Rain Catchers Program Reduces Stormwater Impact

Durham stormwater utility enlists the general public in an award-winning campaign to tackle small projects on private property.
Rain Catchers Program Reduces Stormwater Impact
Laura Webb Smith, public education coordinator with the Stormwater and GIS Services Division of the Durham Public Works Department, checks the water clarity of South Ellerbe Creek in Durham, North Carolina. (Photography by Al Drago)

Durham, North Carolina, has no small challenge when it comes to managing the community’s stormwater.

The city has to do more than just make sure the rain gets out of the way. It’s also charged with keeping the runoff from polluting local drinking water supplies — the same bodies of water to which the stormwater returns.

Durham has taken a two-part approach to its stormwater battles. One part consists of an array of big projects and some experimental strategies that the city and its stormwater utility are using to help ease the flow of runoff. The other part consists of enlisting community residents to take on small projects in their own backyards — or front or side yards for that matter.

By encouraging, educating and supporting property owners in the simple, home-based projects, Durham’s stormwater utility can more effectively focus on its own bigger projects, says Laura Webb Smith, public education coordinator for Stormwater and GIS Services in Durham’s Public Works Department.

Regulators have taken notice. In June 2015, the U.S. Environmental Protection Agency’s Region 4, which includes the Tarheel State, gave Durham its regional 2015 EPA Rain Catcher Award in the municipal category. The award honors excellence in the implementation of stormwater green infrastructure practices.

‘Most regulated city’

Durham, with a population of about 250,000 people, has operated its own stormwater utility since the early 1990s, although its stormwater management infrastructure is a lot older than that.

Including both privately and publicly managed parts, the stormwater collection system consists of 923 miles of pipe. About half of that, 48 percent, is the responsibility of private property owners. Another 17 percent is associated with state roads in the city and is maintained by the North Carolina Department of Transportation.

But 35 percent of the total — about 323 miles — is within the city’s right-of-way or on city property and falls directly under the city’s control. A city stormwater maintenance group takes care of the upkeep, while a capital improvements group is in charge of larger new design and construction projects.

Durham’s average yearly rainfall, about 44 inches, is below the national average, but stormwater is still a major problem for the city.

The city’s location is one major reason for the concern. “We are the most regulated community when it comes to stormwater in the State of North Carolina, and that’s just because of where we sit geographically,” Webb Smith says.

Essentially, Durham is atop a ridge between two major bodies of water that supply drinking water not just to the city, but to surrounding communities as well. Southwest of the city, the water flows to Jordan Lake, which feeds the Cape Fear River and into the Atlantic Ocean. Water from the northeastern part of the city goes first to Falls Lake, which feeds the Neuse River, the Albemarle-Pamlico Sound, and the ocean.

From stormwater to drinking water

“We’re in these two major watersheds that happen to be the drinking water for one of the largest metro areas of the state,” Webb Smith says, with Jordan Lake supplying Durham’s drinking water while the other bodies supply other communities.

Under the federal Clean Water Act, Durham has been classified as a phase one city for implementing the National Pollution Discharge Elimination System requirements to clean up stormwater pollution.

State regulations for runoff have gotten tighter in the last half-dozen years, although Durham and other cities affected have known they were coming. That’s intensified the urgency of the task, and the city has been trying to tackle the problem using any approach it can.

Some big projects — including some that experiment with new technology and bring market forces to bear on the problem, are part of its arsenal, but so too is the work Durham has done to encourage individual property owners to install small stormwater abatement projects.

Public pilot

That ongoing program began with a pilot project — also called Rain Catchers — that ran from 2012-14. A total of 880 households in the South Ellerbe Creek watershed were contacted, and 156 properties were selected for rain gardens, rain barrels or cisterns, and planting trees chosen for their particular stormwater abatement suitability.

Downspouts were also disconnected so that water would be dispersed rather than flowing straight into the stormwater collection system.

“Basically what I tell people is, what you want to do with the stormwater in your yard is slow it down, spread it out, and soak it in,” Webb Smith says.

