Rock formations placed in river at St. Louis to aid currents
Thursday, September 20, 2007
ST. LOUIS (AP) -- The Army Corps of Engineers is hoping rock formations placed strategically in the Mississippi River at St. Louis will force current toward the middle of the river and help eliminate the need for dredging.
Three of the formations, called chevrons, are being built near the McKinley Bridge. Officials say the idea is that by forcing current toward the middle, silt will be scoured from a stretch of barge channel that regularly needs costly dredging.
"We can be up there with the dredge several times a year," said Leonard Hopkins, project manager for the corps.
The $5.1 million cost of the chevron project is slightly less than what was spent to dredge the stretch of river from 1999 to 2005, corps officials said.
The corps is charged with maintaining a navigation channel in the river that's at least 9 feet deep and 300 feet wide.
Work on the horseshoe-shaped chevrons began last month. Workers are dumping bargeloads of rock, their rounded fronts facing into the current.
They sit closer to Missouri than Illinois. The open, downstream ends are about 300 feet wide. The chevrons create quiet pools of water within the rock walls that will make good fish habitat, Hopkins said.
The curved design splits the current, forcing water into the navigation channel and toward the Missouri bank.
Hopkins said the current slows near the McKinley Bridge, dropping silt and making the river more shallow. He said the chevrons counter the river's natural tendency to silt up.
Tom Dunn, director of operations for Gateway Arch Riverboats, said his pilots already have noticed a difference in the river. The company runs the Becky Thatcher and Tom Sawyer excursion boats upstream from near the Arch to just below the three chevrons.
"The current picks up considerably up there, and that's the intention of it," said Dunn.
Information from: St. Louis Post-Dispatch, http://www.stltoday.com