The role of aquatic vegetation on oscillatory flows and sediment transport

San Juan Blanco, Jorge Emilio

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https://hdl.handle.net/2142/110818 Copy

Description

Title

The role of aquatic vegetation on oscillatory flows and sediment transport

Author(s)

San Juan Blanco, Jorge Emilio

Issue Date

2021-04-16

Director of Research (if dissertation) or Advisor (if thesis)

Tinoco, Rafael O

Doctoral Committee Chair(s)

Tinoco, Rafael O

Committee Member(s)

• Garcia, Marcelo H
• Parker, Gary
• Chamorro, Leonardo P
• Mullarney, Julia C

Department of Study

Civil & Environmental Eng

Discipline

Environ Engr in Civil Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

vegetation, oscillatory flow, PIV, turbulence, suspended sediment transport

Abstract

Accelerated erosion endangers coastal wetlands along with their ecological services. Aquatic vegetation drives morphological changes by modifying flow and sediment transport within and around vegetated regions. The lack of accurate suspended sediment predictors for vegetated oscillatory flows compromise our capabilities for the prediction of sediment transport rates. To fill this knowledge gap, we investigate suspended sediment transport for non-cohesive sediments under the influence of flow-canopy interactions in vegetated oscillatory flows. The study is divided in three stages: 1. Assessment of plant morphology, 2. Hydrodynamics of oscillatory flows through patches of vegetation, and 3. Vegetation-sediment interactions driven by oscillatory, vegetated flows. First, our study evaluates experimentally the effect of vegetation morphology, array density, and wave parameters on the turbulence characteristics and their impact on suspended sediment transport. We find that vegetation morphology (shape and biomass arrangement) and biomechanical characteristics of aquatic plants impact the temporal and spatial distribution of turbulent features in the flow. The effect of morphological parameters of the vegetation in turbulence characteristics can thus be quantified by identifying correlations between oscillation period, wave amplitude, and plant excursion. The second part of our study focuses on the vegetation drag discontinuity at the top of the canopy and near the bed. Our work shows that turbulence levels depend on the non-linear contributions from the mixing layer at the canopy top, near-bed turbulent events, wake-production, and bed shear stress. Parameterization of these variables allows us to develop process-based simplified predictors for field conditions with limited data. The third part addresses the study of suspended sediment transport, and shows that the presence of aquatic vegetation regulates the temporal variability of sediment concentration inside the canopy, not only by the changes in the turbulence field, but also by modulating the development of bedforms. We observe the dual protective/erosive impact of vegetation in oscillatory flows and propose that vegetation effects on sediment transport must be assessed through both mean and turbulent metrics. We present a modified Shields parameter that predicts the near-bed sediment concentration as a function of near-bed turbulent kinetic energy (TKE) and in-canopy velocity. Our predicted near-bed concentration allows us to develop a model for suspended sediment distribution. Overall, our study shows, from the single-plant scale to the vegetation patch scale, how aquatic plants alter the near-bed and in-canopy hydrodynamics. The processes and predictors we develop will allow for a better assessment of the work of aquatic vegetation as eco-engineers in wave-dominated environments, where they regulate sediment mobility and mixing in the ecosystems, providing an ecological service to aquatic habitats by sheltering benthic communities, decreasing turbidity, stabilizing the bed, and providing protection under extreme events.

Graduation Semester

2021-05

Type of Resource

Thesis

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Copyright and License Information

Copyright 2021 Jorge Emilio San Juan Blanco

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