US Army Corps of Engineers
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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.

2020 Opening Pace

After heavy rains in the Mississippi and Ohio River valleys increased river stages, the Corps opened the spillway on April 3, 2020.

*Updates will be posted the morning after closing operations

*Leakage was included in total Discharge calculations

Day Date Bays Opened Total Opened Computed Discharge Discharge with estimated Leakage
1 April 3 10 10 4,850 cfs 16,000 cfs
2 April 4 0 10 5,190 cfs 16,000 cfs
3 April 5 0 10 5,490 cfs 16,000 cfs
4 April 6 10 20 15,705 cfs 24,700 cfs
5 April 7 25 45 40,500 cfs 48,000 cfs
6 April 8 5 50 42,290 cfs 50,000 cfs
7 April 9 20 70 55,350 cfs 63,000 cfs
8 April 10 20 90 68,370 cfs 76,000 cfs
9 April 11 0 90 71,070 cfs 78,000 cfs
10 April 12 0 90 72,975 cfs 80,000 cfs
11 April 13 -10 80 71,970 cfs 80,000 cfs
12 April 14 0 80 73,780 cfs 81,000 cfs
13 April 15 0 80 75,385 cfs 76,000 cfs
14 April 16 0 80 81,070 cfs 90,000 cfs
15 April 17 0 80 80,515 cfs 90,000 cfs
16 April 18 0 80 78,355 cfs 87,000 cfs
17 April 19 0 80 74,575 cfs 84,000 cfs
18 April 20 0 80 73,575 cfs 83,000 cfs
19 April 21 0 80 68,110 cfs 77,000 cfs
20 April 22 0 80 66,125 cfs 74,000 cfs
21 April 23 0 80 63,155 cfs 71,000 cfs
22 April 24 -10 70 52,580 cfs 60,500 cfs
23 April 25 -10 60 45,920 cfs 54,000 cfs
24 April 26 -10 50 35,255 cfs 43,000 cfs
25 April 27 -10 40 28,105 cfs 36,000 cfs
26 April 28 -10 30 20,405 cfs 28,000 cfs
27 April 29 0 30 21,100 cfs 28,000 cfs
28 April 30 -20 10 9,100 cfs 16,500 cfs
29 May 1 -10 0 0 cfs 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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).  The river stages reminded high following the closure of the Bonnet Carre Spillway. Heavy rains across the valley prompted a second opening of the spillway May 10.

Spillway Opening Pace: 2019 First Opening

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. 1 40 88 74,000 cfs
4 Mar. 2 20 108 91,000 cfs
5 Mar. 3 0 108 94,000 cfs
6 Mar. 4 40 148 138,000 cfs
7 Mar. 5 0 148 148,000 cfs
8 Mar. 6 0 148 148,000 cfs
9 Mar. 7 20 168 169,000 cfs
10 Mar. 8 20 188 187,000 cfs
11 Mar. 9 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
28 Mar. 26 -20 176 158,000 cfs
29 Mar. 27 -24 152 135,000 cfs
30 Mar. 28 -17 135 131,000 cfs
31 Mar. 29 0 135 131,000 cfs
32 Mar. 30 0 135 135,000 cfs
33 Mar. 31 0 135 133,000 cfs
34 Arp. 1 0 135 135,000 cfs
35 Arp. 2 0 135 126,000 cfs
36 Apr. 3 0 135 114,000 cfs
37 Apr. 4 0 135 107,000 cfs
38 Apr. 5 0 135 105,000 cfs
39 Apr. 6 0 135 96,000 cfs
40 Apr. 7 0 135 85,000 cfs
41 Apr. 8 -36 99 66,000 cfs
42 Apr. 9 -47 52 38,000 cfs
43 Apr. 10 -34 18 11,000 cfs
44 Apr. 11 -18 0 0 cfs

 

Spillway Opening Pace: 2019 Second Opening

Day Date Bays Opened Total Opened Discharge
1 May 10 60 60 79,000 cfs
2 May 11 10 70 83,000 cfs
3 May 12 0 70 86,000 cfs
4 May 13 58 128 116,000 cfs
5 May 14 10 138 127,000 cfs
6 May 15 0 138 128,000 cfs
7 May 16 0 138 122,000 cfs
8 May 17 0 138 124,000 cfs
9 May 18 0 138 127,000 cfs
10 May 19 10 148 142,000 cfs
11 May 20 0 148 148,000 cfs
12 May 21 20 168 161,000 cfs
13 May 22 0 168 161,000 cfs
14 May 23 0 168 158,000 cfs
15 May 24 0 168 155,000 cfs
16 May 25 0 168 158,000 cfs
17 May 26 0 168 159,000 cfs
18 May 27 0 168 158,000 cfs
19 May 28 0 168 157,000 cfs
20 May 29 0 168 149,000 cfs
21 May 30 0 168 145,000 cfs
22 May 31 0 168 141,000 cfs
23 June 1 0 168 143,000 cfs
24 June 2 0 168 135,000 cfs
25 June 3 0 168 140,000 cfs
26 June 4 0 168 138,000 cfs
27 June 5 0 168 136,000 cfs
28 June 6 0 168 138,000 cfs
29 June 7 0 168 138,000 cfs
30 June 8 0 168 144,000 cfs
31 June 9 0 168 146,000 cfs
32 June 10 0 168 146,000 cfs
33 June 11 0 168 147,000 cfs
34 June 12 0 168 147,000 cfs
35 June 13 0 168 144,000 cfs
36 June 14 0 168 147,000 cfs
37 June 15 0 168 150,000 cfs
38 June 16 0 168 146,000 cfs
39 June 17 0 168 147,000 cfs
40 June 18 0 168 142,000 cfs
41 June 19 0 168 137,000 cfs
42 June 20 0 168 131,000 cfs
43 June 21 0 168 130,000 cfs
44 June 22 0 168 124,000 cfs
45 June 23 0 168 115,000 cfs
46 June 24 0 168 116,000 cfs
47 June 25 0 168 110,000 cfs
48 June 26 0 168 108,000 cfs
49 June 27 0 168 108,000 cfs
50 June 28 0 168 104,000 cfs
51 June 29 0 168 105,000 cfs
52 June 30 0 168 99,000 cfs
53 July 1 0 168 110,000 cfs
54 July 2 0 168 108,000 cfs
55 July 3 0 168 104,000 cfs
56 July 4 0 168 103,000 cfs
57 July 5 0 168 102,000 cfs
58 July 6 0 168 106,000 cfs
59 July 7 0 168 109,000 cfs
60 July 8 0 168 112,000 cfs
61 July 9 0 168 108,000 cfs
62 July 10 0 168 110,000 cfs
63 July 11 0 168 117,000 cfs
64 July 12 0 168 131,000 cfs
65 July 13 0 168 133,000 cfs
66 July 14 0 168 117,000 cfs
67 July 15 0 168 111,000 cfs
68 July 16 0 168 106,000 cfs
69 July 17 0 168 103,000 cfs
70 July 18 0 168 103,000 cfs
71 July 19 0 168 96,000 cfs
72 July 20 0 168 90,000 cfs
73 July 21 0 168 84,000 cfs
74 July 22 -10 158 72,000 cfs
75 July 23 -22 136 57,000 cfs
76 July 24 -42 94 40,000 cfs
77 July 25 -30 64 25,000 cfs
78 July 26 -38 26 11,000 cfs
79 July 27 -26 0 0 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