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Success Story: Brevard No Adverse Impact Requirement
Brevard manages flood risk with a “No Adverse Impact” development standard
*Disclaimer: In September 2024, Tropical Storm Helene caused historic rainfall across western North Carolina. Flash flooding and landslides caused devastating damage and loss of life. Infrastructure and properties throughout the region suffered major damage during the storm. The project outlined in this case study describes a planning approach to flood risk management that had success in the years before Helene. Data has not yet been available to indicate if this approach helped protect against the storm. This case study will be updated with input from the City of Brevard’s project managers as more information about storm impacts becomes available.
Project Purpose
In 2004, Hurricanes Frances and Ivan dropped 33 inches of rain in the Brevard region. The French Broad River flooded, causing immense devastation in the area. Following this disaster, Brevard’s City Council decided to update the city’s Flood Damage Prevention Ordinance. The updates aimed to ensure future development would not worsen the community’s flood vulnerability.
Quick Facts
Directly east of Brevard is the French Broad River, which is fed by multiple local creeks that run through parts of the city.
In 2009, the City Council updated the Flood Damage Prevention Ordinance to include a “No Adverse Impact” (NAI) determination requirement. NAI is a longstanding floodplain management strategy that “ensures the action of any community or property owner, public or private, does not adversely impact the property and rights of others” (ASFPM, 2003). To get approval, builders must demonstrate that their projects will not increase the flood risk faced by downstream property owners and communities (The Pew Charitable Trusts, 2019; City of Brevard, 2023).
The ordinance reduces flood risk downstream by limiting new impervious surfaces and structures upstream and within Brevard.
The City places the burden of proof on development applicants, so NAI certification requirements have a low cost for the City.
What is No Adverse Impact?
NAI floodplain management requires developers to review their proposals for adverse impacts to other property and the natural environment. Example adverse impacts include increased erosion or changes in floodwater speed or volume. Under NAI, developments must include measures to reduce or eliminate those negative effects.
How is a No Adverse Impact policy different from a No-Rise requirement?
In most cases, communities must prohibit development in the floodway that would increase flood levels during a base flood. In other words, a project must have a “no-rise” or “zero-rise” certification from a qualified professional engineer (FEMA, 2019).
Under a No Adverse Impact policy, developers cannot change the water-carrying capacity of the entire floodplain. When a developer proposes a project that would decrease the amount of water the floodplain can handle, the developer must add a measure to the project that would manage the additional water on-site.
Image of characteristics of a floodplain. (Source: Louisiana Watershed Initiative)
Spotlight on Equity
The policy implemented in Brevard protects those who already live in a floodplain. Land prices are often lower in the floodplain because of flood risk, and lower income households are often concentrated in these more vulnerable lands. Therefore, NAI requirements may protect socially vulnerable populations that already reside in a community. This policy could help those currently living in floodplains by minimizing increased stormwater impacts.
The elevation of mobile homes in Brevard, N.C., to come into compliance with the updated Flood Damage Prevention Ordinance. (Source: Brad Burton)
In 2009, the City of Brevard updated its Flood Damage Prevention Ordinance to protect residents and educate about specific risks to their properties. The adopted ordinance also aims to minimize the need for future public spending on flood control and maintain a consistent tax base.
The new ordinance includes a “No Adverse Impact” determination requirement, which mandates that proposed developments not increase danger to residents or other properties in the floodplain. The standards of the NAI regulations are beyond federal minimums.
The ordinance defines development as “any man-made change to improved or unimproved real estate, including, but not limited to, buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling operations, or storage of equipment or materials” (City of Brevard, 2023).
The ordinance lists alterations to the floodplain that must not occur. These include no creation of increased sediments or debris from construction; no increase in the base flood elevation; and no reduction in the size of the floodway. A floodway is the river or stream itself and any land that regularly floods during a 100- or 500-year flood event.
The ordinance requires that developers address comments from any nearby property owners or tenants who may face potential flooding from the proposed development.
Developers must provide documentation from professional engineers that determine NAI. Only then can the developer receive project approval.
The City has continued to update the ordinance since its adoption.
Costs, covered by the City of Brevard’s budget, included staff time to draft the ordinance and carry it through adoption.
Because the burden of proof of NAI lies upon the property developer and not the City, the cost of maintaining the ordinance is low. Brevard estimates costs at less than $5,000 annually.
Brevard Planning Department, Brevard Public Works, Brevard City Council
For the community, ongoing costs of limiting and mitigating unsafe development in the floodplain has positive safety and economic effects long term because it protects life and property from new or increased flooding impacts.
The ordinance also helps maintain a natural floodplain with minimal disturbance, which benefits waterways, fish habitat and other native ecosystems.
The ordinance reduced the costs of flood insurance for residents, thanks to incentives in FEMA’s National Flood Insurance Program (NFIP). The ordinance made the city eligible for a voluntary rating under the NFIP, “which insures property owners and renters at risk of flooding. The Community Rating System (CRS) discounts insurance premiums for communities that take measures to reduce flooding. To participate, a community’s flood prevention ordinance must meet certain standards for mitigation, floodplain management and outreach activities, which Brevard’s certification requirement exceeds” (The Pew Charitable Trusts, 2019).
After more than 10 years since its adoption, City staff believe the regulation has been effective in protecting life and property and returning parts of the city to more sustainable environmental states. For example, the city had relatively few substantially damaged structures from Tropical Storm Fred in 2021. In addition, all structures elevated because of the flood ordinance survived without incident.
Adopting an NAI ordinance can enhance safety for future development without high ongoing administrative costs. In addition, new regulations should always evaluate the potential to disproportionately affect minority or disadvantaged community members.
