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Home > Missions > Mississippi River Flood Control > Bonnet Carre' Spillway Overview > Spillway Operation Information

Spillway Operational Effects

During operation of the spillway, materials suspended in the Mississippi River's water are deposited in the floodway and Lake Pontchartrain and Lake Borgne. In addition, the vast input of fresh water into these brackish and saline lakes has an immediate, short-term, adverse environmental effect.

The long-range effect, however, is extremely favorable because it simulates the natural flooding cycle of the river and provides a replenishment of valuable nutrients to the ecosystem. Spillway openings are strongly associated with increased oyster, crab and other fisheries production in Lake Pontchartrain and Lake Borgne for several years after the flood events.

With each opening, the river deposits an average of 9 million cubic yards of sediment, mostly silts and sand, within the floodway. These deposits are removed by private contractors and local government agencies for use as fill material in residential and industrial developments. This sediment is a valuable local resource since most of the surrounding region is near or below sea level.

In addition to the infrequent operation of the spillway for flood control, about every other year a small portion of the Mississippi River leaks through the spaces between the timbers of the spillway. This minor diversion of fresh water normally occurs for a few weeks in the spring or early summer when the river is high enough to exceed the elevations of the spillway weir but not high enough to warrant project operation. These minor diversions are termed leakage events (less than 10,000 cfs in comparison to a spillway opening with its design flow of 250,000 cfs).

The introduction of fresh water during leakage events simulates the natural cycle of overbank flooding and provides numerous ecosystem benefits to the aquatic and terrestrial resources in the spillway. These benefits include improved water circulation in the spillway's water bodies, nutrient introduction and restocking of fishery resources. Recreational crawfishing, for example, increases significantly due to the optimal conditions produced by these events. These frequent, small-scale diversions of Mississippi River water are also beneficial to the Lake Pontchartrain estuary.

2018 Opening Pace

After heavy rains in the Mississippi and Ohio River valleys increased river stages, the Corps opened the spillway on Jan. 10, 2016.

The Bonnet Carre Spillway will be partially opened on Thursday, March 8, 2018 in order to keep the volume of the Mississippi River flows at New Orleans from exceeding 1.25 million cubic feet per second (cfs).  

 

  Spillway Opening Pace: 2018

Day

Date
Bays Opened                        

Total Opened

Discharge
1 March 8 8 8 2,000
2 March 9 13 21

15,000            

 

3 March 10    8         29 25,000

 

4 March 11 29 58 49,000          

 

5 March 12    34 92 91,000

 

6 March 13 56 148 153,000

 

7 March 14      0 148  130,000      

 

8 March 15      20 168 161,000

 

9 March 16 0 168 155,000

 

10  March 17 0 168 160,000

 

11 March 18 0 168 167,000     
12 March 19 15 183 196,000  
13 March 20 0 183 181,000  
14 March 21 0 183 177,000  
15 March 22 -13 170 163,000  
16 March 23 -12 158 140,000  
17 March 24 -12 146 123,000     
18 March 25 -15 131 110,000  
19 March 26 -28 103 80,000     
20 March 27 -34 69 54,000  
21 March 28 -32 37 19,000  
22  March 29 -15 22

7,000

 
23 March 30 -22 0 0  

 

 

2016 Opening Pace

After heavy rains in the Mississippi and Ohio River valleys increased river stages, the Corps opened the spillway on Jan. 10, 2016.

The Bonnet Carre Spillway was partially opened on Monday, Jan. 10, 2016 in order to keep the volume of the Mississippi River flows at New Orleans from exceeding 1.25 million cubic feet per second (cfs).  

Spillway Opening Pace: 2016
Date Bays Opened Total Opened CFS

    

Day 1 Jan. 10 20 20 21,500

 

Day 2 Jan. 11 18 38 32,000

 

 

Day 3

Jan. 12

22 60 52,270

 

 

Day 4

Jan. 13

30        90 91,800

 

 

Day 5

Jan. 14 

10 100  104,000

 

 

Day 6

 Jan. 15

30 130  132,000

 

 

Day 7

 Jan. 16

52 182  196,000 

 

 

Day 8

 Jan. 17

28 210  203,000

 

 

Day 9

 Jan. 18

0 210  201,000

 

 

