DURHAM - I’m watching a good downpour through the office window right now. It’s been dry, so I’m sure the plants in my garden needed the water. But let’s face it, unless rain cancels our outdoor plans or is unusual severe, we don’t think much about it.
The rain landing on the grass seems to disappear, absorbed quickly into the soil. But the rain that lands on the sidewalk seems to meander, lost about which way to go. There’s a small stream forming in the parking lot. It’s all flowing into a storm drain at the lower end of the sea of blacktop. However Maverick Raber, a water quality specialist with the City of Durham, believes that is a potential problem.
“In an urban setting we have a lot of impervious surfaces, like parking lots, and that surface acts as a pathway for pollutants to get into our waterways,” said Raber.
Rain that takes a short cut through a storm drain goes straight into the nearest body of water. It picks up chemicals from the road and fertilizers and animal waste from yards. The water also doesn’t get filtered by the ground or treated in a water treatment plant.
So the City of Durham is launching a five-year program to test possible solutions to the pollution problem caused by stormwater runoff. The test is being conducted along the South Tributary of Ellerbe Creek.
The storm water that flows into this tributary goes right into Ellerbe Creek, then into Falls Lake, which supplies drinking water for Raleigh. Falls Lake eventually drains into the Neuse River, then into the estuary of the Albemarle-Pamlico Sound, and then out the inlet into the ocean.
A watershed is all of the land that drains into Ellerbe Creek. Ellerbe Creek’s watershed has the highest population density in Durham, because it runs through the city, close to downtown.
“What’s in here now is not what we would consider pristine water, “ admits Raber. “But we’re trying to figure out what is in this water and where it is coming from. Part of this project is how can we reduce the impact of being in an urban setting.”
The project requires setting up five water sampling/monitoring sites at key points along Ellerbe Creek, including the South Ellerbe Tributary. Sensors in a drainage pipe detect when water levels are rising, which signals the start of a storm. The machine, which looks like a computerized shop-vac, begins to automatically take water samples.
“We collect six liters at the rising end of the storm, at the peak and at the end, so we are trying to characterize the water quality throughout the hydrograph,” Raber explains.
But it’s what the city is installing around south Ellerbe Creek that is so important.
Participating in the project to reduce runoff into the creek are 109 local residents. So the city is installing rain gardens in the front and back yards of some houses. Rain gardens are shallow depressions, lined with 3-4” of mulch, and planted with native, deep-rooted plants, that capture and absorb runoff. Typically, one or two downspouts are directed into a raingarden.
Other houses are having cisterns attached to downspouts. The gardens and cisterns are being installed for free. The locations were chosen for having the greatest potential to reduce runoff.
The program wants to test the theory city that clustering significant numbers of raincatchers, such as rain gardens and cisterns, around a body of water such as the South Ellerbe Creek Tributary, can have a significant effect on what goes into a stream. That’s because water quality improves when water slows down, spreads out and soaks into the ground. The program also wants to see if raincatchers can not only have a positive effect on what goes into the creek but also how fast it goes in. Communities around the state, which are required by state law to reduce the pollution going into rivers and streams, are watching this program to see the results.
Two rain gardens are being installed in a main drainage point along Onslow Street. It’s a few blocks from Duke’s East Campus. One of the gardens will be in Paul Sapp’s backyard. Sapp says there is almost always standing water on the sidewalk and street in front of his house. Standing water that eventually flows into the creek across the street. Sapp is anxious to see what effects the rain gardens will have.
“My father grew up on a farm, and he knows the importance of the water running into the land and not right into the creek or the sewers, and then the ocean and carrying all the nutrients and pollutants,” Sapp explains. “It’s better to let it settle into the land and let it do what it is supposed to do.”
Laura Webb Smith, the Public Education Coordinator with the City of Durham’s Department of Public Works, calls rain gardens like those that will be installed on Onslow Street the best way to reduce the storm surge that is rushing into creeks.
“You would think that simply running a downspout into a yard would be enough to slow down the runoff into a creek, but it doesn’t slow it down very much,” said Smith. “That’s because grass roots are only a couple of inches deep and our soil is pretty clay rich and tightly compacted. So a lot of the water still flows off into the drainage system if it’s just going over the lawn. With a rain garden you’re able to capture the water and let it soak in. You’ve got native plants with deeper roots that create places for the water to go, and you’ve built it with a depression to let the water sit and soak in.”
To be clear, rain gardens only hold water for a day or two. If there is standing water in the garden for a longer period of time, there could be a mosquito problem.
Smith believes the answer to whether raincatchers are effective and cost effective ways to reduce pollution and stormwater runoff will be found by comparing the water quality readings from the monitoring stations along the South Ellerbe Creek Tributary, with stations along the creek itself. If the tributary water quality readings improve over time, it is likely the raincatchers worked.
“Cleaning up the water in streams is key to ensuring enough clean drinking water, recreation opportunity and livable habitat for fish and wildlife and I believe this is a cost effective and environmentally friendly way to do that,” said Smith.
- Reporter's Blog: How To Build a Rain Garden
- What's My Story: Water Quality Engineer
- Infographic: How The Rain Flows
- Photo Gallery: Rating the Rain Catching
- Teacher Resources
- Article: Ellerbe Creek Project
- Interactive: Catching The Rain