Northcote Avenue Bridge undergoing unique rehab

admin Engineering, News

August 30, 2014 – Rob Earnshaw

The Northcote Avenue Bridge over the Little Calumet River will begin a transformation Tuesday and, once complete, will be a structure so unique officials say there are only a few of its kind in the Midwest.

The bridge is not being elevated or replaced, but rehabbed so it becomes an integral part of the levy system. The top of the levy and the top of the rail on the bridge will be at the same elevation. When water reaches that point, it flows under the bridge like a siphon — hence the name siphon bridge.

The idea for the siphon bridge came from Munster Town Engineer Jim Mandon, who knew of a similar structure in Minnesota.

The siphon bridge doesn’t require any human intervention when a flood is occurring. It boxes the river in with solid concrete walls that are tied in structurally to the walls the U.S. Army Corps of Engineers installed.

The water is allowed to rise above the bridge deck until head pressure on it pushes it under the bridge faster where it equalizes so it doesn’t come over the top.

“It’s something I’ve been pushing for a number of years now,” Mandon said. “It’s gratifying to me to finally see it being constructed. It’s kind of a strange thing but it does work.”

Hammond City Engineer Stan Dostatni said there’s a similar structure in Michigan on M-94 crossing the Manistique River. According to the city of Manistique, the bridge was famed by “Ripley’s Believe It or Not” because the roadway was lower than the water level.

Dostatni said one comparison he likes to give is the Bible story of Moses parting the Red Sea.

Currently the bridge has an open metal railing so, during a big rain event like in 2008, water flowed over the top of the bridge.

“This one isn’t going to allow that,” Dostatni said. “It’s going to stay at its existing elevation.”

“This is going to be really neat,” he said. This is a very unique situation. We’re gonna retrofit it to create this siphon effect.”

Dostatni said the bridge will have a decorative railing that won’t have openings but give an appearance it does. Under the bridge, they’re going to create riprap walls on both sides and take out enough material so when the river widens under the bridge, the water can drop and flow under it.

It means sandbagging won’t be required and the bridge won’t be closed when there is a big rain event, Dostatni said, although the first few times there are heavy rains the Army Corps of Engineers wants it sandbagged to make sure it’s working.

The bridge rehab is a $400,000 improvement versus about $2.5 million to elevate it, Dostatni said. Hammond and Munster are splitting the cost.

Dostatni said it made sense to replace and elevate Columbia Bridge because that bridge was old and needed to be replaced. Northcote Avenue Bridge is less than 20 years old and the county didn’t want to pay to replace it.

“I think it’s going to work,” Dostatni said. “I think it’s a good idea. It’s a good way to save money and actually build a structure for like 20 percent of the cost of a new elevated bridge.”

The project is expected to last 90 days. Most of that time Northcote Avenue will be closed to traffic.