County Home  |  Online Services  |  Visitors  |  Jobs  |  Government  |  Economic Development

What is a 100 year flood?

The 100 year flood is a national standard for determining the 1% chance (1 out of 100) of a flood of such magnitude that would require the purchase of flood insurance. But just so you know, this magnitude of flood could occur in any given year. It is a base measurement for regulating development in a floodplain.

Natural and Beneficial Functions of Floodplains

Floodplains are a natural part of the ecosystem and serve many functions.  They contain both cultural and natural resources that are of great value to society.  Flooding occurs naturally along every river, stream, and wash.  Flood waters can carry nutrient-rich sediments which contribute to a fertile environment for vegetation.  Floodplains are beneficial for wildlife by creating a variety of habitats for insects, wild birds, and other animals.

In addition to providing a habitat to many of Pinal County's native plant and animal species, floodplains also have direct benefits to humans.  The vegetation often found in floodplains also absorb more flood water than barren land due to reducing the impact to downstream property.  This flood mitigating action also has the effect of recharging our groundwater supply.

Human development and industrialization take a toll on the natural functions of the floodplains.  Development in the floodplains causes decreases in water quality, lost of wildlife habitats, and an increase in severity and frequency of flood losses.  Understanding the importance of maintaining the natural functions of floodplains can lead to better floodplain management approaches that will better protect the natural and beneficial functions of floodplains.

What is a Base Flood Elevation (BFE)?

Base Flood Elevations are the high water marks for the 100 yr flood. They are measured in mean sea level (MSL) or depths above the natural ground. This is the means by which we set the home’s lowest floor or bottom of frame if it is a manufactured home in order to give it maximum protection from flooding. This number is a limiting factor for floodplain building—do not go below the BFE. The Regulatory Flood Elevation, or RFE is one foot above the BFE to further protect from flooding.


Flood Control District

Physical Address:
31 N Pinal Street
Building F
Florence, AZ 85132

Postal Address:
Pinal County
Public Works
Flood Control
P.O. Box 727
Florence, AZ 85132

Toll Free:
Email Us

Main Contact List


Pinal County Government Web Disclaimer