New Orleans officials long failed to respond to the growing threat posed by a broken drainage system, and that neglect contributed to the severity of flooding in July and August last year, according to a draft report on the causes of the inundation.

The report, issued by outside consultants, confirms much of what came to light after Aug. 5: that the flooding that day was the result of several converging factors, including failed drainage pumps, busted turbines, clogged catch basins and undersized pipes.

But as much as anything, the report highlights the long-term failure of city and Sewerage & Water Board officials to take measures to overhaul the decrepit system, or even to probe its inadequacies.

"The root causes of these (problems) and local government's insufficient awareness of the risk they posed stem from a myriad of budgeting prioritization shortfalls, bureaucratic and leadership silos, communication disconnects, insufficient data gathering and analysis, operational inefficiencies and oversight gaps among relevant governmental entities," the report says.  

But the report also suggests that New Orleans' drainage system couldn't have handled the Aug. 5 storm even in the most optimistic scenario, though it notes that no clear standard was ever developed to gauge its performance.

The long-awaited report, a "root cause analysis" of the widespread flooding, was commissioned by former Mayor Mitch Landrieu last year. 

The report was written by ABS Group, a Houston consulting firm. The draft was released to The New Orleans Advocate on Monday evening — a year and a day after the flooding — through a public records request.

The report details now well-known mechanical failures and limitations of the city's drainage system. But it also focuses on breakdowns in priorities and a lack of concern and attention to the drainage system in the "years, months and days" before the flood.

All that contributed to a situation in which the S&WB had only 10 percent of its power available during the storm and the hardest-hit areas had only 45 percent to 70 percent of the pumping capacity they theoretically could have had.

As an example, the report notes that after the S&WB was alerted in March that all the turbines that run the drainage system had failed and were offline, there was "no evident follow-up or inquiries regarding what would happen during a severe rain event."

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It says that was true despite multiple meetings of the S&WB's governing board, the City Council and Landrieu's cabinet, which included S&WB representatives. 

The report also faults the city and S&WB for failing to better communicate with residents about the possibility of flooding, arguing that the damage caused could have been mitigated if residents had been warned when a major storm was coming.

However, it says, the city's Office of Homeland Security was barred from issuing flood advisories without prior approval from higher officials, and it did not issue warnings when the S&WB anticipated heavy rains.

Since the storm, the S&WB has poured about $82 million into upgrades to the system, bringing pumps and turbines back online and buying backup generators and other equipment to bolster the system.

Even if it all works as designed, however, the city's current system would be unable to keep up with a storm that has a 10 percent chance of occurring in a given year, and such a rainfall would cause at least 6 inches or more of standing water, according to the report.

The July and August floods both exceeded the rainfall that would be expected in such an event, according to the report. 

Follow Jeff Adelson on Twitter, @jadelson.​