upper Derwent whereas in the headwaters of the Esk the minimum SSY was found with tributaries draining the central valley having maximum SSYs. Analysis of the absolute particle size observed significant downstream fining in both catchments and strong positive relationships between flow and particle size of the transported sediment. The data collected are also applied to four real-world scenarios to demonstrate the effectiveness of this approach. This research has enhanced our understanding of fine sediment delivery to upland channels through the assessment of the fine sediment dynamics at a range of temporal and spatial scales rarely studied in these environments.