The Morganza Spillway is seen with a few bays open on Sunday morning May 15, 2011 in Batchelor, La. The Army Corps of Engineers could open the spillway again — for the third time in its history — on June 2 because of rising water on the Mississippi River.
By Mark Schleifstein, NOLA.com | The Times-Picayune
Heavy rains expected in the Midwest portion of the Mississippi River Valley during the next week have prompted Army Corps of Engineers officials to warn interests within the Morganza Floodway portion of the Atchafalaya River Basin that the Morganza Spillway structure could be opened as soon as June 2.
More than 5 inches of rain is expected to fall across parts of Kansas, Nebraska, Missouri and Iowa over the next seven days, according to the National Weather Service’s Weather Prediction Center.
The river will crest at 62 feet on June 6 at Red River Landing, only a foot and a half below that location’s all-time high crest, according to Wednesday’s forecast by the weather service’s Lower Mississippi River Forecast Center, based in Slidell.
Red River Landing is only about 16 miles above the Morganza Spillway.
Forecast rainfall in the Midwest could total more than 5 inches during the next seven days, according to the National Weather Service’s Weather Prediction Center.
Forecast rainfall in the Midwest could total more than 5 inches during the next seven days, according to the National Weather Service’s Weather Prediction Center.
Red River Landing is one of several locations along the river where records have been set or about to be set for the number of days above flood stage. At Red River, the record is 152 days, set in 1927, the year of the great Mississippi River Flood. On Wednesday, the location had seen 146 days above flood stage this year.
This chart shows how many days various locations have seen river heights above official flood stages, and how that compares to record flood stage years.
This chart shows how many days various locations have seen river heights above official flood stages, and how that compares to record flood stage years.
The forecast also calls for the river to remain at 16.7 feet at the Carrollton Gage in New Orleans through June 19, well into the beginning of the 2019 hurricane season. Water heights aren’t predicted to rise in New Orleans because the corps already has opened a number of bays in the Bonnet Carre Spillway, which funnels part of the river’s water into Lake Pontchartrain.
But it’s the rising river at the Morganza location that has the corps worried, said spokesman Ricky Boyett on Wednesday evening.
“We have not made a decision on operation (of the spillway) but we did send a notice this evening to stakeholders that have a role in Morganza,” Boyett said in an email response to questions about the rising river.
“Based on the current forecast – specifically projected rain in the valley over the next several days – we could encounter the potential of overtopping the Morganza Control Structure,” he said, adding that the spillway structure – which contains 125 gates that are opened and closed by two cranes rolling on special tracks atop the structure – “cannot be safely operated if overtopped.”
“There are a couple of factors regarding safety that we must consider, but primarily it is unsafe for our personnel. Additionally, the structure is designed to hold back water, but was not designed to be operated while overtopped,” he said.
Boyett said the corps believes the overtopping might occur even before the river reaches a flow speed of 1.5 million cubic feet along the structure, which is the usual trigger for opening gates. “Based on today’s data, that could occur as soon as 5 June.”
But Boyett said the corps could move more quickly to open the structure because it agreed to a “slow opening” strategy to help with evacuating wildlife from the broad floodway leading from the spillway into the Atchafalaya River basin, after the spillway’s opening during a 2011 high river threatened a variety of wildlife species, including protected Louisiana black bears.
The slow opening also expected to reduce scouring in the tail bay area, where the water is released into the floodway, which also occurred in 2011.
The forebay – mostly farmland on the river or batture side of the structure – has been flooded for months during this year’s unusually long high-water season.
Boyett stressed that the decision to open Morganza still will depend on the actual rainfall that occurs over the next few days in the Mississippi floodplain upriver.
Meanwhile, the corps, local river forecast center hydrologists, and the National Hurricane Center’s storm surge prediction team have been conducting a series of drills to assure they can all predict the consequences of storm surge from an early tropical storm or hurricane attempting to push up what will be a near-full river bed through June, and now possibly well into July.
Barges and tugs lines the west bank levee of the Mississippi River in Plaquemines Pairsh on Sept. 10, 2005, left there by storm surge that moved up the river during the storm.
THE TIMES-PICAYUNE
Barges and tugs lines the west bank levee of the Mississippi River in Plaquemines Pairsh on Sept. 10, 2005, left there by storm surge that moved up the river during the storm.
During both Hurricane Isaac in 2012 and Hurricane Katrina in 2005, surge pushed well upriver, swelling the river significantly. But in both cases, the river was at 3 feet or less when the surge moved upriver.
Hurricane Isaac, which became a Category 1 storm with top winds of 80 mph before making landfall at Southwest Pass on Aug. 28, caused the Mississippi to rise to 9.5 feet in New Orleans, from a height of only 3 feet on Aug. 26.
Hurricane Katrina, which was a Category 3 storm with top winds of 125 mph when it made landfall at Buras on Aug. 29, 2005, caused the river to swell to at least 15.24 feet that day before the gage stopped measuring water heights. Several barges ended up beached near the top of the river levee in Algiers, which was then about 17 feet above sea level. On Aug. 27, the river height was only about 3 feet.
“An elevated river is obviously a concern,” said Jamie Rhome, the National Hurricane Center’s lead surge forecaster, during a May 17 interview. “In this case, projections have the river keeping up during the first few weeks of the hurricane season and we have that factored into operational readiness along the coast.”
The testing has included making sure the surge modeling systems used by the center are operating properly, and how they would handle early storms forming in the Gulf, which will have different characteristics from storms occurring later in the hurricane season.
Using the modeling results and applying information about how the river will react to incoming surge – how the weight and speed of the river’s fresh water moving south will in part lessen the effect of the surge moving north – officials have been running case studies aimed at developing strategies for forecasting surge effects on the river, and the kinds of warnings that might have to be given to both emergency managers who have to plan for evacuations, and to the public, Rhome said.
“We look at the output collectively as a team,” he said. “How to interpret the results, what to do, what decisions are made.
“We have several warning tools in our toolbox, and we have to determine which one is most appropriate to clearly address the risk,” he said.
“Thankfully, we have one of the most advanced and interactive river forecast centers in Louisiana,” which has provided key information about how the high river’s water flow will affect surge heights in the New Orleans area and farther upstream, he said.
https://www.nola.com/environment/2019/05/another-mississippi-rise-threatens-to-trigger-morganza-spillway-opening.html
Mark Schleifstein covers the environment and is a leader of the Louisiana Coastal Reporting Team for NOLA.com | The Times-Picayune. Email: mschleifstein@nola.com. Facebook: Mark Schleifstein and Louisiana Coastal Watch. Twitter: MSchleifstein.
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