Mullet Slough – Lake O inversion
SFL Weekly Watersheds Summary: Aug 14-20

LAKE O. Lake O had an interesting water budget this week. Structural inflows and outflow were almost negligible for the entire week. The lake only saw very minor inflows from the Kissimmee (50 cfs), with also some minor inflows from Harney Pond Canal (285 cfs), Fisheating Creek (23 cfs), and the S4 backpump (6 cfs). Structural outflows were also neglible. Rainfall on the Lake and evaporation from the Lake balanced each other out perfectly, both at around 5000-6000 cfs (~2 inches each). From a water budget perspective, the result of the lack of structural flows and the near perfect balance between evaporation and rainfall translated into Lake stage staying steady at 12 ft above sea level. So even when the lake doesn’t move there’s still a story behind it.

Also of interest, its worth noting that wetland water stage forty miles to the south of Lake O, five miles south of I75, in an area of Big Cypress National Preserve called Mullet Slough, is currently 12.6 ft msl. That means that Mullet Slough stage is currently higher than Lake O by over a half foot. This is not as unusual at it might appear at first glance. The Kissimmee Basin has received only 10-15 inches over the past 3 months, whereas areas south of the Lake have received 20-30 inches over the same 3-month period (with the Big Cypress getting closer to 30 inches). This Mullet Slough – Lake O stage inversion also occurred during the summer season of the droughts of the late 80s and early 1990s, the during the entire year of the mega-drought of 2000-01, and also very briefly (a week each) at the startup of the rainy season in 2002 and 2004. None the less, its a rare occurrence, and one to take note of when it does occur. We’ll have wait and see how long this one lasts.

Lake O stage is also currently 4 feet lower than stage at Site 1-7 in WCA 1 (Loxahatchee), which is currently at 16 ft msl, but unlike the Mullet Slough – Lake O stage inversion, stage is WCA 1 is routinely higher than Lake O stage by several inches to a few feet. Lake O stage has risen above WCA 1 stage only a handful of times over the past fifteen years, usually by only a few inches and for a very short duration (a few weeks).

Be sure to take a look at the new Big Cypress Watershed Summary. It’s new and improved.

(1) US41 FLOWS: I worked with Carolyn Price (USGS-Miami) to add the US41 flow data to the watershed summary. This is a major addition, not only from a Big Cypress water budget perspective, but also because the data extends so far back in time, which helps give us a better historical perspective on the system. The US41 flow data is shown as the second graph from the top on the left-hand side of the page. It shows current freshwater flow across the western (Carnestown-Monroe Station) and eastern (Monroe Station-40 Mile Bend) sections of US41 in the preserve. The current year is graphed relative to the average year, previous year, and 5-year range. Also, if you want to look at the historical record of this flow data for the entire history of the preserve (from 1970 to present), click on the map on the right-hand side of the map as shown.

As of last week, US41 flows in the preserve were way down, flowing at around half the rate of the 5-year average of 2000 cfs for mid August. The abundant rains we saw this week (>3 inches in the preserve) will likely boost these flows in the near future. Not surprisingly, last year set the 5-year high water mark for flows under the trail. Flows stayed about 4000 cfs between early July and early November, and peaked close to 6000 cfs.

(2) RAINFALL: The color-coded raindrops on the top right-hand side of the page show weekly rainfall for the entire preserve. Click on those drops to see a comprehensive breakdown of historical rainfall for the preserve. This data was all provided by the Meteorology Team over at the SFWMD.

(3) PRESERVE-WIDE WATER DEPTH is shown on the left-hand side of the page. This graph shows perserve-wide stage with respect to wetland depth (ft) and wetland landscape type, and also references water levels relative to the 5-year average, 5-year range, and previous year. Click on it to see historical calendar of the hydroperiod in the preserve from 1990 to present, so you can see where we are at now relative to Augusts of year’s past.

(4) INTERACTIVE MAP. The interactive map on the right-hand side of the page is just the same as its always been. Click on the inside of the diamonds to see a hydroperiod history at the site with respect to water depth (ft) and click on the outside of the diamonds to see a hydroperiod history at the site with respect to flooded landscape types.

(5) BIG MAP. Click on the “Big Map” tab at the top of the interactive map to see a bigger rendition of the Big Cypress area map with names of major flow ways and features. This map is not intended for navigational purposes, but does put a name to a handful of the major places in the Big Cypress neck of the woods.

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