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CISSP · Question #510

What does the term "100-year floodplain" mean to emergency preparedness officials?

The correct answer is B. The odds of a flood at this level are 1 in 100 in any given year.. The '100-year floodplain' is a statistical concept describing annual flood probability, not a time interval between floods. It refers to a 1% annual chance of flooding, which emergency planners use to assess risk zones.

Submitted by mike_84· Mar 5, 2026Security and Risk Management

Question

What does the term "100-year floodplain" mean to emergency preparedness officials?

Options

  • AThe area is expected to be safe from flooding for at least 100 years.
  • BThe odds of a flood at this level are 1 in 100 in any given year.
  • CThe odds are that the next significant flood will hit within the next 100 years.
  • DThe last flood of any kind to hit the area was more than 100 years ago.

How the community answered

(29 responses)
  • A
    3% (1)
  • B
    93% (27)
  • C
    3% (1)

Why each option

The '100-year floodplain' is a statistical concept describing annual flood probability, not a time interval between floods. It refers to a 1% annual chance of flooding, which emergency planners use to assess risk zones.

AThe area is expected to be safe from flooding for at least 100 years.

This reverses the meaning entirely - a 100-year floodplain identifies an area at risk of flooding, not one that is protected or safe from it.

BThe odds of a flood at this level are 1 in 100 in any given year.Correct

A 100-year floodplain, formally called the 1% Annual Chance Flood Hazard, means there is a 1-in-100 (1%) probability of a flood of that magnitude occurring in any given year. This is the standard definition used by FEMA and emergency management officials to delineate Special Flood Hazard Areas (SFHAs) on Flood Insurance Rate Maps (FIRMs). The term describes annual statistical probability, not a fixed recurrence schedule.

CThe odds are that the next significant flood will hit within the next 100 years.

This incorrectly implies a deterministic timeline for the next flood; flood probability is an independent annual probability, meaning a major flood could occur in consecutive years or not for centuries.

DThe last flood of any kind to hit the area was more than 100 years ago.

The designation has nothing to do with historical flood records or when the last flood occurred; it is a forward-looking statistical risk assessment based on hydrological modeling.

Concept tested: Annual flood probability and floodplain risk designation

Source: https://www.fema.gov/glossary/one-percent-annual-chance-flood-hazard

Topics

#Risk assessment#natural disaster#floodplain#emergency preparedness

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