Former county stormwater engineer believes breach in earthen dike led to inundation of Laurel Meadows
During a Jan. 21, 2025 workshop, Sarasota County Public Works Director Spencer Anderson is scheduled to present to the County Commission the results of analyses, along with recommendations, from an outside consultant — plus the details of staff evaluations — regarding the cause of flooding in the Laurel Meadows community and other county neighborhoods in the wake of Tropical Storm Debby’s rainfall in early August, Anderson told The Sarasota News Leaderin a Dec. 10 email.
The consultant is Steve Suau, a stormwater engineer who was involved with the county’s stormwater program from the time it was established in the early 1990s, as Suau explained during an Oct. 24 program hosted by leaders of the Sarasota Citizen Action Network (SCAN).
SCAN was organized to put a focus on the county’s land-use planning decisions, its Facebook page says.
Suau declined to work as a paid consultant to the county on the project, as he thought his comments “would be better received” if he worked independently, Anderson added in his email to the News Leader.
Anderson called him on Aug. 7, following Debby’s inundation, to discuss with him his working on a third-party review, Suau told the audience during his Oct. 24 presentation. Suau added that it had been more than 20 years since he had been a county Public Works employee; he has been semi-retired since he sold his water resources consulting firm a couple of years ago, he added.
After he told Anderson that he would do the work for free, Suau continued on Oct. 24, Anderson promised him that staff members would provide him “whatever you need” for his work, “and they’ve been pretty true to that.”
On Aug. 28, as part of the regular County Commission meeting that day, Commissioner Mark Smith proposed the workshop that will be held next month, given the devastation that Laurel Meadows residents and others suffered after Tropical Storm Debby stalled over the northern part of the county for about 36 hours, dumping more than 18 inches of rain in some locations.
During an Aug. 27 presentation to the commissioners, Rich Collins, director of the county’s Emergency Services Department, pointed out that the National Weather Service had informed county staff that the rainfall from the storm would be in the 6- to 8-inch range, over five days.
Data, hypothesis and confirmation
When stormwater engineer Suau addressed members of the public the evening of Oct. 24 at Selby Public Library in downtown Sarasota, he pointed to data and imagery in pinning the Laurel Meadows flooding on a breach in a decades-old earthen dike created between Phillippi Creek and Cownpen Slough.
That dike, he pointed out, was built to prevent water from Cowpen Slough from flowing north. County staff also wanted to prevent water flowing from the east into the Phillippi Creek Basin.
Suau explained that Sarasota County has rain gauges located throughout the county that are always measuring water. Within the Phillippi Creek Basin, he said, approximately 18 gauges have been put in place — what he characterized as “a good spread of ’em.”
Using the data from those gauges, Suau added, he found that, “for the most part, the highest [amount of] rain fell out east” and in the northern part of the county during Debby’s rainfall. The total, he noted, was about 13.2 inches over three days, though some sites had even higher numbers.
When he delved into the distribution of the rainfall, Suau continued, he found that “it was pretty consistent” in the Phillippi Creek Basin. However, he pointed out, approximately 83% of the rain came down in the middle 24 hours of the event. That total, he said, was about 11 inches.
The county’s stormwater model, he noted, was developed to deal with 10 inches in 24 hours, as Anderson of Public Works has explained to the County Commission.
During Anderson’s Aug. 28 presentation to the board, he stressed, “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, Anderson continued. Statistically, that involves a 1% annual chance of 10 inches of rain falling in 24 hours.
Suau explained that infrastructure in urban areas cannot deal with rainfall as intense as the amount that Debby dropped on the county.
In many locations, he continued, the water levels were higher than that of a 100-year storm. “Those generally happened in low-lying areas.”
Moreover, he noted, he was able to compare the water levels to what the stormwater model would have predicted.
The model for the Cowpen Slough Basin was pretty accurate, he said.
