By Mark Fulkerson, Ph.D., P.E.
Chief Professional Engineer
Water Resources Bureau
Southwest Florida Water Management District
- Rainfall is the source of water for our region’s lakes, rivers, and underground aquifers.
- After record rainfall this summer in some portions of the Withlacoochee Watershed, we ended the year in less dramatic fashion.
- Over the past month, our region received just 1.3 inches of rain, half the historical average (2.6 inches) for December.
- Overall in 2021, the District’s northern counties received an average of 61 inches of rain, higher than the annual average (54 inches).
- Flow in area springs remains strong due to high aquifer levels from rainfall several months ago.
- Region-wide aquifer (groundwater) levels are currently in the 84th percentile, well above average and much higher than they were a year ago (50th percentile).
- Higher aquifer levels help keep water in our lakes/wetlands, supply continuous flow to our rivers, and has been the cause of flooding in some areas this year.
Withlacoochee River (from the Green Swamp downstream past Hwy 200):
- Water levels and river flows dropped along the entire Withlacoochee in December.
- Most areas saw modest declines, about 6-12 inches last month, while other areas (with higher banks and narrower channels) saw 2-to-3-foot declines in December.
- River flows dropped an average of 45% last month and much of the river’s flow is now coming from underground connections with the aquifer (aka “springflow”).
- Upstream portions of the river (Green Swamp through Croom State Forest) are lower than they were a year ago, a product of less rainfall this year in the Green Swamp.
- Farther downstream (Hwy 48 through Hwy 200), in areas that have received much more rainfall in 2021, the river is currently higher than it was a year ago.
- Declining river levels and flows are normal for this time of year, and that trend should continue throughout the winter/spring.
- The table below compares current river conditions to what they were last month and a year ago.
Tsala Apopka Chain of Lakes:
- The Tsala Apopka Lake Chain includes three distinct pools of water, each with unique open water lakes (10-20 feet deep), shallow wetlands that periodically dry up, and miles of canals and airboat trails for navigation.
- The lakes surpassed their normal high levels this summer due to record rainfall but have slowly declined in recent weeks.
- All three pools dropped about 2 inches in December and are currently 1-2 inches higher than they were a year ago.
- Water control structures throughout the lake chain remain closed, helping to conserve water as our dry season continues.
- Water levels are expected to slowly decline until our region receives significant rainfall again.
Lake Panasoffkee and Wysong:
- Lake Panasoffkee is a spring-fed lake that receives continuous inflow from Little Jones Creek, Shady Brook, and numerous aquifer connections beneath the lake.
- Water also flows out of the lake year-round, joining the Withlacoochee River upstream of the Wysong water conservation structure.
- Lake levels fell about 2.5 inches in December.
- The main gate (230-foot-wide) of the Wysong structure remains partially raised.
- The independent gate (19-foot-wide) remains fully lowered.
- Lake Panasoffkee is currently about 3 inches lower than it was a year ago.
- Our water quality staff continue to monitor lake clarity after a widespread algae bloom appeared this fall.
- As of last week, the northern end of the lake is mostly clear with abundant eelgrass, while the middle and southern portions remain brown with suspended particles in the water.
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.
- Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) decreased by 27% over the past month.
- Flow in the Rainbow River (which reflects changes in aquifer levels) decreased by 6% in December.
- Overall inflows are about 9% higher than they were a year ago, due to greater rainfall in 2021.
- Currently the Rainbow River is contributing 45% 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).
- Back in July, this structure reached its capacity and was unable to handle inflows which had increased from summer rains.
- For the past 5 months, the Inglis Main Dam has been open, discharging excess water through the Barge Canal and into the Gulf of Mexico.
- In mid-December, the Inglis Main Dam was finally closed again.
- The Inglis Bypass Spillway is still flowing near capacity, providing over 900 million gallons of freshwater per day to the tidally influenced Lower Withlacoochee River.
Happy New Year!