The U.S. Army Corps of Engineers opened the Old River Overbank Structure above Baton Rouge, La., today when the Mississippi River was projected to reach the trigger of 52 feet at the Knox Landing gauge.
“This operation is one of our lessons learned from the 2011 flood that we have incorporated into our emergency response efforts,” said Mike Stack, chief of the New Orleans District Emergency Management. “By opening the Overbank Structure now, we are adding another tool to help ensure we safely pass the required flow through the Old River Control Complex.”
The Overbank Structure, only operated during high water events, increases the Corps’ ability to relieve pressure from the Auxiliary and Low-Sill control structures, helping to reduce the potential for structural damages as a result of diverting large river flows.
In accordance with the Water Control Manual, the Overbank Structure is opened in advance of water reaching the structure to limit the risk of operator safety during initial opening. Based on the most recent National Weather Service forecast, the river is expected to reach the sill of the structure on Friday. This opening marks the 15th time the structure has been operated and only the third time since 1990. When the structure was last operated in March 2015, flow reached a maximum of 9,000 cu. ft. per second during a 158-day opening.
The Overbank Structure is one of three Old River Control Complex structures designed to implement the 70/30 distribution rate between the Mississippi and Atchafalaya rivers. Throughout the year, the Corps operates the Auxiliary and Low-Sill structures to maintain the current distribution where 30% of the combined flow of the Mississippi and Red rivers is diverted into the Atchafalaya River. In total, the complex can discharge 700,000 cu. ft. per second (approximately 300 million gpm).