100-Year Storm#
Rainfall Standards: The 100-Year Storm#
Floods will happen.
The City's floodplain regulations and capital improvement projects are designed to mitigate flooding.
A 100-year storm is the amount of rainfall measured at a certain location, during a specified length of time, that has a 1% chance in any given year of being equaled or exceeded.
It is normal in Colorado to experience many storms that locally equal or exceed rainfall defined as the 100-year storm. It is likely that between 100 and 300 "100-year storms" occur somewhere in Colorado in a typical year. This graphic compares 100-year storms to storms of other sizes.
What are the Odds?#
100-Year Flood
A 100-year storm (rainfall) does not always create a 100-year flood (runoff). Many variables exist that determine how much water runs off and where it goes.
In mapping the 100-year floodplain, officials assume that the 100-year storm occurs uniformly over the entire basin. Therefore, if a 100-year rainfall occurs in only an isolated location, it may not result in a 100-year flood.
Similar to the 100-year storm, the definition of the 100-year flood is the specific streamflow that has a 1% chance in any given year of being equaled or exceeded. That streamflow amount is determined from:
- Long-term streamflow records, such as records for the Poudre River, or
- Modeling of the runoff from the 100-year storm
Flood Risk
A property in the 100-year floodplain has a 1% chance in any given year of being flooded. Over a 30-year mortgage, that percentage jumps to 26%. As a comparison, only a 5% chance exists that the house will catch fire during that same 30-year period. This is why flood insurance is recommended. Some properties have an even higher risk of flooding since they are in areas where smaller, more frequent storms cause damage.
| Event | Odds of Occurring: |
|---|---|
|
Structure in the 100-year floodplain being flooded in any given year |
1 in 100 |
|
Matching 1 number plus the Powerball in the Powerball lottery |
1 in 124 |
|
Structure in the 500-year floodplain being flooded in any given year |
1 in 500 |
|
Annual chance of being killed in a car accident if you drive 10,000 miles a year |
1 in 4,000 |
|
Being struck by lightning |
1 in 600,000 |
|
Winning the Powerball lottery jackpot (matching 5 numbers plus the Powerball) |
1 in 120,526,770 |
Did You Know?
Pre-cooling your home before 2 p.m. during the summer and coasting through the on-peak hours can save money on your utility bill.
It is recommended that you aerate your lawn once a year.
Mowing with a dull blade tears grass and stresses the lawn. Always be sure to mow with a sharp mower blade.