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A wet future: South Florida’s plan to fight flooding if sea levels rise 3 feet by 2075

A portion of Southwest Seventh Street flooded in Miami’s Brickell neighborhood on Nov. 20, 2022.
National Weather Service Miami
/
The Miami Herald
A portion of Southwest Seventh Street flooded in Miami’s Brickell neighborhood on Nov. 20, 2022.

Everyone had to soak: South Florida’s western suburbs faced rain floods, and coastal properties were inundated by king tides.

Last month, over the course of a few days, 12 inches of rain fell on much of Broward and Miami-Dade counties. As western suburbs began to flood, king tides pushed in from the ocean, and there was nowhere for the floodwater to go.

Twenty years ago, the South Florida Water Management District would have simply opened spillways and sent the flood water to the ocean. But not this time. The king tides were just as high or higher than the flood waters to the west.

This scenario is a harbinger of things to come for South Florida, as sea-level rise creeps inland and storms become more intense. The multitude of canals and spillways that drain Miami-Dade and Broward counties are becoming obsolete, and the Army Corps of Engineers and SFWMD are concerned enough to hatch a plan.

“We experienced that in the southern Miami canals,” SFWMD Director Drew Bartlett said during a resiliency panel discussion at the recent Southeast Florida Regional Climate Leadership Summit. “As the storms were coming, we couldn’t do anything to lower the canals because the tides were too high. You could open the gate two to three hours a day to try to get some water out to prepare for that storm, then when the storm hit, you had to wait for the canal water to get to a level that was higher than the coast to let it out.”

The plan, currently in an exploratory phase known as the 216 Study, will end up being very complex and very expensive. In a nutshell, the entire flood control system of South Florida, built in the 1950s and ’60s when Florida had a population of 5 million people, relies on gravity.

We now have a population of 22 million, with less open space to absorb rainfall. Sea levels have risen 8 inches since 1950, according to Florida State’s Florida Climate Center, and NOAA projects them to be 3 feet higher than they are now by 2075.

As sea levels rise, gravity will no longer do the trick. Most, if not all, of the canals and spillways, which send water east toward the Atlantic, will need pumps to keep the western two-thirds of the region from flooding during heavy rain events.

Bartlett said that it’s not the coastal communities that benefit from these plans, as much as the inland communities. “These canals run all the way to the Everglades. … It’s not a coastal issue. It’s an urban-area issue.”

“You used to be able to operate (spillway) gates whenever you needed to,” said Broward County’s chief resiliency officer Jennifer Jurado. “Now, because of the amount of sea-level rise, there are times when you can’t open them, and you have to wait several hours, and of course several hours can generate massive volumes of water that could then take extensive time to discharge.” In other words, vast inland flooding.

Jurado said that 75% of Broward’s taxable real estate lies on the west side of the flood gates, making the 216 Study crucial to the region’s future.

If everything goes to plan, the Army Corps of Engineers and SFWMD would install 20 pumps in the matrix of canals in Miami-Dade and Broward counties. “Some gates would be raised in height, but we would also have to tie in the gates to higher lands,” said SFWMD resiliency officer Carolina Maran.

The need for taller gates is not lost on Jurado. “Water can actually lap over the top of some of the gates during extremely high tides,” she said.

Gauging sea-level rise

The “study” phase means the Army Corps of Engineers is asking lots of questions about what life looks like 100 years from now in South Florida, and what the flood infrastructure will need to be to protect it, said Col. James Booth of the Army Corps of Engineers during the panel discussion.

“The Corps is taking into consideration what sea-level rise curves we’re going to be using, what’s actually going on with rain intensification, are we using the right models? Are we designing a system that’s ready to handle that?”

In an email, Tim Gysan, the Corps’ project manager for the study, and lead hydraulic engineer Amanda Bredesen, said that their study will assess sea-level rise across the project life cycle of 50 years, from 2035 to 2085, and will be “evaluated under low, intermediate, and high sea-level rise scenarios to determine the overall project performance.” The low scenario shows 1.2 feet of rise since 1992, intermediate shows 2 feet or rise and the high scenario predicts 4.4 feet of rise since 1992.

Maran said SFWMD is doing its own sea-level rise modeling. “When we run our studies we look at plus-one feet, plus-two feet and plus-three feet of sea-level rise.”

According to NOAA, plus-three feet will be the sea-level rise in the year 2075. NOAA uses various models, and Maran said 3 feet by 2075 was an “intermediate” scenario.

The most vulnerable spot in Broward

SFWMD studies show that the most vulnerable spot in Broward are gates in C14 West Basin, which encompasses Tamarac, Coconut Creek, North Lauderdale and Margate adjacent to the Stranahan River. They only provide service for a five-year event.

“One of the big reasons, of course, is the higher sea levels,” Maran said. “But it’s also because development occurred in this basin, and when we have a five-year rainfall event, we already see some ponding — the capacity of the system is undersized for the development we have there.”

The Middle River spillway in Oakland Park shows higher water on the inland side, and low water on the downstream side. During king tides, or as sea levels rise, salt water can breach the top of the spillway, making flood control impossible. (Mike Stocker/South Florida Sun Sentinel) Maran said that a five-year rain event or a 50-year rain event mean different things in different flood basins, so she could not say what that specific amount of rain would be countywide.

Adding canal storage

Jurado said that in addition to beefing up gates and adding pumps, the county should consider making canals larger to hold more water.

The Army Corps study does not currently address this. “We may need to be able to hold more water for longer periods of time, and you can’t do that without widening the cross section, which might mean dredging deeper, wider, and elevating banks. So that’s something that we would intend to take up,” she said.

Who’s going to pay for all this?

This a vastly expensive tentative plan, with costs in the billions of dollars.

Each gate and therefore each pump is different, but the ballpark cost to design, build and install each pump is $100 million, Maran said.

Bartlett said SFWMD is chasing funding sources with federal and state partners, and that the Army Corps of Engineers is a “partner for funding and expertise.”

Booth said he wants to get the plan considered by congress for the Water Resources Development Act of 2026.

If the Corps’ chief of engineers approves the recommendations, Congress can consider it for approval. Then comes appropriations and detailed designs.

Another concern is drinking water supplies. “Typically (we) have gates close to prevent salt water from coming inland. The gates protect the water supplies,” Jurado said.

Fresh water from the Everglades is one of the primary buffers against saltwater intrusion.

Bartlett said that’s why the Comprehensive Everglade Restoration Plan, which congress passed in 2000 but which has languished in fits and starts, is so crucial.

“We’re trying to get more water in the Everglades to supply that head to keep the saltwater out. Trying to keep the water in the canals and keep the saltwater from coming in the canals has that same effect.” Expanding canal volume with higher gates and deeper canals would aid that effort.

More than pumps

Three feet of sea-level rise may require more than just pumps.

“It’s going to become challenging with additional sea-level rise because the coastal areas that are not behind a gate are subject to what’s happening tidally. With time, we might choose to add additional gates, to expand the areas farther east that is provided flood protection by these gates,” Jurado said.

“Or we might find that there’s a need for some other sort of tidal barrier that is enclosing these areas. It could be that there are areas that with enough sea-level rise we’re just pulling back, and in time we might not occupy that area.”

Jurado said that Broward does not have a “managed retreat” policy, but that the 216 Study could illuminate the situation.

“The study and adaptation strategies that we put in place will reveal areas that longer-term might look difficult in terms of residential occupancy. But it would be premature to offer conjecture as to where those areas might be.”

This story was produced in partnership with theFlorida Climate Reporting Network, amulti-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.

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