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Wk of 6/26-2: End of June summary

Lake O stage seems to have bottomed out at 12 ft above sea level, but has not yet begun to rise. Last year this time lake stage was 4 feet higher. As it stands now, lake levels are still 1.5 feet below the bottom of the littoral zone (13.5 ft above sea level) and about 1.25 ft below the 5-year average for the start of July.

Down in Loxahatchee, water levels are still flooding at the slough level. Just to the south in WCA2, water levels have not yet risen to the slough level. Both sites 2-17 and 2-19 are reporting an absence of surface water, although just upstream of the S11s surface water is backing up above the slough level into the ridge zone. Interestingly, water levels at Site 99 down in WCA2B have declined about a foot since the start of June, whereas the water levels just upstream in 2A have stayed steady during the same period. This must be caused by either (1) lack of water flowing from 2A to 2B, (2) water being drained out of 2B (for water management reasons), or (3) a combination.

Down in Water Conservation 3, regulatory stage has risen about a half foot from its early June low water mark. In the area north of I75, surface water is now flooding in the slough zone. Surface water is pooling up higher to the south where it accumulates on the north side of US41. Both sites 65 (in 3A) and 71 (in 3B) are showing water levels to have risen into the bayhead landscape type zone. If you click the “outer diamond” (http://www.fgcu.edu/bcw/WCA3A/Ha65.gif) for site 65 you’ll see by looking at its period of record (using the hydrologic calendar) that for the past 10 years its low-water mark rarely (if ever) drops below the ridge landscape type. In comparison, the hydrologic calendars for the rest of the sites in the conservation areas show their low-water marks to routinely drop below the slough landscape zone and become dry. I don’t know which one is more natural, probably somewhere inbetween.

Down in the park, the S12s are not yet flowing. This time last year the S12s were flowing at a combined total of 2500 cfs, but that was due to all of last year’s big June rainfall, and in attempt to provide relief to rising water levels in 3A. You can look at period of record for flow through each of the S12 structures if you click on the individual S12 structures on the interactive ENP map. You’ll see a very noticeable difference in the magnitude and duration of flow between the S12A and the S12D. The S12D stays open longer, plus its in a deeper part of the system which allows more water to move through it. The marl prairie south of S12A tends to minimize flows through it relative to the other S12 structures. At this point, with all the rain we’ve received, I would suspect that inflows to the park are occurring across US41 in the Big Cypress. Hopefully that will be reflected in the graph in time for next week’s update. Special thanks to the USGS-ENP partnership to monitoring flows across the trail. That’s one of the best and longest hydrologic data sets we have in the Everglades.

Over in Big Cypress, water levels have rebounded over 3 feet from the mid-May low water mark, and are now tracking very closely to the 5-year average for early July. Surface water is now flooding at the prairie and cypress landscape level throughout most of the preserve, although the area to the north of I75 is still only reporting water in the lowest wetland zone, the swamp forest. A rainy end to June helped make up for lost ground earlier in the month. Preserve-wide, this year’s June rainfall chimed in at 8.1 inches, only about 2 inches below the 10-year June average.

Regards,
Bob

Wk of June 19-25: Big Sunday rain fills up swamps
http://www.fgcu.edu/bcw/hcu.htm

