Public Works Director Anderson explains how model is used by developers to ensure new construction will not have adverse effects on existing neighborhoods
On Aug. 28, during the board’s regular meeting that day, Sarasota County Commissioner Mark Smith recommended that he and his colleagues conduct a workshop with Public Works Department Director Spencer Anderson to try to determine whether higher standards regarding stormwater runoff and development need to be implemented in the county.
Smith’s proposal came one day after county department leaders’ presentations about Tropical Storm Debby’s effects on the county — and residents’ pleas for a pause on approval of new residential communities. (See the related articles in this issue.)
Both Chair Michael Moran and Commissioner Joe Neunder supported Smith’s proposal, though Moran pointed out that he will be stepping down from the board in November. Moran indicated his expectation that such a workshop would come after he no longer is a commissioner. He is term-limited.
Commissioner Neil Rainford, whom Gov. Ron DeSantis appointed to the board in June 2023, to fill the District 3 seat left open by the April 2023 death of Commissioner Nancy Detert, also will be leaving the board. He lost the District 3 Republican Primary to former Sheriff Tom Knight on Aug. 20. Rainford did not comment on Smith’s Aug. 28 proposal.
Smith offered his remarks after Anderson recapped some of the comments that he had made during the Aug. 27 commission meeting.
The county watershed most affected by Tropical Storm Debby was the one involving Phillippi Creek, Anderson pointed out both days, and that is part of the Sarasota Bay watershed.
“Our regulation for stormwater and development is very stringent,” Anderson said as he addressed the board members during their Aug. 28 meeting, which was held in downtown Sarasota.
In fact, Anderson emphasized, “We have the highest level of requirement for development in the state of Florida, that I’m aware of.”
That standard is based on a 100-year storm event, he continued. Statistically, that involves a 1% annual chance of 10 inches of rain falling in 24 hours.
A developer has “to use our existing conditions model,” he stressed.
Beginning in the late 1980s and continuing into the early 1990s, he indicated, the Sarasota County commissioners decided that they wanted a higher level of service in regard to stormwater regulations than any other standard established in Florida.
Any developer proposing a major land-use change, Anderson continued, must hire a licensed engineer to create a model that will be compared with the county’s stormwater model, to show that a proposed new community will not increase stormwater runoff more than one-hundredth of a foot “anywhere outside of [the boundaries of the new development].”
Such a model is not required of a person planning to construct just a solitary new home, he noted.
The model the county uses is unique to Florida, Anderson pointed out, as it takes into account the low elevations statewide. It also factors in all of the existing developments in the county. Anderson added, along with other land uses.
It uses rainfall data from the Southwest Florida Water Management District (SWFWMD), which dates to the early 1990s, along with data from the University of Central Florida and the South Florida Water Management District, Anderson said.
To his knowledge, he said, SWFWMD has not updated its rainfall tables since the early 1990s. However, he noted, the National Atmospheric and Oceanic Administration (NOAA) has alternate tables that do provide have more localized data. He referred to those as the “Atlas 14” data.
Anderson added that those NOAA tables include higher rainfall figures than those available from SWFWMD, but he was not certain when they last had been updated, either.
If the commissioners were interested in refining the county’s stormwater model, he continued, the county could hire a climatologist or meteorologist to develop a higher standard, perhaps one based on a 500-year event.
He added that SWFWMD characterizes 12.4 inches of rain in 24 hours a 500-year event. The county’s model could be updated to call for that 500-year standard, he pointed out, with corresponding measurements of anticipated stormwater impacts on county residential developments.
Nonetheless, Anderson emphasized that the rainfall from Debby “was significantly historic, especially for duration” — 18 inches in 36 to 48 hours, when 6 to 8 inches was the National Weather Service prediction for five days of Debby rainfall in Sarasota County.
He also showed the board members a graph comparing flood insurance claims with rainfall events. Approximately starting in the early 2000s, he said, the number of claims fell significantly. That was a reflection of the county’s investing hundreds of millions of dollars in infrastructure improvements and the removal of homes from the 100-year floodplain, he indicated.
However, he acknowledged, the graph did not show a large number of heavy rain events since the 1990s.
Considering current climate factors
Following Anderson’s remarks, Commissioner Smith raised the prospect of a workshop with Public Works staff, so the board members could discuss options in regard to future determinations regarding stormwater and development.
“I believe that we need to adapt [the county] model,” Smith said. Perhaps it should account for longer periods of rainfall associated with tropical storms and hurricanes over the county, he added, as well as new data related to the increase in the number of rain events that have become associated with tropical systems in recent years.
His goal, Smith said, is to ensure that the county provides for an extra margin of safety for residents, just as modern building codes require specific adjustments for storm surge in floodplains.
“I believe, with the warmer [Gulf of Mexico and Atlantic Ocean] water,” Smith continued, “these storms are absorbing more water before they hit us.”
“Debby was a freak storm,” Smith pointed out. “It was slow moving,” with its “tail” dragging “over us like no other I’ve seen since I’ve been looking at storms.”
He summed up his proposal for the model: “Let’s make sure that we’re doing it right.”
Commissioner Ron Cutsinger asked Anderson whether data is available showing how rainfall since the early 1990s has been dispersed throughout the year. For example, Cutsinger inquired, did any events produce 20 to 30 inches of rain over two to three days in the county?
Referring to Tropical Storm Debby, he added, “This certainly seems like a very unusual, one-off kind of event.” He wanted to be sure, he continued, that the county has as much information as possible for making future stormwater decisions.
Further, Cutsinger asked that staff obtain the data that NOAA has in regard to local rainfall.
Then Commissioner Neunder voiced his support for Smith’s recommendation for the workshop. “I would be completely, 100% in favor of [that],” Neunder said.
Moreover, he concurred with Smith about the climate conditions that are conducive to more rain production from hurricanes and tropical storms. “Water temperatures are rising. … Our Gulf is hot.”
Perhaps it would be prudent for staff to engage a climatologist or an environmental specialist, Neunder said, to assist with collection of more data to facilitate development of a new model.
He, too, expressed interest in seeing data that show amounts of rainfall during specific events.
Chair Moran stressed comments that Rich Collins, director of the county’s Emergency Services Department, made the previous day: The National Weather Service predicted that Debby would produce 6 to 8 inches of rainfall in Sarasota County over five days, when the result was more than 10 inches in 24 hours.
Moran also sought confirmation from staff that Sarasota County was one of 11 counties — out of the 67 in the state — to win a federal disaster declaration. County Administrator Jonathan Lewis replied that that was correct.
Moran encouraged his colleagues to pursue a workshop with a regional focus, including representatives from SWFWMD who could provide data for a broader area.