Withlacoochee River System Update - 5/31/2024

Dry Weather Continues as Wet Season Approaches

 

Rainfall:

• Depending on weather patterns, May can either be a very hot/dry month, or it can bring flooding rain.
• Most areas within the Withlacoochee River Watershed saw some rain in the middle of the month, but it’s been very hot and dry lately.
• In May, our region averaged 2.9 inches of rain, less than the historical average (3.7 inches) for the month.
• So far this year (January through May), our region has received 15.5 inches of rain, slightly above the historical average (15.9 inches) for the first 5 months of the year.
• We have not seen any significant rainfall for at least the past couple weeks…
• …and with hot temperatures this time of year, water levels are dropping quickly.
• Aquifer (groundwater) levels continue to drop and are currently in the 47^th percentile, slightly below average for our region, but higher than this date last year (41^st percentile).
• The wet season (June to Sept) is right around the corner, and we normally see increased thunderstorm activity by mid-June.
• The figure below shows how much rainfall different areas received last month. The green and blue colors represent above average rainfall in May.

 

 

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

• Water levels and flows along the Withlacoochee River have been declining recently.
• This is a normal trend during the warmer, dry season months.
• River levels and flows dropped in early May, then rose in the middle of the month from some rainfall, but have steadily declined since.
• The net result is river levels that are 5 inches lower on average, and flows that are 50% less than they were at the start of the month.
• There is currently no flow exiting the Green Swamp (where the river starts).
• In fact, river flow is minimal from there all the way past Hwy 48 between Bushnell and Floral City.
• Groundwater (spring flow) is the only source of water to the Withlacoochee River right now.
• This includes flow from Lake Panasoffkee (upstream of Hwy 44) and other spring-fed tributaries.
• From the Green Swamp past Hwy 476 (Nobleton) the Withlacoochee River is about 6.5 inches lower than it was a year ago.
• From Hwy 48 past Hwy 200, the river is about 10 inches higher than last year’s levels (due to more rainfall in that region this year).
• Overall, the Withlacoochee River is in decent shape as the wet season approaches.
• The table below compares current river levels and flows to what they were last month and last year.

 

 

Stagnant Waters in the Green Swamp (May 2024)

 

 

Tsala Apopka Chain of Lakes:

• Water levels in all three pools of the Tsala Apopka Lake Chain dropped in May, despite above average rainfall in eastern Citrus County.
• This time of year, the lakes/canals/wetlands need about 8 inches of rainfall each month, just to maintain their current levels.
• Last month, the Floral City and Hernando Pools dropped about 3 ½ inches each, while the Inverness Pool (which received more rain in May) only fell 1 ½ inches.
• Despite these declines, lake levels are several inches higher than they were a year ago.
• Water control structures remain closed, helping to conserve water in the lake chain.
• Water levels are not expected to rise again until our region receives heavy rainfall later this summer.
• Work is progressing on the Golf Course structure which connects the Floral City and Inverness Pools.

 

Moccasin Slough in the Tsala Apopka Lake Chain (May 2024)

 

 

Lake Panasoffkee and Wysong:

• The water level on Lake Panasoffkee fell about 3 ½ inches last month, despite nearly 4 inches of rainfall in the area.
• Spring flow, which continues to enter the lake from Shady Brook and Little Jones Creek, slowed by 23% in May but remains higher than a year ago.
• Outflow from Lake Panasoffkee to the Withlacoochee River is also higher than a year ago, due to more rainfall so far in 2024.
• Lake Panasoffkee is currently about 13 inches higher than it was last year at this time.
• A few miles downstream along the Withlacoochee River, the Wysong Structure remains partially inflated.
• The main gate (230-ft-wide) at Wysong is fully raised.
• The independent gate (19-ft-wide) remains partially raised, allowing all river flows to pass downstream.
• Withlacoochee River flow at Wysong declined by 30% in May but remains higher than 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) fell 2.5% in May but is currently 9% higher than a year ago.
• Withlacoochee River flow (which depends on rainfall and runoff from adjacent lands) fell 13% last month but is still nearly double what it was a year ago.
• Overall, inflows to Lake Rousseau are substantially higher than last year, due to more rainfall this past winter/spring.
• The Rainbow River is currently providing nearly two-thirds 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.
• Currently, the Bypass Spillway is flowing at 50% of its 900 MGD capacity, which is 22% more flow than a year ago.
• The Inglis Main Dam remains closed and won’t be open again until the Bypass Spillway reaches its capacity (possibly later this summer).
• Freshwater flow from Lake Rousseau to the Lower Withlacoochee River declined by 13% in May.

 

 

Have a wonderful weekend!

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