Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Power, Christopher

2nd Supervisor

Robinson, Clare

Co-Supervisor

Abstract

Bioretention systems are an increasingly popular low-impact development (LID) stormwater management approach that are used to reduce the water quantity and quality impacts of urban stormwater. The study investigated the feasibility and benefits of using non-invasive time-lapse electrical resistivity tomography (ERT) to understand the infiltration and soil moisture dynamics within bioretention systems. This was achieved through monitoring two field-scale operational bioretention systems in London, Ontario, Canada. High-resolution two-dimensional time-lapse ERT surveys were first completed during synthetic and natural rain events to assess the viability of time-lapse ERT to monitor soil moisture changes during events. Following this, three-dimensional ERT surveys were conducted during synthetic and natural rain events to provide increased spatial understanding across the entire bioretention system and thus provide new insights into the infiltration and soil moisture dynamics. Overall, this study shows that ERT is a viable method for in situ monitoring of bioretention systems and that soil moisture dynamics in bioretention systems are highly complex and spatially heterogeneous.

Summary for Lay Audience

As areas become more urbanized, infrastructure such as buildings and impermeable surfaces including roads and parking lots replace natural undeveloped areas. This leads to increased stormwater runoff, flooding and more harmful pollutants being delivered to surface water bodies. The concept of stormwater management was developed to combat the effects caused by the increase in stormwater runoff, but in some cases, traditional stormwater management infrastructure (e.g., wetlands and stormwater ponds) are insufficient in countering the effects. As a result, there has been a shift to low-impact development (LID) stormwater management infrastructure (e.g., bioretention systems, green roofs, permeable pavement and infiltration trenches) that are able to treat stormwater more locally. This study focuses on monitoring bioretention systems, sometimes called rain gardens, which allow stormwater to soak into the ground and use natural methods such as detention and filtration to reduce the volume of stormwater and improve the water quality. Although many studies have monitored the ability of bioretention systems to reduce stormwater volumes and improve water quality, few studies have monitored the infiltration rates, water flow and chemistry within bioretention systems. This limits our understanding of how these systems function. This study explores the feasibility and benefits of using a geophysical technique that is based on using electrical current to produce images of the subsurface to monitor soil moisture changes within bioretention systems – similar to taking an x-ray of the ground. The study uses this technique to monitor soil moisture conditions within bioretention systems located in London, Ontario during artificial and natural storm events. The geophysical technique allows 2D and 3D images of the subsurface to be generated with each image produced representing a certain point in time during a monitoring period. The study results indicate that this geophysical technique is valuable for understanding infiltration areas and soil moisture changes within bioretention systems with the data highlighting the complexity and heterogeneity of the processes occurring within bioretention systems.

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