There is no evidence that operator error caused a power turbine to trip offline, or that the turbine’s temporary loss caused additional flooding during a morning rainstorm on June 10, the Sewerage and Water Board of New Orleans (S&WB) said Wednesday.
The department conducted an internal after-action review examining logbooks and holding briefings with members of the operations team, according to an S&WB press release.
The pumps that remove water from the city are powered by a variety of turbines and backup generators that can be adjusted to meet the drainage needs of a given rainstorm. The after-action report outlines, in detail, a timeline of decisions made by the operations team that morning as staff powered turbines up and down.
The turbine in question, known as T4, went offline around 8:52 that morning and was out of commission for about two hours. According to the report, a safety mechanism meant to keep the turbine from firing too quickly erroneously took T4 offline, forcing the operations staff to find the power from other generators. It’s still not known why the safety mechanism was tripped, the S&WB said.
Executive Director Ghassan Korban praised his team’s handling of the event.
“No one predicted that more than 3 inches of rain would fall in little more than an hour that morning,” Korban said in the statement. “But our team responded well. They did — and continue to do — a tremendous job operating a drainage system that still runs practically the same way it did a hundred years ago.”
The July 10 downpour dropped 3 to 6 inches of rain on the region in a short period of time, with some areas seeing rainfall rates of close to 4 inches per hour at the peak of the storm, National Weather Service forecaster Robert Ricks told WWNO last week.
“In our area … probably a couple times a year we get rain rates that much,” Ricks said.
The report notes that the National Weather Service issued a flash flood warning at 7:51 a.m., but that the flooding had already begun at that point, and that 3 inches of rain had already fallen at its Mid-City pump station between 6:40 and 7:45 a.m.
Citing evidence from the city’s real-time crime cameras, the S&WB says the peak of the flooding occurred before T4 tripped offline.
“There is no question that, had T4 stayed online, we could have finished pumping the city dry earlier,” the utility admits in the report, “...however, it does not appear that the loss of T4 significantly affected the depth of the flood waters (likely because the great majority of the rain had fallen by that point).”
Moving forward, the S&WB said it plans to be “more aggressive” as it prepares for rainstorms that are not predicted to be severe, especially since unexpected downpours have been increasing in frequency.
“Power equipment, such as the Electro-Motive Diesel (EMD) generators, may be started sooner than normal in anticipation of sudden intense downpours within these rain events,” the press release said.
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