Success Story: Landslide Risk Management Ordinance
Buncombe County uses zoning ordinance to manage landslide risk
*Disclaimer: In September 2024, Tropical Storm Helene caused historic rainfall across western North Carolina. Flash flooding and landslides caused devastating damage, displacement and loss of life. The project in this case study details an approach Buncombe County took to reduce the number of households and structures exposed to landslide risks before Helene. Data from the County is not yet available to showcase the effectiveness of this approach during this latest storm. This case study will be updated with input from Buncombe County’s project managers as more information about storm impacts becomes available.
Project Purpose
In the early 2000s, Buncombe County experienced increased development on steep and unstable slopes. Worried about landslides, the County considered how it could direct development in a safer direction and provide environmental protections.
Quick Facts
- In its zoning ordinance, Buncombe County restricts the elevation and slope on which buildings can be constructed. The restrictions are included in the following overlay districts:
- The Steep Slope/High Elevation Overlay District requires that structures above 2,500 feet be constructed on soils with a slope no greater than 35%.
- The Protected Ridge Overlay District requires that structures above 3,000 feet be constructed on soils with a slope no greater than 35% and be at least 500 feet away from a ridgeline.
- The County ensures that developers adhere to the ordinance by requiring an initial geotechnical analysis as well as a second geotechnical analysis once a project is complete.
- The ordinance also includes impervious surface restrictions, tree cover requirements and height standards on steep slope developments.
- The County believes the overlays have prevented landslides and helped preserved ridgetop environments. Other governments have since adopted similar development requirements in their zoning ordinances.
What is geotechnical analysis?
Geotechnical analysis is a study of the composition and stability of the ground. Geotechnical engineers look at the rock, soil and other earth materials on a site to understand the load bearing properties of soils and their susceptibility to stress that could result in land slumping or sliding. These engineers can make decisions about construction design on steep slopes and ridges.
Spotlight on Equity
The zoning ordinance updates were not designed specifically with equity in mind. However, the overlays can help prevent development that would increase landslide hazard for lower-elevation homes. Homes built below the ridgeline, especially those in flatter areas, are typically more affordable for lower income families. Decreasing the risk of landslides helps decrease the chances for future impacts to disadvantaged residents.
| Key Info | |
|---|---|
| Location | Buncombe County, N.C. |
| Estimated Costs | Unknown |
| Published | March 1, 2024 |
| Related Resources |
|---|
- In the late 2000s, Buncombe County engaged the North Carolina Geological Survey (NCGS), local geotechnical engineers, the Land of Sky Regional Council, a NOAA consultant and county residents to craft regulations that could help preserve the county’s natural landscapes and reduce landslide risk. The technical partners studied soil and topographic maps to identify areas with the highest potential for landslides and loose soils.
- Buncombe County included ridge protection in its first 2009 countywide zoning ordinance. A year later, the County added steep slope development restrictions into the ordinance. This addition to the ordinance was the first of its kind in the region.
- Around the same time, the City of Asheville also added a ridge protection and steep slope to its Unified Development Ordinance (Sec. 7-12-3 and Sec. 7-12-4). Other counties and municipalities adopted similar restrictions shortly after.
- The City of Asheville partnered with Buncombe County to release an online Steep Slope Calculator to help developers calculate the slope on any parcel in the county.
County staff drafted the zoning ordinance and its updates, so no outside funding was required.
Buncombe County; City of Asheville; NCGS; local geotechnical engineers
- Construction on high-elevation steep slopes is restricted by the Buncombe County Zoning Ordinance. The Protected Ridge and Steep Slope sections have remained relatively unchanged since their introduction, even as the County has updated its zoning code.
- County staff continue working with partners and consultants at conferences and workshops to incorporate slope protection and landslide hazards into regional planning. Staff continue examining the slope and ridgetop development restrictions to consider if revisions are needed.
- The County included slope and ridge protection in the 2021 Buncombe Madison Regional Hazard Mitigation Plan (PDF) and the 2043 Comprehensive Buncombe County Plan. For example, Action 8 of the 2043 Comprehensive Buncombe County Plan calls for increased protection of steep slopes over 25% grade (compared to the currently restricted 35% in elevations over 2,500 feet) and recommends a variety of potential slope and ridge protection measures (e.g., slope and soil evaluation requirements for lots containing steep slopes, expanding the steep slope/high elevation overlay to provide greater protection for steep slopes in high elevation areas) that could be adopted.
- The Blue Ridge Parkway Overlay within the Buncombe County ordinance, the Land of Sky Regional Council’s Mountain Ridge and Steep Slope Protection Strategies Plan (PDF) and the City of Asheville’s Unified Development Ordinance use similar requirements that help protect slopes and ridgetops in specific situations. The policies in these documents work in tandem to help ensure slope protection.
- An added benefit of the ordinance overlays is that they keep the county’s mountain tops and ridges less developed. The natural scenery of North Carolina’s mountains is a major driver of the tourism that supports local economies.
County Planning Director Nathan L. Pennington recommends that communities borrow resources from others with similar topographies and lean heavily on state resources and maps. “Don’t recreate the wheel,” he says. Communities should also prepare a robust GIS system and map what they want to do ahead of time, since maps are useful for planning and decision making. Furthermore, Pennington notes that working with geotechnical engineers is important so they can help set the standards for requiring geotechnical analysis.
“The zoning ordinance is a great planning tool and asset to the community. It just took some time and effort to create. No matter what side of the aisle you are on, we are all interested in the protection of our mountains. Seeing them sparsely developed and protecting them is key. I think [the overlays] work very well. [They] balance property rights and appropriate development on the most environmentally sensitive areas,” noted Pennington.
Pennington also noted that the County has a better sense of where to add new development now that the areas it wants to preserve are identified. Understanding wise locations for future development benefits the local government, developers, current and future property owners, and the environment.