Unlocking Efficiency: Flow Monitoring, SSES, and Predictive Modeling, City of Victoria

In the summer of 2021, Victoria endured severe rainfall events that overwhelmed its wastewater collection system, leading to widespread overflows. The excessive inflows pushed the City to close the inflow gates at the Regional Wastewater Plant to prevent the plant from becoming inundated and suffering a catastrophic washout. This incident underscored the critical need to improve system efficiency, even in the absence of rapid population growth. Recognizing these vulnerabilities, the City prioritized reducing inflow and infiltration (I/I) and embarked on a strategic initiative to address the issue comprehensively. The strategy centered on three key components: flow monitoring, hydraulic modeling, and sanitary sewer evaluation surveys (SSES). These efforts aimed to optimize resource allocation, improve system resilience, and identify and address the root causes of I/I in both public and private sectors. A temporary flow monitoring program was implemented, deploying 32 flow meters and 8 rain gauges across the City. This monitoring effort provided valuable insights into the system's performance during wet weather events. Analysis of the data revealed that quick-response inflow posed a more significant challenge than slower groundwater infiltration. Approximately two-thirds of the City's collection system experienced excessive inflow, with rates exceeding 10,000 gallons per day per 1,000 linear feet of pipe. This overwhelming inflow emphasized the importance of prioritizing targeted areas for immediate intervention. As a result, seven of the 32 basins were identified as high-priority zones for further investigation through SSES activities. The condition assessment program for these basins included detailed manhole inspections, smoke testing, and CCTV evaluations of wastewater gravity mains. These activities aimed to identify structural defects, inflow sources, and infiltration pathways that compromised the integrity and efficiency of the system. Additionally, the assessment extended to areas near the Regional Wastewater Plant, as questions about system connectivity in this region required resolution to ensure comprehensive coverage. Field investigations were designed to identify I/I sources in both public and private sectors, enabling the City to address issues holistically. The evaluation of public assets, such as manholes and sewer mains, was complemented by assessments of private properties to locate inflow sources like illegal stormwater connections and compromised lateral lines. This dual approach ensured that all contributors to the I/I problem were considered in the planning process. Concurrently, a hydraulic model was developed to analyze the capacity of the sewer collection system and identify areas with restrictions. This comprehensive model incorporated flow monitoring data from all 32 meters and was calibrated for both dry and wet weather conditions. InfoWorks ICM software was used, leveraging Wallingford's fixed runoff methodology and the Groundwater Infiltration Model (GIM) to simulate the hydrologic response of the system. This dual-method approach allowed the model to capture both rapid inflow events and slower infiltration processes accurately. The calibrated model provided a detailed analysis of the system's performance, highlighting capacity constraints across gravity sewers, lift stations, and force mains. It also accounted for future development areas, ensuring that the City could plan for long-term growth without compromising system efficiency. Importantly, the model simulated various I/I reduction scenarios to evaluate their impact on capacity needs and minimize the extent of required upgrades. One key finding was that areas experiencing capacity constraints were not always the same as those with significant I/I. This insight led to a balanced approach in the City's Capital Improvement Plan (CIP), combining I/I reduction projects with targeted capacity improvements. By addressing both types of issues simultaneously, the City could maximize the effectiveness of its investments and reduce the risk of future overflows. The results of this initiative were transformative. The original 350 miles of the wastewater collection system were narrowed down to 56 miles of high-priority basins requiring SSES. Further analysis identified just 5 miles of sewer mains as critical for rehabilitation. In addition to these public-sector improvements, recommendations were made for addressing manhole defects and private-side I/I sources, ensuring a comprehensive strategy for reducing inflow and infiltration. This phased approach allowed the City to focus its resources on the most impactful areas while planning additional SSES studies in lower-priority zones. The integration of flow monitoring, hydraulic modeling, and condition assessment created a data-driven foundation for decision-making, enabling the City to address vulnerabilities effectively and build a more resilient wastewater collection system. By prioritizing I/I reduction alongside capacity enhancements, Victoria set a strong example of proactive infrastructure management that balances immediate needs with long-term sustainability.