Watershed lenses

What we call “watersheds” in the south Florida peninsula, they call “lenses” on Cape Cod, Massachusetts – or as I call it: The Cod.

Lenses are just a fancy name for self-contained ground water bodies surrounded on all sides by saltwater – say, as you might see underlying an island – but in this case, on The Cod, it being a peninsula, there are 6 of them in total, lined up one after the other … with 4 of them on The Cod’s outermost arm.

Although the lenses of The Cod are physically connected to each other (and the presence of ground water ubiquitous – pretty much anywhere you drill on The Cod you’ll find fresh ground water), they behave as hydraulically independent water bodies.

A molecule of rain water that seeps into one mound, say, the Chequesset Lens, cannot flow up-gradient into the Nauset Lens, or vice versa.

Instead, it gets discharged out to tide, either to the Atlantic or Cape Cod Bay side … or in between the lenses through special rivulets they call interlens discharge zones, (shown as arrows on the map).

But here’s where it gets tricky:

The water table only rises around 20 ft above sea level at its highest point on the Outer Cod. But because fresh water is less dense than salt water, the lenses “floats” on the sea saturated sediments below. That means that fresh water reaches as much as 200-300 ft below sea level on The Outer Cod.

That may seem “thick” if you’re drilling a well,

But if you draw it to scale with the rest of The Cod, the true reason for their peculiar name becomes “optically” clear: 

They’re as “thin” as a lens!

As for the even more peculiar term – “The Cod?” As far as I know I’m only one of two people who uses it.

Everyone else knows it as “The Cape.”

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