Those projects were completed last year. Now the utility is studying the results and assessing both the quantity and quality of the stormwater coming from the properties that took part. “We want to see a reduced level of water going to the creek during and immediately after the storm,” says Webb Smith, while the expectation is that slowing down the water will also cleanse it of pollutants, improving its quality.

The utility assembled a year’s worth of stormwater data before implementing the Rain Catchers program. As the study measures outcomes on the Rain Catchers properties, it will also compare those with a separate nearby watershed that did not use the 250 different abatement practices that were part of the Rain Catchers project.

Meanwhile, the utility continues to work with property owners to encourage more of the same improvements, even though the Rain Catchers pilot project is now finished.
Effectiveness with simplicity

A backyard rain garden doesn’t have to be elaborate or complex to be effective. “It can be as simple as digging a hole and putting in some plants,” says Sandi Wilbur, Durham’s engineer for special projects watershed planning and implementation.

The garden is sized to capture the runoff from the area that drains to it in a typical rainfall. Soils in the region are rich in clay — “not the best for soaking in water,” Wilbur says — and must be replaced with much sandier materials mixed with loam through which the runoff can drain. “You’re letting the water go through that before it returns to the native soils.”

In addition to the rain garden projects, property owners are also encouraged to install larger rain barrels — 200-gallon capacity units nearly four times the size of the standard 60-gallon barrels. The smaller size “just fills up too quickly,” says Webb Smith, despite the below-average annual rainfall.

“This is a stormwater management project, not a water conservation project,” says Webb Smith. “This is not about just saving water and reusing it.” With the jumbo-size rain barrels, about one-third of the water collected is slowly drained out after each rain; property owners use what’s left to water their plants, and the rest is typically released between storms.

Alongside those low-tech and small-footprint individual projects, Durham continues to work on other much larger projects to combat runoff.

Community collaboration

For some of those efforts, the utility works with local watershed groups and soil and water conservation districts.

Big or small, a primary goal of the work is to reduce nitrogen and phosphorus levels in the bodies of water to which the city’s stormwater ultimately returns. Its ridgetop location makes Durham’s runoff the assumed source of nutrient pollution in Jordan and Falls lakes, Wilbur notes, so it’s up to Durham to reduce those levels and keep them in check.

Estuaries that are part of the network of water bodies through which the stormwater returns “are especially challenging,” says Webb Smith. “They hold the pollution in. Ever since the 1990s we’ve been under a nutrient rule for the Neuse River estuary.”

Both new and existing development must comply with standards to reduce nutrients carried by stormwater. “You have to reduce nitrogen and phosphorus from wherever you can get it,” Wilbur observes.

In compliance with a statewide nutrient strategy, Durham enacted a law setting limits on how much nitrogen and phosphorus new development sites could emit. Levels are calculated by measuring effluent concentration as well as volume reduction by measures installed to control stormwater, such as wet ponds and bioretention facilities.

“Stormwater control measures must be built to standards found in the North Carolina BMP Manual,” Wilbur points out. In addition, the city requires annual checks that stormwater control measures are working properly.

“For existing development, there are several stages of reductions required,” she continues. “The first stage requires the city to reduce nitrogen and phosphorus that was added from development that has occurred since 2006. The city must then reduce the pounds per year of nitrogen and phosphorus through nutrient-reducing measures.” The state requires monitoring Falls Lake itself to see if the target levels have been met.

If levels exceed the maximum standard, then additional steps are required.

“The city is working collaboratively with a group of governments and others who are also affected by the rules to provide additional data, tools and information to help inform the adaptive rules for later stages,” Wilbur says. “The city has been monitoring local streams for over 15 years and is working on a project to monitor effluent concentrations of industrial stormwater control measures in addition to our regular monitoring and the monitoring being done for the Rain Catchers project.”

The city tracks additional sources of pollution in streams besides nutrients, and has a program to identify illicit connections to the stormwater system, such as bathroom plumbing being piped directly to a stream, with the power to enforce compliance with the regulations when such violations crop up.

