ANALYSIS OF HYPORHEIC FLOW INDUCED BY A BAR IN A GRAVEL STREAM: AN EXPERIMENTAL STUDY

Pipelines are one of the safest means to transport crude oil, but are not spill-free. This is of concern in North America, due to the large volumes of crude oil shipped by Canadian producers and the lengthy network of pipelines. Each pipeline crosses many rivers, supporting a wide variety of human activities, and rich aquatic life. However, there is a knowledge gap on the risks of contamination of river beds due to oil spills. This thesis addresses this knowledge gap by focussing on mechanisms that transport water (and contaminants) from the free surface flow to the bed sediments, and vice-versa. The work focuses on gravel rivers, in which bed sediments are sufficiently permeable that pressure gradients caused by the interactions of flow with topographic elements (gravel bars), or changes in direction induce exchanges of water between the free surface flow and the bed, known as hyporheic flows. The objectives of the thesis are: to present a new method to visualize and quantify hyporheic flows in laboratory experiments; to conduct a novel series of experiments on hyporheic flow induced by a gravel bar under different free surface flows. The new method to quantify hyporheic flows rests on injections of a solution of dye and water. The method yielded accurate flow lines, and reasonable estimates of the hyporheic flow velocities. The present series of experiments was carried out in a 11 m long, 0.39 m wide, and 0.41 m deep tilting flume. The gravel had a mean particle size of 7.7 mm. Different free surface flows were imposed by changing the flume slope and flow depth. Measured hyporheic flows were turbulent. Smaller free surface flow depths resulted in stronger hyporheic flows (higher velocities, and deeper dye penetration into the sediment). A significant finding is that different free surface flows (different velocities, Reynolds number, etc.) produce similar hyporheic flows as long as the downstream hydraulic gradients are similar. This suggests, that for a specified bar geometry, the characteristics of the hyporheic flows depend on the downstream hydraulic gradients, and not or only minimally on the internal dynamics of the free surface flow.

Sydenham Street Revived: A Public Space Experiment

In 2015, the Sydenham Street Revived pop-up park project (SSR) transformed Sydenham Street between Princess and Queen Streets into a temporary pedestrian-only public space. The goal of the project was to test out the idea of permanently pedestrianizing this street section. But what did this urban experiment ultimately prove? Using video footage, photographs, and observations recorded before and during the project, this report analyzes the use of the space in order to evaluate the claim that SSR created a successful public space and to make recommendations for a permanent public space on Sydenham Street. Two research methods were used: quantitative data collection, consisting of headcounts of both pedestrians and stationary users of the space; and a qualitative observational survey, based on the criteria for successful public spaces developed by the Project for Public Spaces. Data collection occurred two days one week prior to the project, and two days during the project, on days that were similar in terms of temperature and weather. The research revealed that the SSR did create a successful public space, although additional research is needed in order to determine how the space would function as a public place throughout different seasons, to study the street closure’s impact on surrounding residents and businesses, and to understand how private commercial activity would influence use. Recommendations for a permanent public space on Sydenham Street include considerations for flexible street design and a continuous, barrier-free surface; ensuring that there is an abundance of places to sit; making opportunities for public and community-created art; and to improve walkability by connecting the grid using a mid-block walkway.