Some South Florida canals failed during no-name storm. Sea rise will make that worse
More than a foot of rain fell in some spots in Broward County last week, double or triple the amount most streets in the region are designed to handle.
As residents in a handful of coastal communities — including Dania Beach and Oakland Park — anxiously waited for floodwaters to drain out of their neighborhoods and roads, the opposite was happening. A few critical canals designed to move water east were overflowing, spilling into streets, parks and yards.
The multi-day rain event coincided with a king tide, one of the highest tides of the year. That high tide effectively backed up the canals South Florida relies on to drain water to rivers, bays and the Atlantic Ocean. They’re largely the same canals dug hundreds of years ago to drain the Everglades and open what were once wetlands to sprawling development.
Sea level rise, driven by unchecked human greenhouse gas emissions, has gradually made king tides higher, meaning that South Florida’s 80-something-year-old canal system fails more often. The drainage system, run by the South Florida Water Management District, was originally designed for a far smaller population than South Florida has now, and for lower sea levels with less frequent and intense rainstorms. Though massive pumps help move water now, the system also relies on gravity — water from higher elevations flowing down toward the coast. Rising tides reduce that flow as well.
“The system is over capacity already, we have results showing that,” said Carolina Maran, the resiliency officer for the district. “We can normally capture about six inches of rain. We know it’s going to get lower and lower if we have more sea level rise.”
That’s a huge problem for coastal cities, which rely on space in the district’s canals to drain the water on their streets.
On stage at the Southeast Florida Regional Climate Compact Summit last week, the district’s executive director, Drew Bartlett, said the heavy rainstorm was a good example of the problems the district is already starting to see more frequently.
“We’re seeing it in Miami-Dade, we’re seeing it in Broward and eventually we’re going to see it in Palm Beach, all the way up,” he said. “We couldn’t do anything to lower the canals because the tides were too high.”
Failure, in the district’s case, can look like what happened in Broward last week.
The worst of the rain happened overnight Wednesday, and on Thursday morning, the city of Oakland Park found itself with extra water flooding city streets, swamping some cars and filling local parks. The C-13 canal, which it relies on to drain water, was spilling over its banks. The gates to an upstream floodgate and pump were wide open, pouring out a steady stream of water into the overburdened canal.
The city asked the district to shut its gates for a few hours, so the coastal city had some time to drain. That’s a tough decision for the district, whose primary mission is to avoid flooding people’s homes and businesses. In this case, Maran said, the district determined it could safely shut the gates for a while and avoid flooding any western cities.
By Friday, Oakland Park said, the water receded.
“We found a balance to see how much we could safely hold and avoid flooding,” Maran said. “This is the only way out. All of us are trying to get to this one canal to get the water out.”
In this case, the solution worked, and few — if any — homes or businesses flooded. But Maran said conflict like this could become more common as climate change raises sea levels further and makes heavy rainstorms more likely, potentially pitting inland cities against coastal cities.
That prospect is frustrating for eastern cities like Dania Beach, where Mayor AJ Ryan said they depend on the water management district’s canals to stay dry and undamaged after a big storm.
“King tides, groundwater levels, inches of projected rain, I can calculate,” he said. “What I can’t calculate and can’t get answers on is how the South Florida Water Management District makes decisions.”
Ryan said he met with the mayors of Fort Lauderdale and Hollywood on Friday to discuss how to better collaborate with the district during rainfall events like last week’s. All three coastal cities agree that they need to come up with an answer that will keep their communities from flooding during the next storm.
“We’re facing an issue right now in the present that we need to address and we need to come up with solutions for the future,” Ryan said. “We need to work with the South Florida Water Management District, the county, the state, whatever it takes. I’m willing to talk to whoever is willing to listen and whoever will help us.”
One of the possible solutions to this problem was already on display for this storm, in Miami-Dade. While Miami-Dade did see less rain than Broward did, the other reason the county saw less flooding was because of a giant retention pond the district built about a decade ago. The C-4 reservoir is a massive open pool that the district can direct excess rainwater toward during a storm, which keeps inland communities like Doral and Sweetwater drier. It was part of a $70 million project to reduce flooding in western Miami-Dade after another no-name storm swamped more than 90,000 homes in 2000.
No such structure exists in Broward, but officials with the district are trying to find federal grants to help make one. And beyond the grants, the district is also in line for a multi-billion dollar upgrade to its system, courtesy of the U.S. Army Corps of Engineers.
Last year, the Corps agreed to take a look at the failures in the SFWMD drainage system and write up a study suggesting ways to fix it, like installing more powerful stormwater pumps, raising the banks of canals or moving the floodgates more inland.
Moran, the district’s resilience director, said the study — and its fixes — are crucial for allowing South Florida to remain habitable in the next 50 years.
“For us to continue to live here and minimize flooding, we need to minimize impacts on that system,” she said. “We need to bring the system up to speed for what we need now and what we will continue to need.”