In this section
Rock Springs head
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
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.
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 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.
Summary statistics of water quality and discharge at Rock Springs
|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|
|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|
|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|
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.