On the morning of Christmas Eve 2016, residents of a house in Fraser, Michigan, heard a curious pop, pop, popping sound coming from their walls. After initially dismissing it as melting snow falling from the roof, they soon realized the truth: The noise was the result of bricks being squeezed out of place as their home slowly crumpled into a sinkhole.

The house and several nearby were evacuated as authorities assessed the situation and determined its cause: a collapsed sewer interceptor, threatening several homes and a long stretch of Fraser’s busy 15 Mile Road. It was hardly the start to the festive season anyone would wish for.

“This was quite the impact to our system and community,” says Vince Astorino. As operations director at the Macomb County Public Works Office, he’s responsible for overseeing the daily operations of the county’s wastewater infrastructure, including some 68 miles of sewer lines. “An 11-foot diameter sewer, approximately 70-feet deep, experienced a failure which drastically reduced wastewater flow. This section of pipe is near the main outlet of our system, and approximately 800,000 residents rely on it to convey their wastewater downstream.”

Prompt action from Astorino and his team got bypass systems in place in time to prevent sewage from backing up into residents’ homes, and in the end only one building—the house where the popping sound was heard—required demolition. But it was nine months until the offending stretch of pipe, roughly 4,000 feet of it, would be fully replaced. The direct cost to taxpayers was around $75 million, not taking into account the added costs to residents and nearby businesses as a result of the disruption.

The key to preventing disasters like this is regular inspection of sewer lines, hunting down any cracks and fissures that, if left unattended, can lead to soil ingress and eventual collapse of the pipe. But sewer pipes can be dark, cramped, and filled with pockets of gas, making inspecting large networks using traditional methods (typically a tethered, remotely operated crawler fitted with a camera or even in-person) a slow, costly, and often hazardous process.

This is where drones come in. Designed and engineered to operate in confined spaces, a new generation of flying robots is being sent into sewers to perform inspections in a safer, more efficient way.

The Elios 3 drone is a popular option for sewer inspections.

Flyability