Trail slows to a trickle

Around 310,000 acre feet flowed under the Tamiami Trail between Carnestown and Krome Avenue in 2007.

That’s the lowest volume to flow under that 60-mile segment of the Trail for at least the past 30 years. (The data set that I am looking at only goes back to 1978).

Carnestown is located at the western edge of Big Cypress Nat’l Preserve, about 30 miles to the east of Naples. Krome Avenue forms the de facto eastern edge of the Everglades, around 20 miles to the west of Miami Beach.

Big Cypress Nat’l Preserve accounted for 75 percent of the 2007 flow volume, but it was the western half — the 20 miles that extend from Carnestown to Monroe Station — that accounted for around 50 percent of the 60-mile total.

Just how little was the past year’s flow volume?

The 10-year average for the 60-mile stretch is five times higher, at around 1.5 million acre feet.

You have to go all the way back to the drought of the late 1980s to find similarly low flows under the trail, when around 500,000 acre feet flowed under the Trail for two consecutive years in 1989 and 1990.

What were the largest flow volumes in recent memory?

Over 2.5 million acre feet passed under the Trail in 2005, with about half of that volume passing through the S12s.

But 1995 was the real record topper, during which over 4 million acre feet flowed under the Trail, with the S12s also accounting for about half of the total. To put that in perspective, Lake O holds between 4-5 million acre-feet.

Here’s a few representative photos of the Big Cypress, S12s, and L29 segments of the Trail.

A bridge to the one shown below is located around every three-quarters of a mile in Big Cypress National Preserve; and those flows are unimpeded, not controlled by gates.Flows through the S12s occur through the four S12 structures (A,B,C, and D), each of which has 6 gates — as dictated by the regulatory schedule for upstream Water Conservation Area 3A and downstream in Everglades Nat’l Park. Below is a photo of the S12B structure, located near the entrance to the Park’s Shark Valley Visitor Center (tram and tower).
Flows into the eastern-most segment of the Trail — which flow downstream into the Park’s northeast corner of Shark River Slough — occur through The L29 Culverts, fed by upstream L29 Canal.
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Currently, the L29 Canal gets its water from the S333 structure — which taps water directly from Water Conservation Area 3A, and not from the wetlands located immediately to the north in Water Conservation Area 3B which would hypothetically be delivered through the dormant S355 structures.
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The reason?

WCA3B is the headwater recharge source of the Biscayne Aquifer, making it a vital management link for maintaining water supplies and effective flood control for Miami-Dade and Broward’s coastal communities.

These structures may come into play as Everglades Restoration and water management efforts move forward, but for the time being its the S333 that forms the source to NE Shark River Slough.

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