New Orleans is a city often inundated by water and, just as often, a city frustrated in its attempts to deal with it.

Now, joining a movement that supporters say will help mitigate flooding and soil subsidence, the City Council has decided that all new commercial parking surfaces in New Orleans must be porous.

BY DAN SWENSON | Graphics Editor ▲

The rules unanimously approved by the council last week require businesses to use pervious paving — which lets rainwater flow through it, to be absorbed by the soil beneath it — for any new projects. The rules do not require businesses to replace existing concrete lots and do not affect residential construction.

Parking spaces must be porous under the new rules, but “driving lanes” in parking lots do not need to be. That's because heavily traveled parts of parking lots tend to need the heavy-duty support that impervious materials provide.

Porous parking surfaces obviously won't solve the problem of street flooding in New Orleans or clear the canals and pipelines that drain the city. But they will lighten the burden placed on the city’s drainage system during heavy rainfalls and curb stormwater runoff to Lake Pontchartrain, council members said.

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“Simply put … water cannot simply be absorbed through traditional pavement and concrete,” said Councilman Jason Williams, who co-sponsored the ordinance. “Permeable solutions ... allow water to be absorbed into the ground, reduce runoff volumes, mitigate flooding and reduce subsidence.”

Those solutions include pervious concrete or asphalt, connected plastic paving that can be filled with rock or gravel, or other methods.

Costs for porous surfaces can vary, ranging from 5 to 10% less than for traditional concrete to 10 to 20% more expensive, according to estimates from city stormwater managers.

A representative from a company that installs one type of connected plastic paving, TrueGrid, said its system costs about $7-$9 per square foot. That's compared to about $10-$12 per square foot for traditional concrete.

The ordinance comes more than a year after amendments to the city's code that required certain developments to keep the first 1.25 inches of rainfall out of the city’s drainage system during storms.

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It also comes six years after experts encouraged the city to build rain gardens and other water-holding mechanisms as part of a broader sustainability strategy, dubbed the Greater New Orleans Urban Water Plan.

Since the plan's release, New Orleans has launched more than $120 million in "green" infrastructure projects, including porous paving, that officials say will add millions of gallons of stormwater storage capacity.

"We cannot pump our way out of this problem, and we need to hold water before it goes into the drainage system," Deputy Chief Administrative Officer for Infrastructure Ramsey Green said at a press conference on the city's efforts last week.

Elsewhere in the U.S., at least six miles of porous pavement has been installed in several Atlanta neighborhoods. Atlanta also requires that new and rehabilitated developments be able to hold the first inch of stormwater runoff with devices such as rain gardens and permeable pavement.

Palo Alto, California, and Gresham, Oregon, offer rebates and credits for residential and commercial permeable pavement installations, but do not mandate them.

Even before the mandate, some New Orleans businesses began to embrace the practice.

Concerned about repeated flooding near his business on Hagan Street in Mid-City, Jay Nix, the owner of Parkway Bakery and Tavern, traveled to Houston to learn more about TrueGrid's interlocking plastic pavers.

He liked what he saw and had the pavers installed in his 100-car parking lot in 2015. Since then, the street outside his business has flooded during deluges, but his customers' cars have stayed dry.

"All that water that falls in my parking lot goes in the ground and actually feeds all my plants and trees," Nix said. The pavers, which are 100% permeable, also allow dirt and oil that are washed off cars during rainfalls to go into the ground, rather than into the drainage system and Lake Pontchartrain, he added.

The New Orleans Bio­Innovation Center on Canal Street, Xavier University’s Convocation Center and Ruby Slipper Cafe on Banks Street also have permeable parking spaces.

There are some drawbacks to certain types of permeable paving. It can clog if not washed regularly, according to a U.S. Geological Survey study.

For that reason, the city outfitted its vacuum trucks recently with power-washing attachments to clean the permeable concrete that has been installed on city projects in the Pontilly and Mid-City neighborhoods, Green said.

Still, council members said the practice has more benefits than negatives.

The city's 100-year-old drainage system was built at a time when there were far more grassy, water-retaining spaces in the city than there are today, said Councilman Jay H. Banks. Pervious paving can help ease the system's burden and combat subsidence that has accelerated in the years since then.

"If that water cannot go underground, it must go into the drainage system, which has a limited capacity," he said. "Using permeable concrete makes sense."