Holistic Transient Analysis of a Large Pressure Zone

AECOM, on behalf of the city of Calgary Water Supply Division completed a comprehensive system wide hydraulic transient analysis of two pressure zones, including the second largest zone within the system. The study objectives were to determine areas at risk of and mitigation for high and low transient pressures. Primary goals of effective transient management are to: 1) maintain the structural integrity of system components—control extreme pressure variations and lower magnitude cyclic loading that can damage piping and equipment; 2) protect the quality of the delivered water—reduce the potential for intrusion contamination under negative pressures as well as reduce extreme velocity changes that can loosen biofilms from the pipe walls; and 3) improve operations—ensure controlled valve and pump operations, reduce breaks and long term wear on system components, improve management of air within pipelines, prioritize inspection and maintenance of protection equipment, and improve hydraulic performance. Study components included an investigation and analysis phase. A risk based approach was followed for the evaluation of transient management for the system. This identified portions of the distribution network that are vulnerable to watermain structural integrity and water quality risk by correlating transient model results for high and low surge pressures with watermain condition rating across the zones. This facilitated intelligent decision making with respect to enhanced transient protection. In addition, the study developed best practices for management of transients, including transient friendly operational practices, maintenance prioritization, prioritization of water system rehabilitation, and operational response to major transient events.