Big Cypress National Preserve is finally starting to fill up with surface water after Sunday’s big rain storm. The preserve and Water Conservation Area 3 received around 2 inches of rain last week. In comparison Naples received 3 inches and north of Lake 0 received <1 inch. However, even with Sunday's rain, the preserve has still only tallied 7 inches of rain in June to date. That still leaves us 3 inches below the 10-year June average of 10 inches. Last year we had 20 inches in June. I would say that preserve-wide sheetflow is still not up and running as of yet. The sheetflow index for the preserve (aggregate of stations A2, A13, A6, and A10) is still charting surface water at the top of the swamp forest landscape type (our lowest lying wetland type), with almost a full half foot of additional water needed to boost surface-water flooding into the wet prairies. Preserve-wide sheetflow officially takes root in the preserve when the prairies become flooded. Surface water does not rise as a homogenous mass in the preserve, however. Areas in proximity to Turner River Road and near Loop Road are already flooded at the prairie level. In comparision, areas to the north of I75 are still dry. This could change in the next week as Sunday's rain moves through the system. In the Water Conservation Areas, water levels in Loxahatchee are still at the slough level and water levels in WCA2 are still below ground. Water levels are at the bayhead landscape type in southern 3A and are at the slough level in northern 3A north of I75. As of Sunday, regulatory stage in Areas 3, 2, and 1 were 0.75, 1, and .25 ft, respectively, below the 5-year late June average for those areas. As of Sunday there continue to be no flow into ENP from along its entire northern boundary (from Carnestown to Krome Avenue). Flows along the C111 flow system were also neglible. Water stage at P33 is tracking very close to the 5-year late June average. The majority of station in ENP are reporting water levels at the slough level. Lake O stage dropped below 12 ft above sea level on Sunday. That puts it a full foot below the 5-year average for late June and 4 feet lower than it was in late June of 2005. Flows from the Kissimmee (S65E) averaged under 400 cfs last week. This year’s absence of early wet season outflows down the S79 (Caloosahatchee) and S80 (St Lucie) are in major contrast from last year when +5000 cfs discharges down the S79 occurred pretty much for the month of June and +3000 cfs dicharges down the S80 occurred for most of July.

Week of June 12-18, 2006

Lake Okeechobee continues to drop. Currently lake stage is 12.1 ft above sea level, which is about 1 foot lower than the 5-year average for late June and 3.5 feet lower than it was this time last year.

In the Water Conservation Areas, water levels have yet to rebound from their springtime lows. Last year this time Area 3A regulatory stage was 1.5 ft higher than it is now, Area 2 regulatory stage was over 2 ft higher than it is now, and Area 1 regulatory stage was about a half foot higher than it is now. Area 1 is currently flooded at the slough level. Area 2 is currently dry. Area 3A is flooded at the ridge/bayhead level in the south and at or below the slough level north of I75.

To the south, water levels in ENP at P33 are tracking closely to the 5-year average for this time of year. Most of the Shark River Slough sites seem to be holding water at the slough level.

Over in Big Cypress National Preserve, surface water is still mostly absent from the preserve. Current preserve-wide water levels are 1.5 ft lower than the 5-year average for late June, and 2 feet lower than they were this time last year. As an aggregate, water stage in the preserve is still a few inches below the bottom of the swamp forest habitat type. This means that water levels will still need to rise 0.5-1 ft before the sheetflow surface water regime is established.

This year’s slow start to the sheetflow season is reminiscent of similar slow starts to the wet season that occurred in 1998, 2000, and 2004; and contrasts the fast startup of the wet season that occurred last year.

Regards,
Bob

Week of Jun 5-11, 2006

A look back on this year’s low-water mark.

Surface water systems in south Florida typically hit their low-water mark in mid May. It varies from year to year depending on how much spring rainfall we get, and if and when the summer rains get started. In 2003 for example over 10 inches of rain fell in late April and May leading to an absence of a deep or prolonged dry down. In 2000 a relative lack of May and June rainfall in the Big Cypress extended the drydown well into June. With the past couple of weeks chiming in at about 1.5 inches per week, followed by the sideswiping of TS Alberto*, surface water levels appear to have bottommed out and have begun their rise back up toward summer conditions.

Here’s a quick look back on where this year’s low-water mark fell in each watershed.
Lake Okeechobee stage continues to drop and appears not yet to have reached its low-water mark. As of Sunday Lake stage dropped to 12.37 ft above sea level. That’s a little over a foot below the bottom of the Lake’s littoral zone and almost 3 ft below where Lake stage was this time last year. Inflows from the Kissimmee River are still less than 500 cfs and from what I can see the Kissimmee watershed escaped the bulk of the rain from TS Alberto.

