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UBC Theses and Dissertations

Modelling channel morphodynamics associated with large wood in an intermediate-sized stream Davidson, Sarah


The primary objective of this research is to investigate the relationship between wood load and reach-scale morphodynamics using a model system. Previous re- search has shown that large wood significantly impacts channel dynamics, espe- cially in small and intermediate sized forested streams where wood pieces are similar in length to channel width. Five experiments, each comprised of several five hour runs, were conducted using a stream table with wood loads scaled to 0 m³/m², 0.011 m³/m², 0.016 m³/m², 0.022 m³/m², and 0.028 m³/m². The addition of large wood significantly increased the flow resistance and decreased the reach-averaged velocity in all experiments. These hydraulic changes were associated with decreased sediment transport and increased sediment storage within the reach. Over time, increases in bed and water surface slope compensated for the loss of potential energy to flow resistance and enabled the system to reach a new steady state. The heterogeneity in the spatial distribution of the hydraulic changes – with flow velocity and shear stress decreasing upstream of obstructions and increasing downstream of log steps – increased the facies complexity and pool frequency in the reach at the new steady state, and thereby increased habitat complexity. These results show that wood load is a primary control on channel morphodynamics and the availability of aquatic habitat in intermediate sized streams.

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