High-precision Sediment Tracking for Characterization of Sediment Transport of a Rural Stream in Southern Ontario Conditioned by Glacial Legacy Deposits

Abstract

Semi-alluvial rivers are common in Southern Ontario and are characterized by sections of exposed highly consolidated glacial till and other sections of mobile sediment. Such rivers are typically characterized by a series of downstream fining trends (sediment links) as a result of the discontinuous distribution of sediment sources. Evolutionary models have been presented that describe these streams and tend focus on the feedback between river morphology, hydraulics and sediment transport. Sediment transport that occurs on the channel bed is the most important component for understanding this feedback and is typically quantified using bulk sampling, indirect sampling or sediment tracking. All of these methods are useful but also miss important details of the process such as active width and burial depth. This methodological deficiency was used as motivation for the development of a new type of Radio Frequency Identification tracer (“wobblestone”) that has the potential for increased tracer recovery rates and the assessment of tracer burial depth. The goal of this thesis is to demonstrate the effectiveness of this new high-precision tracking technology and to characterize the sediment regime of a rural semi-alluvial glacial till river. The first goal was accomplished by developing a methodology to determine the burial depth of tracers and testing this method in both the lab and field setting. The second objective was achieved by measuring the longitudinal profile, identifying the location of sediment links and sediment tracking using the newly developed wobblestones at a field site located on the western branch of Ganatsekiagon Creek in Pickering, Ontario. Ganatsekiagon Creek is a semi-alluvial river that is of interest because in the next 5 years its watershed will see a rapid increase in urban-residential land-use (from 2% to 43%). The site has also been identified as an important habitat for Redside Dace, an endangered species in Canada, which makes it important for research partners such as the Toronto Region Conservation Authority, who are responsible for managing the watershed. Wobblestones show potential as a new sediment tracking technology that can determine the burial depth of stones and increase the recovery rates of tracers. Field tests indicated improved recovery rates and that the burial depth can be determined with an accuracy of +/- 4 cm. Additional fieldwork should be conducted in order to confirm the accuracy of the burial depth measurements. In addition, flume investigations should be conducted to determine the mobility difference between wobble and non-wobblestones. Two sediment links have been identified on the western branch of Ganatsekiagon Creek. The field tracer results show that the gradients of bed slope and particle size lead to significant differences in sediment dynamics over short distances along the river. In addition, the results supported the hypothesis that the upstream site is a source of bedload and that this reach may be sensitive to hydrologic changes in the watershed as a result of the ongoing urbanization. The study site should remain the focus of future monitoring in order to verify the apparent differences in the mobility and transport through these semi-alluvial glacial till rivers and to assess their sensitivity and evolution as a result of urbanization.