Beyond rule enforcement

Just enforcing the rules for developers is far from enough, though, so Durham is marshaling other tactics.

“We’re looking for cost-effective measures to reduce nitrogen and phosphorus,” says Wilbur. “In addition to some of these small-scale projects, we have some larger regional projects.”

Green area restoration is one big priority, turning once-developed but now unused land back into green space that can absorb runoff more easily. Of various such projects underway, the fastest moving are those on city-owned land, where the hurdles tend to be lower, she notes.

One of the biggest such projects involves private property, which the utility is negotiating to acquire to convert to a wetland. Once that is complete, the land would collect and help filter runoff from a large part of downtown Durham.

Another tactic is technological innovation. Durham is exploring the use of an algal turf scrubber for lakes that are already high in nutrients and therefore becoming populated with algae as a consequence. Algal turf scrubbing entails drawing water from the lake, passing it through a flow way where the water leaves algae behind in the form of a matted mass that’s something like dryer lint in its texture and consistency.

“We’re trying a lot of different types of things,” Wilbur says. “At this point we’re trying to figure out what are the best methods.”

Watershed wisdom

Along the way, utility personnel are studying much more closely the many watersheds that drain into each other and ultimately into the lakes. “We’re actively trying to find locations to implement these practices,” Wilbur says. “We do some water-quality modeling and try different kinds of scenarios to determine what might be causing the pollution.”

There are 10 major and several smaller watersheds in the community. So far, Durham has examined five watersheds and is working its way through more. With each one it assesses the ease or difficulty of completing the project against the likely degree of benefit.

For the Falls Lake watershed, the city must reduce nutrient levels in the water to what they were in 2006. (The Jordan watershed requires reductions to 2001 levels.)

Considering how much new development there has been since then, that raises the bar considerably, Wilbur and Webb Smith point out.

Stream regeneration

Still another approach has been regenerative stream conveyance, a technique that Durham has been exploring in collaboration with North Carolina State University.

A drainage channel near the city’s public works operations center is a test site for that sort of work. Water flows have eroded the stream bed and damaged vegetation in the area, leaving steep banks and reducing the ability of the area to absorb nutrients, which instead get sent downstream where they aren’t wanted.

To slow down the stormwater and protect the stream banks, the utility is putting rocks in the stream bed, planting native vegetation, and scattering small pools filled with mulch and sand in the area to further soak up water in hopes of reducing both nutrient pollution and erosion. If the results are satisfactory, the technique will be employed elsewhere in the area.

Even as Durham makes progress on its stormwater control, the bar is being raised ever higher.

“The field of stormwater treatment is young and evolving,” Webb Smith says. “Stormwater is considered a nonpoint source, so as we evolve, more sources are being identified and innovative tools are being used to help pinpoint and reduce pollution in stormwater.”

Nutrient banks

In one of the more unusual ways of reducing nitrogen and phosphorus pollution that can cause overgrowths of algae in area lakes, the Durham (North Carolina) Stormwater Utility is looking at employing market forces and something called “nutrient banks.”

So-called “nutrient bankers” are typically contractors or others involved in projects that have an impact on waterways and wetlands. They develop projects to mitigate nitrogen and phosphorus runoff from the site — for instance, planting trees and other vegetation in order to create a buffer to runoff in the area of a stream.

Qualified projects that reduce the flow of nitrogen and phosphorus back to the original water sources generate credits for nutrient reduction, explains Sandi Wilbur, Durham’s engineer for special projects watershed planning and implementation. The “nutrient banker” can then sell those credits to other parties — such as the stormwater utility — which can use them to offset their total production of nitrogen and phosphorus in their runoff.

In the 1980s and ’90s, a similar approach was successful in reducing pollution that caused acid rain in the southeastern U.S. and in Europe, notes Laura Webb Smith, public education coordinator for Stormwater and GIS Services in Durham’s Public Works Department.

Durham has a request-for-bid out to seek nutrient bankers who will build such projects in the city that would generate nutrient credits that Durham could then purchase to offset its own nutrient output.


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