Withlacoochee River System Update - 6/1/2020

Water Resources Continue to Decline as our Wet Season Approaches

  

Rainfall:

• For the most part, May was a very dry month.
• We did receive some rainfall over the past week, but it had little effect on our region’s water resources.
• In May we received an average of 2.6 inches of rainfall, less than the historical average (3.7 inches) for that month.
• Aquifer (groundwater) levels, which rise and fall from rainfall, are about normal for this time of year (52^nd percentile).
• Overall, our rainfall deficit for 2020 rose from 4 to 6 inches after a relatively dry May. This means, on average we would have received 6 more inches of rainfall by now (Jan to May).
• Over the past 12 months, however, we’ve received average rainfall (53.5 inches) and this is the reason our water resources are still in good shape (no significant drought again this year).
• Stay tuned, because our wet season (June to September), when we average 6-8 inches of rainfall, is just around the corner.
• There is a potential for heavy rains later this week due to a tropical system in the Gulf.

 

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

• As expected, river levels and flows continued to naturally decline in May.
• Water levels dropped an average of 4 inches along the entire river last month and are very close to what they were this time last year.
• There are several locations along the river that are becoming quite shallow and difficult to navigate by boat.
• River flows declined an average of 30% in May.
• The current source of most of the river’s flow is groundwater and flows exiting the Green Swamp (where the river begins) are still zero.
• Lands that contribute flow to the river during the wet season are still dry and it will take a lot of rain to fill them up
• We can expect river levels to remain low over the next several weeks until we get enough rainfall to saturate area soils and create flow to the river.
• The table below compares current river levels and flows to what they were last month and last year.

 

 

Rock Outcroppings on the Withlacoochee River near Hwy 200 (May 2020)

 

Tsala Apopka Chain of Lakes:

• Hot temperatures and minimal rainfall had their effect on lake levels this past month.
• Water levels in the Tsala Apopka lake chain fell about 7 inches in May and are currently about 14 inches lower than they were this time last year.
• These declines are normal since water levels can drop 2 inches/week this time of year when we don’t get any rain.
• All the lakes/canals/marshes are currently about 2.5 feet lower than their high guidance levels.
• We can expect lake levels to rise later this summer after our region receives higher rainfall amounts or when inflows are available from the Withlacoochee River.
• All the water control structures (aka “locks”) remain closed, helping to conserve water in the lakes.
• The table below compares current water levels to what they were last month and last year.

 

Lake Panasoffkee and Wysong:

• Water levels on Lake Panasoffkee rise and fall each year from changing rainfall patterns that affect inflows to and outflows from the lake.
• In May, the lake level fell 6 inches and is currently 3 inches lower than it was at this time last year.
• Inflow from the lake’s largest tributaries (Little Jones Creek and Shady Brook) declined by 33% over the past month.
• Outflow from the lake to the Withlacoochee River also fell sharply over the past month and is less than half of what it was in early May.
• The Wysong Water Conservation Structure remains raised, helping to conserve water upstream and in Lake Panasoffkee.
• The main gate (220 ft wide) is currently fully raised while the independent gate (19 ft wide) is partially lowered.
• An underwater (dive) inspection of the Wysong Structure was conducted in May to assess the condition of the structure.
• We can expect lake levels to continue to decline over the next few weeks, until our region receives consistently higher rainfall.
• The table below compares current lake levels and flows to what they were last month and last year.

 

Diver Inspecting Wysong Main Gate (May 2020)

 

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.
• Inflows to Lake Rousseau include combined flows from the Withlacoochee and Rainbow Rivers.
• Withlacoochee River flows (which depend on rainfall and runoff from adjacent lands) decreased by 39% over the past month.
• Flow in the Rainbow River (which reflects changes in aquifer levels) decreased by 5% over the past month.
• The Rainbow River is currently contributing twice as much flow to Lake Rousseau as the Withlacoochee River is.

• Outflows from Lake Rousseau have decreased slightly over the past month and remain lower than they were at this time last year.
• All flow exiting the lake is currently passing through the Inglis Bypass Spillway to the Lower Withlacoochee River.
• The Inglis Bypass Spillway will be briefly closed on Tuesday (June 9^th) during a scheduled underwater inspection of the structure.
• The Inglis Main Dam, which conveys excess flow to the Barge Canal, has been fully closed for the past few months.

 

Have a great week!

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