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Know Your Flood Hazard

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Collier County is a very flat community along the Gulf Coast of Florida. The climate is sub-tropical which can create large numbers of intense thunderstorms during the summer “wet” season. The County is also subject to severe impacts from tropical cyclones (tropical storms and hurricanes). This combination of flat terrain, sub-tropical climate, and coastal boundary creates large areas subject to flood risk. The DFIRM shows the areas subject to flooding from coastal surge as well as rainfall.  The DFIRM delineates the broad areas subject to shallow flooding.  Visit the Flood Map Information webpage to view the DFIRM.

Coastal Surge Flooding 

stalled cars

Coastal surge flooding is primarily caused by tropical storms and hurricanes. Because tropical systems spin in a counterclockwise direction, in Collier County the highest storm surge occurs along the coastline just south of the center of the storm. The combination of atmospheric pressure differences in the storm and the effect on the Gulf waters from the high wind speeds creates a “mound” of seawater that is pushed onshore. Surge flooding can occur quite rapidly with extremely damaging impacts to structures and quickly create life threatening conditions.

NFIP Coastal Surge Flooding

There are two types of mapping available on the County website to show the potential impacts from coastal surge flooding. The DFIRM shows the extent of the 1% annual chance storm event using computerized coastal flood modeling developed for the National Flood Insurance Program. This analysis consists of a stillwater elevation and a wave height. Flood water elevations (stillwater plus wave height) are provided along with the type of flood zone. VE zones show areas where the wave height is equal to or higher than three (3) feet. AE zones show areas where the wave height is less than three (3) feet. Buildings in the VE zone must be constructed so that the flood water and wave can safely pass beneath the structure without causing major damage.

State of Florida Coastal Surge Flooding

The Southwest Florida Regional Planning Council prepared coastal storm surge risk mapping utilizing a computerized analysis developed by the National Weather Service known as Sea, Lake and Overland Surges from Hurricanes (SLOSH). This analysis is different from the FEMA surge flooding analysis. The basic concept in the SLOSH analysis is to identify the maximum storm surge that could be created by various strengths of storms. For a more detailed explanation of SLOSH, please visit the National Weather Service/National Hurricane Center webpage. The Collier County SLOSH information can be found on the County’s Emergency Management webpage

Rainfall-Induced (Riverine) Flooding

flooding at apt complex

Collier County is located within a sub-tropical environment and is subject to intense thunderstorms and tropical cyclones (hurricanes). The summer “wet” season is vital to the region’s environment to offset the winter “dry” season. Roughly 80% of the 52” average annual rainfall occurs during the months of May through October, with approximately 65% of that occurring during the months of June through September.

Combining the intense rainfall with a topography that averages approximately 1 foot of elevation change for 1 mile of travel can produce broad expanses of shallow sheetflow flooding conditions. This broad shallow flooding can create severe property damage conditions for older houses and buildings that were constructed to prior building code. Driving conditions are also seriously impacted with standing water over roads.

Stay Out of Flood Waters

Coastal surge flooding is generally considered as posing the greater risk to life due to the rapidly changing water levels and other accompanying dangers associated with a tropical cyclonic storm event. Rainfall-induced flooding generally rises very slowly with almost no horizontal flow movement. The calm water surface is often very deceiving, but can be very harmful or fatal. Floating Fire Ants

  • Submerged culverts can create very strong currents and the locations of roadside canals and ditches are often not recognizable.
  • Attempting to drive through flood waters can be very damaging to the automobile. If you cannot clearly see the location of the roadway, do not attempt to drive through floodwaters.
  • Obey the rule of Turn Around, Don’t Drown! 
  • Flood waters may contain harmful pollutants and critters, including floating fire ant colonies!

 

 

For assistance: Contact the Flood Information Hotline at (239)252-2942 or email floodinforequest@colliercountyfl.gov 

Visit: Growth Management Department, 2800 N. Horseshoe Dr., Naples, FL 34104

Page updated as of 04/05/18