Enhancing downstream hydraulic geometry measurements in the Black Creek River Basin, Toronto, Canada | Faculty of Environmental and Urban Change

by Mereille James

Introduction

*Figure 1. Black Creek River channel at a few of the study reaches.*

This project examined the downstream hydraulic geometry (DHG) of the Black Creek River Basin under the supervision of Professor Adeyemi Olusola. The research focused on understanding how channel width, depth, velocity, and grain size vary with discharge as the river flows downstream. Black Creek, a tributary of the Humber River in Toronto, is situated in a highly urbanized watershed characterized by residential, commercial, and industrial land uses. The creek extends approximately 18 km from its headwaters in Vaughan, through North York, before joining the Humber River near Weston (Figure 1). Along its course, the channel alternates between naturalized and engineered sections, reflecting the profound influence of human activity on urban rivers. As Black Creek flows downstream, its geomorphology and hydrology adjust to changes in discharge. DHG provides a framework for understanding these adjustments by examining how physical characteristics such as channel width, depth, and velocity respond to varying flows. These relationships are fundamental for assessing sediment transport, flood risk, and the resilience of river systems under both natural processes and anthropogenic pressures such as channelization and impervious land cover.

Aim and Method

*Figure 2. Measuring DHG variables along the Black Creek.*

Understanding fluvial geomorphology is essential, as rivers continually adjust their shape and flow, reorganizing channels, and sediments in response to natural and human pressures. These adjustments directly influence erosion, sediment transport, flood risk, and overall watershed health. The goal of this project was to evaluate how downstream hydraulic geometry (DHG) relationships vary along Black Creek and to examine how sediment size and channel form respond to both geomorphic processes and urbanization.

To achieve this, I carried out intensive fieldwork across fifteen reaches along the Black Creek, beginning near its headwaters in Vaughan and extending downstream to its confluence with the Humber River (Figure 1). Over the course of 35 field days, I measured bank full channel width and depth using measuring tapes and meter sticks, while velocity data were collected with a Flow Tracker Acoustic Doppler Velocimeter (ADV) (Figure 2).

These measurements provided the DHG data necessary to achieve the aim of this project. In addition to hydraulic parameters, I collected sediment samples using the Wolman Pebble Count to characterize grain size distributions across reaches. This analysis enabled me to evaluate whether Black Creek followed the expected downstream fining trend, where sediment size typically decreases downstream, or whether urban influences produced deviations from this natural pattern (Figure 3).

Study Area

*Figure 3. Sediment analysis using Wolman pebble counts in the field and sieve tests in the lab to assess grain-size distribution along Black Creek.*

The study sites encompassed a variety of landscapes and conditions, ranging from heavily channelized segments to more naturalized reaches with vegetation and restored banks. Field sites included upstream sections near the source in Vaughan on Weston Road (43.82526° N, 79.55580° W), midstream urban stretches through Black Creek Pioneer Village Parkland and Downsview Dells Park, and downstream reaches such as Tretheway Park East (43.69471° N, 79.48451° W), where the river becomes channelized before joining the Humber River (Figure 1).

Preliminary Results

Preliminary observations indicate that downstream variations in channel width, depth, and velocity were shaped not only by effective discharge (Figure 4) but also by urban infrastructure and management practices along the creek.

Similarly, while some reaches exhibited the expected downstream fining of sediment, others showed irregularities caused by localized factors such as stormwater inputs, surface runoff, erosion, and engineered bank stabilization. By integrating hydraulic geometry analysis with sediment sampling and geomorphic observations, this study provides a more comprehensive understanding of how Black Creek functions as an urban river system. The findings underscore the interaction between natural fluvial processes and human modifications, offering insights that can inform watershed management, flood mitigation strategies, and urban stream restoration planning.

Conclusion

*Figure 4. Effective discharge (Black Creek) using archival records (1966 – 2024).*

This project will contribute to more accurate hydrological models, enhancing flood forecasting and watershed management in urban settings. By integrating detailed field measurements with sediment analysis, the research offers practical insights on sediment transport, channel efficiency, and the behaviour of downstream hydraulic geometry along the Black Creek River.

I intend to continue working on this project, as I am looking forward to expanding this work to other river systems, particularly those undergoing rapid urbanization or experiencing extreme hydrological events, to further test innovative approaches for monitoring flow and sediment dynamics in support of sustainable water resource management. I plan to build on this foundation in my honour’s thesis, where I will continue to investigate river hydraulics and sediment transport dynamics with a focus on estimating the channel forming and effective discharge (the discharge that maintains river form and sediment transport over time). Beyond my undergraduate studies, I aspire to advance this line of research, contributing to the development of more resilient strategies for river basin management in the context of climate change and urban growth.

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*Mereille James, BSc Hons. Environmental Science*

Mereille James was a recipient of EUC’s Undergraduate Research Award (EUCURA) in Summer 2025. She is currently pursuing an Honours degree in Environmental Science at York University. Her academic interests include fluvial dynamics, river geomorphology, stream restoration, and watershed management, with a particular focus on how rivers in urban settings respond to both natural processes and human-induced pressures. Through this project, Mereille has developed strong field research skills, including velocity measurements, sediment analysis, and systematic channel surveys, which have deepened her understanding of river dynamics and their role in flood risk and watershed health. She is especially interested in how urban rivers, such as Black Creek, can inform broader strategies for climate adaptation, restoration planning, and sustainable water resource management.

Looking ahead, Mereille plans to continue building her expertise in river geomorphology through her Honours thesis. Her long-term goal is to advance research that bridges geomorphic science with practical strategies for sustainable water resource management in cities facing the pressures of climate change and rapid development.