Water cycle clock turned back

Rain or Shine Report for March 11
1-hour spring forward, 3 month fall back

Cartoon depicting how water cycle interacts with mosaic of lilliputian valleys and swales in Big Cypress National Preserve. The high ground is the pinelands, where rising summer waters get to last and for the shortest duration. Water depths are deepest and longest in the swales among the cypress, pond apple, and marshes.

The annual ritual of turning the clocks forward came early this year. It caught me by surprise to say the least, as I had only a few weeks ago finally adjusted to turning the clocks back in Fall (which came later than usual).

I always joke around this time of year about that extra hour of sunlight is what causes the plants to leaf out, and also adds an hour of evaporation to the day, thereby causing water levels to drop down faster.

Granted, it’s a bad joke and has no physical basis in reality, but it does generate some interesting conversations in the hallway, and – from a seasonal timing standpoint – the Spring-time turning of the clocks does more or less with an inflection point in the dry season recession, after which the drop in the water table seems to accelerate.

In Big Cypress National Preserve, the inflection point kicks in on average in late March. It’s not an exact onset: last year it came early, in late February.

The onset of that inflection point can be disrupted by rain, in both its absence and deluged abundance. That’s what has happened with the stalled fronts that swept through south Florida in recent weeks.

The Water Cycle Clock has been turned back weeks, even months, in some watersheds.

Big Cypress Nat’l Preserve is on top on that list.

Preserve-wide stage is at the same level now as it was near the fledging part of the dry season back in late November. Sometimes the dry-season rains soak right in, almost as fast as they fall, and disappear below ground into the aquifer.

But this deluge has had staying power in the swamps. The wetting front still has the cypress domes and strands filled to their brims, and about a half-foot higher than the 5-year average for early March.
Graph showing dramatic rise in water levels in Big Cypress Nat’l Preserve. Colors show habitat types: pinelands, prairie, cypress, and swamp forest.

That was mostly from the 4-inch deluge that fell on Big Cypress Nat’l Preserve in mid February. The most recent stalled front dropped its rain most plentifully in West Palm Beach. The Sun-Sentinel reported that West Palm Beach set a new record for March 6th with almost 3 inches of rain.

As a result, the Water Cycle Clock swung back 2 months in Loxahatchee: it’s at the same level now as it was back in mid January.
Last year by comparison, wetland water depth dropped a half foot over the same 2-month span (from January to March); and slough depth in the central marsh – currently at 1.5 ft deep – is about a half-foot higher than the 5-year early March average.

Just across the levee, the Water Cycle Clock also swung back 2 months in downstream Water Conservation Area (WCA) 2. And that’s without the help of the S10s, which are still closed (which is normal for this time of year), and holding around 3.5 ft of water on the upstream side of the levee.

Wetland stage in WCA2 has dropped 2 feet since its early Fall high-water mark. Over the same time period, Loxahatchee stage has dropped under a foot.

Why the difference? That’s a good answer for a future post.

Slough water depths in central WCA2 are only around 0.5 ft deep. That’s a full foot shallower than sloughs in upstream Loxahatchee, and 1.5 ft shallower than sloughs in southern Water Conservation Area 3, just north of the Trail.

Speaking of the Trail, it made a big splash in the news this past week. You can read about in the Miami Herald, if you haven’t seen it already. Restoration planners are trying to move forward on modifying water deliveries under Tamiami Trail into downstream Everglades National Park. That will not only open the door to getting more water into the right places of the Park, but also open door for moving ahead on other aspects of the broader Everglades restoration blueprint.

Symbolically speaking, it couldn’t come at a better time: the S12s – the primary gates that release water into the downstream Park – logged their lowest flow total in 17 years, dating back to the drought years of 1989, 1990, and 1991. The S12s were recently opened, but only briefly at a low capacity (~50 cfs max) – for about 2 weeks – following the mid February deluge.

Annual flow (in millions of acre feet per year) across Tamiami Trail, as measured by the US Geological Survey

The past year’s trickle through the S12s has been reflected in downstream Shark River Slough. Slough water depth in the center part of the slough is currently around 8 inches deep. That’s still higher than the 1989-1991 severe drought, but shallow in comparison to recent years.

The duration of shallow conditions is what really sets it apart from recent years. Shark River Slough (as measured at the Park’s P33 monitoring station) went through and entire summer at or below a 1.5 ft depth. That’s a depth it typically sustains as a baseline for 5-8 months of the year, often rising as deep as 2 feet deep or more.

If our time-keeping clocks sprung forward, and the Water Cycle Clocks in Big Cypress and Loxahatchee fell back, the Lake O is stuck in perpetual Groundhogs day in comparison.

Lake O’s much anticipated milestone drop below 10 ft keeps getting delayed. Wasn’t it back in early February that it ceremoniously dropped a decimal below 10, only to rebound a few inches from the stalled front? Once again, last week’s rain inched the Lake back about 2 inches above 10 ft.

Graph showing Lake’s current drought versus the 2000-01 drought. They are at very similar early March levels.
That makes it 5 straight months now that the Lake has held steady just barely above 10 ft.
That’s unexpected good news. Remember, we still have almost 4 months ahead of us before we reach the late June calendar date that the Lake bottomed out at its all-time low last year (in 2007). So there is a lot of dry season real estate left.

Yes, current Lake stage is still around 8-10 inches above early March of last year. But, it was just a few months ago in mid October that Lake stage was 3 ft lower than the previous year.

So, sometimes you can gain ground by holding steady. That’s what the Lake’s done since October.

That hasn’t solved the issue of getting flows to the estuaries, to keep salinity from creeping to far into the mouth of the Caloosahatchee and St Lucie. A steady trickle of freshwater can keep the salt wedge at bay, and keep the brackish balance in check. That will be interesting to track as the dry season marches forward, and is a big contrast to the high-water flows of 2003-2005.

To the north, around 800 cfs flows are being released from Lake Toho (through S61). I had noticed the releases several weeks ago, but didn’t have the full story on them. A news release by the South Florida Water Management District reports that the releases are being strategically timed to provide a more suitable nesting habitat for snail kites who have found a home in Lake Toho and upstream East Lake Toho. Usually the releases occur several weeks later, and at a more rapid rate. The early and more gradual release rate is anticipated to benefit the snail kite’s nesting season.

Be sure to turn your clocks forward if you haven’t done so already. Isn’t it 45 minutes this year; (that’s another bad joke). And don’t forget to stay in tune with water cycle in your neck of the watershed as it unfolds.

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