In Loxahatchee (WCA1) surface water levels bottomed out this year at a level where sloughs still remained flooded with water. This contrasts to WCA2 where sloughs went dry as early as late March and April (and remain dry as I type). Water levels in the southern part of WCA3A remained flooded at or above the ridge landscape type during this year’s low-water mark in that area. In comparision, slough surface water levels in the northern part of 3A went dry in the early part of May and still remain dry at Site 63 as I type. Slough surface water levels in northeast Everglades National Park (NE Shark River Slough) also went in the early part of May and remain just below ground surface as I type.

In Big Cypress NP, surface water levels dropped below our lowest lying wetland type (swamp forest) in early April, and as of today most of the preserve’s stations are still reporting water levels at or below the swamp forest wetland type. However, the southern part of the preserve seems to be filling up first with the onset of the summer rains. Most of our stations south of US41 are currently showing water levels at or above the swamp forest wetland type.

In Everglades NP, water levels have risen to the slough level in most areas. Note that currently there are no flows entering the park from its northern boundary — The S12s are all closed, inflows from the US41 culverts between S333 and S334 (ie, NE SRS) are negligible, and inflows to the western arm of the park from the Big Cypress are also still neglible. The ENP watershed summary is still a work in progress which I hope to refine with Kevin Kotun and other ENP staff over the next couple of weeks.

Regards,
Bob

* This week’s update does not include most of the rainfall from TS Alberto which brushed up against southwest Florida starting Sunday through Monday.

Week of May 22-28, 2005

It appears that the wet season has begun. Night-time temperatures have stayed above 70 degrees for the past week. This trend has been accompanied by a greater abundance of cloud cover in the afternoon and re-emergence of cumulonimbus clouds anvilling out at the top of the troposphere (bottom of stratasphere). So it looks like the south Florida summer rain machine is back up and running.

Typically we average somewhere around 2 inches of rain per week (or about 8-9 inches per month) during the wet season. However, the wet season never drops its rain uniformly throughout the summer, and each year the wet season seems to unfold in a slightly different pattern.

Last year we started the rainy season fast out of the gate with 20 inches in June. In the Big Cypress Basin, June is our most abundant rainfall month, averaging 10.6 inches of rain in June over the past 10 years. June consistently gets the most rain of any month because there is still a large amount of instability in the air from springtime fronts swooping down from the north and funnelling in moisture from the south.

Somewhere in July a less active second phase of the wet season tends to take control. July is our least abundant summer rainfall month, averaging 7.4 inches over the past 10 years in the Big Cypress. This dip in rainall is caused by the presence of more homogeneous atmosperic conditions up north, which tends to bring more stability and less rain to the south Florida weather machine. Other factors such as the position of the Bermuda high (which steers the directionality of the easterly trade winds blowing across the peninsula) and upper atmospheric warming are also at play.

As the summer progresses and sea breezes from both coasts collide with increasing severity in the middle of the peninsula, the localized convectional showers of the early wet season season give way to convergence fronts that form immense cells of storm clouds that can drop heavy amounts of rain over large areas, hitting the preserve first then moving on towards Naples. These convergence storm fronts mark the third phase of the wet season. (These are the really impressive, and often very scary storms). Some old-timers consider the onset of the convergence storms to be the start of the rainy season, even though these things don’t start up in earnest until late July or August. The months of August and September have averaged 8.3 and 8.9 inches of rain, respectively, over the past 10-years for the Big Cypress.

The fourth and final hurricane phase of the wet season tends to become a factor from August through October. South Florida seems to get the heaviest drenching from tropical storm activity (waves, tropical storms, and hurricanes) in September and October, but these events are hit and miss and more difficult to predict than the first three phases of the wet season. The 1998 wet season seemed to be over by mid October only to be hit by almost a foot of rain by Hurricane Mitch at the start of November. The same thing happened last year with Wilma.

Let’s all hope for a less eventful fourth phase of the wet season this year.

Regards,
Bob