Withlacoochee River System Update - 11/1/2023

Low Water Levels to Start the Dry Season

 

Rainfall:

• Will we ever get decent rainfall again? That’s what a lot of folks are starting to wonder.
• The answer of course is yes, but it has certainly been dry lately.
• Last month our region received an average of 2.2 inches of rainfall, with most of that coming on a single day in mid-October.
• So far this year (January to October) we’ve received 40 inches of rain, about 9 inches below the historical average (49 inches) for the first 10 months of year.
• By this time last year, our region had already received 47 inches of rain.
• Historical average rainfall for the year is about 54 inches, so we’ll need 14 inches of rain in November and December to break even.
• Less rainfall in 2023 has resulted in lower water levels in area lakes, rivers, and the aquifer.
• Aquifer (groundwater) levels are currently in the 33^rd percentile, much lower than this date last year (62^nd percentile).
• The figure below shows how much rainfall different areas received last month. All red, orange, and yellow areas received below average rainfall in October.

 

 

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

• Water levels and flows along the Withlacoochee River are much lower than what we normally see this time of year.
• The river normally peaks much higher in late summer, and slowly drops during the winter/spring months.
• This year, the river didn’t get very high during the wet season, so we’re already starting out quite low as our dry months begin.
• Flows from the Green Swamp have nearly ceased, a phenomenon that typically only happens at the end of the dry season (late spring).
• Along the Withlacoochee, river levels are currently several feet lower than they were a year ago.
• Weather forecasts have suggested El Nino patterns which could mean a wet winter.
• We certainly need substantial rainfall in the coming months, or the Withlacoochee River could end up drier than we’ve experienced in many years.

 

 

 

Withlacoochee River near Lacoochee (September 2023)

 

 

Tsala Apopka Chain of Lakes:

• This time of year, the lakes are typically near their high levels following substantial rainfall during the summer months.
• But minimal rainfall in 2023 has prevented the lakes from reaching their normal high levels this year.
• The Floral City, Inverness, and Hernando Pools are currently 25, 23, and 16 inches lower than they were a year ago, respectively.
• Over the past month, water levels in all three pools dropped 2 to 3 inches.
• Water control structures, which were opened to mid-July to evenly share river inflows between the pools, remained open the entire month of October.
• River levels are currently dropping about twice as fast as the lakes, and soon all structures will need to be closed to help conserve water in the lake chain for the dry season.
• No water has been released from the lakes at all during 2023, which is different than previous years, when the lakes have consistently risen above their high levels.
• Over the next several months, we can expect water levels to continue to drop from evaporation and downward leakage to the underlying Floridan Aquifer, unless our area receives heavy rainfall.

 

 

Construction has begun at the Golf Course Structure (October 2023)

 

 

Lake Panasoffkee and Wysong:

• Lake Panasoffkee rises and falls each year due to changing rainfall patterns that directly affect the lake itself, the Withlacoochee River, and regional groundwater levels.
• Little Jones Creek and Shady Brook, which flow into the lake at the north and south ends, respectively, continue to provide decent flow to Lake Panasoffkee.
• Outflows from the lake to the Withlacoochee continue to decline and are currently less than half of what they were a year ago.
• Over the past month, Lake Panasoffkee fell about 3 inches, and is now 9 inches lower than it was last year at this time.
• The Wysong Structure remains inflated, helping to conserve water upstream.
• The main gate (230-ft-wide) at Wysong has been fully raised since mid-February.
• The independent gate (19-ft-wide) is now partially raised.
• River flow at Wysong has been steadily dropping and is currently only 10% of what it was a year ago.

 

 

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

• Downstream from Dunnellon, the Withlacoochee River is influenced by water control structures on Lake Rousseau.
• Inflow to Lake Rousseau includes combined flows from the Withlacoochee and Rainbow Rivers.
• Rainbow River flow (which reflects changes in aquifer levels) remained steady over the past month.
• Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) is 75% lower than last year at this time.
• Overall inflows to Lake Rousseau are half of what they were a year ago.
• The Rainbow River is currently providing two-thirds of the total flow into Lake Rousseau.

 

• The primary outlet from Lake Rousseau is through the Inglis Bypass Spillway to the Lower Withlacoochee River (see maps below).
• When the Bypass Spillway reaches its capacity, the Inglis Main Dam is opened to discharge excess flows to the Barge Canal.
• So far in 2023, 99% of the flow leaving Lake Rousseau has passed downstream to the Lower Withlacoochee through the Bypass Spillway.
• Last year, which was closer to an average year, 90% of the flow exited the lake to the Lower Withlacoochee, while 10% was discharged through the Main Dam.
• The Inglis Main Dam has been closed all year, except when Lake Rousseau was lowered ahead of Hurricane Idalia or other storm events.
• All flow is still passing downstream through the Bypass Spillway, which is currently flowing at about 53% of its capacity.
• Freshwater flows from Lake Rousseau to the Lower Withlacoochee River decreased by 14% last month, as river flows upstream have continued to decline.

 

 

Best regards,

Mark

 

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

Chief Professional Engineer

Water Resources Bureau

Southwest Florida Water Management District

 (352) 269-6073 (office)

(352) 279-4493 (cell)

Mark.Fulkerson@WaterMatters.org

 Withlacoochee River Watershed Initiative