Green Infrastructure & Sustainable Stormwater Management
Ellerbe Creek Green Infrastructure Partnership
A New Approach to Restoring Durham’s Streams and Rivers

The most densely developed areas of the City and County were built along and on top of the headwaters of Ellerbe creek. The creek receives almost half of all the stormwater runoff from the city creating a huge problem for Ellerbe creek. The 2010 Durham State of Our Streams Report lists numerous pollutants in the creek that are directly related to excess stormwater runoff. Ellerbe Creek has been on the list of North Carolina’s most polluted water bodies since 1998 and stormwater pollution makes the creek nearly uninhabitable for aquatic life and at times dangerous for people.

Impact of Polluted Stormwater Runoff
Stormwater runoff is a major source of pollution for Durham’s streams. When rain falls on hard surfaces such as roofs, streets, turf yards, and parking lots, the water cannot soak into the ground and it ‘runs off’. It washes trash, fertilizer, bacteria, heavy metals, and other pollutants sitting on those surfaces into the creek polluting the clean water. Stormwater also moves faster across these surfaces dumping more water in the creek in a shorter span of time which increases floods and destroys wildlife habitat.

Ellerbe Creek is the dirtiest stream in the Falls Lake Reservoir Watershed. High levels of nitrogen and phosphorous contribute to the current pollution problem in Falls Lake causing algae blooms and elevated bacteria levels leading to human health hazards, fish kills, drinking water contamination, and closed recreational beaches in the lake. Clean-up goals for the reservoir are in place and call for a 40% reduction in nitrogen and a 77% reduction in phosphorus. To restore clean water to the creek, the City of Durham will need to spend hundreds of millions of dollars using traditional stormwater management practices. A new innovative approach was developed to address these problems relying on integrating green infrastructure (e.g. rain gardens, green roofs, permeable pavement) into the city’s urban landscape to absorb and filter polluted stormwater and slowly release the cleaned, cooled water into the creek to restore its health and make it a more valuable resource for the community.

Stormwater Management: Traditional Infrastructure vs. Green Infrastructure

A city’s urban landscape has not been designed or built to manage stormwater to protect and restore water quality. Traditional stormwater management consists of a network of pipes that collect stormwater, removing it as quickly as possible from the landscape and pipe it directly into nearby creeks and rivers. In contrast, Green Infrastructure mimics the natural landscape; water is cleaned through a network of stormwater management practices that capture and filter rain where it falls. Green Infrastructure reduces stormwater runoff and improves the health of surrounding waterways.

Project Goal

Demonstrate a new approach to stormwater management by integrating green infrastructure into the urban landscape to begin the restoration of the hydrologic balance in Ellerbe Creek. These changes can make the creek an important asset for the community and add value throughout the city. An additional goal was to show that these techniques can help the city comply with regulation to clean up Falls Lake Reservoir.

Research Method

The Ellerbe Creek Green Infrastructure Partnership with the support of an EPA Urban Waters Grant studied pollutant reductions and stormwater volume reductions that could be made in the Ellerbe Creek Watershed through the implementation of dispersed Green Infrastructure practices. A 467 acre drainage area within the watershed was selected to intensively study because it contains a good mix of both residential and commercial land uses, has a high percentage of impervious area, has significant traditional stormwater infrastructure and is the headwaters of the creek. These factors combine to create an unusually high volume of polluted stormwater runoff and ability to measure impact.

A detailed analysis of the green infrastructure opportunities included a Geographic Information Systems (GIS) analysis, field verification and additional analysis, and detailed modeling using the current regulatory tool (Jordan and Falls Lake Stormwater Nutrient Load Assessment Tool) to estimate the pollution controls.

Results

Read the Green Infrastructure Partnership Full Technical Report.

The research and analysis clearly shows that the implementation of many dispersed green infrastructure practices would result in significant pollution reductions.

Predicted Pollution Removal:

  • 38% reduction of nitrogen pollution
  • 43% reduction of phosphorous
  • 57.3 million gallons of polluted storm water will be captured and cleaned per year

 

Green Infrastructure to be built:

1 inch of rain falling on a square foot of surface area yields approximately 0.6 gallons of water. So in a 1 inch storm, a 1,500 Sq Ft roof produces ~900 gallons of stormwater!

  • Green Street: 2.08 million sq ft treated
  • Cisterns: 246
  • Bioretention: 279
  • Green roofs: 40
  • Permeable Pavers: 3.7 acres
  • Wetlands: 2

 

Next Steps

The Ellerbe Creek Green Infrastructure Partnership has developed this vision for new method of stormwater management.

  1. Public participation in advancing this vision and implementing various aspects of the project
  2. City and County policy adoption to evaluate public works projects and integrate stormwater management for water quality where appropriate
  3. Funding for the implementation of green infrastructure practices identified
  4. Additional study to increase the scope of the benefits

 

And most importantly, long-term positive improvements to our local streams and lakes.