Here’s your chance to be a detective: The next time it rains, notice what happens to the rain falling on your roof. It probably flows into a rain gutter and then into a downspout pipe. But, then where does it go? Quite often our downspouts are piped directly into the street or a storm sewer system, transporting all kinds of pollutants into our creeks and rivers.
In Asheville, during a typical year, a 1,000-square-foot roof would shed almost 30,000 gallons of rainwater. Now, imagine the volume of water generated from the roofs of thousands of homes, and we’re dealing with many millions of gallons of runoff, and often pollutants, flowing into our creeks and rivers every year.
Disconnected Impervious Surface, or DIS, is a simple, inexpensive type of stormwater green infrastructure, recognized by the state of North Carolina. DIS involves redirecting roof runoff to a relatively flat, pervious, vegetated area. From there, the water can infiltrate into the ground, support plant life and habitat, remove pollutants, reduce the burden on urban stormwater infrastructure, reduce downstream flooding and protect water quality.
Although DIS is a simple and cost-effective practice, it is generally limited to slopes of 8 percent or less. Within our mountain region, DIS is often not considered as an option because with our steep slopes, runoff can flow too quickly, resulting in erosion, flash flooding and even slope instability.
To address the challenges of applying DIS in the mountain region, the North Carolina Land and Water Fund awarded a grant to RiverLink to conduct a pilot research project to develop designs particularly suited to the steep slope conditions of our mountain region. RiverLink is partnering with Green Built Alliance member Blue Earth Planning, Engineering & Design to conduct the research and develop and install pilot designs.
The focus of the project is on residential sites in the Central Asheville Watershed near downtown Asheville that meet specific criteria, including having slopes greater than 8 percent. For six selected sites, the project team worked with homeowners to develop designs that direct stormwater runoff from rooftops into storage areas on steep slopes where it can soak into the ground.
The innovative and aesthetic DIS designs included “earth works” such as swales and basins with compacted earthen berms. Downspouts were piped underground via 4-inch PVC pipes with overflows managed through 4-inch diameter riser pipes.
And in October 2021, the pilot sites were constructed by local contractor Asheville Drainage + Rainwater Harvesting. The native soils were mechanically “fluffed” to a depth of 18 inches in order to increase infiltration. All of the sites were mulched and planted with native and edible vegetation. A total of 900 plug plants were planted at the six sites with RiverLink volunteers.
With help from the homeowners, the project team is now monitoring these innovative stormwater practices for their performance effectiveness and resilience. Monitoring data is being collected through a smart phone application and includes rainfall, runoff, outflow and infiltration rates.
In addition to the technical challenges, stormwater management also involves social challenges, such as the perception that stormwater management may be too difficult and costly for homeowners. In order to address social obstacles in implementing DIS on a wide scale, faculty and students from the Sustainability Studies Program at Lenoir-Rhyne University Asheville are conducting social research as part of the pilot project.
The Lenoir-Rhyne team members are using focus groups, surveys and interviews to assess residents’ awareness, understanding and perceived benefits and barriers of DIS. A particular focus of the social research is a method known as Community Based Social Marketing, or CBSM, that is based in social psychology and draws from the idea that sustainable behavior change is most effective when it involves direct contact with people and carried out at the community level. CBSM includes five main steps:
- Selecting the specific behaviors to address
- Identifying the perceived barriers to (and benefits of) a behavior
- Developing CBSM strategies to engage the community in overcoming barriers
- Pilot testing the strategies and making necessary changes
- Implementing and evaluating the program across a community
The Lenoir-Rhyne team members have already made many interesting discoveries related to the social aspects of stormwater management in our region and will be publishing their findings soon. With many of the potential early adopters that were surveyed, there is a desire to develop stormwater management practices on their properties, even if they have never heard the term “Disconnected Impervious Surface.” Many respondents desire to implement rain gardens, rain barrels as well as other stormwater practices.
One significant perceived barrier, shared by many, is a “lack of technical knowledge.” The DIS pilot sites and other strategies, like educational materials, are being pilot-tested in an effort to help overcome the technical knowledge barrier. One promising sign is that a majority of those surveyed believe that the responsibility for addressing stormwater on private property is shared among many parties including local governments, businesses, neighbors and “myself.” This indicates a great potential for future collaboration among many stakeholders.
The entire RiverLink team is excited to partner with our local community in conducting this innovative research project and demonstrating that DIS can be an effective tool in the effort to protect our creeks, rivers and watersheds, even in our challenging mountain region. Our hope is that these simple effective practices will become widespread in our mountain region and beyond.
And if you happen to be in the Central Asheville Watershed, we invite you to once again put on your detective hat and be on the lookout for the educational signs and observe these innovative practices in action.
Tim Ormond, P.E. is a water resources engineer with expertise in hydrology, stormwater management, green infrastructure, and innovative research. Tim is co-founder of Blue Earth Planning, Engineering & Design, a Certified B Corporation specializing in regenerative systems that are mindful of the interconnections of the water cycle, ecosystems, and people. Connect with Tim at blueearth.us.
Renee Fortner serves as RiverLink’s Watershed Resources Manager leading water conservation initiatives, including stormwater, stream restoration, and watershed planning projects. She has 20 years of experience engaging the public in environmental conservation. Renee was RiverLink’s project manager for the development of the Central Asheville Watershed Restoration Plan. Connect with Renee at riverlink.org.
Keith McDade, Ph.D. is a Professor of Sustainability Studies at Lenoir-Rhyne University- Asheville, a Director of the Master of Science in Sustainability Studies program, and a Director of the Reese Institute for Conservation of Natural Resources. Connect with Keith at lr.edu/sustainability-studies-ms.
If you’re interested in implementing these or other water-management techniques on your own property, check out RiverLink’s WaterRICH program, a free resource for residential stormwater management.
Funding — North Caroina Land and Water Fund
Project Sponsor — RiverLink
Lead Consultant — Blue Earth Planning, Engineering & Design
Social Research — Lenoir-Rhyne University
Construction — Asheville Drainage + Rainwater Harvesting
Monitoring — RiverLink, Blue Earth, Wildlands Engineering
You can also view this article as it was originally published on page 28 of the 2022-23 edition of the directory.