Of Floods, Droughts and Floodgates

The Midwest (and beyond) has been plagued by months of drought followed by severe floods causing evacuations, limiting barge traffic on its rivers, and disrupting farmers’ planting schedules.  And it may not be over yet:  additional rain may cause rivers to remain high into May.  Both cities and rural areas have suffered.

Steel fabricators provide part of the solution to the challenges of Mother Nature – whether drought or floods – when they manufacture flood gates.  For example, flood gates are now being installed at the Olmsted Locks and Dam Project, the largest project of its kind in the history of the U.S. Inland Marine Transportation System.  Located on the Ohio River where Illinois and Kentucky share a border, this project is “essential to the regional and national economy” according to the Army Corps of Engineers.  Indeed, this is the busiest stretch of river in America’s inland waterways:  it’s a hub where it all comes together – the Mississippi, the Ohio, the Tennessee and the Cumberland rivers.

Olmsted Lock and Dam Project

But until the project is complete, river traffic will depend on two 80-year-old locks and weak wooden wickets.  (Wickets are large planks that are manually raised to a steep angle or lowered flat to control the river flow.)  Should they fail, barges that haul some 90 million tons of rock, coal and other goods could not travel because the river’s height fluctuates as much as 50ft in the course of a year.

Two popular types of floodgates are Tainter gates and sector gates.  Both served to control the flow of water in dams and canal locks.  The Upper Mississippi River Basin alone has 321 Tainter gates.

A Tainter gate (named after the Wisconsin structural engineer, Burnham Tainter) has the shape of a piece of pie set on its side.  The round section faces the source or upper pool of water; the pointed end faces the destination or lower pool.  At the point is a trunion on which the gate pivots as it is raised or lowered by an assembly of chains and a gearbox above.

Tainter Gate Diagram

The virtue of the Tainter gate is its design for efficiency.  Closed, the water pressure is on the convex side of the gate.  When the gate is rotated, the water passing under the gate helps it open or close more easily than a flat gate.  Sector gates look like Tainter gates turned vertical.  They, too, incorporate a radial arm.

The component parts of the steel fabrication in either type of gate include plate rolling of the curved face or skin plate of the gate as well as section bending of stiffeners on the back side of the plate.

Tainter Gate with Rolled Plate and Plate Stiffeners

For the Olmsted project, Chicago Metal Rolled Products split 245 ea W24 x 55# wide flange beams into 490ea WT 12 x 27.5 tees.  The company subsequently curved the tees stem-out to a 59ft 3/16in radius measured to the tip of the stem.  Holding that outside dimension guaranteed a close fit-up to the concave side of the plate.  Since the usual measurement process of drawing a chord and measuring the mid-ordinate rise would not work, a special plate template was rolled to check the radius.  A tolerance of +/- 1/8in was held for both the splitting and the curving.

Close Tolerance Tees Rolled Stem Out as Stiffeners for Tainter Gates

These Tainter gates will replace older ones, the last before the Ohio spills into the Mississippi.  Especially during periods of drought, the gates help pool the water when low to improve its navigability.  Five each 110ft-long Tainter gates function with some 500ft of wicker gates to span the Ohio which is very wide there.  Chicago Metal Rolled Products has rolled beams as large as W40 x 297 for companies specializing in flow control.

Hauling freight on this river is more environmentally friendly than moving it by truck or railroad.  “One barge can tow the equivalent of about 890 trucks on the roadway,” says Bill Gilmour, the Corps resident engineer for the project.  The locks and dam should be finished by 2016.


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