The City of Yorkton engaged Associated Engineering (AE) to complete a study of the West Storm Drainage system within the City of Yorkton, SK. Ongoing development had exceeded the capacity of the existing drainage system constructed in the 1960s and 1970s. Although the system performed adequately during minor rainfall events, surcharging and flooding were frequently reported during larger storm events.
AE provided recommendations regarding design criteria and level of service standards, completed an analysis of the system to identify system constraints, and provided the City with recommendations for system improvements.
AE developed a fully dynamic dual drainage model to simulate surface flows and their interaction within the pipe system, to assess the potential for flooding. The capacity of the existing system was evaluated to determine alternatives to improve performance. The model was calibrated to accurately reproduce flow rates and water levels. Data collected by two rain gauges and two flow gauges within the study area were used to calibrate the model to five different rainfall events of varying magnitude. Model flow rates and water levels were compared to observed values, and the model was adjusted until they agreed within acceptable tolerance.
On July 1, 2010 the City experienced extensive flooding from a rainfall event that exceeded the statistical 100-year return period storm event. Significant flooding was experienced at several locations within the study area when the pipe and overland conveyance systems became extremely overloaded. Rainfall data and observed flow rates and water levels from this event were used to validate the model calibration.
AE identified nine comprehensive upgrade scenarios to meet level of service targets. Upgrade scenarios were modelled individually, and in conjunction with other options, and analysed for effectiveness during three storm events. A conceptual cost estimate of each alternative was also developed.
The preferred upgrade solution was determined by evaluating performance improvements and associated costs. AE made recommendations to incorporate the preferred solution into the City’s 20-year capital works plan.