Forever glades

I was out at Everglades Nat’l Park’s Shark Valley earlier this summer, when waters were peaking in the weeks following Fay – and “seemingly” climbing to the tippy top rung of the water cycle ladder – thanks to early October rains (a common occurrence in Miami).

“Surely waters couldn’t rise any higher” I thought to myself.

Turns out I was wrong: they could, but they wouldn’t, although they have in the past.

Let me explain.

The gates that deliver water into the park were open as high as they could go, but the water, quite literally, had “no place” to go. Why so? Waters on the downstream side of the gates were just as high as the pooled water behind the gates … or almost.

In the hydrologic trade, we call that – somewhat quizzically (and with forlorn face) –a “tailwater control” situation.

Up north – in the land where gates are “headwater” controlled – you open a gate and the water does exactly what you tell it to do. It flows downstream.

In the Everglades, trying to coax water through a gate is a careful calculus of head and tail water stage, topographic slopes, and – where gravity needs some extra help or the underlying lime rock is particularly leaky – also add surface water pumps to the mix.

Chalk it up as another hydrologic irregularity (and complexity) of the Everglades.

In any regard, in looking at the data, I was surprised to see that not only was this past summer not all that remarkably high (despite the epic deluge from Fay), but that water levels in Shark River Slough, as we speak, are currently at a 15-year low water mark for late March.

That puts Shark River at the same mid March stage as the droughty spring that followed the “summer without a wet season” of 2007. That was the year that Shark Valley stage stayed relatively low all summer (a full foot lower than Fay’s 2008 peak) – and it’s headwater gates stayed mostly closed.

That makes it all the more surprising that current stage have dropped to a similar low spot this spring.

“Surely waters can’t get any lower?”

That’s a question we’ll be watching in the weeks to come.

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