Sea levels are rising faster than expected. And there are already floods caused by annual high tides, called king tides. So Miami Beach is embarking on the second stage of a $400- to $500-million project to raise the city’s roads and install new pumps — and safeguard the city’s future.

Rising sea

Projections show the ocean off Florida’s coast could rise up to almost a metre by 2060, but the city is already being flooded by annual king tides, the highest high tides, which occur due to gravitational forces on Earth’s water exerted by the position of the sun and moon. During that time, water gurgles up from underneath roads in Miami Beach and turns many of them into rivers. The tides can raise water levels by about 1.2 metres. Streets begin to flood at about one metre, according to the Miami Herald. But the risks haven't stopped construction in Miami Beach. Meanwhile, all low-lying coastal cities in the U.S. are threatened including Miami proper, which could lose $3.7 trillion in financial assets by 2070 due to rising ocean levels, more than any other coastal city, according to a National Wildlife Federation report from 2016.

Nervous neighbourhood

The city, which began elevating roads in the southern part of Miami Beach in 2013, will start construction in the fall in the Lakeview neighbourhood — the first residential area of largely single-family homes to undergo improvements. The city will raise roads and curbs, replace gutters and water mains, and connect the new roadway to existing driveways. Residents there are worried about who will pay to connect drainage on their property to the city’s new system, as well as water runoff from the elevated road. The city is also installing three pumps, in Lakeview and the nearby La Gorce neighbourhood, to reroute excess water back to the ocean. The neighbourhood project will cost $100 million and take two years.

Raising the roads

The road in front of Pubbelly’s restaurant on Purdy Ave. at 20th St. has been raised about 60 cm (about two feet). The city also installed floor drains in the patio area to connect it to new storm drainage pipes underground, which carry the water away so it can be pumped back into the ocean. Eric Carpenter, the head of public works, says most roads need to be raised 45 cm or less to meet a target height that will protect them from flooding until at least 2050. The city is also raising the height of sea walls on Biscayne Bay and on canals by about 75 cm.

Pumping it out

Flood water is collected in storm drains and rerouted to concrete vaults. Debris are removed and the water flows into the main well and is pumped out into the bay at a rate as high as 300,000 litres a minute. A valve at the end of the discharge pipe prevents backflow. So far, the city has installed 24 new pumps and upgraded 10 others.

The beach

The east side of Miami Beach is protected by coastal dunes, which are on the highest point of the island. The dunes minimize erosion and block storm surges. The city is continually restoring the dunes by removing invasive plants and replacing them with native species. The city also has to deal with erosion and in 2013, trucked in huge amounts of sand from the Ortona quarry in central Florida to replenish the beach in the La Gorce neighbourhood.

Source: Eric Carpenter, Director of Public Works City of Miami Beach; Miami Herald; Southeast Florida Climate Compact Organization; Public Works Magazine

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