When imagining how to fix the nation's public housing problems, the head of the U.S. Housing and Urban Development Department said Tuesday he needs to look no further than public-private developments that have sprouted up in post-Hurricane Katrina New Orleans.

At the same time, Ben Carson readily admitted that "lessons have been learned" about the private companies that funded such New Orleans developments not setting aside enough affordable units for the city's low-income residents most in need of shelter.

Standing in Columbia Parc, a mixed-income housing development built through a public-private partnership to replace the former St. Bernard public housing complex, Carson praised the 12-acre site that boasts 685 units, a new $9 million early education facility, a fitness center, an outdoor pool and a 46-seat movie theater.

"One of the reasons I wanted to come to New Orleans is just that I’ve heard about this development, which is a perfect example of public-private partnerships and what can be done," Carson told reporters.

"It's not just putting people under a roof but looking at ways to develop healthy communities that are walkable, that are looking out for education, for health care, that ensure that they’re not food deserts. ... I believe this is a very excellent example of how it can be done."

Carson also praised the developers behind Bienville Basin, the mixed-income, mixed-use community that has redeveloped buildings in the former Iberville housing development.

The benefits of the public-private partnership in that instance were echoed by Joshua Collen, senior vice president of development services for developer HRI Properties, which designed Bienville Basin.

Collen cited the company's use of historic tax credits to renovate the structures. The credits were secured in part by preserving the structures' historic wrought iron detailing and clay tile roofs.

"We can leverage a lot of capital that public entities can’t," Collen said. "So if people are developing market-rate apartments and hotels around the country and those same people can do a mixed-income development of affordable housing, you're really getting your best in class."

Public-private housing developments became prominent after a 1992 law designed to tear down traditional public housing across the country and replace the units with mixed-income developments.

The amount of traditional public housing, heavily subsidized and operated by the government, reached its peak in the early 1990s, when there were 1.4 million such units.

About 20 percent of those units have since been demolished, according to public housing policy researcher Edward Goetz, as the federal government continues to share the reins with private developers.

Proponents of private-public partnerships say they help produce safer communities with less crime and better opportunities for low-income residents. Critics say the developments decrease investment in housing for the nation's poorest.

Recent statistics show the federal government provides subsidized housing or alternative programs, like housing vouchers, to only 1 in 4 in-need households throughout the nation.

The Housing Authority of New Orleans's first experience with the public-private partnership model came when HRI converted the St. Thomas housing development into the River Garden neighborhood in 2004, anchored by the city’s first Wal-Mart.

HANO then began regularly leasing its complexes to private developers under a plan that was speeded up following Katrina, when many hundreds of units were flooded and otherwise damaged. 

After Katrina, HANO demolished its Big Four projects — C.J. Peete, St. Bernard, Lafitte and B.W. Cooper, which accounted for about 60 percent of public housing in the city — in order to make way for new housing models. In some cases, by 2015, fewer than half the new units had rents comparable to those in public housing. Some were market-rate, and others were in-between.

As subsidized units declined, the number of housing vouchers for privately owned apartments rose — as did the waiting list for people waiting to get them. 

There are 24,207 families on the local waiting list to receive vouchers, according to Andreanecia Morris, executive director of HousingNOLA. She said the problem could get worse under the budget proposed by President Donald Trump. 

HANO, she said, would be severely impacted by a proposed 68 percent cut in public housing repair funds, a $300 million cut to the Housing Choice Voucher program and elimination of Community Development Block Grant funding.

Carson said that "lessons have been learned" about some of the developments built after Katrina, in that "early on, some of the contracts did not involve setting aside enough units as affordable units."

He also said that while "there's a lot of anxieties about budgets," he is working to make HUD "extremely efficient" with the funds now in place and to run things on "business principles" rather than "bureaucratic principles."

One way to do that, he said, is to continue to develop smart public-private partnerships when designing new housing models meant to incorporate low-income tenants.

Regardless, he said, the ultimate idea is to "move people" through subsidized housing, using it as an "assistance" rather than a "permanent residence."

"If we do that, over the course of time we need less rather than more," Carson said.

Follow Della Hasselle on Twitter, @dellahasselle.