Withlacoochee River System Update - 12/28/2023

Forecast of a Wet Winter Becoming a Reality

 

Rainfall:

• Weather predictions of a wet winter are coming true.
• Both November and December have brought above average rainfall, a much-needed change from the drier than normal year we’ve had.
• So far in December, our region has received about 4.6 inches of rain, much higher than the historical average for the month (2.6 inches).
• That brings the total rainfall for the year (Jan 1 thru Dec 25) to 47.5 inches, still about 6 inches less than our annual average of 53.5 inches.
• In 2022, our region received about 52 inches of rain, and the prior year (2021) we received nearly 60 inches.
• Additional rainfall this winter has increased flow in areas rivers and caused lake and aquifer levels to rise in recent weeks.
• Aquifer (groundwater) levels are currently in the 53^rd percentile, now only slightly lower than this date last year (58^th percentile).
• The figure below shows how much rainfall different areas received in 2023. Green and blue areas received above average rainfall this year.

 

 

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

• A drier than normal 2023 has left the Withlacoochee River lower than average for this time of year.
• That would normally be a concern heading into the dry season, but our wet winter has river levels and flows on the rise.
• In the Green Swamp, where both the Withlacoochee and Little Withlacoochee Rivers originate, flows have increased substantially in recent weeks.
• All along the river, water levels are up anywhere from 0.5 to 2 feet, compared to the start of December.
• River levels are still a couple feet lower than they were a year ago.
• Flows along the Withlacoochee River are still less than half what they were last year at this time.
• The table below compares current river levels and flows to what they were last month and last year.

 

 

 

Bridge Over the Withlacoochee River in the Green Swamp (December 2023)

 

 

Tsala Apopka Chain of Lakes:

• All three pools of the Tsala Apopka Chain of Lakes are higher than they were a month ago.
• Heavy rainfall in mid-December caused water levels in the lakes/canals/marshes to rise several inches and recent lighter rains have kept them there.
• Despite recent gains, lake levels are currently about a foot lower than this date last year.
• The Withlacoochee River is still a couple inches higher than the lakes, allowing structures to remain open to bring some flow in the chain.
• Construction continues at the Golf Course Structure between the Floral City and Inverness Pools.
• The old gates have been removed as workers continue to prepare the site for renovations.

 

 

Floral City Structure Remains Open with Minimal Flow (December 2023)

 

 

Lake Panasoffkee and Wysong:

• Lake Panasoffkee has continued to rise, thanks to 5 ½ inches of rain so far this month.
• In December, Lake Panasoffkee rose 4.8 inches, and is now nearly 6” higher than it was last year at this time.
• The spring fed creeks that contribute flow to Lake Panasoffkee have also benefited from recent rains.
• Little Jones Creek and Shady Brook both saw increased flows this month and flows are now higher than they were a year ago.
• Outflow from the lake to the Withlacoochee River is also greater due to higher lake levels.
• 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) remains partially raised, allowing river flows to pass downstream.
• Withlacoochee River flow at Wysong more than doubled in December but remains much lower than what it was a year ago.

 

Main Gate at Wysong Structure (December 2023)

 

 

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) declined slightly in early December, then rose again in late December, breaking even for the month.
• Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) increased by 33% in December.
• Overall, inflows to Lake Rousseau remain about half of what they were a year ago.
• The Rainbow River is currently providing a little more than half of the total flow entering 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.
• 2023 was unique because nearly all year the Bypass Spillway was able to handle all flows coming down the Withlacoochee and Rainbow Rivers.
• Normally, rainfall is greater during the wet season (June-Sept), causing river flows to exceed the capacity of the Bypass Spillway, prompting the Inglis Dam to be opened.
• This year, the Inglis Dam has been closed 96% of the time, and only opened when storms like Hurricane Idalia threated the coast.
• All flow is still passing downstream through the Bypass Spillway, which is currently flowing at 77% of its capacity.
• Freshwater flows from Lake Rousseau to the Lower Withlacoochee River increased by 32% last month, due to above average rainfall in December.

 

 

Happy New Year!

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