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What's the difference between a levee and a floodwall?
Here are definitions of these and other terms for U.S. Army Corps of Engineers’ hurricane-protection projects.
PARALLEL PROTECTION – Hurricane protection works such as floodwalls along a canal, as opposed to structures at the canal's outlet. Parallel protection is used in New Orleans along three drainage canals leading to Lake Pontchartrain . Purpose: Protect from hurricane storm surge. Under construction: See next two items below. Completed: Floodwalls along London Avenue , 17th Street and Orleans Avenue canals.
FLOODPROOFING OF BRIDGES – Extension of floodwall across a bridge to connect with floodwall on the other side. Requires demolition of existing bridge and construction of an entirely new bridge, including pilings. Purpose: Eliminate weak link in hurricane protection and dispense with sandbags and keep the roadway open during storms. Under construction: Hammond Highway over 17th Street Canal in Metairie/New Orleans. Completed: eight bridges: Veterans Boulevard over 17th Street Canal in Metairie/New Orleans; and Gentilly Boulevard, Mirabeau Avenue, Filmore Avenue and Leon C. Simon Boulevard over London Avenue Canal, and Robert E. Lee Boulevard, Harrison Avenue and Filmore Avenue over Orleans Avenue Canal. Remaining to be built: Robert E. Lee Boulevard over London Avenue Canal .
FRONTING PROTECTION – Extension of floodwall across the front (outflow side) of a pumping station. A major feature is sluice, or vertical-lift, gates installed on the outflow pipes. Purpose: Protect pumping station from storm surge. Gates prevent backflow through the pumps, and thus back into neighborhoods, in case of breakdown. Completed: three stations: Pumping Station No. 6 on 17th Street Canal in Metairie/New Orleans, Pumping Station No. 4 on London Avenue Canal at Prentiss and Warrington streets in New Orleans and Orleans Marina Phase 5 Pumping Station at West End in New Orleans. Remaining to be built: Pumping Station No. 3 on Orleans Avenue Canal and Pumping Station No. 7 on London Avenue Canal .
LEVEES AND FLOODWALLS – Levees are earthen structures, made of clay (sedimentary particles smaller in diameter than sand and silt), in cross section forming a truncated triangle. The base is commonly 10 times as wide as the height. Floodwalls are concrete and steel walls, built atop a levee, or in place of a levee, often where space is insufficient for a levee's broad base.
SLIDE, SWING AND FOLD-UP GATES – Floodgates on land that provide access through levees or floodwalls. Type of gate depends on site circumstances, such as space available. Swing gate: Lakeshore Drive at Marconi Drive , a miter gate, analogous to double doors meeting at an angle. Slide gate: Lake Marina Drive , New Orleans , horizontal slide gates; at Galvez Street Wharf on west side of Industrial Canal , overhead slide gate. Fold-up gate: Namasco Steel Corp., New Orleans (west side of Industrial Canal ).
SECTOR GATES – Used in a waterway, floodgates that permit continued navigation. Gates remain open until a storm approaches. Purpose: Continue flood protection over a waterway. Completed: Sector gates at each end of the Larose to Golden Meadow Hurricane Protection Project, which straddles Bayou Lafourche. Under construction: Sector gate on the Harvey Canal in the West Bank and Vicinity New Orleans Hurricane Protection Project. Completion is expected in 2006. In a bird's eye view, sector gates are like a slice of pie. They possess the ability to hold back higher water from either direction.
BREAKWATER – Concrete and steel structure that decreases wave force against lakefront pumping stations. They have been built in Jefferson Parish where drainage canals meet Lake Pontchartrain . Purpose: Protect pumping stations from hurricane storm surge. Completed: At Pumping Station No. 2 on Suburban Canal , 1,000 feet long, and at Pumping Station No. 3 at Elmwood Canal , 1,500 feet long.
DRAINAGE STRUCTURE – Concrete and steel dam with gates, which are lowered only when a storm approaches. Purpose: Continue the flood protection where hurricane levees intersect a stream draining rainwater. Completed: Bayou Trepagnier, St. Rose, Almedia, Walker Canal and Cross Bayou, all in east St. Charles Parish.