As sanitary sewer overflows become less tolerated by state and federal agencies, more utilities are turning to advanced flow monitoring programs to predict, record and monitor inflow and infiltration.

Monitoring flow through a system wasn’t always as simple and efficient as it can be today. In the past, recording was performed by collections personnel out in the field, or even through residents reporting overflows. Through that method of recording, it was very common to see the end result of the problem and not necessarily the leading cause of the issue.

Technological advancements in flow monitoring allow users to rely on sensors and recording equipment to automatically read and document flow depth and flow rate to determine if I&I issues are occurring within a system. The data gathered is useful in designing a rehabilitation plan to correct the issues at their specific locations. Once the rehabilitation has been completed, the monitoring data is also valuable as a follow-up measure to depict the success of the improvements made.

Through utilization of technological flow monitoring programs, it is much easier to keep eyes on your system in multiple areas at all times. In many cases, they help determine what is causing a problem or notify personnel that a problem is developing before it becomes a costly or detrimental issue.

Starting a program

Setting up a proper flow monitoring program isn’t as easy as just plugging in a sensor and waiting. It takes well-designed monitoring technologies and careful planning and preparation.

“Step number one is to understand what you want to get out of a system like that,” says Kevin Enfinger, product manager for ADS Environmental Sciences. “Then it’s important to understand the layout of your system. Where do these things need to be deployed is often a big question.”

Using your objective with an understanding of the layout of your system, it’s much easier to develop a plan and figure out how many monitors are needed and the potential places to set them up.

“Sometimes locations are at odds with their purpose. For example, where you might locate monitors in ideal places for a hydraulic model to be most successful may not be the same places you would locate them for an I&I study,” says Enfinger.

Picking a location where a monitor or sensor is likely to succeed is crucial to getting the most accurate results. A lot of high-level planning for monitoring studies is done initially at the map level, usually through GIS information, but sometimes choosing the best location with only a map is difficult.

“Once you actually go out to install and deploy these devices, you have to put some expertise on the ground — people who are familiar with installing these devices,” Enfinger says. “They may find the desired location for one reason or another doesn’t have the right conditions to be monitored successfully.”

There are a lot of factors that can lead to placing the sensor in a location different from what was chosen at the map level. Perhaps the manhole is in the middle of a busy street, or it may be difficult to divert traffic to service at that particular location, or it ends up being in an area that has confined spaces or other limitations affecting safety.

The variability in locations available to utilities for sensor placement — and the number of unforeseen restrictions — means that one sensor does not fit all applications.

Sensor options

Various sensor technologies are available for different applications. Depending on the goals of a program, more than one sensor style may be needed to perform the task, so it boils down to understanding the objective before purchasing and placing.

Different sensor technologies have different strengths and weaknesses and are built for different applications or variations in placement, according to Enfinger. “I think of sensors in terms of tools in a toolbox. You may need several tools or a combination of tools to get a job done.”

For example, the type and location of a sensor will differ depending on the size of the pipe where the sensor is to be placed. Some sensors will also have tradeoffs in accuracy versus cost or ease of use, and when selecting technology for I&I, accuracy matters.

Inflow sensors mount to the bottom of a pipe and gather information as the fluid flows over them, providing the most accurate velocity reading, but they do require technician entry for installation and can be corrupted by debris over time.

Downward-looking sensors are also mounted inside the pipe at the top, using a beam to bounce off the surface of the fluid to measure velocity and depth. The top-mounting location makes it less likely to gather debris, but these sensors tend to be more costly, and they still require technician entry for installation and may not be as accurate for velocity readings.

As far as maintenance goes, most times if the sensors are installed properly and in good locations, they will run for a long time without intervention, with battery life being the limiting factor. However, there are certain situations when the sensor needs to be placed in a position that is not ideal.

“Probably the most common area we see that causes problems would be in a site with slower velocities that are prone to silt or sediment buildup,” says Enfinger. There may be situations when sensors need to be placed in those areas to achieve the desired monitoring objective, and in those situations, it should be noted that the equipment may need more maintenance than the others.

Organizing the data

One of the biggest improvements to flow monitoring technologies is the way we are able to collect, assemble and share the data. In the past, Enfinger says he’s seen many cases where people were overwhelmed by the sheer amount of data points collected from a group of flow monitors. The number of different data sets they are collecting and the frequency at which they are taking the measurements can equate to what seems like an infinite amount of data over the span of the study. A proper way to sift through the information is critical.

“We have found in recent years that cloud-based technology allows us to put data in one place at people’s use very easily,” he says. “Another thing these modern applications allow is to interface more easily with other applications.”

Applications like webhooks allow data to be pushed from one system to another and can be used in alarm instances. For example, an alarm signifying infiltration or changes in flow can be pushed instantaneously to a SCADA system to where an operator can see it.

These software advancements also open the door to displaying collected data in a way that is easier to consume. “The brain processes large amounts of data quite easily in graph form,” Enfinger says. “There are two types of graphs we rely heavily on in the flow monitoring world — a hydrograph and a scatter graph.”

A hydrograph displays depth, flow velocity, flow rate and similar data points over time. These allow viewers to easily see what is coming down a pipe and when. A scatter graph in flow monitoring specifically plots depth versus velocity. Displaying the data in these straightforward graphs can be useful when presenting the data to the public in an effort to illustrate how effective renovations were, or to show potential problem sites where funding is needed.

Why it matters

Closely monitoring flow in a system is a critical step in identifying, predicting and eliminating I&I, helping to prevent sanitary sewer overflows. By compiling data in an organized way and having the resources to interpret it, utilities are able to prevent water quality problems, protect public health from back-ups in homes and reduce the release of untreated flow into natural waterways.

The knowledge gained from data gathered helps reduce I&I before the design and construction of wastewater treatment upgrades, identifying where I&I exists and allowing communities to make informed decisions about how best to tackle the problem.