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 1,289,000 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 now estimated to be 83,000 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) have now passed the structure (April 10-April 19) and a gradual and slow decrease in flow is expected to begin.
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. The river stage at Baton Rouge has now been above flood stage levels for the last 94 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|
|4/20/20||17.10 feet||N/A||0||80||83,000 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:
“ During the past 24 hours, one to four inches of rainfall occurred over most of the LMRFC. Renewed minor to moderate flooding occurred over Louisiana and Mississippi. Minor to moderate flooding continues on smaller tributaries in Tennessee and Arkansas. On Wednesday, another round of 1 to 2 inches of rainfall is forecast over the LMRFC and more renewed minor to moderate flooding will be possible.
Over the next 5 days on the lower Mississippi River, rises of less than 1 foot will occur from New Madrid, MO to Tunica, MS and falls of 1 to 1 1/2 feet will occur from Arkansas City, AR downstream to Donaldsonville, LA.
The 16 day future rainfall guidance shows a secondary rise on the lower Ohio River at Cairo, IL which is slightly over flood stage. This crest in the first week of 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.”