One is wary to give much credit to the cable news channels, which have shunned much of the business of reporting in favor of regurgitating political talking points and tawdry tabloid headlines. But during the aftermath of Hurricane Katrina in 2005, cable news came to the rescue as never before.

In the hours and days after the storm submerged New Orleans, the networks set about interviewing the director of the Federal Emergency Management Agency, Michael Brown, and began to recognize the glaring disconnect between the reality of the situation on the ground and the way Mr. Brown was talking. As he tried to assure the nation that the situation was under control, news helicopters were capturing images of men, women, and children stranded on the roofs of their houses, waiting outside the ravaged Superdome, and pleading for food and water that had yet to arrive.

For better or worse, the evident disparity between bureaucracy and reality made the Katrina blunder riveting television. Thanks to CNN, Fox News, MSNBC, and others, viewers could literally count the hours as they ticked by without the delivery of water, food, or rescue. Carl Deal and Tia Lessin’s vital and visceral documentary “Trouble the Water,” which opens Friday at IFC Center, allows us to experience this disconnect not in hours but in minutes and seconds. We are dropped into the middle of the chaos — that of the storm and of the bureaucratic bungling that followed.

Unlike Spike Lee’s “When the Levees Broke,” which attempted to reconstruct the events and deconstruct their larger meaning, “Trouble the Water” is less a postmortem than a potent dose of here-and-now. It is a first-person, real-time documentary, built not from archival news footage (though some does appear) but from amateur digital video captured on the streets of New Orleans by the subject of the film, Kim Rivers Roberts. One is hardly surprised to read reports of spontaneous emotional outbursts from the first audiences to see the film at the Sundance Film Festival.

Initially hoping to tell the story of National Guardsmen returning to the ruin that has become their hometown, Mr. Deal and Ms. Lessin were denied access and instead focused their film on Ms. Roberts and her husband, Scott Roberts, almost by accident. A former resident of New Orleans, Ms. Roberts had begun filming Katrina even before the first drops of rain. We are transported to the Ninth Ward prior to the storm’s landfall through her handheld video camera. As she walks the neighborhood, she awakens a drunken man passed out on a front stoop and tells him to get inside before the storm arrives. He will later be found dead in his house.

As the storm kicks up, Ms. Roberts delivers an eerie, prescient, and poetic monologue. With the camera in one hand, she explains that she wanted to flee New Orleans for safety but did not have money to afford “the luxury.” Around this time, Mr. Deal and Ms. Lessin cut to footage of a news conference held by Mayor Ray Nagin, who urges people to leave the city. A second later, a title card exposes the first major chasm between officials and citizens: The city had not organized free transit out of the city. As the mayor speaks, Ms. Roberts’s footage shows a startling lack of emergency vehicles coming through her neighborhood to assist the neediest citizens.

From her living room, then attic, then neighbor’s house, Ms. Roberts records the rising floodwaters. With no police officers or firemen within sight, ordinary citizens start trying to rescue stranded residents. Underscoring the lack of official assistance, Mr. Deal and Ms. Lessin incorporate audio from recorded 911 calls — haunting recordings of elderly women pleading for help and 911 operators informing them that police will not be dispatched until the weather calms.

After the storm, disorientation reigns. One of Ms. Roberts’s neighbors recalls being told by officials to seek refuge at the nearby naval base. But when he and a group of fellow citizens arrived, not only were they denied entry, they claim they were threatened at gunpoint by Navy servicemen. Later, Ms. Roberts tries unsuccessfully to flag down military Humvees for assistance in removing from houses corpses that have gone ignored for days. Then weeks later, she’s told by FEMA that she should have received emergency financial aid, but the agency doesn’t know where the check went.

It cannot be understated how devastating this footage is. We can see here the ways in which a society can break down when its leadership fails. As Ms. Roberts walks out of the FEMA center penniless, her determination is moving. She is a fiery, ferocious individual, and no matter how many times she is brushed aside by troops or dismissed by government officials, she keeps pushing. In one unforgettable scene, she pops a CD into a boom box and plays a rap tune she wrote, singing along with lyrics that point to a life of fear, pain, and anger.

She doesn’t miss a beat as she gestures and rhymes, her lyrics forming a coda not of self-pity but of self-reliance. She’s had a rough life but she’s not giving up, and while Katrina has kicked her to the gutter, she’s turned to her video camera (just as she once turned to music) as a tool of self-preservation. As the weeks drag on, we realize her video footage hasn’t helped her. But that is what makes it all the more powerful: This wasn’t a filmmaker heading down South, but a Southerner outraged by the incompetence to which she and her loved ones fell victim. She’s talking emotions, not policy, and Ms. Roberts is one infuriated American. So are we.

ssnyder@nysun.com