Stage in southern and northern 3A are receding in unison
SFL Weekly Watersheds Summary: Feb 26 – Mar 4
WEATHER. This year’s dry season is already long in the tooth. With the turning of the calendar to March the dry season officially entered its sixth month thanks to an early end of the rainy season in early October and El Nino’s late season fizzle to the hurricane season. District-wide has received 6.5 inches over this 5-month span, which breaks down to 1.3 inches per month. Lake O and Southwest Coast have received the lowest rainfall over that 5-month span, with only between 4 and 5 inches falling in those areas. The east coast basins (including WCAs 1&2) lead the way with over 10 inches over the same 5-month span. The Big Cypress and Kissimmee areas fall in between, more or less matching the District-wide average. The long-term (past 10 years) dry season average in the preserve is around 11 inches, as calculated from the start of November to the end of April. The two biggest El-Nino affected dry season of recent past, in 1994-1995 and 1997-1998, recorded over 20 inches for those 6 dry season months. Last year was on the lower end of the spectrum, with 6.4 inches, as was the drought year of 2000-01, with only 5.7.
BIG CYPRESS. Preserve-wide water stage has dropped a half foot over the past 4 weeks. That’s on the heels of preserve-wide stage holding steady for the 4 weeks prior. So the reemergence of a steady downward trend is significant, especially with 2-3 months of the dry season still to go. Preserve-wide stage has now dropped below the tall cypress landscape type. That breaks an 8-month consecutive streak of the preserve’s tall cypress holding surface water, from early June to late February. Currently, standing surface water is only present in the deeper ends of our swamp forest and marsh wetland habitats. If the trend continues, I would expect those wetlands to go dry sometime later in March, leaving only the deepest holes of natural refugia (plus our canals and borrow pits) with water. Interestingly, the southeast corner of the preserve is our wettest area. Surface water is still holding on in cypress habitats and fully flooding marsh habitats in that area.
LAKE O. Current lake stage is about 11.17 ft msl. That places current lake stage at about 4 ft below late February of last year, about 4 ft below the 5-year late February average, and about 8.5 inches above late February of the 2001 drought year. Its now been almost 11 months in a row that lake stage has been below the level of the lake’s interior wetlands.
EVERGLADES. Regulatory stage in 3A has been dropped 0.75 ft since the start of the new year. That puts it at a pace of about an inch a week over that 2-month period. Keep in mind that regulatory stage for 3A is an average of Sites 63, 64, and 65. Interestingly, the recession rates for all three have been very similar over the past 2 months. I’m assuming that’s caused by the virtual absence of external structural flows to or out of the system, plus the absence of internal flows — meaning that ET has been ruling the recession rate for the past 2 months, and that is applied by equally by the sun across the whole system.
The system-wide steady recession rate over the past 2 months is a night and day difference compared to 3 months immediately following the end of the rainy season. Stage in southern 3A dropped 7 inches in the month of October, in comparison to twice that (14 inches) in northern 3A. Then for the final two months of the year (Nov and Dec) water stage more or less held steady in southern 3A (dropping less than 2 inches), in comparision to an additional 8 inch drop to the north. In total, that means stage in northern 3A dropped over a foot more than southern 3A during the first 3 month period of this year’s dry season. So its interesting to see southern and northern 3A dropping in unison for the past 2 months.
In terms of a water depth and hydroperiod comparision of the two areas, southern 3A just recently dropped below a slough depth of 2 feet. That means that southern 3A held a 2 ft (or greater) water depth in its sloughs for a 7-month period from late July to late February. In comparison, northern 3A (at Site 63) held a slough depth of 2 ft or greater for less than 2 months (in September and early October). Slough depth in northern 3A is currently just a few inches in comparison to over 20 inches to the south.