Withlacoochee River Update - 1/2/2019

High December Rainfall has Water Levels and Flows Rising Again

(This update contains information for the entire system including the Withlacoochee River, Tsala Apopka Chain-of-Lakes, Lake Panasoffkee, Lake Rousseau and the Lower Withlacoochee River.)

 

Rainfall:

• Our water resources normally decline this time of year, because we typically only get a couple inches of rain each month during the winter.
• But last month was anything but normal.
• Our region received over 9 inches of rainfall in December, nearly four times the historical average (2.5 inches) for that month.
• This brings our total rainfall for 2018 to 66 inches, 12 inches above the historical average and 14 inches more rain than we received last year.
• You’d have to go all the way back to 1983 to find a year with more rain.
• A very wet 2018, has aquifer levels currently in the 91^st percentile.
• This means that aquifer levels have only been higher 9% of the time (in recorded history for this region).

 

 

Withlacoochee River (from the Green Swamp downstream past Hwy 200):

• High rainfall in December quickly halted the natural declines in river levels and flows that had occurred during October and November.
• Over the past month, river levels rose anywhere from 1.5 to 6.5 feet.
• This sharp rise is due to high rainfall on saturated soils and evaporation rates which are lower during the cooler winter months.
• Simply put, more of the rain that falls is making its way to the river right now.
• River flows have also increased tremendously over the past month.
• In the Green Swamp, where river flows had nearly ceased in early December, they’re now as high as they were in late-July and mid-September.
• The table below compares current river levels and flows to what they were one month ago and one year ago.
• The water levels reported in this table are elevations (approximately above sea level), not river depths which can vary significantly even at the same location in the river.

 

 

 

Tsala Apopka Chain of Lakes:

• Citrus County received about 10.7 inches of rain in December, higher than the regional average of 9.3 inches.
• As a result, lakes levels in the Tsala Apopka chain rose about 11 inches over the past month.
• Water levels in Tsala Apopka are currently at or near their target levels, which is abnormal for the month of December, when lake levels are typically declining.
• The Van Ness Structure which had been opened on Dec 20 (due to high levels in the Hernando Pool) was closed this morning.
• Over the past couple weeks, water had been flowing from Tsala Apopka through the Van Ness Structure to Two-Mile Prairie, which is also currently full.
• All the Tsala Apopka structures are now closed, helping to conserve water in the lakes.
• If we continue to receive above average rainfall this winter, additional structures may be opened as needed to help maintain current water levels.
• The table below compares current water levels in the Tsala Apopka Pools to what they were one month ago and their target levels.

 

Lake Panasoffkee:

• Over the past month, water levels in Lake Panasoffkee rose more than 7 inches because of high rainfall in December.
• Both inflows to the lake (measured in Little Jones Creek and Shady Brook) and outflow from the lake are twice as high as they were a month ago.
• The independent gate (19-foot-wide) at the Wysong structure is now fully lowered in response to increased river flows and water levels.
• The main gate (230-foot-wide) at the Wysong structure remains partially inflated, helping to conserve water levels upstream and in Lake Panasoffkee.
• River levels both upstream (Hwy 48) and downstream (Hwy 44) of the Wysong structure both rose a couple feet during the month of December.

 

Lake Rousseau and the Lower Withlacoochee River (from Dunnellon to the Gulf of Mexico):

• Between Dunnellon and Inglis, the Withlacoochee River enters Lake Rousseau (an in-stream lake created over a century ago by the original Inglis Dam).
• Lake Rousseau inflows are a combination of incoming flow from the Withlacoochee and Rainbow Rivers.
• Both the Withlacoochee and Rainbow Rivers are flowing significantly greater than they were a month ago, due to high rainfall in December.

• Outflows from Lake Rousseau have also increased over the past month, since more water is entering the lake.
• The Inglis Bypass Spillway, which conveys flow to the Lower Withlacoochee River is currently at capacity (~900 MGD).
• The Inglis Main Dam, which conveys excess flow to the Barge Canal, is also currently open helping to maintain water levels in Lake Rousseau.

 

Happy New Year!

Mark

 

Mark Fulkerson, Ph.D., P.E.

Southwest Florida Water Management District

 (352) 796-7211, ext. 4410

(800) 423-1476 (FL only)

(352) 279-4493 (cell)

Mark.Fulkerson@WaterMatters.org

 Withlacoochee River Watershed Initiative