Is Houston flooding a possibility here?
Robust drainage unable to handle a Harvey
There is little doubt among Central Florida authorities about what would happen if a Hurricane Harvey wobbled into the region and unleashed a tidal wave of rain.
“I don’t think that any developed area is ready for that,” Orange County Mayor Teresa Jacobs said.
Destruction from such a storm — which most experts say would be unlikely to happen here — almost certainly would be widespread: flash flooding initially at lakes and then an agonizingly slow and unstoppable rise of stagnant water along rivers.
After seeing the destruction from Harvey in Texas — and now worries about Hurricane Irma churning across the Atlantic — Central Floridians wonder if their homes are safe. Some areas are more worrisome than others.
The St. Johns River in Sanford and Seminole County, the Econlockhatchee River system not far from the University
of Central Florida and Shingle Creek along west Kissimmee in Osceola County all would be susceptible to flooding. Neighborhoods south of downtown Orlando, including the Delaney Park and Lake Davis areas, could also be at risk.
“It would be pretty devastating and, just talking generalities, everything would fill up pretty significantly,” Orange County’s top stormwater engineer Mike Drozeck said. ”How much, I can’t really say.”
If flooding has occurred somewhere previously, the experts say, chances are it would return more fiercely by magnitudes. If a home is near a flood plain, they say, survival chances are iffy.
“We’ve never seen anything like that so I’d have to say everywhere, all over, you would have to watch,” Winter Park’s city engineer Don Marcotte said of flooding from a Harvey deluge.
Even for high and dry neighborhoods, including where there is more elevation north and west of Orlando, there is the specter of an oak tree toppling, plugging drainage and causing a mega-storm’s deluge to rapidly bring on localized flooding.
Seminole’s head of emergency management, Alan Harris, draws from Tropical Storm Fay in 2008, which caused that county’s worst flooding in history.
“That was only 16 to 20 inches of rain, depending on where you were in the county,” Harris said. “The flood caused major damage to homes along the St. Johns River.”
A Hurricane Harvey may play out as a much larger version, he said.
“We would get the instant, localized flooding,” he said. “We would also a week later be looking at some slow flooding along the St. Johns River, which is painful for people.”
Harris said a Harvey-scale storm for Seminole County may spread more widely than in Houston.
“It would look much worse but it wouldn’t be as deep,” Harris said. “I don’t think you would see rescues here by helicopters but certainly by boats.”
The heaviest rainfall expected in a century in Central Florida amounts to less than 11 inches within 24 hours. That’s the standard for design of highways, realestate development and stormwater systems.
Hurricane Harvey delivered nearly five times as much in a couple of days; Cedar Bayou, Texas, recorded 51.88 inches, a record for the most from a storm in the continental United States.
But precise and realistic calculations of where, when and how fast flooding would occur, and whose frantic efforts with sandbags would succeed and whose home would be left uninhabitable for a year, can be extraordinarily complex, experts say.
In fact, Orlando Mayor Buddy Dyer is optimistic his city would fare better with a Harvey-scale storm than Houston.
Porous soil in much of Orlando would absorb some storm water, while Houston has mostly one choice for flooding: “It has to carry it away,” Dyer said. Orlando is fortunate, too, for its elevation. Original sections of the city were built at 100 feet or more above sea level.
The city also has 168 drainage wells, or wide holes drilled more than 100 feet into the ground. Their job is to dispose of excess water in lakes that don’t otherwise have a sufficient outlet.
But the wells are likened sometimes to a straw draining a bathtub; they can take days, not hours, to lower a swollen lake.
Because of the wells’ limits and because of lower elevations, neighborhoods of Orlando’s “Southeast Lake District” — which includes lakes Davis, Cherokee, Lancaster and others — have more to worry about.
A photo in the Orlando Sentinel in July 1960 depicts that area with the caption: “Flood waters join two lakes … Lake Cherokee and Lake Davis.” Thousands of residents were homeless after that flooding, from a series of thunderstorms during a wet summer, rose as high as mailboxes.
The city since has equipped the area with buried pipes connecting the lakes as a way to shuttle floodwater.
But that core area of the city remains a bowl. Its bottom is Lake Greenwood at 58 feet above sea level and its lowest rim is 103 feet above sea level near Michigan Street.
And that large depression has relatively little natural drainage.
“If we were to get feet of rain in a couple days’ time, we would have flooding,” said Jim Hunt, Orlando’s deputy director of public works.
Area residents may give little thought to flooding potential — there are only about 10,000 flood-insurance polices in Orange County and nearly 300,000 single-family homes and business properties — because stormwater systems have gotten better over the years.
Regional flood controls absorb deluges of 2 or 3 inches without leaving puddles behind an hour later.
“For many years, we had this old, broken-down, junk equipment,” said Jeff Charles, a stormwater-operations manager with Orange County for three decades. “We have gotten a lot better at being proactive and not reactive and we’ve gotten a lot better equipment to maintain the big, primary outfall canals.”
Those systems may more than meet their match with a Harvey but Orange County’s engineer, Drozeck, suggested it’s nearly inconceivable the region would commit to stormwater plumbing designed for a Harvey.
“Our costs would be enormous, our pipes would be gigantic, our ponds would be gigantic,” he said.