The Corps’ Mississippi Valley New Orleans (MVN) began closing bays on the Bonnet Carré Spillway on April 13, 2020 but has not closed any additional bays since. The MVN expects to slowly close the structure until all bays are closed, but is going to wait until this extended crest passes. The bays are operated to manage the maximum flow at New Orleans and ensure it does not exceed the target flow of 1.25 million cubic feet per second (cfs). The Spillway’s operation is based on the estimated flow at Red River Landing which is utilized to manage the number of bays opened to ensure the flow of 1.25 million cfs is not exceeded below the flood control structure. The estimated flow at Red River Landing today is reported to be 1,306,000 cfs.
The Bonnet Carre´ Spillway is a flood control structure extending from Mile 128.8 Above Head of Passes to Mile 127.3 Above Head of Passes that is designed to pass flood water from the Mississippi River into Lake Pontchartrain to prevent flooding below the Spillway.
The MVN had previously opened 90 bays and then closed 10 bays earlier this week, the forecast flow with a total of 80 bays open is approximately 84,000 cfs is being diverted from the Mississippi River and into Lake Pontchartrain via the floodway. The flood control structure has a total of 350 bays and just over one-quarter of the bays were opened to pass these flood waters.
The Mississippi River forecast indicates that the maximum flow (cresting conditions) at the structure will continue to pass between April 10th and April 19th (2020) this extended crest is coming to an end. A more pronounced fall in stage levels is predicted in the long term forecasts, but is not estimated to start until the second week of May. The maximum flow through the flood control structure for this opening thus far is 90,000 cfs. The MVN has ceased closing operations until the Carrollton Gauge begins to fall.
The overall duration of the Bonnet Carré Spillway operation is expected to last a total of 30 days.
BONNET CARRÉ SPILLWAY OPERATION 2020
|DATE||CARROLLTON GAUGE (NEW ORLEANS)||DAILY NUMBER OF BAYS OPENED||DAILY NUMBER OF BAYS CLOSED||TOTAL NUMBER OF BAYS OPENED||SPILLWAY DISCHARGE CUBIC FEET PER SECOND (CFS)|
|4/3/20||16.30 feet||10||N/A||10||16,000 cfs|
|4/4/20||16.38 feet||0||N/A||10||16,000 cfs|
|4/5/20||16.60 feet||0||N/A||10||16,000 cfs|
|4/6/20||16.70 feet||10||N/A||20||24,700 cfs|
|4/7/20||16.75 feet||25||N/A||45||48,000 cfs|
|4/8/20||16.70 feet||5||N/A||50||50,000 cfs|
|4/9/20||16.70 feet||20||N/A||70||63,000 cfs|
|4/10/20||16.80 feet||20||N/A||90||76,000 cfs|
|4/11/20||16.90 feet||N/A||N/A||90||76,000 cfs|
|4/12/20||17.00 feet||N/A||N/A||90||80,000 cfs|
|4/13/20||17.10 feet||N/A||10||80||80,000 cfs|
|4/14/20||17.15 feet||N/A||0||80||81,000 cfs|
|4/15/20||17.30 feet||N/A||0||80||76,000 cfs|
|4/16/20||17.30 feet||N/A||0||80||90,000 cfs|
|4/17/20||17.30 feet||N/A||0||80||90,000 cfs|
|4/18/20||17.30 feet||N/A||0||80||88,000 cfs|
|4/19/20||17.30 feet||N/A||0||80||84,000 cfs|
A forecast update provided by our colleagues from the National Oceanic and Atmospheric Administration’s (NOAA) Lower Mississippi River Forecast Center is attached, highlights from this update specific to the New Orleans are reproduced below:
“ On the lower Mississippi River, major flooding has ended at Vicksburg, MS and should end this weekend in Natchez, MS. Major flooding will continue at Baton Rouge, LA for the next couple of weeks. Minor to moderate flooding will continue into May. Impacts are mainly agriculture and navigation.
Cresting conditions continued on the lower Mississippi River from Red River Landing, LA to New Orleans, LA. Slow falls should start over the weekend from Red River Landing, LA through Donaldsonville, LA. Significant falls should start to approach Red River Landing, LA by early next week.
The Bonnet Carré Floodway continues to operate and cresting conditions continue at New Orleans, LA and Reserve, LA. Both locations will continue to crest and remain at the same level until the floodway is no longer operating. The USACE will continue to make reductions as the flow falls over the next week.
The 16 day future rainfall guidance shows a secondary rise below flood stage on the lower Ohio River. This crest in early May would only slow recessions on the lower Mississippi River.”
The Bonnet Carré Anchorage was closed by the U.S. Coast Guard at 6:00 a.m. on April 3, 2020, vessels shall not enter the anchorage or the area extending 600 feet into the river from the Bonnet Carré Spillway, between MM 127 and MM 129 and the shoreline of Lake Pontchartrain.
“MARINERS ARE ADVISED THAT THE M/V KENT WILL BE STATIONED ON THE LEFT DESCENDING BANK JUST NORTH OF THE SPILLWAY TO MONITOR MARINE TRAFFIC ON VHF MARINE CHANNELS 16 AND 67. SHOULD AN INCIDENT OCCUR BETWEEN THE SPILLWAY AND MISSISSIPPI RIVER MILE 140 ABOVE HEAD OF PASSES (AHP) INVOLVING AN ADRIFT VESSEL, BARGE, ETC., THE ATTENDING VESSEL OR ANY OTHER VESSEL IN THE VICINITY SHOULD IMMEDIATELY REPORT THE INCIDENT TO THE M/V KENT.”