Determining Operational Vulnerabilities in Gravity Wastewater Sewer Systems

Effective management of wastewater collection systems requires an understanding of the probability and consequences of asset failure. In an operational context this is often equated to the hydraulic capacity of the system as dictated by the configuration and sizing of individual elements. While effective at identifying system constraints, this approach offers little value in measuring system response to loss of individual pipe elements, due to blockage or collapse.Traditionally, utilities have relied on staff experience to identify ‘hot spots’ and focus maintenance and inspection. With the growing turn-over and retirement of key personnel, much of this information is being lost, leaving municipalities vulnerable and ill prepared. An objective, repeatable method, capable of identifying system redundancies and the collective impact of a given pipe failure, is needed to define the operational ‘criticality’ of individual pipe segments and guide the targeting of maintenance and inspection activities.While ‘pipe failure’ scenarios can be modeled for individual elements with conventional hydraulic modeling software, technical limitations and the large number of potential flow combinations make it difficult to complete this assessment on a wide spread basis. An iterative, data driven approach was developed to streamline this process and support the network level assessment of operational consequences associated with sewer ‘failure’.This paper examines Regina and Saskatoon's development and use of operational criticality models in formalizing risk-based asset management planning and the prioritization of inspection and maintenance activities. The paper and presentation covers the philosophy used in model development, the technical framework combining GIS, calibrated hydraulic models, and Excel VBA programming, and the use of outcomes in assessing operational criticality on a system-wide basis. Lessons learned through system set-up and application will also be discussed.