September’s above-average rainfall improves Floridan aquifer conditions

High surface water flows in the Middle St. Johns River Basin, some flooding in the Lower St. Johns River Basin

PALATKA, Fla., Oct. 13, 2020 — High September rainfall has boosted the St. Johns River Water Management District’s cumulative 12-month rainfall totals over its long-term average by 2.65 inches. While abundant rainfall continued to shrink a yearlong rainfall deficit in Putnam, St. Johns and Flagler counties, it also caused flooding from Astor through the Lower St. Johns River Basin.

A map illustrates rainfall conditions in September across the St. Johns River Water Management District.

Highlights included:

Rainfall

• Districtwide, September rainfall averaged 7.70 inches, nearly an inch above the long-term average for the month.
• A large zone of above-average rainfall was recorded from Orange County through northern Brevard, Volusia, Flagler and St. Johns counties. Orange County had the highest county-wide total, 10.4 inches. Volusia, Flagler and St. Johns had greater than 9 inches of rain.
• Along the north, west and south boundaries of the District, rainfall was below average. Counties with the smallest rainfall totals were Baker, Indian River and Duval.
• Districtwide, the cumulative rainfall total over the last 12 months is 53.66 inches, which is 2.65 inches above the long-term average.
• Putnam, Flagler and St. Johns counties continued to benefit from above-average rain and are now within 5 inches of their long-term averages.
• Volusia County received the most rainfall over the last 12 months, with a countywide total of 60.2 inches.

Groundwater

• Upper Floridan aquifer conditions (groundwater levels) at the end of September were in the high range across much of the central and southern portions of the District, while the northern portion of the District recorded conditions in the normal range.
• Groundwater levels are at the 81^st percentile districtwide. This means that since 1980, aquifer levels have been higher than they are now about 19 percent of the time.

Surface water flows

• Surface water flow conditions in the St. Johns River’s headwaters were in the average range for this time of year.
• Flow in the headwaters at the Melbourne station was 1.09 billion gallons per day (bgd) on Sept. 1, which is in the 68^th percentile of flow conditions for this time of year.
• Flow in the Econlockhatchee River near Chuluota was 603 million gallons per day (mgd), which is in the 77^th percentile of flow conditions for this time of year.
• Orlando-area tributaries were in the high or very high flow ranges. Flow conditions in central Florida were in the high range on Sept. 1, with the DeLand station reporting 5.3 bgd, or in the 90^th percentile, while the Satsuma station reported 8.06 bgd (83^rd percentile).
• Flows in the Wekiva River near Sanford were in the high to very high range at 526 mgd (98^th percentile).
• The St. Johns River at Astor, just south of Lake George, has been at moderate or minor flood stage since mid-September, and minor flooding has occurred along the lower St. Johns River and its tributaries related to tidal cycles.
• Flows in the Ocklawaha River, the largest tributary to the St. Johns River, were 810 mgd, or in the 71^st
• Flows in the St. Marys River near Macclenny were 738 mgd (78^th percentile).

Lake levels

• Lake Brooklyn water levels increased slightly in September to 100.4 feet, remaining below its long-term average.
• Lake Weir increased 0.2 foot during September to 54.2 feet.
• Lake Apopka’s water level increased near the end of September, but the District allowed discharges through the downstream structure to lower it to regulation schedule.
• Blue Cypress Lake levels increased more than a foot to 22.7 feet during September, resulting in discharges. Keeping water levels low in the Upper St. Johns River Basin helps the District prepare for greater rainfall during the tropical season.

Spring flows

• The mean monthly flow at Silver Springs increased to 652 cubic feet per second (cfs), or 421 This represents a 36 cfs increase compared to August.
• At the Blue Spring station in Volusia County, the mean monthly flow was recorded at 151 cfs, or 98 mgd, which is within the normal range for the time of year.
• At Rock Springs, the monthly mean flow was 60 cfs (39 mgd), an increase of 2 cfs compared to August.
• Mean monthly flow at Wekiwa Springs was 68 cfs (44 mgd), an increase of 2 cfs.

To learn more about rainfall totals and other hydrologic data collected, visit sjrwmd.com.