US Army Corps of Engineers
New Orleans District

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.

2019 Opening Pace

After heavy rains in the Mississippi and Ohio River valleys increased river stages, the Corps opened the spillway on Feb. 27, 2019.

The Bonnet Carre Spillway will be partially opened on Wednesday, Feb. 27, 2019 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: 2019

Day Date Bays Opened Total Opened Discharge
1 Feb. 27 28 28 23,000 cfs
2 Feb. 28 20 48 37,000 cfs
3 Mar. 1st 40 88 74,000 cfs
4 Mar. 2nd 20 108 91,000 cfs
5 Mar. 3rd 0 108 94,000 cfs
6 Mar. 4th 40 148 138,000 cfs
7 Mar. 5th 0 148 148,000 cfs
8 Mar. 6th 0 148 148,000 cfs
9 Mar. 7th 20 168 169,000 cfs
10 Mar. 8th 20 188 187,000 cfs
11 Mar. 9th 0 188 176,000 cfs
12 Mar. 10 10 198 197,000 cfs
13 Mar. 11 8 206 198,000 cfs
14 Mar. 12 0 206 196,000 cfs
15 Mar. 13 0 206 202,000 cfs
16 Mar. 14 0 206 207,000 cfs
17 Mar. 15 -10 196 207,000 cfs
18 Mar. 16 0 196 207,000 cfs
19 Mar. 17 0 196 199,000 cfs
20 Mar. 18 0 196 207,000 cfs
21 Mar. 19 0 196 213,000 cfs
22 Mar. 20 0 196 210,000 cfs
23 Mar. 21 0 196 196,000 cfs
24 Mar. 22 0 196 194,000 cfs
25 Mar. 23 0 196 184,000 cfs
26 Mar. 24 0 196 179,000 cfs
27 Mar. 25 0 196 177,000 cfs

 

2018 Opening Pace

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 Mar. 8 8 8 2,000 cfs
2 Mar. 9 13 21 15,000 cfs
3 Mar. 10 8 29 25,000 cfs
4 Mar. 11 29 58 49,000 cfs
5 Mar. 12 34 92 91,000 cfs
6 Mar. 13 56 148 153,000 cfs
7 Mar. 14 0 148 130,000 cfs
8 Mar. 15 20 168 161,000 cfs
9 Mar. 16 0 168 155,000 cfs
10 Mar. 17 0 168 160,000 cfs
11 Mar. 18 0 168 167,000 cfs
12 Mar. 19 15 183 196,000 cfs
13 Mar. 20 0 183 181,000 cfs
14 Mar. 21 0 183 177,000 cfs
15 Mar. 22 -13 170 163,000 cfs
16 Mar. 23 -12 158 140,000 cfs
17 Mar. 24 -12 146 123,000 cfs
18 Mar. 25 -15 131 110,000 cfs
19 Mar. 26 -28 103 80,000 cfs
20 Mar. 27 -34 69 54,000 cfs
21 Mar. 28 -32 37 19,000 cfs
22 Mar. 29 -15 22 7,000 cfs
23 Mar. 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.

 

Year Days Bays Opened (%) Opened Ideal flow capacity
1937 48 285 81.4% 203,571 cu ft/s
1945 57 350 100% 250,000 cu ft/s
1950 38 350 100% 250,000 cu ft/s
1973 75 350 100% 250,000 cu ft/s
1975 13 225 64.3% 160,714 cu ft/s
1979 45 350 100% 250,000 cu ft/s
1983 35 350 100% 250,000 cu ft/s
1997 31 298 85.1% 212,857 cu ft/s
2008 31 160 45.7% 114,286 cu ft/s
2011 42 330 94.3% 235,714 cu ft/s
2016 22 210 60.0% 203,000 cu ft/s
2018 30 186 48.0%

196,000 cu ft/s