Funding sources to be part of report
Sarasota County Commissioner Teresa Mast has won the full support of her colleagues in seeking a report from county Stormwater Department staff regarding initiatives to improve Cow Pen Slough, as well as options for paying for that work.
During discussions about county stormwater issues since her election to the board in November 2024, Mast frequently has noted her District 1 constituents’ desire for county measures that would prevent residential flooding from Cow Pen Slough.
The report she requested last week will be handled as a “Board Assignment,” a designation that commissioners and staff use for such requests of staff. It typically takes 30 days for staff to complete those assignments, County Administrator Jonathan Lewis has explained in the past.
During their regular meeting on March 3, Mast reminded her colleagues that, following the 2024 storm season, stormwater engineering consultant Steve Suau of Sarasota determined that a breach in a berm between Cow Pen Slough and Phillippi Creek likely was the cause of the unexpected inundation of the Laurel Meadows neighborhood in the eastern part of the county. That flooding occurred as a result of the significant rainfall that Tropical Storm Debby dropped in certain areas in early August 2024.
County Emergency Management Chief Sandra Tapfumaneyi was able to obtain video from the University of Miami that showed how Debby lingered over part of Sarasota County, as Rich Collins, director of the county’s Emergency Services Department, reported to the commissioners in late August 2024.
Collins told the commissioners that the highest level of rainfall recorded in the county was more than 18 inches, and the period during which it fell was approximately 36 hours.
In October 2024, during a public presentation at Selby Library in downtown Sarasota, stormwater engineer Suau explained that an earthen dike created between Phillippi Creek and Cow Pen Slough decades ago was designed to prevent Cow Pen Slough’s water from flowing north. County staff also wanted to halt water flowing from the east into the Phillippi Creek Basin, he noted.
Using the data from county rainwater gauges, Suau added, he found that, “for the most part, the highest [amount of] rain [from Tropical Storm Debby] fell out east” and in the northern part of the county. 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. Moreover, 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, Suau said, was developed to deal with 10 inches of rain in 24 hours. He explained that infrastructure in urban areas cannot deal with rainfall as intense as the amount that Debby dropped on the county.
A waterway that never has been surveyed
On March 3, in addressing her fellow commissioners, Mast said, “I’ve spoken with our county administrator at length, and I know that he and staff, including our wonderful [stormwater] engineer Ben Quartermaine, have been working on different options on what could be [done in regard to Cow Pen Slough].”
Mast pointed out, “Cow Pen Slough has never, ever been engineered — or surveyed.” It was created by people involved in agricultural operations in the county, she explained, to help with drainage from farmland. “It is an intricate part of the community,” she noted.
“I actually stood in 3 feet of water, helping toss sandbags in homes that had been affected [by the flooding from Tropical Storm Debby],” Mast told her colleagues.
Then she asked for the other commissioners’ support in directing Lewis to bring to the board a report, soon, on staff’s ideas about how to improve the situation with Cow Pen Slough, “so we can look for some funding to get this resolved … as early as possible.”
At Lewis’ request, Mast formally made her request a motion, and it passed unanimously.
A historical perspective
A 1997 report on a basin master plan for Cow Pen Slough, prepared by the U.S. Department of Agriculture’s Natural Resources Conservation Service in Gainesville for the county’s Stormwater Environmental Utility (SEU), explains, “The Cow Pen Slough Basin contains 63.2 square miles which ultimately drain into Dona Bay,” which is in the area of Nokomis. The basin “is bordered on the east by the Myakka River basin and on the west by the Phillippi Creek Basin and other coastal streams,” the report added.
(The Sarasota News Leader found the report through an online search.)
As of the latter part of the 1990s, the report continued, the Cow Pen Slough Basin was “primarily rural in nature, with the majority of the land uses being classified as rangeland, crop and pastureland, orchards and groves, and upland forests. There ae localized areas that are primarily urban in nature around Bee Ridge and north of Venice, with the majority being classified as residential.”
In explaining the purpose of the master plan, the report said, “The population of Sarasota County is increasing rapidly. Existing flood free structures within the county need to be protected from increased flows caused by increased impervious surfaces caused by development. New developments need to be designed in recognition of existing floodplain patterns and need to consider the impacts of storm events on upstream and downstream watersheds.”
In 1991, the report noted, the county’s Stormwater Environmental Utility “initiated a county-wide Basin Master Planning program. Each Basin Master Plan will include a detailed study of the existing and potential water resource problems within the Basins of the county.”
Another section of the report pointed out that “Cow Pen Slough has 14 miles of improved channel with gravity drains entering from both sides. … The original Watershed Plan called for five flood control structures. However, only three were built. The structures were designed for grade stabilization and water conservation and consist of concrete drop spillways with 20 foot weirs and 4 foot high radial gates. These structures were designed [like islands,] with overflows being diverted around the structure to prevent overtopping.
“Structure 1 is located just north of Laurel Road,” the report continues, while Structure 2 “is located a little more than a mile south of Highway 72, and Structure No. 3 is located approximately midway between Highway 72 and Highway 780 [Fruitville Road].”
The report added that, as of 1997, Structures No. 1 and No. 2 still were in operation, while Structure No. #3 “failed in 1967 after a 5.17 inch rainfall event,” and it never was replaced.