Feb 19, 2014

How To: Drought proof a watershed

Is the Caloosahatchee River drought proof?

This year that could be the case with Lake O still high.

This hydrograph shows a hydrograph of freshwater releases into the Caloosahatchee Estuary via the S-79.  The green horizontal band depicts the desirable flow envelop for maintaining the ecological balance of the estuary.

Not "high" high, but high enough ...

So that regulatory releases are still occurring through the Moore Haven Dam and Lock (S-77). That's kept releases into the estuary through the WP Franklin Dam and Lock (S-79) within the desirable freshwater flow envelope of 300 and 2,800 cubic feet per second since November (and before that for all but a few months over the past year and half).

Being connected to a headwater source has its advantages:

In this case by providing a means for moderating against effects of the developing spring drought, i.e. saltwater intrustion. The twist for the Caloosahatchee is that its connection to the Lake (at least by direct channel) is man made, not natural.

But there are disadvantages, too.

The big one is the undesirable overflow of high-nutrient Lake water that overwhelms the estuary during the summer when the Lake is high.

This hydrologic calendar shows the full history of freshwater discharges into the Caloosahatchee estuary through the S-79 from 1967 to present.  Green dashes indicate when the discharge levels fell within the desirable flow envelop (i.e. 300 to 2,800 cfs), blue and black dots indicate when the flow envelope was exceeded, and orange and red data points indicate when neglible flows occurred.  

And its not as simple as simply maintaining the envelope:

Ideally, the Lake could hold more water (during summer and fall) which if we could ensure a large enough supply all winter long -- and it were cleaner -- and better plumbed to the Everglades it could be fed south to fuel a more spatially expansive and attenuated sheetflow.

It's the Everglades and Big Cypress that need drought proofin'.

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