2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
Sediment characteristics in stormwater ponds and wetlands in Calgary Alberta

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Author(s)
Dr. Tadros Ghobrial, Dept. of Civil and Environmental Engineering, University of Alberta (Presenter)
Mr. Sherif Ahmed, University of Alberta
Dr. Wenming (William) Zhang, Dept. of Civil and Environmental Engineering, University of Alberta
Dr. David Zhu, University of Alberta
Dr. Mark Loewen, University of Alberta
Mr. Khizar Mahmood, City of Calgary Water Resources
Mr. Bert van Duin, City of Calgary Water Resources
Abstract

In urban areas stormwater ponds and constructed wetlands are commonly used to prevent flooding by temporarily storing surface runoff and then releasing it at a decreased rate. These water bodies also improve water quality by removing pollutants such as sediments and nutrients. In this study the characteristics of sediments from two stormwater ponds (~3 m deep) and two constructed wetlands (~1 m deep) in Calgary, Alberta, has been investigated. This is a part of a comprehensive research study aiming at quantifying the sediment and nutrient loadings to ponds/wetlands and to investigate the processes that govern their transport, deposition and cycling within the ponds/wetlands.

In order to understand sediment behavior in these water bodies, sediment cores were sampled at four to six locations along the flow path in each pond/wetland. Additional core samples were also taken away from the flow path to investigate the internal loading within the water body. In total, twenty-six core samples were taken from the four water bodies. Each core was processed in the lab and sediment samples were extracted based on visual inspection of the different layers of deposited sediments. Seventy sediment samples were extracted from the cores and were analyzed for particle size distribution, nutrients (Nitrate and Phosphorus), metals (Na, Mg, K, Ca, etc.,), and moisture content. In addition to deposited sediments, water column samples were also collected intermittently along the flow path and were analyzed for suspended sediments particle sizes distribution. Water samples were also collected during rain storms (where possible) using autosamplers installed within the inflow/outflow structures. These samples were analyzed for particle sizes distribution and provided an estimation of the removal efficiency of the ponds/wetlands.

Preliminary results show that in most cases, the sediment is being deposited in the sedimentation bay close to the pond/wetland inlet, and there is hardly any sediment deposition observed away from the flow path. Also, in general, the mean particle size of suspended sediment decreased along the flow path from the inlet to the outlet.