Better Stormwater Management

North Carolina utility takes a multi-pronged approach to maintaining clean creeks, streams and lakes

Better Stormwater Management

A double-barrel box culvert safely guides rainwater runoff under the housing development at the Cedars East Storm Drainage Improvement Project in Charlotte, North Carolina. The project wrapped up in 2021 and has eliminated flooding issues from creek runoff. (Photography by Logan Cyrus)

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Through massive investments in stormwater-control projects in Charlotte, North Carolina, the Charlotte-Mecklenburg Storm Water Services utility is proactively taking steps to mitigate the flooding that used to plague parts of the fast-growing city and the surrounding county.

The utility — actually comprised of two joint organizations, Charlotte Storm Water Services, which serves the city of Charlotte, and the Mecklenburg County Storm Water Services, which serves the county and six surrounding towns — also is charged with protecting the Catawba River from contaminants in stormwater runoff. The 224-mile-long river is a vital artery that serves as the primary drainage center for the region’s watershed and supplies drinking water to more than 2 million people in North and South Carolina.

The joint utility relies on a multipronged approach that includes replacing aging storm-drainage infrastructure with larger-capacity pipes; restoring failing creeks and streams, many that drain into the Catawba River; and building wetlands, detention basins, rain gardens and other stormwater-control measures that retain and then filter rainfall as it’s slowly dispersed into creeks and streams, says Daryl Hammock, CSWS assistant manager.

“Charlotte is a booming city — one of the fastest-growing in the country,” Hammock says. “We have a lot of development going on — homes, businesses, shopping centers and so forth — and all the impervious surfaces that come with those kinds of developments generate a lot of stormwater runoff.”

In fact, as of 2021, there were 2.2 billion square feet of roads, parking lot, rooftops and other impervious surfaces in the city of Charlotte alone. Just an inch of rainfall in the city, which covers about 300 square miles, equates to more than 5 billion gallons of water, according to CMSWS statistics.

“We want to be sure that the runoff is as clean as possible when it reaches local creeks and streams,” Hammock says. “Our mission is to underpin a thriving city with sound infrastructure and clean creeks, streams and lakes.”

Another facet of the ongoing flood-mitigation and water-quality efforts is stronger regulations implemented over the years, including one that require developers to fund and build their own stormwater-control measures on real estate they’re developing.

“Over the years, we got smarter on the land-development side,” Hammock says. “We put in place better regulations that help prevent problems. We’ve progressively gotten more and more protective.

“In the end, it’s a lot cheaper to prevent problems than it is to fix them.”

Open and closed systems

The utility’s stormwater system features 3,800 miles of “closed systems” (underground storm sewers) and 2,400 miles of “open systems” — things like ditches, creeks and streams. The area’s sewers aren’t combined, so there’s no need to treat stormwater at a facility.

“These components all work together, with stormwater going back and forth between open and closed systems,” says Hammock. “This kind of system is very common in the South.”

That system is supplemented by approximately 2,000 stormwater-control measures built by either the utility or by private entities. They collect stormwater from about 11,000 acres of paved surfaces — almost one-fifth of the city’s roughly 61,000 acres of impervious surfaces.

Before the utility was formed in 1993, there was no cohesive stormwater-management strategy in place. The result was frequent flooding of streets, homes and businesses as the city rapidly grew, Hammock says. (On average, Charlotte receives 43 inches of rain annually.)

“People didn’t like that, so the CMSWS was created to address the problems,” he explains.

The utility also was charged with improving the quality of surface water to meet standards the 1972 federal Clean Water Act set.

“Through public and private investments, we’ve mitigated more and more pollution sources,” he points out. “But we still have a long, long way to go.”

CMSWS projects are funded with user fees assessed on every property with impervious surfaces. The more impervious surface there is on a property, the higher the fees.

“A shopping mall might pay thousands of dollars a month while a homeowner might pay $10 a month,” Hammock says. “The fees were controversial back then, but we needed a funding source to mitigate flooding and contain pollution sources from stormwater run-off in order to comply with Clean water Act requirements.”

Award-winning project

The Cedars East Storm Drainage Improvement Project, completed in late 2021, exemplifies the utilities’ efforts to upgrade stormwater-control systems. The project was named the North Carolina Stormwater Project of the Year by the American Public Works Association.

