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What Are Floodplains and Why Are They Important?
What Are Floodplains and Why Are They Important?
A floodplain is the relatively flat area of land next to a river, creek, or stream that is naturally prone to flooding when water levels rise above the channel’s banks. Floodplains temporarily store excess water, slowing flood peaks and reducing downstream damage. Floodplain management utilizes zoning, preservation, and smart development to protect people and property by keeping high‑risk areas free from flood‑prone development. Proper floodplain management balances public safety with the natural functions of rivers, ensuring communities are more resilient to both frequent and rare flooding events.
What Do "100-Year" and "500-Year" Floods Really Mean?
What Do "100-Year" and "500-Year" Floods Really Mean?
When you hear the term “100‑year flood” or “500‑year flood,” it’s easy to assume it means a flood of that size happens only once every 100 or 500 years. In reality, these terms describe probability, not a schedule. A 100‑year flood means there is a 1% chance of a flood of that size occurring in any given year, while a 500‑year flood has a 0.2% chance in any given year. The probability remains the same each year and does not reset after a flood occurs, so it’s possible to have multiple “100‑year floods” within a short period. This statistical approach enables engineers, planners, and emergency managers to understand flood risk and inform decisions about infrastructure design, zoning regulations, and emergency preparedness.
*These “days” are not actual flooding days; they are another way to understand probability. For example, a 100-year flood means there is a 1% chance each year of such a flood occurring, equivalent to a 1 in 365 chance of it happening on a given day, assuming every day is a new random draw.
Terms:
Channel- The lowest part of the stream or riverbed that carries water during normal flows.
FEMA Flood Fringe- The portion of the 100-year floodplain that lies outside of the floodway. It may flood, but water moves more slowly.
FEMA Floodway- The central, high-velocity part of the floodplain where water flows fastest and deepest during a flood.
Base Flood Elevation (BFE)- The computed elevation that water is expected to reach during the base (100-year) flood.
One-foot Rise- FEMA's regulatory threshold that development in the floodway cannot cause more than a 1-foot increase in BFE elsewhere.
How Can I Determine If I Am In a Floodplain?
How Can I Determine If I Am In a Floodplain?
In North Carolina, one of the best tools for determining if your property is located in a floodplain is the NC Flood Risk Information System (FRIS). This free, interactive online map is maintained by the North Carolina Emergency Management (NCEM) Floodplain Mapping Program.
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