2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
PCSWMM Modeling of pollutants loading to wet ponds and constructed wetlands in Calgary, Alberta

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Author(s)
Ms. Arlette Fernandez, University of Alberta (Presenter)
Dr. Tadros Ghobrial, Dept. of Civil and Environmental Engineering, 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. Bert van Duin, City of Calgary Water Resources
Mr. Khizar Mahmood, City of Calgary Water Resources
Mr. Lei Chen
Abstract

Stormwater ponds are constructed to mitigate flooding in urban environments by retaining a certain volume of storm runoff before discharging it at a controlled rate. These ponds are also used to treat stormwater pollutants, such as sediments and nutrients, before releasing it. In order to better understand the behavior of these ponds, a comprehensive research study is undergoing to quantify the sediment and nutrient loadings into ponds and to investigate the processes that govern their transport, deposition and cycling within the ponds.

A 2-year field monitoring program is being undertaken to monitor two wet ponds and two constructed wetlands in Calgary, Alberta. The field data will be used in the development of a watershed model (PCSWMM) to investigate the suspended sediment and nutrient loads entering the ponds. Also, field data and PCSWMM results will support the application of the Environmental Fluid Dynamics Code (EFDC) model to investigate sediment transport and nutrient cycles in ponds/wetlands. Both the field monitoring data and computer modelling will be used to improve the design and operation guidelines of stormwater facilities.

Meteorological stations were installed at each pond to monitor rainfall events. In the inlet/outlet structures of each pond, flowrate, turbidity and water temperature were monitored and water samples were collected during rain storms using autosamplers. Water samples were analyzed for total suspended solids, total nitrogen, total phosphorus, dissolved organic carbon and chemical oxygen demand. A PCSWMM model for each of the ponds will be developed. Pond catchment characteristics such as land use information, topography, geology, and minor/major drainage systems will be included in the model. At the inlet and outlets of the ponds, measured flowrates will be used to calibrate the model hydrodynamics (e.g. hydrographs). The calibrated model will be used to simulate pollutant loading. Analyzed water samples will be used to validate built-in washoff and buildup functions in the model.

This paper presents preliminary results from PCSWMM modeling. Early findings show that the calibrated model accurately simulated flow hydrographs at the inlets of each pond. A sensitivity analysis on the catchments characteristics (catchment width, slope, infiltration, roughness, etc.) showed that catchment width is the most important parameter affecting the hydrographs. The effect of each land use parameter in the buildup and washoff functions will be investigated and a set of calibrated parameters will be proposed for predicting sediment and nutrient loads in un-gauged catchments.