Withlacoochee River System Update - 5/24/2022

Wet Season Starts Early; Water Control Structures Opened

 

Rainfall:

• Most years we see water levels drop sharply in May.
• That hasn’t been the case this year.
• With the wet season officially starting next week, water levels (both surface water and groundwater) are already higher than normal.
• Over the past 12 months, 70% of the Withlacoochee River's watershed has experienced above average rainfall (between 54 and 84 inches).
• A good indicator of surplus rainfall is how high the aquifer (groundwater) is.
• Region-wide aquifer levels are currently in the 85^th percentile, much higher than they were a year ago (42^nd percentile).
• This means there’s less storage available to capture our summer rains.
• The only exception is portions of the Green Swamp in Northern Polk County, near the start of the Withlacoochee River.
• So far in May, our region has received 4.2 inches of rainfall, the third month in a row we’ve had above average rain.
• The map below shows rainfall totals over the past 12 months. The historical average is 53.6 inches.

 

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

• Downstream portions of the Withlacoochee River are flowing higher than normal for this time of year.
• What’s interesting is there’s essentially no flow leaving the Green Swamp (where the river begins).
• From the Green Swamp downstream past Hwy 50, river conditions are very similar to last May.
• But from Nobleton downstream past Hwy 200, river levels and flows are much higher this year, a direct result of surplus rainfall over those areas.
• The Little Withlacoochee River, which was stagnant this time last year, has decent flow heading into the rainy season and is more than 2 feet higher than it was last May.
• Between Citrus and Sumter Counties, where the river swamp spreads wide into the flat forested wetlands, there will be less storage available this summer to absorb potential floodwaters from heavy rains.
• The table below compares current water levels and flows to what they were last month and last year.

 

 

Withlacoochee River near Potts Preserve (surrounded by conservation land)

 

 

Tsala Apopka Chain of Lakes:

• Water levels in the Tsala Apopka Lake Chain typically decline from March through May, naturally creating room for the wet season rains.
• But higher than normal aquifer levels, coupled with above average rainfall in recent months, has kept lake levels high throughout the dry season.
• Water levels are currently 12-15 inches higher than last May and only 3 inches below their target high levels for the end of the summer rainy season.
• As a result, water control structures are being opened this week to help move some of this excess water from the lakes.
• The goal is to try to keep the lakes a few inches below their target high levels, at least for the next month.
• This will also help circulate water through the lakes, a benefit that we don’t normally see this time of year.
• Since the lakes are nearly full, we don’t plan to open the Leslie Heifner or Floral City structures, because river levels are 4” higher than the Floral City Pool right now.
• If we continue to receive above average rainfall, the structures may be open for much of the summer, discharging this extra water from the lakes.

 

Downstream side of S-353 structure - currently closed (May 2022)

 

Lake Panasoffkee and Wysong:

• Lake Panasoffkee received 7.7 inches of rain over the weekend.
• This caused higher than normal lake levels to rise an additional 8 inches since last Friday.
• Little Jones Creek and Shady Brook are currently bringing over 100 million gallons of water per day into the lake, 3 times more than last May.
• Outflows from Lake Pan are also very high for this time of year, with nearly 200 million gallons per day flowing into the Withlacoochee River.
• Due to May’s abnormally high water levels, the Wysong structure on the Withlacoochee is now almost fully lowered.
• We typically don’t lower Wysong until July or August, after summer rains increase river levels, so having it lowered in May is quite remarkable.
• Our water quality staff continue to monitor the algae bloom that has persisted on portions of Lake Panasoffkee.
• Dissolved oxygen levels in the lake remain high and I hear the fishing has been excellent.

 

Outlet River between Lake Panasoffkee and the Withlacoochee River (May 2022)

 

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, both of which are flowing above average for this time of year.
• Flow in the Rainbow River has remained strong all dry season, thanks to above average rainfall keeping aquifer levels high.
• Overall, inflows to Lake Rousseau are 80% higher than they were a year ago.

 

• Outflows from Lake Rousseau are also high for this time of year.
• All water exiting Lake Rousseau is currently able to pass downstream through the Inglis Bypass Spillway to the Lower Withlacoochee River.
• The Inglis Main Dam (which connects to the Barge Canal) remains closed.
• Freshwater flow to the tidally influenced Lower Withlacoochee River is currently twice as high as it was a year ago.

 

Be safe and enjoy Memorial Day weekend!

Mark

 

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

Chief Professional Engineer

Water Resources Bureau

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