Saltwater Intrusion
Climate Change Daily Repost

Climate Change Goes Local – Day 1: Saltwater Intrusion

Miami

The old adage “all politics are local” might be rewritten as “real climate change is personal.” The front line of climate change adaptation is formed in local communities as their way of life is challenged by environmental stress. They don’t have the luxury of pondering the grand scheme of global warming or rising sea levels because they are too busy coping with the fallout of climate change in their daily lives. We will take a look at three geographically and culturally different localities, and the breadth and scope of issues they face as the future arrives at their doorsteps. Today is Miami.

Miami: Salt and the city

Jennifer Jurado, chief Climate Resilience Officer for Broward County Florida, points out the greater Miami area is under threat. She talks about the encroachment of saltwater into the daily lives of local residents. “As the seas rise, that saltwater front moves farther inland.” It’s not a future threat, “It is already happening.” Communities are now raising funds for costly water treatment plants that turn salty water into drinking water, and taxpayers feel the pinch (Sun Sentinel).

Fort Lauderdale also faces some harsh realities as the city soaks in sewer waste. Six sewage spills recently leaked over 126 million gallons of raw sewage into the city waterways. The volume of discharge is large, but half of it is actually groundwater. Of course, the purpose of sewage lines is to separate nasty waste materials from the rest of the environment. But corrosion, enhanced by saltwater, turned the city’s sewage pipeline networks into leaky sieves. Groundwater leaks into the pipes, and raw sewage leaks out. Fixing the problem in Fort Lauderdale will take $1.4 billion they don’t currently have.

The saltwater problem is getting worse because mean sea levels around Southern Florida rose about eight inches between 1950 and today. The rate is picking up, and one inch of sea-level rise is now expected every three years. Take a ruler and stand on an average beach. Place the ruler at the water’s edge and observe the eight-inch mark. It certainly doesn’t look like much. But a little change goes a long way, and there are knock-on effects, like tidal flooding, to consider.

Flooding from above and below

Living at sea level increases a person’s exposure to tidal changes. Anyone who has lived on the Florida coast is familiar with king tides, which occur when the gravitational pull of the sun and moon align, the Gulf Stream slows, and the combined effect increases water levels during high tides by about one foot. This effect leads to a rise in nuisance flooding.

Each time seawater inundates a local community, some of the salty water seeps into the ground, contributing to corrosion of the city’s water and sewage pipes. More flooding translates into more corrosion. Last year Key West made the news as one of its neighborhoods reached the three-month milestone of continuous flooding.

However, there is a second factor contributing to the saltwater problem. Seawater does not always soak into the ground from above—it can flow in from below through a process called “saltwater intrusion.”

The coast of Florida is particularly susceptible to saltwater intrusion due to its geology. Very porous limestones underlie much of the state. Because geology doesn’t stop at the coastline, these same porous limestones extend into the ocean. The high porosity within these limestones provides a direct flow conduit between the sea and the coastal groundwater aquifers.

Generally, in a coastal aquifer, water from rain forms a freshwater lens over the saltwater intruding from the ocean. If too much groundwater is pumped from the freshwater lens, saltwater will rise to fill the void. Rising sea levels and extra high tides also take a toll on the freshwater supply. The added water pressure forces more saltwater into the aquifer, displacing existing freshwater supplies for municipalities and farms.

A saltwater invasion from climate change and rising sea levels are some of the local challenges to Miami from a changing planet.


Sources:

Invading seawater jeopardizes South Florida’s drinking water, but we can lessen the threat | Editorial (Source: Sun Sentinel)

Half the stuff in Fort Lauderdale’s sewage system isn’t waste. Sea rise makes leaks worse (by By Adriana Brasileiro and Alex Harris— Miami Herald)

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.

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