Rain, rain, and more rain…at least in some areas

June 1st To August 30th 2021

Rainfall

Florida has a distinct wet season the runs from June through September.
It is during these 4 months that we receive 60% of our annual rainfall, or about 30 inches of rain on average.
Since June 1st of this year, some portions of the Withlacoochee watershed have already received more than 40 inches or rain, and there’s still one more month to go in our wet season.
Other areas, farther upstream along the Withlacoochee (including the Green Swamp) have seen far less rainfall in recent weeks.
Overall, portions of Citrus, Sumter, Marion, and Levy Counties have experienced much higher water levels this summer, compared to Polk, Lake, Pasco, and Hernando.
Above average rainfall in the more northern Counties has kept aquifer levels high and increased flow in area springs.
Aquifer (groundwater) levels are currently in the 85th percentile, well above average and much higher than they were a year ago (47th percentile).
Flows in our area springs continued to rise in August and are currently at the high end of their normal range for this time of year.
Last year (2020) our region received below average rainfall, but this year we’re on pace to receive over 60 inches of rain!

It has been an interesting summer along the Withlacoochee River.
Upstream areas (including the Green Swamp) have received far less rainfall this summer and as a result river levels in those areas have not risen as high as we’ve seen in recent years.
The river normally peaks in September, but this year the upstream portions peaked in early July and levels/flows have fallen since then.
Downstream areas along the river (Citrus, Sumter, Marion) received much more rainfall in August, causing them to reach minor flood stage a few weeks ago.
If the entire river’s watershed had received this surplus rainfall, we would have experienced more substantial flooding along the entire river this year.
The Little Withlacoochee, which also peaked in early July, has seen levels/flows decline in recent days.
The table below compares current river conditions to their peak levels from earlier this summer.

Here’s a quick run-down of the different regions of the Withlacoochee River Watershed (see map below):

Peak level at Croom this year (July 2021) - Notice how far below previous flood (marks on trees)

Tsala Apopka Chain of Lakes:

Heavy rainfall in early August pushed water levels in the Tsala Apopka lake chain well above their target levels.
As of last week, the lakes had returned to normal, but more rainfall yesterday caused lake levels to rise again.
As a result, several water control structures were opened again to help move this excess water out of the lakes.
These structures can only move a limited amount of water from the lakes/canals/marshes that are directly connected to the Tsala Apopka chain.
There are many other flooded low-lying areas or wetlands that are isolated from the lake chain which must rely on natural evaporation or infiltration for water levels to recede.
It may take several more weeks/months before we start to see many of these flooded areas dry out again.
Once the Tsala Apopka Chain-of-Lakes return to their target levels, the structures will be closed to help conserve this water for the upcoming dry season.
Remember, these structures cannot prevent flooding or drought. Water levels fluctuations are ultimately caused by rainfall changes.

Brogden Bridge Structure moving water out of the Inverness Pool (August 2021)

Lake Panasoffkee has also experienced high water conditions this summer.
After peaking in mid-August from above average rainfall, lake levels have dropped more than 10 inches in the past couple weeks.
The Wysong structure (on the Withlacoochee River) which was lowered in early July, remains fully lowered.
With Wysong fully lowered, boat traffic is still able to safely pass through the center of the river over the structure.
Flows along the river at Wysong are currently about twice as high as they were a year ago.
When river conditions return to normal, Wysong will be incrementally raised again.
Inflows to Lake Panasoffkee have been declining in recent days but they remain strong for this time of year.
Lake Panasoffkee is currently about 4 inches higher than it was a year ago.

Lake Rousseau is an in-stream reservoir, created 112 years ago (1909) when the original Inglis Dam was built on the Withlacoochee River.
For much of the year, water levels on Lake Rousseau are relatively flat as far upstream as Dunnellon.
During times of high flow (wet season) river levels at Dunnellon can rise significantly higher than the west end of Lake Rousseau (where the Inglis Dam is located).
The influence of the Inglis Dam extends just upstream of Dunnellon, where the Rainbow River contributes constant flow to the Withlacoochee.
Flows in the Withlacoochee River at Hwy 200 (which vary based on rainfall) have declined by 27% after peaking in mid-August.
Rainbow River flows (which are driven by aquifer levels) increased by 13% in August as groundwater levels continue to rise from recent rainfall.
Overall, inflows to Lake Rousseau are more than twice as high as they were a year ago.

Heavy rainfall yesterday caused Lake Rousseau to rise several inches above its normal level.
As a result, the Inglis Main Dam (which has been open since July) was opened further to increase outflows from Lake Rousseau to help bring lake levels back down to normal.
The Inglis Bypass Spillway is still flowing at capacity, providing nearly 900 million gallons of freshwater per day to the tidally influenced Lower Withlacoochee River.
The Inglis Main Dam continues to discharge excess flows from Lake Rousseau to the Barge Canal and into the Gulf of Mexico.
Overall, outflows from Lake Rousseau are nearly twice as high as they were a year ago.