Or Shine

Early Snapshot of 2007-08 Dry Season

— sfwj — nov 13 to 18 —

Wetland water depths in Big Cypress National Preserve have dropped around 4-5 inches since the start of October. That means that the wetting front is slowly but surely retreating out of the wet prairies and into the lower-lying cypress, doing its annual disappearing act.

The S352 structure feeds water from Lake Okeechobee to West Palm Beach Canal. These photos were taken earlier this Summer when Lake stage hovered around 9 ft msl. Lake stage is currently over a foot higher at 10.3 ft msl.
Last year, the wetting front retreated out of the preserve’s wet prairies by early January, out of its tall cypress (think domes and strands) by February, and out of its lowest lying wetlands — the orchid-hiding swamp forests and marshes — sometime in March. That meant that the “heart of darkness” (or in this case “dryness”) of our Dry Season drydown prevailed for a 3 month period between March and May of last year. The wetlands started to fill up again in early June with the start of the Summer rains.

How long will this Dry Season last? And how fast will the really dry part of the Dry Season get here?
We are currently around 2-3 inches below our 5-year average for mid November. With a La Nina taking control of the meteorological palette for the winter, we stand a higher chance of getting below average dry season rains this Winter. That could accelerate the wetting front’s descent down the wetland ladder. Back during our last big drought in 2000, the “heart of the dry season” lasted for a 5 month period from February to mid June. In 1998, the “heart of the dry season was delayed to mid May due to El Nino stoked winter rains.
But its a wait-and-see as usual.

Over in Water Conservation Area 3, regulatory water stage has actually increased 7-8 inches since the start of October. That’s somewhat interesting considering the 4-6 inch drop in neighboring Big Cypress — both areas of which received equivalent 4 inches of October rain –compared to 10 inches of October rain in nearby Miami-Dade and 8 inches in east Broward.

The big difference maker has been rains in upstream Water Conservation Areas 1 and 2 which have resulted in increased discharges through the S11s. The S11s have been discharging at 1,500 cfs since the start of October, and briefly spiked to 3,000 cfs for the first week of November, before dropping down to their current 200 cfs flow rate. At 130,000 acre-feet, this year’s annual flow total (to date) through the S11s matches the 130,000 acre-feet of 2000, but exceeds the drought year of 1989 when virtually no water discharged through the S11s for the entire year.

On the downstream end of WCA3, S12s are discharing around 200 cfs into Everglades National Park. That puts them on track to have their lowest annual discharge total in 17 years, since 1989. At 30,000 acre-feet, this year’s annual flow total (to date) through the S12s is an order of magnitude below the 300,000 acre-feet discharged through the S12s in 2000, and around the same as the 30,000 acre-feet of the 1989 drought year.

Wetland water depths throughout the park are at a 17-year November low as a result. But don’t forget that the Park just got done going through a 13-year wetter-than-usual period from 1993 to 2005. This November’s water depth in central Shark River Slough (at P33) is around a foot (or more) shallower than 10 of the past 15 Novembers, starting in 1993.

At Shark Valley Tower, water depths of over 18 inches deep have routinely prevailed into November, even into December, since 1993. Current wetland depths at the tower are only around 6 inches in comparison, and have been at or below 8 inches for almost 13 months straight extending back to October 2006.

That takes us up to Loxahatchee. Slough water depths are currently around 2 feet deep. That means that Loxahatchee is still hovering at a 5-year November high-water mark, but the waters have begun to recede. Wetland stage has dropped about 5 inches since the early part of October.

You may remember that around 10 inches of rain fell on Loxahatchee and Water Conservation Area 2 in a 3 week period in late September and early October. That’s pushed Loxahatchee up to a 5-year high-water mark since the start of October. That makes this the deepest November in Loxahatchee’s wetlands since November 1999. But you have to go back to 1997 when slough depths in Loxahatchee stayed at or above 2 ft deep for a 3 month period from October to January, and briefly spiked to over 3 ft deep in mid December.


The cause?
Blame the El Nino of the Century and the plentiful winter rains it brought to south Florida in winter of 1997 and 98. Over 20 inches of rain fell on WCAs 1 and 2 between Nov 1 1997 and April 1 1998.

Lake Okeechobee stage has risen 5-6 inches since the start of October. Current stage is around 10.3 ft mean sea level. Lake stage is about 8 inches below its lowest lying wetlands within the perimeter of the Herbert Hoover Dike. They start of flood when Lake stage reaches 11 ft mean sea level. Lake stage has been below 11 ft for over 8 straight months. Lake stage is about 2 ft lower than mid November of last year, and 5 ft lower than the average over the past 5 Novembers.

The Lake-O-ulator shows that the Lake has been holding over 2 million acre feet of water since mid October.

Only 110,000 acre feet have been discharged down the Caloosahatchee through the S79 so far this calendar year. That’s the lowest annual flow volume through the S79 in at least 25 years, going back to 1983 — which is as far back as my data set reaches. I will have to scrounge around to see if and how far back the data set goes. Incidently, the S79 has averaged 1,400,000 acre feet per year over the past 25 years.

On the other coast, only 10,000 acre feet of water has been discharged into the St Lucie estuary through the S80 so far this calendar year. That’s also at least a 25-year low, with the 20,000 acre feet in 1985 and 1990 being the next lowest annual flow volumes. The S80 has averaged 405,000 acre feet per year over the past 25 years.

Happy holidays to everyone. Plenty of turkey, family, and friends to you all.
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