Modelling Pollution Transport in Vegetated Flow Environment

Vegetation is often present in environmental flow domains (e.g. streams, rivers, wetlands, and estuaries), playing an important role in maintaining the water quality by providing oxygen and reducing the suspended sediment concentration. The presence of vegetation enhances solute mixing and diffusion within the vegetation due to the effects of the plant stem wake and the resulting complex hydrodynamic structure. Hence, modeling the flow and pollutant transport in the presence of vegetation is vital for understanding solute mixing and the diffusion within a canopy, and environmental flows.

Vegetated environmental flow systems are significantly important for freshwater ecology and biodiversity. The combination of soil, sediment bed, vegetation, and organisms in environmental flow systems can facilitate treatment of water and removal of solute and solid pollution. It is the interplay between water-vegetation-soil that governs the physical, chemical and biological processes influencing pollution transport and fate. Dynamics of water movement and the interactions with vegetation plays a key role in determining the mixing and dispersion of pollutants in environmental flow systems. Plant communities have a prominent effect on the hydrodynamics and performance of these flow systems, as they generate flow resistance, changes the velocity field, and affect mixing characteristics, enabling suspended material to fall to the bed of the flow domain. Seasonal variation in vegetation growth and die-back influences the performance of these systems. However, critical knowledge gaps remain in sources and fate of pollutants in vegetated environmental flow systems.

The main aim is to identify and quantify key mechanisms that govern the transport and fate of pollutants using laboratory studies and field-based data collected by our industry partner, Norfolk Rivers Trust. This project will also use the physical and field-based data to develop and validate numerical model to simulate the interaction of solute and microplastics with vegetated flows and sediment bed. The new insights offered by this project will enable understanding the dynamics of pollutant transport in vegetated freshwater flow systems. Hence this project will provide a step change in environmental protection and integrated catchment management by understanding and
quantifying the pollution transport and fate in vegetated flows, and significantly, be influential at a time of considerable pollution stress on freshwater systems.

This project will undertake laboratory-based physical modelling measurements and fieldwork data collection to understand the dynamics of pollutant transport in rivers and wetlands. We will create an interacting mesocosm river and wetland environments using the world class experimental facility at Warwick Water Laboratory. Fluorometric tracing along with novel particle staining techniques will be applied, alongside planar laser-induces fluorescence (PLIF) with the aim of identifying and quantifying underlying physical transport mechanisms of pollutants and the impact of hydraulic conditions on the transport and fate of the pollutant.

The effects of vegetation on the flow (in rivers and wetlands) and pollutant characteristics will be modelled by developing numerical models based on the Reynolds averaged Navier-Stokes (RANS) and large eddy simulation (LES) method. We will develop particle model of scalar transport for both rigid and flexible vegetation. The numerical model will be validated against experimental data and scenario modelling will be performed.