The catastrophic flooding of New Orleans in the wake of Hurricane Katrina in 2005 was not a natural disaster, but a human-made calamity.

Such is the carefully buttressed contention of “The Big Uneasy,” writer-director Harry Shearer’s documentary investigation into the policies and missteps that led to a critical dismissal of danger and the ultimate failure of the levees — a failure, the film asserts, of faulty engineering and bureaucratic inertia that has ramifications for other American cities.

Shearer’s principal culprit: the oft-maligned (and under-staffed) U.S. Army Corps of Engineers.

Moving from the satirical TV programs and mockumentaries (“The Simpsons,” “This Is Spinal Tap”) for which the one-time “Saturday Night Live” writer-actor is best known, to complex, serious filmmaking is a challenge Shearer embraces. He knows that simply bludgeoning viewers with a mere ideological rant serves little purpose. The goal was to be as fair as possible, not to limn his reportage with notions of bad people vs. good people.

“To do that would be unfair to the subject matter, and to ignore the fact that two different (presidential) administrations from two political parties have not responded to the disaster in any meaningful way,” says the part-time New Orleans resident, who will accompany his film to Charleston on Friday for a 7:30 p.m. screening at the Terrace Theatre. A question-and-answer session follows.

“I come from a world of comedy and satire and of making fun of documentaries, and now I’m asking you to take me seriously, so I have to be as responsible as humanly possible and not just drag people’s names through the muck. I live here too. It was essential to the film that the Corps of Engineers also have their say.”

Even, as Shearer documents, when the Corps’ independent, post-Katrina investigators were saddled with a policy of refusing to look at the past.

“How do you conduct a serious investigation without looking into the past or without affixing responsibility?” asks Shearer.

The director also examines how the findings — and warnings — of respected scientists such as those of state-appointed Team Louisiana were ignored, and how in some cases these individuals were censured or lost their jobs. Even those on the inside, such as a Corps engineer dispatched to New Orleans pre-Katrina to assay the integrity and efficiency of the pumps, were subject to reprisal for their candor.

“To a certain extent we are calling for the attention of people in local communities around the country who have their own battles with the Corps of Engineers, but that is not the main goal of the project,” says Shearer, who also pokes fun at a number of persistent myths about the city’s current condition. “The main goal is to counter the tsunami of misinformation on the part of the news media about what happened in New Orleans in 2005, so people can get an idea of what a strange and unaccountable organization the Corps is, and why calls for reform always have been rejected by Congress.”

The errors in engineering design (“You can’t out-engineer Mother Nature”) and judgment that “The Big Uneasy” alleges were the main causes of such widespread damage easily could happen elsewhere where cities are vulnerable, Shearer says. The film insists that many of the same flawed designs remain in use, not least in rebuilding the system expected to protect the “new” New Orleans from future hazard.

In some instances, millions are being given the Corps to reverse ill-advised projects it was charged with creating in the first place, such as the ecologically unsound Mississippi River Gulf Outlet, essentially a gigantic, little-used trench that critics claim is accelerating the loss of wetlands that long absorbed the brunt of storms.

But the long-term answer, “The Big Uneasy” suggests, is a biological one, not a matter of engineering.

“It is really important for people to understand that this is not just a New Orleans story,” says Shearer. “They need to know there has been laziness and incompetence and bureaucratic lassitude in compiling the kind of record that at least one federal judge has called ‘criminal negligence.’

“There are good engineers in the Corps. But it’s about how you offer incentives for success or incentives for failure. When you don’t end incentives for failure, you get more failure. Ant not one person in the Corps has received so much as a slap on the wrist for the failures surrounding Katrina.”