Miami is the city with the most money to lose from sea level rise. A 2011 report in the journal “Climate Change” named it #1 in terms of assets exposed to damage from rising waters. Most experts worry that the end of the Magic City will come at the hands of a major hurricane that will create a massive storm surge, overwhelming our coastal defenses like dunes and seawalls and sending salt water rushing through our streets.
But there’s a slower, quieter danger.
It’s easy to forget that much of the land we live, work, and travel on was once a swamp. The collection lakes and drainage canals are just part of the scenery of a coastal city. But about a tenth of Miami-Dade County’s land area is less than a foot above sea level. The city manages to stay afloat because of one the largest water management systems in the world, a marvel of engineering that stretches from Key West to Lake Okeechobee — a network of water catchments, channels, and canals that moves both rainwater and groundwater out to the ocean, keeping the land dry.
But sea level rise is going to degrade our gravity-powered water control structures, a crucial part of that system.
Gravity keeps water moving in the right direction and also keeps the sea from getting into the Biscayne aquifer, the source of the city’s drinking water. The flow out of the network is controlled by a series of floodgates. The gradient — the difference in height between the water in the canal and the water in the ocean — creates the gravitational pull that drains half of Miami’s 61.3 inches of yearly rainfall. As sea levels rise, that gradient is shrinking — and without it, the gates don’t work. A few of them are already inoperable.
Back of the envelope estimates based on a 2011 study put the cost overhauling the current arrangement of vulnerable sluice gates, pumps, and barriers at around 2.2 billion, but no one’s really sure yet how big a project it will be.
“We need to figure out how fast the water’s rising, back that up with science, and then engineer a plan to enhance the system,” said Water Management District Spokesman Randy Smith. That will require “funding far outside the capacity of the district. We’re going to need State help, Federal help,” he added.
A 2009 South Florida Water Management District (SFWMD) study identified more than 20 water control structures that would fail with as little as six inches of sea level rise. Three of them will fail with only 3 inches of sea level rise.
The SFWD, which runs the system, is exploring every technical option available to replace the gates, according to Smith, but the scientific consensus is that the only viable option is very large and very expensive pumps, similar to those already installed on Miami Beach, but on a much grander scale. A 2011 Florida Atlantic University study put the cost of a single pump at about $70 million.
While pumps have some advantages over gravity structures (namely, that they can be operated continuously and even during a storm surge), they can’t drain as much water, they require more maintenance, and they need a constant source of energy to run — all things that make operations, not just installation, far more costly than the gravity structures.
Part of the problem is that no one is quite sure just how quickly the waters will rise. The intergovernmental panel on Climate Change’s highest projections put global mean sea level rise at around 4 in. by 2030. A model developed by the US Army Corps of Engineers puts it at between 3 in. and 9 in. by 2030, and 7 in. to 12 in. by 2040.
The gravity structures are not going to fail over night. With 15 to 25 years of lead time, maybe the money will come through to replace the gates before widespread failure. But property values will likely decline as regular, non-catastrophic flooding becomes the norm, leaving municipalities with less of a revenue base to pay for the improvements needed to keep the streets above water.
The sky-high costs of replacing the gravity structures with pumps points towards a new normal in South Florida, one where the region will increasingly have to rely on state and even federal funds just to physically stay afloat.