By Stephen Davis, Ph.D., & Edyna Garcia
This year’s arrival of the King Tide generated quite a bit of traction due to the impressive flooding seen in low-lying areas of South Florida. If you were to login to Twitter, Instagram or Facebook and search the hashtag #KingTide, you would find photos and videos of “sunny day flooding” of seawalls, docks, yards and streets. Impacts to developed areas from King Tide flooding are readily observable and of great concern for many municipalities across South Florida. What is less apparent are the impacts of King Tides on the Everglades and the growing need for Everglades restoration.
In order to understand King Tides, we need to take it back to 8th grade Science class, as the connection between the moon, sun, and ocean is fundamental to understanding the growing contribution of sea level rise on King Tide-induced coastal flooding. The short of it is that tides and oceans are much more complex than we think!
As we all know, the moon undergoes various phases throughout its orbit of the earth, starting with the new moon, waxing into a half moon then into a full moon before waning back to a half moon then a new moon.
During this time frame, the tidal amplitude of the ocean also changes, resulting in higher high tides when during full and new moon phases (i.e., when the gravitational pull of the moon and sun are pulling the oceans along the same plane) and relatively lower high tides during half-moon phases (when the gravitational pull of the moon is perpendicular to that of the sun). We call these “spring” and “neap” tides, respectively.
While this phase-driven tide is continually repeating, the moon’s orbit of the earth is elliptical rather than circular, so there are times when the moon is closer to the earth—a period we call lunar perigee.
During lunar perigee, the gravitational pull of the moon on our oceans is stronger than when it is farther away in the elliptical orbit—the period referred to as lunar apogee. About 3-4 times a year, there is a coincidence of lunar perigee and a full or new moon “spring” tide, resulting in a perigean spring tide. These produce the highest of the high tides and are predictable.
The same is true for the earth’s annual orbit of the sun, resulting in both perihelion (earth at its closest point to the sun) and aphelion (earth farthest from the sun) components to the tide. However, due to its proximity, the moon exerts a much greater influence on the ocean’s tides.
Climatic factors such as wind and temperature are also incredibly important in affecting local sea levels and coastal flooding. Winds, particularly those that are perpendicular against a coastline can have a great effect. We experience this phenomenon regularly in South Florida whether via the passage of a hurricane (i.e., storm surge) or from strong winds out of the east or west that move water towards or away from the coast. Ocean temperatures also contribute to this, as warmer oceans undergo thermal expansion, contributing to a higher tide that can penetrate further inland.
Suffice it to say that a perigean spring tide combined with summertime warm water and an easterly wind can spell trouble for low-lying areas of South Florida. When you add sea level rise from warming oceans and melting of ice caps on top of this, the problem will only get worse.
What about the Everglades? Prior to development, the flat and low-lying topography of South Florida was vital to the formation of the Everglades, allowing for a slow sheetflow of freshwater as much as 50 miles wide from Lake Okeechobee southward into the River of Grass and ultimately to Florida Bay.
Today, we have much less freshwater flowing south to the Everglades, resulting in parched marshes, hypersaline bays, and numerous threatened or endangered species of plants and animals. Another consequence of reduced freshwater flow has been an increased saltwater intrusion into our coastal wetlands, leading to mangrove expansion and even the collapse of coastal peatlands. This man-made impact is certainly amplified by King Tides.
To make matters worse, with a reduction in freshwater flow, we have seen enhanced saltwater intrusion into the Biscayne Aquifer—the water supply for 1 in 3 Floridians that is ultimately recharged by water flowing across the Everglades.
This all speaks to the urgency of implementing the Comprehensive Everglades Restoration Plan that restores the natural fresh water flow from Lake Okeechobee to the south. By restoring this southerly flow, we will not only reduce the harmful dumping of lake water to the Caloosahatchee and St. Lucie Rivers, we will also re-hydrate Everglades habitats that have been made vulnerable to excessive drying and saltwater exposure. Perhaps most importantly, it will help to protect South Florida’s water supply.
Here at the Everglades Foundation, we view this year’s King Tide as a call to action by nature itself. Water managers at the federal, state and local levels of government must re-affirm their commitment to building the necessary water infrastructure projects critical to re-connecting Lake Okeechobee back to the Everglades and Florida Bay. We have to do something about it now. There is no time to waste.
By signing the #NowOrNeverglades Declaration, you can align yourself with over 200 scientists and over 30,000 concerned citizens and call on our local and state government to build a reservoir south of Lake Okeechobee that will send water back south.
To sign the Declaration, visit https://www.evergladesfoundation.org/noworneverglades-declaration/ or text “Water” to 66866.
To read the Miami Herald Article on rising sea levels, please click here: http://www.miamiherald.com/news/local/environment/article65948497.html