SIOUX FALLS, S.D. (KELO) — Drive on Minnesota Avenue and it’s not just asphalt under your tires.

A 42-inch water transmission line that carries an estimated 30% of the city’s daily water supply and about 42% of the supply on a peak day in the summer is under Minnesota Avenue, according to a city official.

The 42-inch concrete transmission line will be replaced with a 42-inch ductile iron transmission line in phases as part of the multi-phase Minnesota Avenue construction project. The line will be about 3 1/2 feet in diameter or around the height of a 7- or 8-year-old child.

Nick Borns, a principal engineer in public works for the city of Sioux Falls, said the 42% of water carried on a peak day in the summer is a reliable figure because the city can track those peak times. The 30% of the daily supply is more of an estimate because the city can draw water from the main as well as from the Lewis and Clark system.

Just how much water can the transmission line carry? Borns did the math.

“If we assume we use 45 million gallons on a peak day that would be about 18 million gallons on a non-peak day,” Borns said.

According to multiple engineering calculator websites, a 24-inch pipe can flow a maximum of 18,000 gallons of water per minute at a maximum 14.4 feet per second. Water may not be traveling through Sioux Falls at that rate or higher as flow and speed depend on gravity, grade and other factors.

The concrete water transmission line extends from the city’s water plant down Minnesota Avenue.

The water line carries water for a system of residential and commercial main lines that are roughly 6 to 8 inches in diameter.

It’s not just businesses and homes near Minnesota Avenue that use that water.

“The Minnesota Avenue main is a direct feed to our south (reserve),” Borns said.

Much of it goes to an underground storage tank where it is pumped out and distributed as needed, he said.

The city has a plan to make sure the water continues to get transported while the transmission line is being replaced, said Paul Sanow of HDR. HDR of Sioux Falls is the consultant engineering firm on the project.

The city will replace six blocks of the water transmission line this year from the intersection with Russell Street south two blocks to West Bailey Street and then on to the intersection with west 2nd Street, Sanow said.

The water will be tied into a smaller diameter transmission line at West Bailey Street, Sanow said.

The goal is to reach Bailey on May 27, Sanow said.

“We will be able to direct water to several transmission lines,” Borns said.

The city will also be replacing a 12” watermain, and an 8” watermain. The project will also include the replacement of the sanitary sewer, storm drainage improvements, and other work.

Temporary water mains will be installed so homes and businesses along the construction route will continue to get water.

The first phase is divided into four stages. Three of those stages involve the water main. Two steps include the water main replacement on the west side of Minnesota Avenue from the intersection with Russell Street to the 2nd Street intersection. The third step includes the water main work on the east side of Minnesota Avenue.

Why ductile iron and not concrete?

The concrete line was installed in 1967.

Although Borns said the city has not had any major structural issues with the concrete line, ductile iron will be easier to repair if there are problems.

“Our water main team has experience working on ductile iron,” Borns said. “Concrete repairs require a different speciality.”

The estimated life of a ductile iron line is about 90 years, Borns said.