The $8.1 million project, which started in September 2018, is designed to mitigate flooding in a largely residential, flood-prone neighborhood, located just southeast of downtown Charlotte. It should protect residents from living-space flooding in up to a 100-year storm, explains Matt Gustis, engineering and design division manager.

“The infrastructure in the neighborhood was built in the 1950s and was reaching the end of its useful life, so we wanted to get ahead of that,” Gustis says. “We also wanted to ensure there was a sustainable and stable drainage system.”

The system captures water that drains from a 256-acre area and then flows into a creek that eventually leads to the Catawba River. The primary component of the approximately 1-mile-long system is a roughly 1,650-foot-long double box culvert that provides more stormwater capacity; each of the side-by-side culverts is 8 feet wide by 4 feet tall and is buried about 11 feet deep.

The system also includes a 95-foot-long triple box culvert — two of them 8 feet wide by 4 feet tall and one 10 feet wide by 7 feet tall — that passes under a road at the other end of the project. The culvert system is designed to withstand a 50-year rainfall, Gustis notes.

“It was a complicated project because we had to maintain vehicle and pedestrian access to an apartment complex,” he says. “There also were a lot of utility lines that we had to either work around or relocate, plus we had to install a lot of shoring because some of the pipe system was so close to buildings.”

The city experienced some fairly large rainstorms recently, with no flooding reported in the neighborhood, Gustis says.

Improving surface-water quality

Another flood mitigation endeavor, called the Reedy Creek project, illustrates an important aspect of the utility’s water-quality strategy: restoring creeks that have been scoured and no longer sustain aquatic habitat like they should because of silt from erosion. The $8 million project, located northeast of downtown Charlotte, started in February 2014 and was completed in February 2019.

“Reedy Creek was an impaired stream due to siltation — it was no longer a thriving ecosystem,” Gustis explains. “Fixing it required more than 5 miles of stream restoration and nearly 3 miles of stream enhancements.”

The main issue was that the stream bed had sunk lower than the surrounding floodplain. So it had to be raised to reconnect it. That, in turn, allowed the utility to restore about a 4-acre wetlands area — another critical part of retaining rainfall and letting nature filter out contaminants stemming from stormwater runoff.

“We also put easements around the wetlands area to protect it in perpetuity from the impacts of future redevelopment activity,” Gustis adds.

The project now is under a five-year monitoring program that includes checking the new in-stream structures, vegetation health and water quality. After five years, the vegetated stream buffer should be fully established, which will complete the restoration.

One of our biggest problems with water quality is stream-bank erosion,” says Hammock, noting that stream restorations play a big role in improving surface-water quality. “People straighten out creeks, cut down trees and destroy stream buffers and developers sometimes even move creeks.”

When combined with an ever-increasing volume of stormwater runoff over the past decades and the highly erodible clay soil that’s common in North and South Carolina, the end result is more and more erosion of stream banks.

Substantial progress

Hammock notes that much has been accomplished since the joint utility was formed. Since 1998, CSWS has restored nearly 45 miles of streams. Furthermore, as part of a buy-back program to reduce damages from flooding, the county utility demolished 458 buildings in floodplains during that time, which led to 194 acres of reclaimed open space. The county also planted more than 18,000 trees.

In 2022 alone, CSWS spent $89 million in capital improvements (including nine major drainage-improvement projects at a cost of $35 million), reviewed more than 4,300 plans for private development, completed more than 5,000 erosion-control inspections, installed more than 22,200 feet of stormwater pipes; inspected more than 300 culverts and drainage pipes and rehabilitated more than 11,500 feet of pipe, according to a 2022 annual report.

The bottom line: The flood mitigation efforts are working.

“We have a lot less flooding compared to, say, 20 years ago,” Hammock says. “We have a much more thorough knowledge base for our drainage system, our pipe capacities, which ones have been replaced and so forth.

“We also now can track how much of our system we inspect and maintain every year. We have a much better handle on all of our assets than we had years ago.”

Nonetheless, the utility’s work is never done, he says. In fact, according to the utility’s website, there are more than four dozen projects in the works.

“We continue to put a lot of energy into making sure new construction doesn’t cause flooding or surface-water problems,” Hammock says. “Our biggest task is to just keeping up with growth and all the land-use aspects that go along with it.

“But we’re up to the challenge.”


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