Or Shine

Rain or Shine Report for Nov 27
Curious Case of the S10s
Cypress needles fall, mostly

Rainfall

The Southwest Coast Basin — which includes Naples and Ft Myers — has been the driest part of south Florida since the start of the Dry Season. It has only received a fifth of an inch of rain in the 30 days since October 25th.

In comparison, Lake O has received around 1.2 inches and Miami-Dade around 2.7 inches over the same 30-day period.

Cypress and pinelands are easy to discern from the air now that the cypress needles have fallen in Big Cypress National Preserve. The wetting front is dropping out of the wet prairies and retreating into the cypress domes and strands.

Looking back the full duration of the Wet Season, its Lake Okeechobee that’s the low-basin-on-the-totem-pole. It received only 25 inches during the 6-month Wet Season from May 1st to October 31st. In comparison, 33 inches fell in the Kissimmee Valley, 35 inches on the Southwest Coast Basin, 40 inches on Big Cypress National Preserve, and 50 inches on Miami-Dade over the same 6-month period.

Looking back a full year, Lake O’s deficit of rain relative to the other basins is actually par for the South-Florida-Water-Cycle course. But at 30 inches per year — the past 2 years have been tracking around 15 inches below the Lake’s long-term annual rainfall average.

Compare that to the Southwest Coast Basin. It received 50 inches last year, as calculated from May 1st 2006 to April 30th 2007 (and 44 inches of the 50 inch total fell during the Wet Season). This year, with the Wet Season already in our rear view mirror, the Southwest Basin has only tallied 33 inches of rain since May 1st. That’s the Southwest Coast’s lowest Wet Season tally since only 30 inches bell in back in 1988.

Kissimmee Valley —

The Kissimmee River has been discharging water into the Lake for 4 consecutive months — from late July to present. Prior to that the Kissimmee endured into a 9-month “no flow” streak — that lasted from November 2006 to mid July 2007 — when the S65E structure remained closed.

Prior to that, and sandwiched between the record droughts of 2000-2001 and 2006-2007, the Kissimmee River discharged into the Lake for 63 continuous months continuously, draining around 9 million acre-feet into the Lake. That averages out to around 1.7 million acre-feet per year during those wet years. That’s a far cry from the 0.2 million acre-feet the Kissimmee has discharged into the Lake in 2007.


Lake Okeechobee —

Lake Okeechobee stage is currently just above 10 ft mean sea level. Last year at the end of November, Lake stage was around 2 feet higher — at a notch above 12 ft mean sea level. Last year the Lake didn’t break 10 ft msl until the beginning of April.

That’s fast-forwarded the hands of our Winter Drydown Clock about 3-4 months ahead of last year.

Even the lowest lying wetlands within the Herbert Hoover Dike — the ones at the 11 ft msl range — have been dry for 8 consecutive months now, from mid-March to present. Higher-elevation wetlands around the perimeter of the levee (ie, wetlands above 14 ft msl) have been dry for a 18 consecutive months and counting.

Interestingly, during the 2001 drydown, Lake stage only descended below 11 ft msl for a 7 month period — from January to August 2001. The higher elevation perimeter wetlands (i.e., wetlands >14 ft msl) stayed dry for 16 consecutive months.

That makes this year’s drought more pronounced both in terms of depth (8.8 ft msl minimum) and duration.

Loxahatchee —

Loxahatchee has been perched at a new 5-year high water mark for the past 9 weeks. Its dropped down around 5 inches since it crested in late October, but at 17 ft msl, it is still a good 3 inches above its late November average and filling central sloughs with 20 inches of water.

The S10s are closed — and have pretty much been closed all year. Looking at the historic data for the S10s, I’m surprised how little water moves through them and how little they are opened in comparison to the downstream S11s and S12s. The S10s average only around 100-200k acre-feet over the past couple of years, and this year have only discharged 20,000 acre-feet.

Compare that to the downstream S11s which — even during this year’s drought — managed to discharge at over 1,000 cfs for about a month straight, from early October to mid November, and peaked at over 2,500 cfs flow rate in early November. That’s added up to around 140k acre-feet for the year, which is down from the annual average 430k acre-feet per year we’ve seen the past couple of years.

The duration of discharge through the S11s — which typically spans for a few months during the Wet Season — also contrasts to the short spurts that have been discharging through the S10s over the the past couple years.

I’ll have to do some homework on this to figure out what’s going on. It’s probably a reflection of new operational rules and the Stormwater Treatment Areas coming on line.

Water Conservation Area 3 —

Regulatory stage in WCA3 has risen a foot over the past 2 months, and is currently tracking right along last year’s late November stage, which is only 3 inches or so below the 5-year average for late November.

That’s a big difference to the 17-year low WCA3 was tracking at through the first part of the summer. WCA3 is about a foot higher than the start of June, but around around a foot lower than November 2005 in the wake of Wilma. Call it somewhere in the middle.

Slough depths in southern 3A (at Site 65) are 2.5 ft deep. Slough depths in northern 3A (at Site 63) are 0.9 ft deep in comparison. A more startling contrast is duration of flooding. Sloughs in northern 3A have been only holding water for a 4-month period from late July to present. You may recall that they went dry for a 5-month period before that from March to late July. Compare that to sloughs in southern 3A that haven’t gone dry since July 1989. That’s an 18-year hydroperiod!

Everglades National Park —

The S12s have gone over 12 months without exceeding a 1,000 cfs flow rate. You have to go back 17 years to 1989 and 1990 to find years with similarly low flows. To date around 30k acre-feet has been discharged throught he S12s this year. Compare that to an annual average of 700k acre-feet from 2001 to 2006.

If you go to Shark Valley Tower, wetlands there have been holding water for a 5-month period since the start of June — but depths have stayed relatively shallow, in the 0.5 ft range, for the entirety of the summer. Compare that to the previous year (2006) when water depths climbed up to 1.5 ft deep, and the year before that (2005) when wetland water depths rose above 2 ft deep.

Big Cypress National Preserve —

Preserve-wide stage is beginning to drop out of the wet prairies — pushing the wetting front deeper and deeper into the taller cypress. The northern half of the preserve is about a half-foot shallower than the southern half of the preserve — south of US41 — where the wet prairies are still holding a few inches of water. Last year, the wetting front didn’t drop below the wet prairie level until mid January. That puts our Dry Season clock a month ahead of last year.

Add another hydrologic mystery to the Big Cypress. In general, the cypress needles have browned and are starting to fall — all except for up in the northeast corner of the preserve cypress are leafing out. So much for using cypress needles as a fall indicator.
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My working assumption is that the cypress went dormant during the especially dry conditions that prevailed in Okaloachoochee Slough for most of the summer, causing them to delay their leaf out. But that’s a guess.

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