The 100-year flood myth
by the Federal/State Joint Disaster Information Center
Washington property owners still recovering from the effects of the 1995 and 1996 winter floods have been heard to wonder whether the state has suffered yet another 100-year flood.
It's a myth that a "100-year flood" occurs only once every 100 years. It is a flood that has one chance in 100 of occurring each year. In fact, it's possible for two 100-year floods to occur in the same week.
The danger here is that folks will think they've survived the worst. They might mistakenly gamble that similar flooding won't return for 99 years.
The 100-year flood standard was originally developed only for use in floodplain mapping. There is no magic reason to attempt to relate every flood that occurs to the standard used for mapping.
In fact, most recent flooding has been well below the 100-year level. Even the floods of 1990 were only in the 20- to 30-year range.
Those floods also are disastrous for homeowners. During the average 30-year mortgage, the 100-year flood has only a 26 percent chance of happening; but the 10-year flood has a 96 percent chance of occurring. Ten-year floods may be almost as damaging as 100-year floods. The difference in water levels is often a foot or less. And, of course, flooding is always a serious disaster for the families affected.
Residents can protect themselves in two key ways: mitigation and insurance.
Mitigation involves taking steps to reduce the amount of damage from rising water. That can range from elevating key appliances in a home to elevating the entire residence. Local building departments or emergency management offices can provide information on steps to be taken.
Insurance is available through the National Flood Insurance Program (NFIP) and can be obtained through any licensed insurance agent.