Work will begin soon on a two-season, $11.2 million project to repair a crumbling guidewall at Lock and Dam 15 next to the Rock Island Arsenal and Government Bridge swing span.

Civil Constructors, of East Moline, is doing the work under a contract with the U.S. Army Corps of Engineers. A guidewall is the structure towboats touch up against to ease their loads into and out of the lock. It is anchored below water level by monoliths, and those need to be replaced, as well as the wall above.

The first work will be to build an access road so that crews can reach the site of the damage which is at the far, downstream end of the lock, according to a news release from the Corps. Once the access road is complete, the contractor will begin drilling shafts for the new guidewall.

Once the winter navigation closure begins, the contractor will continue drilling shafts as well as removing six of the 12 existing underwater monoliths that form the base of the guidewall.

The majority of the work will be done during two winter closures, one in 2018 and one in 2019, with the work finished by the end of 2019, Mark Pratt, construction area engineer for the Rock Island District, said.

Each winter closure will include demolishing six monoliths, installing drilled shafts and then placing concrete to rebuild the monoliths.

A majority of the work has been scheduled for winter to lessen the impact to navigation caused by lock closures.

About 120 feet of the guidewall had to be removed in May 2017 after Rock Island District engineers noticed portions of the wall had moved significantly. At the time, it was determined four monoliths making up a portion of the guidewall needed to be demolished lest they fall into the channel, blocking navigation.

The lower guidewall, like almost of all of the lock’s concrete, is original to the lock project.

Lock and Dam 15 was the first lock completed on the Upper Mississippi River as part of the nine-foot navigation system. Construction on Locks and Dam 15 finished in 1934.