However, Laurel Meadows and the areas next to the Celery Fields Stormwater Management Project “experienced even greater flooding than expected or predicted.”
In regard to the Celery Fields, Suau said, county staff can close a weir on what is called the Main C canal downstream of that property “and basically back water up into the Celery Fields and around it.”
(In a Nov. 14 email to County Administrator Jonathan Lewis, Anderson of Public Works explained, “Main C Weir structure just downstream of the Celery Fields contributed to the flooding in the Celery Fields area (Palmer/Apex).” He added, “The operation of the Main C weir has been standardized since it was installed in the early 2000’s.)
Staff typically does close that weir, Suau told his audience on Oct. 24, to reduce flooding downstream.
With Debby, Suau continued, “It was basically a [manual] manipulation of the water” that resulted in flooding.
However, with Laurel Meadows, he said, it was evident that something was causing a lot of water to flow into the area.
When he began investigating that situation, he added, he speculated that a breach had occurred in the dike between Cowpen Slough and Phillippi Creek. As water flowed through that breach, he pointed out, it flooded Laurel Meadows.
About a week after he conveyed his hypothesis to Anderson of Public Works, Suau said, he found a video on YouTube that a county resident had taken with a drone, showing the flooding in the area of Laurel Meadows.
Suau said he was able to communicate with the person who took the drone video after Debby’s rainfall ceased. Even then, Suau noted, the water was continuing to rise in Laurel Meadows. Therefore, he said, he believed the breach had to be south of the neighborhood, in the area of Delft Road. He also conveyed that information to county staff, he added.
Ultimately, Suau said, lidar indicated that the breach had been growing for about five or six years.
(As the National Oceanic and Atmospheric Administration’s National Ocean Service explains, “Lidar, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses — combined with other data recorded by the airborne system — generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.
“A lidar instrument principally consists of a laser, a scanner, and a specialized GPS receiver,” the webpage continues. “Airplanes and helicopters are the most commonly used platforms for acquiring lidar data over broad areas. Two types of lidar are topographic and bathymetric. Topographic lidar typically uses a near-infrared laser to map the land, while bathymetric lidar uses water-penetrating green light to also measure seafloor and riverbed elevations.”)
County staff sent him a video showing the breach, Suau said. He saw Brazilian pepper trees and woody plants in the breach. However, he added, no leaves were left on them, which indicated that “a lot of water had flown through there.”
After he watched the video, he continued, “We were finally able to simulate exactly what happened.”
The breach was repaired before Hurricane Helene struck in late September, he told the audience.
A county addendum
In an Oct. 28 email to County Administrator Lewis — which Lewis shared with the County Commission — Anderson of Public Works wrote, “Mr. Suau met with me and our stormwater team on October 21, 2024 to review his findings. Ultimately, his conclusion is that a breach in the basin divide (earthen berm) between the Cowpen Slough and Phillippi Creek basins allowed higher water from Cowpen Slough to enter into Phillippi Creek, resulting in the depth and duration of flooding experienced in the Laurel Meadows area. At this time, we do not have any data or findings that differ from Mr. Suau’s but we will not be able to agree or disagree with his findings until our evaluation is complete.”
Anderson then noted, “Regarding the berm breach between Cowpen Slough and Phillippi Creek; following Post-Debby site inspections, we identified the breach located east of the Bee Ridge Landfill just north of Misty Creek. While we can’t say this for sure, the breach is likely to have developed or been greatly exacerbated during Hurricane Debby. There was a large spread of sediment on the Phillippi Creek side of the berm indicating significant positive flow/erosion from Cowpen to Phillippi. Public Works Field Services staff backfilled and regraded the area prior to Hurricane Helene to help prevent future overflows between Cowpen Slough and Phillippi Creek. We surveyed the area before [it was] backfilled and are using the data in our post-Debby hydraulic/hydrologic modeling analysis. This data will help us better understand how this breach influenced the flood stages and duration.”