What is a “100-year flood”? Why do we care?

The term is used to describe an event that has a 1-in-100 chance of happening in any given year. When you do the math, there is a 65% chance that there will be a “100-year flood” in 100 years. Likewise, a “50-year flood” has a 2% chance of happening in any given year, and there’s a 4% chance of a “25-year flood” every year. Keep in mind that calculations are based on less than a hundred years of flood records. The reason you often hear the “100-year flood” mentioned is that it’s a yardstick to measure inundation by flooding. Our Project is being constructed to protect the community from this 100-year event, which would be a larger flood than the 2005 event, larger than 1995, even larger than 1986.

Show All Answers

1. Are our tax dollars going for flood protection or beautification?
2. Are there places that will not have protection after the project is completed?
3. Did the work that’s been completed make a difference in flood on December 31, 2005?
4. Does the Flood District provide sandbags?
5. How does the Flood Project protect the community from flooding?
6. How is the Flood Project funded?
7. I hear people say that because we had flooding in 2005 that means the money we’ve spent so far has been wasted. Is that true?
8. Why is construction of the Project behind schedule?
9. I hear people say we’ve had three “100-year floods” in the last 20 years. Is that true?
10. I live far from the Napa River and Napa Creek. Will the Project protect me from flooding in my neighborhood?
11. Napa Creek floods more often than the River. Why not fix that problem now instead of waiting until later?
12. Was the New Year's Eve Flood on 12-31-05 a "100 year" flood event?
13. What about flooding problems in American Canyon, Yountville, St. Helena and Calistoga?
14. What areas are most prone to flooding?
15. Some people say you cannot control flooding on the Napa River because of the tides. Is this true?
16. What is a “100-year flood”? Why do we care?
17. What kind of public access to the River will be available after the project is built?
18. When will the Napa River-Napa Creek Flood Project be completed?
19. Where can I find out about evacuations, shelters, river levels, road closures, power failures and other flood-related information?
20. The Flood Project construction started in 2000. After five years of work, why didn’t the Flood Project prevent flooding on 12-31-05?