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What is a 100 Year Flood Plain and a 500 Year Flood Plain?

By
Real Estate Agent with Broker 0576813

Understanding the difference between a 100 year flood plain and a 500 year flood can help you factor in various potential events, probabilities, and even the cost of flood insurance. The year number, as in 100 or 500, refers directly to the probability of exceeding flood probability for each year, calculated through statistical mathematics. If you are purchasing a home in a flood plain that is known as a 100 year flood plain the year has to remain distinctive in analysis. You can't compare the year to year charting but simply take the year that it is.

 

The flood plains are areas that are lower lying, and often flat. These are areas that are prone to flooding but are not necessarily going to see catastrophic flooding more than the statistics suggest. The analysis of the flood plain is done to help educate and create more flood awareness. Flood plains can be found just about everywhere so don't be quick to rule it out as a possibility even if it doesn't look like a flood plain at first glance. They can be coastal or they can be farther inland.

 

Every 100 year flood or 500 year flood is not going to act like an alarm clock. The overt idea that every 100 years a massive flood will come along  and wipe out the entire plain is not a predictable factor. In fact, the flood plain of the 100 year flood has perhaps a 63% likelihood of occurring within that time span. This allows for analysts to incorporate the potential for the flood plain to become devastated up sudden flash flooding but it is anything but a guarantee.

 

Weather is an uncertain event. It can not be accurately predicted most of the time by meteorologists even 24 to 40 hours in advance. Rather, weather comes in the form that it is in regardless of our ability to prepare for it. Predicted flooding has led to premature and panic stricken sales of homes and property. Because of the stress of the impending flood that never happened the property owners sold their land and homes at a ridiculously low rate. Imagine what you would see if each prediction were announced formally.

 

A 100 year flood plain and a 500 year flood plain are simply the areas that have seen the highest peak of their flooding stages within that time frame. It doesn't mean that there is a flood pending nor does it mean that you are safe from floods just because it's not that predicted year. 

Comments (2)

Dylan Taft
Dylan Taft Broker/Owner Taft Street Realty, Inc. - Woodstock, NY
Ulster County Area Consultant

My area in Ulster County just got hit with major flooding.  I blogged about Hurricane Irene and the affects on the Hudson Valley area and you can read more below.  Great post!

http://www.taftstreetrealty.com/blog/historic-ulster-county-flooding-poses-biggest-challenge-in-wake-of-hurricane-irene.html

 

 

Sep 05, 2011 03:40 AM
Howard Weiss
Fathom Realty - Arlington, TX
Arlington & DFW, TX

It's important for home owners to understand that a special flood hazard area is designated as having AT LEAST a 1% chance of flooding in any given year.  As for the 500 year flood area, there is AT LEAST a 0.2% chance of flooding in any given year.  The statistical chance of flooding during a 30 year mortgage in a 1% annual flood area (formerly called the 100 year floodplain) is 26%.  Then of course you have areas completely outside the 1% and 0.2% flood areas.  These areas actually make up the majority of flood insurance claims in the U.S.  Flood insurance is always a good idea and affordable, even when not in a mandatory flood insurance area (Special Flood Hazard Area).

Sep 05, 2011 04:10 AM