This post has been updated to reflect new information about installation of the new sensors.

The conventional wisdom after Hurricane Isaac was that the post-Katrina repairs and improvements in the levee system worked well. From the floodgates that kept the surge out of the canals in New Orleans to the Lake Borgne barrier that held back 13.6 feet of water, the U.S. Army Corps of Engineers prevented a repeat of Katrina’s catastrophic flooding.

But a closer look reveals failures in the multimillion-dollar system for measuring the depth of the water in the outfall canals — the primary source of Katrina-related flooding. At Isaac’s peak, some gauges either provided erratic readings or none at all, heightening tensions at the corps.

Along with the failure of the corps’ remote-start system for some of its critical pumps and a fire on one pump, it’s clear that all did not go well during Isaac. These problems could have had greater consequences in a stronger storm.

“It worries me that we have gauges that are potentially out of service because of regular occurrences — Mother Nature,” said Tim Doody, president of the Southeast Louisiana Flood Protection Authority-East.

Corps officials said the gauges didn’t meet their expectations, and they’re working to figure out what went wrong and how to address the problems.

Measurement is key to pumping rainwater from the city

Once the corps closes the floodgates at the Lake Pontchartrain end of the 17th Street, Orleans Avenue and London Avenue canals, it has to pump rainwater out of the canals as fast as the New Orleans Sewerage & Water Board pumps it in. Corps employees monitor eight gauges in each canal to make sure the water doesn’t rise so high that it overwhelms the canal walls.

Click here for a report on this from our partners at WVUE-TV.

Of the 25 gauges in the outfall canals and at the entrance of Bayou St. John, 16 went out or registered false readings at some point on Aug. 29, according to Rivergages.com, which records hourly readings.

When the city was feeling the brunt of the storm, six of the eight gauges on the 17th Street Canal malfunctioned for some period of time. One of them registered 8.12 feet before it went out — well over the 6½-foot limit for that canal.

Gauges in other canals worked intermittently, too, including four in a row near the interior end of the London canal and one on the lake-side of that floodgate.

Corps not hindered by gauge outages

Corps personnel said that doesn’t mean they were clueless about the water levels.

At minimum, the corps needs two gauges in each canal: one at the Sewerage & Water Board pumping station and another inside the lake floodgate. Chris Accardo, chief of operations for the corps’ New Orleans district, said even if one of those gauges goes out, employees at each location can look outside to see how high the water is.

Moreover, the corps was getting more timely, reliable information than was available to the public on Rivergages.com. Gauge readings are sent via satellite to that website every hour. The corps gets readings several times a minute via fiber-optic cable laid on the bottom of the canal. If the cable is cut, they can get readings via microwave dishes.

Ray Newman, the corps’ 17th Street Canal captain, said gauges “were coming and going” during the storm, but for less than a minute at a time — not long enough for the water level to rise dramatically. “I still knew what the level was,” he said.

Two gauges registered alarmingly high levels: 8.44 feet at Pump Station No. 6 and 7.67 at I-10, according to Rivergages.com. The corps doesn’t want water to get higher than 6.5 feet in the 17th Street Canal.

The 6.5-foot “maximum operating level” is just six inches higher than it was before the corps strengthened the canal walls, though the corps had said that work might enable the agency to raise it to 8 feet.

“Had the 17th Street SWE [safe water elevation] been 8 feet, there may have been no crisis that morning,” wrote Matt McBride, a mechanical engineer who tracks and criticized the corps’ systems at his website, Fix The Pumps.

Meanwhile, the gauge just inside the corps’ floodgate topped 6 feet. The corps had to ask the Sewerage & Water Board not to increase its pumping for a couple of hours because it had trouble getting some of its pumps turned on.

The gauges and the pumps are all part of a $5.4 million system, called SCADA, for Supervisory Control and Data Acquisition, which was installed after Katrina along with the flood gates.

