MICHAEL MANGA: Recent Refereed Publications


Manga, M. and J.W. Kirchner, Stress partitioning in streams by large woody debris, Water Resources Research, vol. 36, 2373-2379

Using simple theoretical models and field measurements from a spring-dominated stream, we quantified how large woody debris affects channel hydraulics and morphology at both the local and reach-averaged scale. Because spring-dominated streams have nearly constant discharge, they provide a unique natural opportunity to study flow and transport processes near the channel-forming flow. We quantified the reach-averaged flow resistance due to woody debris by comparing local and reach-averaged measurements of the water surface slope. Our measurements show that, even though large woody debris covers only about 2% of the streambed, it provides roughly half of the total flow resistance. Our measurements also imply that the drag coefficient of large woody debris is identical to the theoretical coefficient for widely separated cylinders, implying that simple theoretical models can be used to estimate the partitioning of flow shear stress between woody debris and streambeds. As large woody debris is added to a stream, the total shear stress increases (because the water depth increases), but the shear stress borne by the bed decreases, as a growing fraction of the total shear stress is borne by the debris. Our analysis shows that simple theoretical models of stress partitioning may provide a convenient mathematical framework for assessing how changes in debris loading affect streams.

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