The Sarasota County commissioners were not invited. The press wasn’t invited. The county PR department didn’t know about it. Yet, the presentation in the county administration center on July 6 could lead to nightmares for policy-makers.
Tim Frazier from Pennsylvania State University presented his Ph.D. thesis titled, "Current and Future Vulnerability of Sarasota County, Florida to Hurricane Storm Surge and Sea Level Rise."
Frazier took the storm surge maps from the National Oceanic and Atmospheric Administration and added modest sea level rises in increments of 30, 60, 90 and 120 cm. That’s about 1, 2, 3 and 4 feet, respectively.
The results for southern Sarasota County are catastrophic. His calculations and maps show the expected areas of flooding after even 1 foot of sea level rise turns the storm surge of a Category 3 hurricane into what’s expected today of a Category 4 or 5 storm. In other words, even a modest rise in sea level increases the flood danger to south county significantly.
Category 4 and 5 storms are rare. Category 3 storms, however, are more commonplace. The 1848 hurricane that created New Pass was likely a Category 3. Army officers at Fort Brooke near Tampa recorded a 14-foot tide and a barometric pressure of 28.18 inches of mercury.
In those days only one family was at risk in Sarasota. Pioneer William Whitaker’s house on Yellow Bluffs (west of today’s 12th Street) was above the flood. After the storm, he searched for his fishing nets and found a new pass had been created.
Today 372,000 people call Sarasota County home. Billions in property and civic infrastructure could be jeopardized by the combination of a Category 3 hurricane and a modest 30-cm rise in sea level (3+30 zone).
Frazier compared his maps with census data and tax parcel information to determine the increase in risk to investment. More than half of the tax parcels in Venice, for example, are in Frazier’s 3+30 zone. For Sarasota County as a whole, about 45 percent of all tax parcels are vulnerable. Areas such as north Sarasota and The Meadows would be untouched, but in Osprey, 65 percent of the parcels are in the "new "surge zone.
When he examined the threat to population, the 3+30 scenario showed a significant jump in threat. For Sarasota County as a whole, the population in the surge zone of a Category 3 storm today is about 25 percent. Add the 30 cm of sea level rise, and the number jumps to 38 percent. However, for Englewood, the numbers are 78 percent for a storm today and 95 percent in a storm plus 30 cm. In south Venice, the numbers are 25 percent and 43 percent, respectively. For Osprey, the threat jumps from 42 percent to 52 percent.
Areas outside the surge zone of a Category 3 storm today suddenly become more vulnerable. Gulf Gate Estates goes from 0 percent of its population at risk to 14 percent, with the addition of 30 cm of sea level rise.
Frazier then compared his maps with the county’s 2050 future land-use map, including the urban service boundary. Areas zoned for increased intensity in south county are swamped by Frazier’s 3+30 schematic.
In his conclusion, Frazier made some observations about the consequences of his findings. One was "the cost of shifting development." His suggestions for county planners include "increase density outside hazard zones" and "strategies to retreat from the coast." He noted these suggestions are "limited by economic realities."
He offered four specific conclusions: "relax the urban service boundary, steer development out of hazard zones, relocate/replace infrastructure, and explore evacuation alternatives."
July 9th 2009 - 12:21PM