Planning - Flood Insurance Information

The Federal Emergency Management Agency (FEMA) defines a Flood Insurance Rate Map (FIRM) as the official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community. These maps help protect citizens' lives and reduce property damage from flood dangers through analyzing the landscape to identify flood prone areas, so that citizens can make safe and informed decisions about their communities.

The Special Flood Hazard Area (SFHA), shown on the flood map is known as the 100-year floodplain. It is more precisely defined as the floodplain associated with a flood that has a 1-percent annual chance of being equaled or exceeded in any given year. The 100-year flood is not a flood event that happens once in a hundred years, rather a flood event that has a one percent chance of occurring every year. Any flood zone that begins with the letter A is subject to the 1 percent annual chance flood.

 

What is a Base Flood Elevation (BFE)?

A Base Flood Elevation (BFE) is the elevation the floodwaters will reach during the 1 percent annual chance flood.

The flood elevations for rivers and streams are based on engineering analyses of the hydrology (how much water will runoff the land during a flood event) of the watershed and the hydraulics (flow carrying capacity of a watercourse) of the river or stream.

 

The amount of runoff during a 100-year flood event is dependent on a number of factors, including rainfall (or snow melt), drainage area, vegetation cover, soil type, moisture content of the soil, land use, slope of land, and presence of wetlands & other flood storage areas. All of these factors are considered in computing the flow rates to be used in the hydraulic analysis.

The hydraulic analysis uses the flood flows to determine how high the water will get during the 100-year (1% chance) flood. The amount that a stream will rise during a flood event is dependent upon a number of factors such as the shape of the channel and the land adjacent to the channel, the slope of the stream, vegetation and obstructions in the stream, and man-made obstructions (including bridges, culverts, and dams). If past flood events have occurred in the area, the hydraulic model will be calibrated to reproduce past flood events. The hydraulic analysis will result in a flood profile being developed which will identify the base flood elevation at any point along the reach of stream that has been studied.

 

Certified Floodplain Managers