Watermain failure here wouldn’t have same impact as in Calgary

By Lethbridge Herald on June 28, 2024.

Crews work this week along 3 Avenue South at the site of a watermain break that forced the closure of the 19 St. S. off-ramp on eastbound Crowsnest Trail. Herald photo by Al Beeber

Al Beeber – LETHBRIDGE HERALD – abeeber@lethbridgeherald.com

Could a watermain catastrophe similar to Calgary’s happen in Lethbridge?

Not likely.

City council on Tuesday in response to an administrative inquiry from Belinda Crowson, heard from Water and Wastewater General Manager Doug Kaupp, that if a single transmission pipe failed, it would only impact two of the six reservoirs that exist in Lethbridge.

And he told council in response to a question from deputy mayor Jeff Carlson that while Lethbridge does have some pipe of the same type that burst in Calgary, this city has far less of it.

 Kaupp said Calgary has about 190 kilometres of high pressure concrete pipe compared to seven kms in Lethbridge.

And Kaupp said from the City’s research and Calgary’s experience, the pipes in Calgary that were manufactured in the 1970s have a high failure rate.

“Fortunately for us, ours are 10 years younger and were installed in 1985-87,” Kaupp said.

An important difference with high pressure concrete from steel pipes, he said, is the way it fails. High pressure concrete is prone to fail catastrophically because of its construction, he said.

In the concrete is a thin steel cylinder that holds the water and within the concrete structure are high tension cables that withstand pressure. That type of pipe was considered an alternative to steel pipe when it was first put into use.

It has been widely reported that the break in the massive main feeder line in Calgary was caused by wires wrapped around the concrete pipe snapping which caused a catastrophic failure.

In response to a question from councillor John Middleton-Hope, Kaupp said the pre-cast pipes in Calgary are about two metres wide with Lethbridge’s largest being 30 inches or 750 millimetres.

Kaupp said there is always a chance pipe will fail but “there is a documented difference in the manufacture in those two decades – between the ‘70s and the ‘80s – and the documented failures that I’ve been able to find were all in 1970s vintage pipe so that gives us some indication that our pipe is of a better quality but depending on if you have aggressive soils that break down the concrete and expose the steel bands you’re still at risk.”

Joel Sanchez, Director of Infrastructure, told council there are two reservoirs on each side of the City and capital projects are in place to twin some of the lines in coming years. Kaupp and his staff are working on an underground infrastructure master plan, he said. 

The Uplands and Garry Drive fill line twinning capital project will start in 2025, that project which not only addresses the need for more capacity in those reservoirs but also twins the older fill line in the river valley from the water treatment plant to the Highway 3 bridge.

“This section of pipe is one of the key areas of concern regarding the transmission system, and it will be beneficial to have redundancy in place,” said Kaupp in a written response to Crowson’s questions.

“The department’s next transmission project is to twin the transmission main that goes to the northeast reservoir from 2A Avenue North to 13 Avenue North, adding capacity and redundancy to the system,” his response added.

Even if inspections are done, Sanchez told council that doesn’t mean a break won’t occur after due to a variety of weather, soil or other conditions.

Kaupp has seen steel pipe in Lethbridge fail, typically due to corrosion, the result being a small hole which leaks and is fixed with a plate being welded over top.

In Calgary’s case, Kaupp stated, because of the way high pressure concrete pipes are designed once the structure is compromised due to the failure of the wires, “then it just explodes and it’s a big mess. And that’s the downside of that material.”

The City of Lethbridge has attempted to do inspections but it’s challenging because of the available technology, he added.

“In recent years, we’ve defaulted to simply twinning the lines so we can take them out of service or when they fail, it doesn’t cause as much anguish, he added.

The storage volume of the six Lethbridge reservoirs “represents about the average volume consumed on an average day when considering the water reserved for fire fighting. The City of Lethbridge water transmission system design and configuration ensures that a single transmission pipe failure will impact only one or two of the six reservoirs, as illustrated on the map provided,” Kaupp said in his written response to Crowson.

“With the water treatment plant at the bottom of the river valley, the transmission mains located at the bottom of the valley are under high pressure in order to get the water up the hill to the reservoirs. These high-pressure areas are a concern because breaks at these locations result in higher impact failures. This being said, it does not necessarily mean that these areas have a greater chance of failure, as failure of these mains is often the result of the deterioration of the outside of the pipe,” he wrote.

The last transmission inspection on the steel line running down 6 Ave. S. was performed more than 10 years ago, said Kaupp’s written response, noting that “inspection of these mains is complicated, costly, and sometimes not possible with the available technology and the way the system is designed. There is also no guarantee that the inspection will give useful data when pinpointing the condition and estimating when upgrades are needed.”