St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District St. Johns River Water Management District
St. Johns River Water Management District - www.sjrwmd.com

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Water bodies, watersheds and storm water
Rock Springs head

Rock Springs head

Rock Springs

Orange County

Description

Rock Springs is a second-magnitude spring situated in a beautiful wooded ravine. The principal discharge is from a partly submerged cavern at the base of a 20-foot-high limestone and sand bluff. In contrast to most large springs in peninsular Florida, Rock Springs has no well-defined large pool at the spring head. The cavern opening is about 5 feet in diameter at its mouth and tapers horizontally inward to a throat about 3 feet in diameter. Clear, blue water discharges with considerable turbulence that cuts into the limestone, eroding sand and fossil shells into the bottom of the 15- to 20-foot-wide spring run. Rock ledges jut out from the banks of the run for about 100 feet below the cavern opening. About 10 feet downstream from the cavern opening, additional water is discharged through a submerged opening in the channel bottom.

Rock Springs head close-up

Rock Springs head close-up

A boardwalk crosses over the run about 120 feet downstream. Several hundred feet below the spring, some of the flow is diverted left from the spring run to a large swimming area mostly bounded by concrete retaining walls. Overflow from the swimming area rejoins the run after passing through a concrete weir in the downstream part of the retaining wall. The run meanders northward, then east, and finally southeast for about 8.6 miles to the Wekiva River, a tributary to the St. Johns River.

Rock Springs is within the Dr. Howard A. Kelly County Park. A part of the spring run is used for swimming and tubing, and the adjacent area contains a bathhouse, picnic tables, grills, and group shelters.

Discharge

Rock Springs run

Rock Springs run

Discharge at Rock Springs was measured by the U.S. Geological Survey (USGS) from 1931 to 2002. St. Johns River Water Management District measured discharge from 1983 to 2010 and currently performs bimonthly discharge measurements. The difference between the minimum and maximum discharges is 49.06 cubic feet per second (cfs) over the period. The maximum measured discharge of 83.20 cfs occurred in October 1960; the minimum discharge of 34.14 cfs occurred in July 1998. The lowest periods of discharge correspond to periods of below-normal rainfall in Florida. The mean and median discharges for the period 1931 to 2010 are 57.58 cfs and 57.50 cfs, respectively (see the table below).

Rock Springs Discharge Graph
Discharge Graph

Water quality

Rock Springs was sampled by USGS from 1956 to 1971; field data only were collected until 1983, then sporadic water quality samples were collected up to 2003. The district sampled Rock Springs from 1987 to 2005, and currently samples the spring four times per year. Summary statistics of the water quality data for selected variables are shown in the table below.

Rock Springs Water Quality Graph
Water Quality Graph

Summary statistics of water quality and discharge at Rock Springs

Rock Springs Min Mean Median Max Count Period
Discharge, cfs 34.14 57.58 57.50 83.20 333 1931−2010
Alkalinity, total, mg/L as CaCO3 66.0 92.5 92.3 126.0 131 1956−2010
Calcium, total, mg/L as Ca 26.0 31.1 31.0 39.0 102 1992−2010
Chloride, total, mg/L as Cl 5.0 8.9 8.8 24.0 138 1956−2010
Dissolved Oxygen 0.49 0.70 0.69 1.04 18 2006−2010
Fluoride, total, mg/L as F 0.10 0.14 0.14 0.18 52 1994−2009
Magnesium, total, mg/L as Mg 8.0 9.4 9.4 11.0 102 1992−2010
Nitrate + nitrite, total, mg/L as N 0.67 1.41 1.44 2.50 100 1984−2010
Orthophosphate, total, mg/L as P 0.04 0.08 0.08 0.10 73 1994−2010
pH, field 6.40 7.59 7.62 8.31 143 1956−2010
Phosphorus, total, mg/L as P 0.05 0.08 0.08 0.10 62 1999−2010
Potassium, total, mg/L as K 1.1 1.4 1.3 2.0 101 1992−2010
Sodium, total, mg/L as Na 4.0 5.4 5.3 9.4 102 1992−2010
Specific conductance, field, µmhos/cm at 25°C 143 251 255 300 105 1984−2010
Specific conductance, lab, µmhos/cm at 25°C 210 251 252 356 132 1956−2010
Sulfate, total, mg/L as SO4 15.0 18.4 18.0 24.0 138 1956−2010
Total dissolved solids, mg/L 118 147 144 289 129 1960−2010
Water temperature, °C 21.5 23.8 23.8 28.5 225 1931−2010
Units: µmhos/cm = micromhos per centimeter
         mg/L = milligrams per liter
         cfs = cubic feet per second

Age of discharge water

The age of water discharging from Rock Springs was determined by measuring the concentration of tritium, delta carbon-13, and carbon-14 in the spring discharge, which was measured in June 1995, and tritium and helium-3, as measured in July 1995. Rock Springs had a tritium concentration of 3.1 tritium units, which suggests that the water is less than 42 years old. The tritium/helium-3 age of the water was 19.8 years. Rock Springs had a delta carbon-13 value of −9.08 parts per thousand and a carbon-14 concentration of 41% modern carbon, which results from the reaction of rainfall with calcite, dolomite, and soil organic matter. The adjusted carbon-14 age of Rock Springs is recent.

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St. Johns River Water Management District
4049 Reid Street, Palatka, FL 32177
(800) 725-5922