How the recent heavy rains led to Carrboro's stormwater management plan

In light of North Carolina’s recent heavy rainstorms, the Carrboro Board of Aldermen has requested to adjust the town's post-development design storm specifications.

At its meeting on April 16, the board discussed an ordinance that would update the town’s stormwater volume control provisions. The purpose of the ordinance is to counteract the increasing volume of runoff associated with new developments.

“We're not sure that the current standard is meeting the needs that are being surfaced because of climate change,” said board member Bethany Chaney.

More recently, Orange County and the state have been experiencing large storm events that cause flooding.

However, storms are not the only contributor to increased flooding in North Carolina. 

Michael Piehler, director of the UNC Institute for the Environment, said development has been shown to have an effect on increasing water runoff.

“That runoff is the primary source of stormwater,” said Piehler. “That water itself would not be as problematic if it didn’t have pollutants carried with it.”

Piehler said stormwater can carry a number of pollutants including hydrocarbons, like gasoline, but also nitrogen and phosphorus. These pollutants can ultimately affect water quality for both humans and aquatic life.

“The more concentrated our development is and the more people are packed in, the more sources you potentially have,” said Piehler. 

However, Chaney said some developers have agreed to higher standards than those in the current ordinance.

“We think that we have opportunity to require stronger standards,” said Chaney. “We want to make sure that we do that but in a way that makes sense, even the cost and the benefit to developers, to property owners and to us as a town.”

The ordinance calls on developments to install stormwater management systems. According to the ordinance, the stormwater runoff volume should not exceed the predevelopment volume by more than the set limits. This would essentially increase the responsibility of new developments to reduce potential negative impacts from stormwater.

Board member Randee Haven-O'Donnell said the board needs to think more long term.

“I think we need to look at the extremes because that's what we have. We are in uncharted territory, and we need to respond as if we understand that it’s uncharted,” said Haven-O’Donnell. “... I think the greater question now is not 25-year events, maybe not even 50-year events, but 101,000-year events. That’s what we’re seeing in terms of where floods are happening in the Midwest, where they’ve never happened before.”

Chaney agreed that extending the ordinance does not address the issue at hand.

“I think that there’s not only issues of the storm events, but the fact that our own infrastructure doesn’t even meet the current standards,” said Chaney. “Older subdivisions for example, the pipes are smaller in certain subdivisions than those that have larger pipes because they were built... after the last ordinance had been updated.”

Chaney said the board has seen fewer problems in subdivisions that are meeting the newest standards than in subdivisions with older infrastructure.

The Board of Aldermen will be holding a public hearing for the ordinance on May 28.

“Having a public hearing to talk about the ordinance and what we can achieve is part of what we need to do to keep everything transparent, to keep our work and goals, not only informed by the public, but informing the public each step of the way,” said Haven-O’Donnell.

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