TROUT CREEK — Cyclists zip through the forests. Fishermen lean over the boardwalks. Picnickers gather under the shelters. As all of this happens at eight Hillsborough County parks near New Tampa, few realize what also could occur: These parks could fill 10 feet deep with floodwaters. The parks are named Trout Creek, Morris Bridge, Off-road Loop Trail, Flatwoods, Dead River, Sargeant, Oak Ridge Equestrian Area and Jefferson Equestrian Area. They are clustered around the Hillsborough River. After torrential, hurricane-caliber rains, they will take the river's overflow, sparing Tampa Palms, Temple Terrace and Tampa downstream. "All of those parks are designed to be under water," said Mike Holtkamp, operations director for the Southwest Florida Water Management District, which owns the land. When they flood, it won't be an accident.
Swiftmud monitors the levels of area rivers at many points. When flooding threatens, the water district pays special attention to the Hillsborough River sensors at Fowler Avenue.
Recently, the water hovered at Fowler around 21.5 feet above sea level. If floodwaters swelled it to 24 feet, Swiftmud's engineers would intervene.
More than 2 miles upstream, pulleys would lower two massive steel gates on Structure 155 at Trout Creek Park. With these, engineers could totally seal off the Hillsborough. Or they could drop the gates only partway into the rushing floodwaters.
The blocked river would promptly back up into the park, trapped by Structure 155 and its attached levee, which flanks 6 miles of Interstate 75.
As the waters rose in Trout Creek Park, they soon would flow to the Tampa Bypass Canal, which would carry them south. The magic number there is 30 feet. Water that high would prompt Swiftmud to begin opening a series of gates on the Bypass Canal to release water on its way to McKay Bay.
Bill Moyer of Lutz has lived in the area for 50 years, and has been enjoying the Hillsborough River for almost as long.
"What's unique about this area is it's so close to town and it's a wilderness," said Moyer, 75, a retired Tampa firefighter.
Moyer boated down the Hillsborough in 1960, when it was the most destructive.
"A bunch of houses floated into the river," he said. "They had been hanging off the banks."
The Hillsborough drains 640 square miles. Its watershed reaches north into Pasco County, almost to Hernando County, and east into Polk County. Rainfall records show only three years since 1915 when the rain landing in the Hillsborough River watershed exceeded 70 inches. Two were 1959 and 1960.
In March of 1960, the river rose into more than 100 homes, including some of Tampa's priciest, forcing the families to evacuate. That August brought another torrent, sending water back inside more than 75 houses.
Then, on Sept. 11, 1960, Hurricane Donna came through. A St. Petersburg Times reporter who viewed the river from a helicopter counted 100 houses swamped by the "muddy brown waters."
The government put its foot down.
As Donna passed, state legislation creating Swiftmud was being drafted. In 1962, Congress authorized major flood-diversion projects. In 1963, Florida voters approved a $50-million bond issue to acquire flood-detention land.
It included 26 square miles that eventually would become known as Lower Hillsborough Wilderness Park, future home of eight county parks.
The Corps of Engineers initially proposed a sprawling lake for the property, Holtkamp said. But a growing appreciation for the biological value of swamps led authorities to scrap the lake. The levee, the Bypass Canal, the parks and flood-control structures were built in the late 1970s and early 1980s.
These changed the development outlook for New Tampa.
"The Tampa Palms that we know today would not be there if we had not built the Lower Hillsborough Flood Detention Area," Holtkamp said. "It had a significant impact on flood levels downstream of the levee."
The last flooding of note occurred in the winter of 1997-98, when Florida's normal dry season became soaked by El Nino rains.
"We actually had people camping out at the structures to make gate changes," Holtkamp said. "It was so wet, all the wild pigs were around the road."
Brooms and hoses
El Nino forced Hillsborough County to close Trout Creek, Morris Bridge and Dead River parks, along with several near south Hillsborough's Alafia River and Lutz's well-named Lake Park.
"We know that they're going to flood," said John Brill, spokesman for the Hillsborough County Parks, Recreation and Conservation department.
"It's a shame to close a park," he said, "but it's not a big deal if we can save some homes down-river from flooding."
Along Morris Bridge Road, Trout Creek and Morris Bridge parks would flood first, because they are the lowest and closest to the river, Brill said. Flatwoods Park, true to its name, is higher ground and less likely to flood.
Holtkamp said that some of the parks' features were designed with flooding in mind. Boardwalks, for example, are supported by pilings with enlarged bases so buoyancy won't pull them out of the ground.
Brill said the parks' few electrical features would have to be checked, and plumbing might require repairs. But few other problems are expected.
"When the waters recede, we go in with brooms and water hoses and clean the stuff out," he said.
Wild animals would have to fend for themselves, Brill said. "They just know they've got to head for high ground."
Holtkamp said the system was designed to manage a flood 25 percent more severe than a "100-year flood" — the worst one-day event expected over a typical century. In that case, the water level would rise to nearly 40 feet.
That's 17 feet higher than last week's level of the Hillsborough at Trout Creek Park. But it's 8 feet lower than the top of the levee. Such a flood would inundate all 26 square miles of the wilderness area.
Last year, consultants tested a scenario even worse, Holtkamp said. They modeled the effect of 48 inches of rain over three days. That would flood an additional 16 square miles. It would raise water in Trout Creek Park to 45 feet.
That's 3 feet shy of the levee, which — given all the displaced wildlife — could be a busy place.
Bill Coats can be reached at (813) 269-5309 or firstname.lastname@example.org.