Effect of plastics on sediment mobility in rivers and coastal areas

Andrade Ramos, Juan Martin

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https://hdl.handle.net/2142/116281 Copy

Description

Title

Effect of plastics on sediment mobility in rivers and coastal areas

Author(s)

Andrade Ramos, Juan Martin

Issue Date

2022-07-21

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

Tinoco, Rafael Omar

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Microplastics
• plastics
• sediment transport
• threshold of motion
• suspended sediment concentration
• PIV
• shear-driven flows, uprush, swash zone, turbulence tank, Odell Kovasznay flume

Abstract

Plastic pollution is an increasing problem in most waterways around the world. In addition to its adverse effect on ecosystems and the health of organisms through all trophic levels, plastic embedded in the substrate can also alter sediment dynamics, resulting in plastic-sediment-flow feedbacks that can determine the capture and release of plastic material from the substrate under various flow conditions. The main objective of this study is to investigate the interaction between sediment and plastic particles in rivers and beaches, to understand whether the presence of plastic particles in the bed enhance or diminish sediment mobility, and how to characterize such interactions as a function of plastics, flow, and sediment properties. The effect of plastics on sediment mobility in rivers and coastal areas was studied in a turbulence tank (turbulent flow with minimum or absent mean shear) and an Odell-Kovasnay type recirculating flume (unidirectional flow). The sediment bed was composed of crushed walnut shells as light-weight sediment mixed with two different plastic particles at various concentrations. Flow hydrodynamics were measured using Two-dimensional Particle Image Velocimetry (2D PIV) to quantify spatial velocity distribution, turbulent kinetic energy, Reynolds stresses, turbulent production, and shear velocities above the sediment bed. Time lapse photographs were used to estimate the suspended sediment concentration (SSC), bed load, bed thickness variation, and percentage of exposed plastic for all the mixtures. Data showed a similar effect of plastic particles on both the turbulence tank and the recirculating flume. The density and size of plastic particles embedded in the sediment play an important role in the plastic mobility, which affects SSC, bed load, bedform formation, and armoring in streams. The heavier plastic particles led to armoring on the sediment bed after getting exposed, which protects the bed from further erosion, while the lighter plastic particles enhanced the bed load and bed thickness variation until they get buried due to bedform formation. SSC does not seem to be influenced by the presence of heavier plastic particles, but lighter plastics seemingly damp SSC at lower velocities, until reaching a critical value at which SSC is boosted by the presence of plastics. Further research, focused on a wider range of velocities and a broader range of particle sizes, shapes, and densities, is still needed to provide a better understanding of the role of embedded plastic on sediment dynamics.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Juan Andrade Ramos

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