Tidal Flooding in City of Miami Beach

The City of Miami Beach| Miami Beach, Florida, USA| Flood protection

The problem

Balancing stormwater run-off capacity with rising tides in Miami Beach.

Miami Beach is a beautiful resort community nestled between the Atlantic Ocean and Biscayne Bay, with picturesque beaches, amazing nightlife, an Art Deco district listed on the National Register of Historic Places and some of the most sought after real estate in the US. It is built on natural and man-made barrier islands, which are essentially sand dunes dredged from Biscayne Bay.  

In all modern cities, good infrastructure is essential for development and the comfort of its residents. Things like roads, bridges, drinking water, sewage systems and stormwater pipelines are often taken for granted. Water comes out of the tap, toilets flush and rainwater is whisked away. And that is almost entirely true for Miami Beach residents too, with one major exception. They are keenly aware of their city’s stormwater drainage system.  

Much of the system was built just a few inches to a few feet above sea level. And not only have sea levels risen over the years, but the outfalls have also settled slightly, which means the stormwater system regularly fills up with seawater. Another problematic element is the vertical wells, which were designed to funnel run-off straight into the groundwater. Increased pressure, caused by rising sea levels, extreme storms and king tides, are overloading the system and seawater is instead pushing groundwater back up the vertical wells and into streets.  

“It’s not just the water coming over the shoreline, it’s also the water under the city that we have to look at,” says Miami Beach chief engineer Bruce Mowry. 

Not only that, but extreme tides can also force salt water up through the stormwater pipes, thereby flooding the city and accelerating the damage. When the stormwater system is full of seawater and groundwater, it forces the seawater out onto streets, homes and commercial properties where it causes blocked roads, inconveniences pedestrians, closes businesses and damages homes. Saltwater damage to roads and landscaping adds to the city’s remedial costs.  

Record precipitation levels have been slowly rising over the past thirty years and a team of scientists at the Potsdam Institute for Climate Impact Research have detected a clear upward trend towards more unprecedented daily rainfall levels. 

These once anomalous events are now 24% more frequent in central and eastern parts of the US. Miami Beach is spending over $500 million in preparation for these scientific projections, which predict a three-foot rise in sea level by the turn of the century. 

“Obviously, when you do the math, $23 billion worth of private property versus the $300-500 million we’re investing in stormwater improvements to buy us another 30-50 years. It makes all the sense in the world,” says Eric Carpenter, director of Miami Beach Public Works.

Wastop Backventil

Solution

WaStop® Inline Check valve

Miami Beach is investing more than $500 million in pumping stations, sea walls and valves in their efforts to deal with the problem. Around 60 pumping stations will be built over the next 5 years, in order to direct excess water away from the city. But they have to be built first. Until then, contractors like Southern Underground Industries are protecting the city by installing WaStop backflow-prevention check valves into the stormwater system. The goal of the city’s Hightide Project is to prevent seawater and groundwater from filling up the system while still allowing rainwater to flow through and out of it. According to Southern Underground Industries, it’s a matter of finding the right balance between protection from tidal events and stormwater run-off capacity.

The first big test came when the 2014 king tides challenged the city’s new stormwater improvements, but the streets of South Beach remained dry. There was some brief flooding after a storm that left a few puddles around the drains, but which quickly drained off into the bay. It was still a far cry from the flooding scenes the city had experienced over the years, with people wading across streets and cars being submerged with saltwater. In 2014, Miami Beach Mayor Philip Levine said that that year’s king tide was just the start. “There’s no-one up here in our city who’s going to declare victory,” he said. “We are encouraged by the results we’ve experienced this week.”

Between 2014-2015, around 100 WaStop check valves were installed in Miami Beach’s stormwater system. Most of them have been fitted inside the original clay pipes, which varied considerably in size. Nevertheless, the WaStop’s unique stainless steel design and mounting brackets mean it can be installed quickly and easily inside any existing pipe. Not only that, but the WaStop’s memory membrane means it works perfectly regardless of installation angle, i.e. both horizontal and vertical orientations. The membrane also has a pulsating flow action, which increases flow speed and keeps the pipe clean by flushing out sediment and debris. Which virtually eliminates blockages and costly maintenance. The WaStops are helping to resolve the city’s vertical wells problem as well, by ensuring rainwater flows freely while preventing groundwater from pushing up into the street.

The WaStop combines unprecedented reliability with virtually no maintenance, giving the residents of Miami Beach peace of mind and dry feet.

Thanks to Wapro Inc, CS3 and Southern Underground Industries for supplying this information. www.southernui.com

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