In addition, one of the corps’ pumps at the Orleans Canal floodgate caught fire that morning, according to Sewerage & Water Board pump logs. Corps spokesman Ricky Boyett said the fire involved leaking hydraulic fluid, and it was extinguished in under an hour.

No wonder there was an air of crisis inside the corps’ emergency operations center on Leake Avenue for awhile, as reported by The New York Times.

The corps believes those readings of around 8 feet were false. Two of the three gauges maintained that reading for hours, indicating that they had malfunctioned. The corps said the water reached about 6.5 feet in the canal.

The outages did, however, contribute to misinformation at a time when, well, you don’t want misinformation.

At a meeting of the Southeast Louisiana Flood Protection Authority-East last month, the corps’ New Orleans District commander, Col. Edward Fleming, recalled hearing that water was at 8 feet on 17th Street.

“That wasn’t right,” he said. “I personally went out there that morning and it was nowhere near 8.”

Flood Authority commissioners said unreliable gauges throughout the region, not just in the outfall canals, were one of the few shortcomings during Isaac. In one meeting, Doody called it a “huge problem.”

Stephen Estopinal, commissioner and treasurer of the Flood Authority, learned from The Lens how many gauges went out during the storm.

“I think the gauge either needs to be reliable or just don’t have it,” he said. “To have an unreliable gauge is a waste of money and it could be misleading.”

New sensors are the culprit

The ironic thing about all these outages is that the gauges were revamped within the last year to make them more reliable than the ones that had been in the canals.

After Katrina, the corps installed mechanical gauges that calculate the water level with a pressure sensor. But they were “maintenance-intensive,” Newman said.

So after the 2011 hurricane season, the corps replaced the sensors with ones that work by radar, which should be more reliable because they are mounted above the water, not below. They work by measuring changes in the radar signal reflected off the surface of the water.

The new sensors are mounted on tall metal frames stuck in the canal bed. The frames may not have been strong enough to keep the sensors in place during Isaac’s high winds. Photo by Steve Myers

The corps is still trying to figure out what went wrong, Newman said. There are two possibilities:

Improper installation: Gauges that pinned at their maximum readings may have been installed too close to the water, so that when the water rose, the sensors couldn’t get accurate readings. On the 17th Street Canal, the gauges are mounted 8 or 9 feet high, which doesn’t offer much of a buffer when the water rises to 6.5 feet. (Since this story was published, The Lens has learned that the sensors in two of the three canals appear to have been installed below the manufacturer’s recommended height.)

Gauges that pinned at their maximum readings may have been installed too close to the water, so that when the water rose, the sensors couldn’t get accurate readings. On the 17th Street Canal, the gauges are mounted 8 or 9 feet high, which doesn’t offer much of a buffer when the water rises to 6.5 feet. (Since this story was published, The Lens has learned that the sensors in two of the three canals appear to have been installed below the manufacturer’s recommended height.) Frames too weak for high winds: The gauges are mounted on three-legged metal frames stuck into the canal bed. The gauges that went out may have been blown about by Isaac’s winds so much that the radar couldn’t get a handle on the water level.

Sustained winds at New Orleans Lakefront Airport reached 54 mph that morning, with a 74 mph gust, according to the National Weather Service.

“I was hoping for better,” Newman said. “We installed them so they would stay online, and we had some go down. I’m looking for 100 percent.”

Whatever the solution, “I have to insist that they’re done before May 2013,” Newman said.

Flood Authority officials have discussed the need for so-called “hardened gauges” that can stand up to hurricane conditions. But they’d probably be installed in open water and lakes Borgne and Pontchartrain, where they’d be susceptible to the worst of the storm. The canals, on the other hand, are relatively protected bodies of water.

Doody opened the Flood Authority’s first board meeting after Isaac by telling people, “Everyone should take some comfort that the system, as designed, worked.”

But he reminded people that the storm was a 40- or 50-year storm, not the 100-year storm that the levees are supposed to protect against.

“It was more of a quiz for the system than a test.”