Insights

Sewer systems don’t come with warning lights. To stay ahead of backups and overflows and prepare for the future, flow monitoring can provide the data communities need to better plan for and understand how their sewer systems operate. 

Flow monitoring is the process of observing the flow of wastewater through a sewer system using various sensors and monitoring devices at different points within the sewer network. These sensors provide important data related to a community’s Inflow and Infiltration (I/I), capacity, performance and more. 

However, collecting data is only the first step. The next step involves analyzing and interpreting the data to identify significant trends that can provide actionable insights to inform more strategic infrastructure decisions. 

Why is Data Important? 

Flow monitoring data provides the foundation for making smart, forward-looking decisions that deliver long-term value to communities. From analyzing existing challenges to providing insight into future scenarios, flow monitoring data is the framework for identifying solutions. Some of these benefits include: 

Reducing I/I and Preventing Backups

Data analytics help identify where excess flow is entering the system or where bottlenecks exist. By targeting areas with the highest I/I, or risk of wet-weather inflow and backups, communities can prioritize improvements that reduce treatment costs, protect public health and extend the life of existing infrastructure. 

Preparing for Growth and Prioritizing Improvements 

Flow data, combined with GIS data and capacity planning, allows engineers to model future conditions and identify where system upgrades are needed. This ensures infrastructure can support planned development without overloading the network, and it enables phased improvements based on priorities. Instead of trying to fix everything at once, analytics support a strategic approach that ranks projects by risk, need and return on investment. This process helps agencies stretch limited budgets further while still addressing the most critical issues first. 

Compliance Management 

Accurate data and modeling give utilities the tools to meet regulatory requirements, demonstrate progress and defend capital planning decisions. Staying proactive with flow monitoring helps avoid EPA violations and supports transparent, data-driven compliance strategies. 

Data Collection 

Effective flow monitoring starts with choosing the right tools. Different types of sensors collect critical data—like depth, velocity and flow rate—that form the basis for accurate analysis and decision-making. 

There are three common types of sensors used in flow monitoring:

Submerged Area Velocity (“Sub AV”) Sensors 

Sub AV sensors are placed in the flow, allowing water to flow over them. A pressure transducer in the sensor measures the depth of the flow by converting pressure into an electrical signal. Sub AVs contain Doppler sensors that emit ultrasonic pulses into the flow and analyze returning echoes to calculate the velocity. 

Non-contact Flow Sensors 

Non-contact flow sensors use radar and Doppler to collect depth and velocity. These sensors sit out of the flow, avoiding issues associated with submerged sensors like high solids content and disturbances. However, non-contact flow sensors may require more particular, straight-through conditions to provide reliable, accurate data. 

Ultrasonic Sensors 

Ultrasonic depth sensors are non-contact sensors that use sound waves only to measure flow depth. These can be beneficial to use in situations where only depth data is needed, as they are typically more cost-efficient and compact than non-contact flow sensors. 

Data Visualization 

After data is collected, downloaded, proofed and evaluated, there are various methods for analyzing and visualizing it to provide suggestions and implement changes. Some common methodologies include:

Hydrographs 

Hydrographs are time-series plots that show how flow in a sewer system responds to a specific rainfall event. These are essential for identifying I/I sources, estimating system storage or lag time and evaluating how quickly and effectively a system conveys stormwater.

Scatter Plots 

Scatter plots are another method to evaluate the correlation between rainfall and system response. A strong linear trend indicates a high sensitivity to rainfall, often pointing to I/I issues within the system. These visualizations also support model calibration and system diagnostics by illustrating flow behavior across a range of wet-weather conditions.

GIS Data/Validation for Modeling 

GIS data plays a critical role in turning flow monitoring data into actionable insights. GIS data provides accurate spatial information about a sewer system's layout, including pipe sizes, slopes, manholes and connectivity. This data, aligned with sensor data, forms the foundation of capacity and hydraulic models, helping validate flow patterns, identify capacity issues and simulate system responses to rain events.

By overlaying flow monitoring results with GIS layers, teams can better visualize where problems occur and prioritize improvements with confidence. The exhibit shown below was used to predict Water-in-Basement Events (WIBs) for the client city during different rainstorms. Meter data was used to calibrate a hydraulic model for the city, then the model output was compared against GIS data to predict the likelihood of sanitary backups in homes and businesses. 

Flow Monitoring & Data Analysis in Action 

B&N worked with the City of Heath, Ohio, to develop a flow monitoring program and system-wide hydraulic model. The project utilized data analytics by incorporating GIS datasets and maintenance records into the development of a sanitary sewer system model. The modeling team used PCSWMM software to integrate these data sources, enabling the creation of a dynamic hydraulic model. This model was calibrated and validated to ensure accuracy and adaptability for future development scenarios. 

B&N’s engineers also looked at rainfall and flow data to see how well the system worked in different situations, which helped identify areas with high inflow and infiltration (I/I) and make suggestions for improving the system. Suggestions were proposed based on data collected and future use scenarios that were conducted. The recommendations included revised sanitary sewer alignments, capacity upgrades and preliminary construction cost estimates to address current deficiencies and prepare for future growth. These recommendations were designed to help the City of Heath make educated, cost-effective decisions for both immediate improvements and long-term planning. 

We Can Help 

Data analytics help turn flow monitoring into a strategic tool for smarter infrastructure planning. With the right approach to analyzing and displaying data, GIS integration and modeling expertise, communities can uncover hidden issues, prioritize improvements and prepare for future growth with confidence. At B&N, we help clients turn raw data into real solutions. Reach out to Aran Whisler and Caleb Zmith to learn how our team can support your next flow monitoring project with clear insights and actionable strategies.