Aquifer

Usually aquifers are out of sight out of mind and more specifically beneath our feet. Well not in Florida when it comes to is famous springs or its sinkholes. | Aquifers | Biscayne | Floridan | Intermediate | Surficial | Springs | Estuaries and coast | Water bodies | Florida’s water districts

Intro - In Plain View

By Robert V. Sobczak

By my count ...

Florida has four aquifers.

Starting at the bottom is the Floridan. And yes, make no mistake: I am not missing an "i." Gerald Parker didn't so much discover it, as he invented it. Yes, it's true: Hydrology (especially ground-water hydrology) takes imagination. Dubbed "The Sunshine State," Florida is equally famous for its copious amounts of rain which accumulates in various groundwater zones. The Floridan is what they call a confined aquifer system. To make a long story short: It's under pressure. Anywhere it finds a break in the surficial crust (called an aquiclude) it gushes to the surface in the form of a Florida Spring. My favorite? There are too many to count. Next up on the list is the Biscayne Aquifer, better described as Swiss Cheese. Prior to drainage of the Everglades, freshwater from the aquifer used to create zones of fresh water in the middle of Biscayne Bay that pirates and other ne'er-do-well (and maybe some good people, too) filled up their ships. Much more boring are the intermediate and surficial aquifers, but equally as important. Wake up folks: Just because we can't see it doesn't mean we don't need to protect it.

What have you done to help protect our aquifers today? Our Florida springs are national treasures, yet what's being done to preserve their flow that's being increasingly pirated by nearby metropolitan water supply wells. Who says pirates no longer exist? There are right here among our midst. And yes, I'm looking into the mirror, too. Just today I let the hose run for too long. That's wasted water that would have much been better kept in the aquifer!

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Geology of the Swamp
Out of sight, out of mind

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Not many people visit the swamp …

To see its geology.

Cross sectional sketch of the swamp’s geology

But really, the geology is an underappreciated treasure of the swamp, and not uncoincidently buried under the ground. Did you know there is about 3 miles of marine limestone underlaying the swamp? In layman’s terms, that’s over 500 million years of deposition, all sitting on top of the Senegal Platform rifted away from the African Plate when the last supercontinent Pangaea rifted apart. Most of south florida’s drinking water is in the top 100 feet. About a thousand feed below ground is the cryptic geologic layer known as the boulder zone where coastal cities pump their treated municipal wastewater. Much farther down is the Sunniland Trend that holds a modest reservoir of hydrocarbons. I’m not saying the geology of Florida is as scenic as Yellowstone or other western parks, but it may be more interesting, even if if visualizing it and understanding it requires a good geology book. In that regard, I highly recommend Geology of Florida by Randazzo and Jones and Land from the Sea by Edward Hoffmeister.

water table

Steephead Valleys
And why they are "spring like"

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Steephead valleys aren’t as famous …

Or as charismatic as a Florida spring.

Steephead valleys have a distinctive rounded shape

But they are similar in they are both groundwater fed. Unlike springs that appear in full force out of nowhere, emerging from a cavernous hold in the ground in the form of a “boil,” steephead streams are smaller in scale and at their upstream end pinch back to a vanishing point. And unlike a gully-eroded dendritic (i.e. branching) stream channel that depends on rainwater for its source, and accordingly erodes from top-to-bottom — a steephead valley contains a single stream that depends on groundwater seepage as its source. Grain by grain, that causes erosion to occur from the bottom-up, giving the ravines their trademark rounded and slumping shape. Another key difference: The gradient between its headwater and mouth are low.

What makes steepheads special? The steady flow and constant (cooler) temperature makes both the ravines and the streams home to endemic and rare northern plants. An endangered fish called the Okaloosa darter is only found in steephead streams. As for their location, they are found in isolated patches in the panhandle where the regional groundwater table and alluvial floodplain intercept.

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Thought: Steepheads are larger versions of the little rivulets you see forming in the beachfront during a low tide, but less salty.

Steady decline
And can it be stopped?

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Nobody can shut off a Florida Spring …

Or can we?

History of discharge (in cfs) from Crystal Spring, FL

The answer is yes. It happened to Kissengen Spring. Once a popular tourist draw and water hole, nearby groundwater pumping dried up the spring the river run it fed. But surely that could never happen to Silver Springs, a first order magnitude artesian spring. Some would call it Florida’s crown jewel. Just a few year back I was at the spring marveling at the volume of water it produced. If you’ve never seen a Florida spring, they are a “must see.” The water manifests itself as the surface as a crystal clear boil of rolling water flowing non-stop day and night all year long.

Looking back at the historical data for the site — and we should all thank the U.S. Geological Survey for having the foresight to start collecting it in 1932 — the volume of water gushing out of the spring has declined over the decades, starting in the 1990s and dropping down even more in the 2000s. The good news? Spring volume rebounded back to near normal levels (between 700-900 cfs) in recent years. It’s still not what it was (prior to 1990), and future depletion is a real threat. But there is a plan in place to save the spring and its flows. Click here to find out more.

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Trends: Baselines decline over time that only an old-timer can tell you. And yes, please listen to them!

Spring-fed swamp?
Proof that water can jump

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Back in the day …

Yes, the swamp was spring fed.

Water gushing to the surface from 600 feet below

It’s source:

The absence of canals allowed hydrostatic pressure to build up. The result was that early settlers were convinced that fissures in the earth, not rainwater, fed the swamp.

Vortex at a submerged culvert site

Sounds like a fun place to visit.

My opinion: Water deserves a place to be free.

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My philosophy: It’s good to see water still doing crazy fun things!

Swamp’s subterranean source?
How the history books got it wrong

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The Immokalee Rise is often viewed …

As the northern “terrestrial” bounds of the swamp.

The myth of a rain-driven swamp falls apart
when you consider its connection to a higher Lake
Okeechobee, the flooded Lake Flirt floodplain,
Ft. Thompson falls and the underlying karst 
and porous sands of the Immokalee Rise,
prior to drainage of course

But “hydrologically” could it have been its source?

Imagine if you would:

  • A higher pre-drainage Lake Okeechobee, 23 feet above sea level (asl).
  • A fully intact Ft Thomson Falls that pooled water in the Lake Flirt floodplain, 20 ft asl
  • Groundwater flowing laterally through the Immokalee Rise’s underlying karst 
  • Rainwater infiltrating down into the porous sands of the Immokalee Rise  

Under that scenario, Immokalee Mountain wasn’t a dam at all, but the underground spigot that supercharged the headwaters of the swamp.

Special thanks to hydrogeologist and swamp emeritus Jack Meeder on this post!

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Fact: “Just because nobody measured it doesn’t mean it didn’t exist.” Bob Says

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