1. Engineering History and 2008 Operation of the Bonnet Carré Spillway: A Controlled Levee Crevasse on the Lower Mississippi River Christopher G. Brantley, Ph.D. June 2008

2. Mississippi River Drainage Basin

3. Floods in the Lower Mississippi Valley n Levee construction begins in 1718 n Increasing state and Federal involvement n Rising flood heights and larger levees n Floods cause crevasses (breaks in the levees which flood adjoining areas) n The Bonnet Carré Crevasses occur between 1849 and 1882

4. The Great Flood of 1927 n Floodwaters cover 27,000 square miles n Approximately 250 - 500 people die n 700,000 people are homeless n 137,000 buildings damaged or destroyed n $347 Million in damages ($4.4 Billion in 1993 dollars) n 13 major levee crevasses occur n Levee at Caernarvon is purposely breached to save New Orleans

12. Corps abandons “Levees only” Policy n Corps recommends Jadwin Plan which drops “levees only” policy n 1928 Flood Control Act gives Corps jurisdiction over flood control in Lower Miss. Valley n Bonnet Carré selected as site for controlled spillway to protect New Orleans

13. MISSISSIPPI RIVER MORGAN CITY MORGAN CITY ATCHAFALAYA R NEW ORLEANS BATON ROUGE BATON ROUGE NATCHEZ VICKSBURG GREENVILLE ARKANSAS CITY ARKANSAS CITY MEMPHIS CAIRO HELENA NEW MADRID ST. LOUIS 1,250,000 1,200,000 300,000 Wax Lake Outlet Wax Lake Outlet 1,500,000 250,000 West Atchafalaya Floodway West Atchafalaya Floodway Morganza Floodway Morganza Floodway RED RIVER 620,000 600,000 Old River Old River 250,000 1,500,000 YAZOO RIVER 2,890,000 540,000 400,000 TENNESSEE RIVER OHIO RIVER 2,250,000 550,000 New Madrid Floodway New Madrid Floodway 100,000 MISSOURI R MISSISSIPPI R 150,000 490,000 Project Design Flood GULF OF MEXICO LAKEPONTCHARTRAINLAKEPONTCHARTRAIN Bonnet Carré Spillway Bonnet Carré Spillway Lower Atchafalaya Floodway Lower Atchafalaya Floodway

14. Old River Control Morganza Floodway Bonnet Carré Spillway New Orleans District

15. GULF OF MEXICO LAKEPONTCHARTRAINLAKEPONTCHARTRAIN NEW ORLEANS NEW ORLEANS BATON ROUGE BATON ROUGE MORGAN CITY MORGAN CITY OLD RIVER OLD RIVER WEST ATCHAFALAYA FLOODWAY WEST ATCHAFALAYA FLOODWAY WAX LAKE OUTLET WAX LAKE OUTLET MORGANZA FLOODWAY MORGANZA FLOODWAY BONNET CARRE’ SPILLWAY BONNET CARRE’ SPILLWAY MISSISSIPPIRIVERMISSISSIPPIRIVER 630,000 600,000 300,000 2,720,000 1,500,000 1,250,000 250,000 680,000 1,500,000 1,200,000 ATCHAFALAYA RIVER RED RIVER 150,000 350,000 Project Design Flood 3 million cubic feet per second at Old River

16. The Bonnet Carré Spillway n Component of the Mississippi River & Tributaries Project authorized in 1928 n Built between 1929 and 1936 n Protects New Orleans by diverting flood waters to the Gulf of Mexico via Lake Pontchartrain n Operated first in 1937 and eight times thereafter (1945, 1950, 1973, 1975, 1979, 1983, 1997, 2008) n Design capacity is 250,000 cubic feet per second

19. Design and Construction n Design Concerns n Preliminary Investigations n Temporary Hydraulic Laboratory on-site n Concrete Testing n Simple and enduring design u 7,000 foot concrete weir u 350 bays, each with 20 wooden timbers F 174 low @ 15 feet NGVD F 176 high @ 17 feet NGVD

20. Construction Photos Untreated wooden pilings Concrete Piers

22. Project Operations n Decision Process u Numerous factors are considered u Predicted river stages and velocities are most important factors n Operation Procedures u Two cranes lift needles over 36 hours u Design allows tight control over flows

23. Spillway Opening Data Year Dates Open Gates Open Peak Flow 1937 Jan 30 to Mar 7 285211,000 1945 Mar 23 to May 18 350318,000 1950 Feb 10 to Mar 19 350223,000 1973 Apr 8 to Jun 21 350195,000 1975 Apr 14 to Apr 26 225110,000 1979 Apr 18 to May 21 350191,000 1983 May 20 to Jun 23 350268,000 1997 Mar 17 to Apr 18 298243,000 2008 Apr 11 to May 8 160115,000

25. Bonnet Carré Spillway

37. Other Activities n Hunting n Fishing n ATV riding n Dog training n Camping n Cycling n Archery n Boating n Crawfishing n Borrow (sand and clay)