River basins are dynamic systems shaped by a variety of active geomorphic processes, their interactions, and climatic and tectonic history. These systems are complex and their controlling elements, intertwined broad-scale geomorphic processes, cause local differences in channel form, which in turn have an impact on the ecology of the river and adjacent environment. This talk will explore the role of three agents in moving sediment along streams, and their competitive but supportive role in shaping the landscape.
First, the lecture will examine factors that affect the stability of channels, the movement of sediment, and the resulting ecology of small streams. The physical and biological complexity of these streams stems from their irregular, granular beds impacted by fluid forces which change dramatically over space and time. Steep channels are the most complex. Stones form structures in the channel that essentially control the movement of sediment, and influence the nature of the stream flow and channel stability. As many steep streams are located in mountainous areas, landslides often travel down slopes and into the channel, leading to major changes and complications in the characteristics of the whole stream system, ecology included.
The second part of the lecture will discuss the impact of salmon and floods on channel form, bed material dispersion and yield, bed surface texture and stability, and fine sediment dynamics. High densities of sockeye salmon can fill stream pools with sediment, remove river bars, and change the entire bed surface of channels. Salmon can do this by disturbing fine sediment, and preventing the river bed surface from "armouring". River bed excavation by salmon plays a major geomorphic role in streams and improves the overall health of the ecosystem.
Finally, the lecture will discuss sediment dynamics along the Yellow, Yangtze and Mississippi river basins, linking these dynamics to land use, soil conservation, channel alteration and dams. During five decades, a sequence of changes in land use practices has been imposed on the landscape where these basins are found. Analyses of precipitation, stream flow, and sediment yield shows that soil conservation has been successful at the landscape scale in the Yellow and the Yangtze Rivers. The lecture will close with a discussion of the linkage between sediment dynamics and recent land use practices in China.
Marwan Hassan is a Professor of Geography at the University of British Columbia. He was born in Nazareth, and earned his PhD in Hydrology from the Hebrew University of Jerusalem. He has over 20 years of experience in water and sediment routing in watersheds, as well as modelling the evolution of channel morphology. He has investigated a wide range of topics in fluvial geomorphology and hydrology, and has worked at experimental sites with flow regimes ranging from arid land flash floods to snowmelt floods. In investigating these issues, he employs interdisciplinary and collaborative methods, including fieldwork, experiments, and modelling. His research priorities include landscape evolution, the role of river systems in aquatic habitats, sediment dynamics, water resources and management, urban hyd rology, and water quality. He has a particular interest in the mechanisms and interactions between human activities and the environment.
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