Water Log 9/9

Watersheds enter traditional high-water point on low note
Week of Sep 3 – 9

Almost 9 inches of rain has fallen in the Big Cypress over the past 30 days. But district-wide the story has been much drier, averaging around 5 inches over the past 30 days. That’s left many of the basins in deficit mode as we near the end of the wet season.

The Lake has received only around 27 inches over the past 365 days. That’s the same amount of rain Big Cypress National Preserve has received since the start of June (past 3 months). Over the past 365 days, Big Cypress National Preserve has received around 45 inches. That’s still down from its 55 inch annual average. (click here to view rainfall data – Source: SFWMD Meteorology)

Its been the summer of sequels in south Florida. This is the second year in a row that hurricane forecasters have adjusted their outlook midstream. Last year the forecast was downgraded mid summer as a result of a burgeoning El Nino whose high altitude wind sheer stiffled storm formation, and gave us a quiet end to last year’s hurricane season. This year the outlook was upgraded in response a La Nina taking hold in the Equatorial Pacific, a condition that tends to increase likelihood of tropical storm formation in the Atlantic Basin. One thing that hasn’t changed over the past couple years is the swing of the Atlantic Multidecadal Oscillation into a positive phase (starting in the mid 1990s) which is expected to increase tropical storm activity over the next several years.

This is also the second major drought since the start of the new millenium, and the second wet season in a row that wet season rain totals are barely scraping above 30 inches of rainfall. That’s a full 10 inches under the 5-year wet season rainfall average (May 1 to Oct 31).

We still have a 30-45 days of Wet Season ahead of us, and I hear thunder out there as I type, so its still too early to call what the final tally will be. The La Nina condition, if it persists into the dry season, is also associated with decreased dry season rainfall. But that may be looking too far ahead as well.

The Kissimmee continues to discharge into the Lake, at around 600 cfs. This time last year Kissimmee inflows into the Lake were peaking at around 3000 cfs (following Ernesto). Last year was only the third calendar year since 1995 that Kissimmee inflows did not rise above 5000 cfs. This year will be the 4th if the current trend continues.

Lake Okeechobee’s current stage is around 6 ft below its 5-year mid September average. Lake O is at its highest level in 4 months, but at around 9.6 ft mean sea level, its at its lowest September stage on record. A year ago around this time, Lake O rose to a late summer peak of around 13.5 ft msl, which brought the wetting front just up to the Lake’s lowest-lying interior wetlands. Lake stage has not fully flooded the littoral zone since Winter 2006 (almost 20 months) and the littoral zone has been completely dry (below 13.5 ft msl) since April 2006 (almost 17 months). That matches a similar 17-month drydown from May 2000 to October 2001. Keep in mind that Lake stage is still 4 ft below the base of the littoral zone.

Low levels have corresponded to low discharges through the S79. Starting in 2001, we’ve had 6 consecutive Septembers of discharges from the S79 exceeded 5,000 cfs for all or part of the month. In comparison, S79 flows haven’t exceeded 500 cfs since the start of October 2006.

All the conservation areas are tracking below average for mid September. The S10s, S11s, and S12s have been closed all summer to date. That’s not a big departure for the S10s. For the last couple years they are only open for around a month or less each summer. The S11s typically flow for a longer duration each summer, typically maxing out at 3000 to 4000 cfs, in the middle part of the summer. The S12s that feed down into the Park also flow for 3-5 months each year, with releases typically occurring at the tail end of the Wet Season in the fall. But this year there hasn’t been any significant discharge through any of them.

Of all the conservation areas, 3A is particularly low. Regulatory stage for 3A is currently tracking around 2 ft below its 5-year average for mid September, and about 1.5 ft below mid September of last year. Regulatory stage for 3A has hovered at its current level since the end of July, and has only risen a foot above its late May low-water mark.

Down in the Park, water levels in central Shark River Slough are around 18 inches below its 5-yr mid-September average. September wetland levels haven’t been this low at Shark River Tower since 1993. This year’s September stages are still a few inches above record low Septembers of 1989 and 1990.

Big Cypress National Preserve is wet in comparison, but that’s due to ample summer shows south of US41, and not from inflows from the north. September flows under US41 haven’t been this low for twenty years (since September 1986). The preserve’s northern reaches are tracking 7 inches below the average September wet season peak, and the preserve’s northwestern corner that includes Bear Island is shaping up as the year without a wet season, as is Corkscrew Sancutary to the north. The wetting front at Corkscrew has yet to spread out of the deep water refugia. One has to go back to 1970 to find a similarly dry wet season.

Aerial photo of Tamiami Trail looking south, with tractor trailer traveling west towards Naples. September flows under Big Cypress National Preserve’s 35 miles of Tamiami Trail haven’t been this low since 1986.

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