Six months after Hurricane Debbie abandoned hundreds of Manatee County homes, the new report answers questions about the role of Lake Manatee Dam in floods.
Some residents wonder whether the release of the 18 billion gallon dam is responsible for flooding in the Braden River area and other parts of the county, including the Lakewood Ranch.
But two separate reports – one commissioned by the Manatee County government and the other commissioned by local developers – refuting these claims.
Instead, they point out that they document rainfall, increased development and other infrastructure issues as causes of local flooding.
Hurricane Debbie Floods urge Lake Manatee Dam investigation
Manatee County was already saturated from a wetier July than in July when Hurricane Debbie arrived in early August and dumped record-breaking rainfall in the Bradenton area.
The vast amount of water threatened to overload the approximately 6 billion gallons of Manatee Lake Reservoir, the source of about two-thirds of Manatee County’s drinking water. The artificial reservoir is located on the Manatee River in East Manatee County.
County officials say that in order to protect the dam’s structural integrity, the flow of water that leaves the lake must be increased from time to time in heavy rain.
“If the water rises to the top of that reservoir, it cannot pass through the reservoir, which means it will flush (the dam) and lose the supply of drinking water on the surface,” Natural Resources Director Charlie Hunsicker said at a September press conference.
Officials said the unprecedented rains from Hurricane Debbie have urged them to release 18 billion gallons of water (around 25,000 Olympic-sized swimming pools) through the dam for several days. Debbie dropped record rainfall of approximately 12-17 inches in Manatee County.
The county acknowledges that the velocity of water flow from the dam can be flooded directly downstream along the Manatee River, where residents have historically experienced flooding.
Authorities defended the release of water from the dam, saying the structure worked as designed. They said the dam was built not to control flooding, but to maintain drinking water and downstream water flow.
However, some East Manatee County residents who did not live downstream of the dam after Hurricane Debbie were convinced that the release was the cause of unprecedented flooding and damage to their homes.
At the time, county officials said it was “impossible” for water from the dam to have flooded a home like a home in the Braden River Basin, more than 40 miles away.
“There were many people who continue to argue that the management of water, levels and releases from this reservoir has caused some kind of problem in the River Club area, Summerfield area, the Braden Woods area of Manatee County,” Hunsicker said. “From a geography perspective, that’s not possible. It was raining, rain, rainfall.”
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Nevertheless, authorities ordered an independent investigation into the causes of local flooding.
At a recent workshop, the county commission heard the results of its long-awaited report.
Analysis found that the dam release had a “minimal impact” on floods downstream of the dam that accepted little or no impact in the Braden River area. The report found that floods were primarily caused by rain.
Another analysis of the Hurricane Debbie Flood commissioned by Lakewood Ranch developer Rex Jensen came to a similar conclusion, saying, “The operation of Manatee River Dam had no effect on Lakewood Ranch floods.”
Patrick Tara, an engineer at Houston-based consulting firm Intera, said his analysis found that rainfall and runoff were primarily responsible for flooding during Hurricane Debbie.
Tara said it used rainfall and flood data from state and federal agencies and counties to map water flows during the storm.
Tara said the water gauge on Ryroad, directly downstream from the reservoir, was the only one that had a strong response to dam release.
The results showed that this release had no significant impact on water levels in other parts of the county, including the Braden River area. Tara said water levels had already peaked in most parts of the basin before the dam’s release began.
“We don’t have enough time,” Tara said. “It’s another weight of evidence that reservoir emissions were not a direct cause of the rising water.”
Tara also adopted the “Coastal Stormwater Surge Model,” a model frequently used by the Florida Department of Transport, simulating the effects of different levels of water on Lake Manatee on downstream flooding.
“The results show that there is little sensitivity to reservoir release,” Tara’s presentation said.
The results of the model showed that high flow from Lake Manatee increased the level around the mouth of the Braden River at less than 1 foot in normal low and high tide conditions. During the flood event, the river will expand and its capacity will increase, resulting in even less water from the dam, Tara said.
“Local rainfall spills have caused a lot of this flood,” Tara said.
Tara also supported the county’s claim that the dam worked as if it was designed during the storm.
“It was never a dam’s mistake,” Tara said. “If the water gets too high in the reservoir, they have to let go of some of it, actually to prevent dams from breaking down.”
However, Tara pointed out that development could play a key role.
“This basin, like the rest of Florida, has experienced a lot of growth and many developments. In addition to that development, there is impermeability. Impermeability areas can affect flooding.”
Tara said Hurricane Debbie has surpassed the state’s design standards for stormwater ponds, which likely has been overwhelmed by many.
Developer Report Pin County’s Responsibility for Some Floods
Another recent report found that the release from Lake Manatee is not responsible for the flooding at Lakewood Ranch.
The Lakewood Ranch developers, first reported by the Florida Trident, Rex Jensen and the Lakewood Ranch Stewardship District, commissioned research to identify potential flooding in the River Club and Summerfield area.
They hired civil engineer Stephen Suau. Stephen Sue worked with the Sarasota County government to address the flood issue. Suau’s analysis found that a lack of stormwater maintenance in Manatee County may have contributed to the flooding of Lakewood Ranch, according to a summary obtained by Bradenton Herald.
The report alleges that the Braden River flow was blocked at River Club Boulevard due to changes at River Club Golf Course, which narrowed the river width as sediment accumulated underneath the bridge.
Jensen shared an email he sent to the county on February 15th, demanding “immediate action” to address allegedly blocked rivers.
Similar to the county’s analysis, the Lakewood Ranch report also found that Lake Manatee dams were not a significant factor in local flooding.
The report concluded that the county should consider stormwater utility fees to fund flood prevention upgrades. This is an issue that the County Commission has addressed in a recent workshop.
East Manatee County residents whose homes were damaged by Debbie’s floodwaters are looking for county officials to come up with solutions as another hurricane season approaches.
During a committee workshop, Valerie Stafford Maris, a resident of Lakewood Ranch, said the Pine Lilly Place neighborhood was flooded three times in 28 years. She raised Jensen’s report and asked authorities to take action on blockages in the Braden River and other issues.
“How can you speed up that so that you can do something before the hurricane season begins?” Stafford Maris asked.
Bill Burns, who lived with his wife Kay Griffin for 46 years from Upper Manatee Road, says the storm caused “the worst flood he’d ever had.”
“It ripped our dock off the deck and washed the river,” Burns told the Bradenton Herald weeks after the storm. “They have built so much around us that we are now one of the lowest places in the river for drainage.”
“And then opens the dam’s outflow gate there… a good god. The dam didn’t violate, so it worked correctly. But it could have been handled better.”
Burns said that when floods from heavy rain threatened the integrity of their homes several years ago, they were forced to build a costly fortress in their homes several years ago.
Burns said he and his wife still work at past retirement ages but could not afford to move.
“There’s no other place to go,” Burns said.
At a recent meeting, county commissioners said they are ready to find a solution to the flood, including reviewing stormwater utility fees, more frequent maintenance and major infrastructure upgrades.
Officials will discuss how a portion of the $252 million federal disaster recovery grant recently awarded to Manatee County can be used at a public meeting that begins Tuesday at the Manatee County Management Building, Manatee Avenue W. and the Manatee County Management Building in Bradenton.
