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UBC Theses and Dissertations

Riparian disturbance sensitivity index for gravel-bed river morphology Bailey, Chad Elliot

Abstract

This thesis is an investigation of the sensitivity of alluvial single-thread gravel-bed rivers with noncohesive banks to riparian disturbances. A riparian disturbance is any natural or anthropogenic disturbance that causes a significant removal of large coniferous trees from the riparian corridor and potentially leads to decreased bank strength and planform morphology towards a braided system. A theoretical riparian disturbance sensitivity index is formulated and tested in terms of its validity in estimating the sensitivity of the rivers by means of change in width from a historic "natural" condition to a present day disturbed condition. The riparian disturbance sensitivity index is tested through the use of case studies at the reach level collected within the province of British Columbia. A methodology is suggested for collecting the necessary data to apply towards the sensitivity index. The methodology includes reach longitudinal and cross-sectional surveys, grain size analysis, discharge analysis through watershed delineation and regionalization techniques, and historic aerial photo analysis. Fourteen out of fifteen data sets used in this study are satisfactory data sets that fit the assumptions necessary to apply the index. Even though there are large uncertainties in the accuracy of the field collected data, the proposed sensitivity index appeared to perform well when tested against the case study data sets. The role of large, or "catastrophic," floods is examined with two flood related indices: flash flood magnitude index and peak/mean ratio. The results lend support towards the theory of vegetation as a control of alluvial channel morphology, in comparison to the control of large floods.

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