Day 10

 Jan. 19

210  201,000 

 

 

Day 11 Jan. 20 0 210 199,000    
Day 12 Jan. 21 0 210 192,000    
Day 13 Jan. 22 0 210 192,000    
Day 14 Jan. 23 0 210 186,000    
Day 15 Jan. 24 0 210 194,000    
Day 16 Jan. 25 -13 197 168,000    
Day 17 Jan. 26 -20 177 150,000    
Day 18 Jan. 27 -22 155 126,000    
Day 19 Jan. 28 -24 131 91,000    
Day 20 Jan. 29 -40 91 62,000    
Day 21 Jan. 30 -34 57  30,000    
Day 22 Jan. 31 -33 24 8,000       
Day 23 Feb. 1 -24 0      

 

 

 

Spillway Opening Pace

After heavy rains in the Mississippi and Ohio River valleys increased river stages, the Corps opened the spillway on May 9, 2011.

The Bonnet Carre Spillway was partially opened on Monday, May 9, 2011 in order to keep the volume of the Mississippi River flows at New Orleans from exceeding 1.25 million cubic feet per second (cfs). It was fully closed 43 days later on Monday, June 20. The recreational areas of the spillway will be open; however, members of the public should use caution when accessing the area and be aware of water hazards, wildlife, such as snakes and alligators, as well as excessive heat and humidity.

 

 

 

 

 

Spillway Opening Pace: 2011 vs. 2008
 
2011 Date
Bays Opened
Total Opened 2011
2008 Date
Bays Opened
Total Opened 2008
Day 1

May 9

28

28

April 11

38

38

Day 2

May 10

44

72

April 12

46

84

Day 3

May 11

38

110

April 13

0

84

Day 4

May 12

102

212

April 14

0

84

Day 5

May 13

52

264

April 15

0

84

Day 6

May 14

36

300

April 16

6

90

Day 7

May 15

30

330

April 17

20

110

Day 8

May 16

0

330

April 18

25

135

Day 9

May 17

0

330

April 19

25

160

Days 10 - 42

May 18-June 20

0

0

April 20-29

0

160



Spillway Opening Pace: 2008 vs. 1997
 
2008 Date
Bays Opened
Total Opened 2008
1997 Date
Bays Opened
Total Opened 1997
Day 1

April 11

38

38

March 17

30

30

Day 2

April 12

46

84

March 18

40

70

Day 3

April 13

0

84

March 19

30

100

Day 4

April 14

0

84

March 20

50

150

Day 5

April 15

0

84

March 21

40

190

Day 6

April 16

6

90

March 22

35

225

Day 7

April 17

20

110

March 23

25

250

Day 8

April 18

25

135

March 24

15

265

Day 9

April 19

25

160

March 25

20

285

Days 10 - 20

April 20-29

0

160

March 26

13

298


Spillway Operation Information

The decision to operate or "open" the Bonnet Carré Spillway is the responsibility of the Mississippi River Commission president who has broad jurisdiction over the entire MR&T Project. The MRC president relies heavily on the recommendations of the New Orleans district engineer who is responsible for the actual operation of the Bonnet Carré structure and floodway.

The decision to operate the Bonnet Carré Spillway is made when existing conditions, combined with predicted river stages and discharges, indicate that the mainline levees in New Orleans and other downstream communities will be subjected to unacceptable stress from high water. Included in the complex decision process are environmental considerations, as well as hydrologic, structural, navigational and legal factors.

Once the decision to open the Bonnet Carré structure has been made, actual operation of the structure is relatively simple. Two cranes, which move along tracks atop the structure, are used to individually lift each timber from the required number of bays. The timbers are raised from their vertical position across the weir opening (where together they serve as a dam against the high water) and are laid horizontally on top of the structure for later use in its closing. A complete opening of all 350 bays requires about 36 hours to lift the 7,000 wooden timbers in the structure. If a quicker opening of the structure is ever required, emergency procedures can release 20 timbers at once and reduce the opening time to three hours.

The Corps of Engineers initiated surveys and preliminary investigations for the Bonnet Carré Spillway in 1928. Construction of the spillway structure began in 1929 and was completed in 1931. The guide levees were completed in 1932, and highway and railroad crossings in 1936. The total project cost was $14.2 million.