In what may be one of the most consequential decisions ever made on the island of Key Biscayne, the Village Council on Tuesday set overall engineering targets to combat sea level rise. No funds were committed, but the move sets the stage for more than $100 million of public works projects to rebuild the barrier island’s drainage system.
The vote was 7-0, but even as the Council made the decision, there was deep uncertainty about the cost of not only the stormwater project, but looming and expensive power line undergrounding and beach renourishment projects — not to mention a potential investment in a redesigned Rickenbacker Causeway that Village leaders also voted to advance Tuesday.
The Council’s vote sets the basic assumptions engineers will use to design solutions — essentially amounting to a big bet. The wager? Just how much will the oceans rise, and how aggressive should the Village be? Voters approved a $100 million dollar resiliency bond in Nov. 2020 in anticipation of borrowing funds for what could be two decades of public works projects, augmented by higher stormwater fees already put in place by a previous council.
The sheer scope of all the projects is expected to renew discussion of raising Key Biscayne’s debt cap later this week, when the Charter Revision Commission meets. The Village Council approved — and then withdrew — a proposal to amend the borrowing restriction in 2020.
Scientists have produced several projections for sea level rise, all accelerating at different rates. Key Biscayne opted for a middle course, accepting the recommendation of AECOM, the Village’s environmental consulting firm. The Council adopted NOAA’s “Intermediate High” prediction, which forecasts up to 25 inches of sea level rise by 2050, said Roland Samimy, the Village’s chief resilience officer.
The plan — which may take several months to produce a first cost estimate — will likely include a mix of methods to fight rising water. Village Manager Steve Williamson briefed council members on AECOM’s recommendations, adding that the total cost estimate “is over $100 million.” In a lengthy presentation, AECOM said the solution could include a dozen large pumping stations, miles of pressurized pipes to quickly move flood waters, scrubbing filters to remove pollutants, redesigned swales and even raised roads.
Even with all that, the targets mean that Key Biscayne will still suffer more frequent flooding as sea level rise accelerates.
“We have to remember that we live on a barrier island and that the water is coming,” said Council Member Allison McCormick, acknowledging there will be more frequent flooding events requiring permanent changes and a reset of resident expectations. “We may need to make one-way streets to capture rainwater and allow for parking,” referring to new swales that would help store rainwater until drainage systems can pump it away.
Chief Resilience Officer Roland Samimy told the Council that the Village’s own rain gauge has documented 75 “severe” rain events since 2018, a number that reflects the inadequacy of the current system. “We actually have been getting a lot of these intense rain events that are only going to get worse,” he said.
The AECOM presentation said the Village network of drainage wells, gravity outfalls, and pipes can handle about 210 cubic feet per second over the island’s 794 acres. But that system is already falling short. “Gravity wells won’t meet the capacity,” said Fernando Vazquez, AECOM’s regional water business vice president. “You’ve got to get the water out.”
A system that would be designed to weather a big storm — the kind that would dump eight inches of water over 24 hours and might be expected every 10 years — would require a discharge rate of 2,381 cubic feet per second, a more than ten-fold increase in capacity over the current system.
The recommended “level of service” that engineers will now proceed to cost out calls for removing water quickly enough to keep roads passable for traffic, with a ponding depth of under half a foot of water, with ponding lasting as long as 12 hours. Swales would be used to store the water while the system worked to move the water off the land.
But even as the Village set the base engineering goals for stormwater, Williamson told the Council that as much as $2 million will be needed to proceed with a beach renourishment application with the Army Corps of Engineers. The Village has been trying to get included in the agency’s shoreline protection program, along with Miami-Dade County, but the Corps wants the Village to pay for participating in a “back bay study” as a prerequisite. Inclusion in the program could shift expensive beach renourishment to the federal government, saving tens of millions.
In meetings with County officials, including top aides to Mayor Daniela Levine Cava, Williamson said the Village is proposing a two-track approach that would allow Key Biscayne to remain part of the County’s overall plan, but would also allow the Village to meet the Corps demands. The Corps is expected to make a major decision about the Village’s participation within a week, but the fact that Key Biscayne passed the resilience bond has been critical to progress with the agency, Williamson said.
Still unknown is how much Key Biscayne will need to pay for utility undergrounding. A previous estimate came in as high as $46 million, but that was before the Florida Legislature passed new rate laws that can transfer much of the cost to ratepayers.
Also unknown: what Key Biscayne’s contribution might be to the Rickenbacker Causeway. The Council told Williamson to come back with a plan to engage the County and other stakeholders about a new roadway that would meet the Village’s needs. Some members of Council have proposed that the Village make its own bid to rebuild, operate, and maintain the system, or partner with another big player to do so.