WHAT IS THE ONE-HUNDRED YEAR FLOOD?

The “one-hundred year flood” gets a lot of attention, but its name is a bit misleading. It simply refers to a flood that has a one percent or greater chance of occurring within any given year. It is increasingly referred to as the Base Flood to avoid confusion. The area expected to be inundated by the Base Flood is known as the Special Flood Hazard Area (SFHA). Some sites located within the mapped SFHA may actually be affected by a smaller flooding event. It is even possible to be inundated by multiple ‘one-hundred year floods’ within the same year, although statistically unlikely. It is also important to note that the Federal Emergency Management Agency (FEMA) estimates about 25 to 30 percent of floods occur outside of the SFHA.

In 1968 Congress made FEMA responsible for the creation of flood maps nationwide. These maps are used to regulate development by local jurisdictions and to assess flood risk by property owners, insurance companies and lenders. Our currently adopted maps are based on FEMA’s original maps for our community. As part of this mapping effort FEMA had detailed hydrological studies performed for the Willamette and Amazon Rivers. Other flooding sources in our area had approximate methods used to determine the floodplain boundary.

This page has links to a variety of flood information. Some are regarding flooding risk, our adopted maps, flood insurance and facts pertinent to construction within the floodplain. This page also has important links to pages on how to prepare for a flood and what to do after a flood.