What to know about river flooding in Tampa Bay this hurricane season

Yahoo

29-05-2025

Much of Mark Fulkerson's work starts after a catastrophic storm has passed and its rain has ceased.
As a chief engineer for the Southwest Florida Water Management District, he spends the weeks following a hurricane documenting high-water marks and measuring how closely the agency's flood maps match up against real flooding.
When Milton made landfall as a Category 3 hurricane last October, it dropped near-record rainfall on the Tampa Bay area and swamped homes along the region's many rivers and lakes.
Fulkerson found that many of the squiggles darting across flood maps his agency has spent decades developing lined up quite accurately with floodwaters reported during and after Milton's deluge.
Still, the storm season of the century took many Tampa Bay residents by surprise.
'I hope it's the flood event of my career,' Fulkerson said. 'I hope we don't have another one like it.'
Fulkerson said the agency's job is to manage water, but Swiftmud can't entirely control flooding.
'We can't stop it from happening. But there are things we can do to help manage flood risk — by doing the modeling we do — to alert people, by trying to work with the cities and counties on projects where they make sense,' he said. 'You get rain like Milton, there's no way you're going to stop that water.'
The onus is on homeowners and residents to know the boundaries of nearby flood zones and stay up to date on local warnings, he added.
Here are some tips water managers, researchers and forecasters say could help prepare for future river floods:
Even days after Hurricane Milton made landfall, many rivers and creeks around the region still hadn't crested. The delayed flooding surprised residents who thought they had been spared from devastating floodwaters, only to have the rain catch up to them later.
Water levels along rivers and lakes often lag weeks or months behind other coastal and inland areas after powerful storms due to natural hydrological processes. Geography, like the elevation around a home and the depth and shape of a river, dictates how and when a water body will flood following extreme rain.
Milton set records for river heights in the Tampa Bay area. At its peak, the Hillsborough River rose above 38 feet and shattered a 2017 record by nearly 4 feet, according to a water gauge at Morris Bridge.
The Withlacoochee River crested at 19.7 feet nine days after Milton made landfall, according to a water gauge near its headwaters. It was the highest water level recorded there in 90 years.
The heaviest of Milton's rain fell in the Green Swamp — vast wetlands stretching across Polk, Lake, Sumter, Hernando and Pasco counties that serve as the headwaters for four major waterways: the Withlacoochee, Hillsborough, Ocklawaha and Peace rivers.
The upstream deluge carried floodwaters down the rivers and flooded communities.
Cypress Creek, a major tributary of the Hillsborough River, crested at a record high of 15 feet four days after landfall. Water levels stayed high for weeks, shocking longtime Pasco residents.
The Cypress Creek wetland basin, which serves as the drain-off for the surrounding developments, was overwhelmed by excessive rainwater from Milton, Fulkerson said. Saturated wetlands in Big Cypress Swamp caused flooding in Land O' Lakes and Wesley Chapel.
About 25% of the water management district's jurisdiction is made up of wetlands, Fulkerson said. They absorb and store rainwater. Levels often fluctuate during Florida's wet and dry seasons. When those wetlands fill up, run-off has to find an alternate path.
Water has three places to go. It can soak into the ground, filling the aquifer — which serves as Florida's main drinking water supply — and raising the water table. Runoff might drain to rivers that rise and cause flooding along its banks. Or water flows across the land and collects into a low-lying area called a closed basin.
'It's got nowhere to drain after that,' Fulkerson said.
After three months of above-average rain last summer, the region's ground was saturated with water. Milton's deluge pushed watersheds to their brink.
The National Water Prediction Service provides a tool that identifies water levels in rivers across the country. If you zoom in on Florida, you'll find little dots lighting up the entire state.
Each dot color represents the river's flood stage: Green (no flooding), yellow (action), orange (minor flooding), red (moderate flooding) and purple (major flooding).
Like tidal gauges that measure coastal water levels, each river has different heights at which flooding can occur.
The tool also provides a forecast for future river heights: A blue line shows observed water levels, while a dotted purple line shows the water level forecast.
But river flooding is difficult to predict, according to researchers.
'Trying to predict how high a river will get, there are different aspects that kind of can complicate some of those predictions,' said Katherine Serafin, a coastal geographer and assistant professor at the University of Florida.
Where exactly the rain will fall, its timing, how many bands of rain a tropical system will bring and how fast the rain will move over land are estimated in order to forecast flood risks.
The river's depth is often an overlooked factor, Serafin said. Submerged debris from past storms may fill up a riverbed, causing it to rise quicker than expected.
The river gauge site also displays current flood warnings imposed by the National Weather Service — shown on a tab under the specific river gauge — laying out hazards and further flooding details.
Original floodplain maps used by the Federal Emergency Management Agency to set flood insurance rates were first developed in the 1980s, Fulkerson said. Development in Florida has boomed in the decades since, making many of those calculations outdated.
One of Swiftmud's longest-running projects has been to update them: Over the past 25 years, the agency has made new renderings of flood maps for more than 130 watersheds, making up 75% of the district.
'The hope is that residents are aware when they buy property, they know what they're getting,' Fulkerson said.
The flood maps take into account factors like elevation, soil type and land use.
Driven by gravity, water drains to the lowest point it can reach and pools there. Sandy soils drain more quickly than dense clay. Knowing what the ground beneath and the topography around your home are like can help evaluate flood risk.
Fulkerson said previous flooding is another big indicator of risk.
'A lot of areas that we saw flooded this past year, they flooded in the past,' he said. 'Whether we lived here or not, it's happened.'
An influx of new Floridians moving to the area has also contributed to a lack of flood awareness.
'One thing that I heard from a lot of the residents is just not having any clue it could happen,' he said. 'You lose a lot of that historical knowledge, too, when people sell or people pass on.'
Driving around the region, even six months after Milton, Fulkerson still sees pockets of standing water in places where it normally wouldn't pool.
'Anytime you have a big flood one year, depending on how much rain you get between then and the next rainy season, we could be starting a lot higher and have less room to breathe before the next hurricane season,' he said.
But below-average rainfall at the start of the year has balanced out the region's saturation.
Tampa Bay's rivers have long flushed out Milton's rain to open seas. Some lakes remain slightly elevated. Aquifer levels are high, but steadily dropping back to normal.
And Fulkerson said there's still time for water stores to deplete before hurricane season again brings the threat of flooding.
'For the most part, we seem to be recovering,' Fulkerson said.
The Tampa Bay Times launched the Environment Hub in 2025 to focus on some of Florida's most urgent and enduring challenges. You can contribute through our journalism fund by clicking here.
• • •
For Tampa Bay, Helene was the worst storm in a century
More hurricanes are slamming the Gulf Coast. Is this the new normal?
Want to know what areas are flooding in Tampa Bay? Here's where to look.
Checklists for building all kinds of storm kits.