It took 30 years and more than $3 billion to construct. Now, the Olmsted Locks and Dam, about 17 miles upstream from where the Ohio River flows into the Mississippi, is set to open with the promise of reducing tow and barge delays through one of the busiest stretches of river in America's inland waterways.

The new structures replace the 80-year-old Ohio River Locks and Dams 52 and 53, which will be demolished.

(Click to enlarge.) The Olmsted project is just upstream from the confluence of the Ohio and Mississippi rivers. Source: USACEThe project, which was undertaken by the U.S. Army Corps of Engineers with engineering firm AECOM, includes two 110 ft x 1,200 ft locks adjacent to the Illinois bank, and a dam comprised of five tainter gates, 1,400 ft of boat-operated wickets and a fixed weir, intended to raise the level of water upstream or regulate its flow.

(A tainter gate is a type of radial arm floodgate used in dams and canal locks to control water flow. It is named for Wisconsin structural engineer Jeremiah Burnham Tainter.)

The Corps of Engineers says that the antiquated design and age of the existing structures made it difficult to meet current traffic demands without significant delays. What's more, the existing structures have deteriorated structurally and are overstressed during normal operating conditions. The existing wicket dam has missing sections and wickets that will not raise, making it difficult to maintain pool levels during low water periods.

What's more, a set of temporary locks installed in 1969 at Locks and Dam 52 and 53 have passed their 15-year design life.

This reach of the Ohio River provides a connection between the Mississippi River, Tennessee River and Cumberland River. According to the Corps, more tonnage passes this point than any other place in America’s inland navigation system. In 2011, 91 million tons traversed this portion of the Ohio River.

A spillway under construction at the Olmsted project. Source: USACEAround 25% of all coal shipped on the inland waterways transits Locks and Dam 52, destined for many of the 50 power plants located on the Ohio River System or the 17 power plants located in eight states on the upper or lower Mississippi River.

In a raised position, the wickets on the new dam are designed to maintain the required navigable depths from the Olmsted project upstream to Smithland Locks and Dam. When river flows are sufficient, the wickets can be lowered to lay flat on the river bottom and allow traffic to navigate over the dam without passing through the locks.

The current schedule calls for the dam to be operational in October 2018 and for Dams 52 and 53 to be removed by December 2020.