Sediment Transport Dynamics around an Emergent Vegetation Patch in Unsteady Flows

Abstract

While recent efforts have promoted riverine vegetation because it can create habitats, enhance biodiversity, and improve nutrient dynamics and bank stability, its geomorphic impact when located in the main channel is not fully understood. This dissertation investigates the influence of an in-stream emergent vegetation patch on sediment transport rates and channel bed morphology for two sediment mixtures over repeated unsteady flows, with the overall goal being to assess the potential of vegetation vi TABLE OF CONTENTS Abstract i Acknowledgements iii Table of Contents vi List of Tables x List of Figures xii List of Symbols xv CHAPTER 1-INTRODUCTION 1.1-Background 1.

Influence of particle size and density, and channel velocity on the deposition patterns around a circular patch of model emergent vegetation

“…That is, for a particular channel velocity, a particular range of particles should segregate into the wake. This conclusion is supported by a recent study of sediment transport around a patch of model vegetation with solid volume fraction, = 0.10, similar to our study, = 0.13 [ Waters , ]. At the start of the experiment, the bed consisted of a uniform mixture of sand and gravel, with particle sizes between 0.063 and 6.3 mm, and d 50 = 0.55mm.…”

“…At the start of the experiment, the bed consisted of a uniform mixture of sand and gravel, with particle sizes between 0.063 and 6.3 mm, and d 50 = 0.55mm. After running several flood hydrographs, the grain size within the wake behind the patch decreased by 20%, because finer particles had preferentially accumulated in the wake [ Waters , , Figure 7.3.2]. The sorting of finer material into the wake is consistent with the range of estimated for the channel.…”

“…Using the same method discussed in section 2.3, was calculated for the maximum, minimum, and d 50 of the original channel mixture (Table ). The peak channel velocity was estimated for the high and low flow rate conditions reported in Figure 3.5.2 of Waters [], using the corresponding flow depth [ Waters , , Table 8.3.2]. The shear velocity was then estimated from equation (6.14) and Table 6.1 in Julien [], using d 50 = 0.55mm.…”

“… The following data were reported in figures and Tables included in Waters []: flow rate (Figure 3.5.2); flow depth (Table 8.3.1); grain sizes (Figure 3.6.1); and channel width was 0.6m (p. 95).…”

“…Importantly, the maximum net deposition in the wake occurs within this range of conditions, because resuspension in the adjacent regions makes more particles available for deposition in the wake. Comparison to mixed bed studies [ Tanaka and Yagisawa , ; Waters , ] suggests that the ratio can be used to predict the preferential accumulation of fine particles in the wake behind a finite patch of vegetation.…”