In this section
Silver Glen Springs aerial view
A view across the pool to the springs’ main boil
Silver Glen Springs main vent
Silver Glen Springs
Silver Glen Springs is a first-magnitude spring with a large, semicircular pool that measures 200 feet from north to south and 175 feet from east to west. Most of the strong flow emerges from two cavern openings in the rock at the bottom of the pool, with large boils at the water's surface over the vents. The vertical cave opening called the Natural Well in the southwestern edge of the pool is about 12 to 15 feet in diameter and 40 feet deep. The vent in the east part of the pool is a conical depression about 18 feet deep. Most of the spring pool has sand and limestone on the pool bottom, with areas of aquatic grasses. Large fresh and saltwater fish are common in the pool and around the vents. Additional flow is from sand boils in the bottom of the spring run downstream from the head of the springs. Water from the springs flows eastward down a run about 200 feet wide for 0.75 mile to Lake George.
Silver Glen Springs run outlet into Lake George
Silver Glen Springs underwater view of pool
The spring is part of the USDA Forest Service’s Silver Glen Springs Recreation Area. The recreation area is used for swimming, snorkeling, picnicking, fishing, and boating. Boating is not allowed in the spring pool, but the spring run is a popular spot for recreational boaters.
Discharge at Silver Glen Springs was measured by the U.S. Geological Survey (USGS) 57 times from 1931 to 2003. St. Johns River Water Management District measured discharge 174 times from 1983 to 2010 and currently measures discharge 12 times per year. The difference between the minimum and maximum discharges is 207 cubic feet per second (cfs) over the period. The maximum measured discharge of 245 cfs occurred in April 1983; the minimum discharge of 38.2 cfs occurred in October 2004. The mean and median discharges for the period from 1931 to 2010 are 102 cfs and 98 cfs, respectively (see the table below).
Silver Glen Springs was sampled by USGS eight times from 1972 to 1997, with additional field measurement at other times through 1999. The District sampled Silver Glen Springs 89 times, from 1984 to 2010, 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 Silver Glen Springs
|Silver Glen Springs||Min||Mean||Median||Max||Count||Period|
|Alkalinity, total, mg/L as CaCO3||59.3||68.2||68.0||80.0||97||1972−2010|
|Calcium, total, mg/L as Ca||61.0||71.0||71.3||93.3||88||1992−2010|
|Chloride, total, mg/L as Cl||380.0||453.4||450.0||707.0||97||1972−2010|
|Fluoride, total, mg/L as F||0.09||0.12||0.13||0.14||53||1994−2009|
|Magnesium, total, mg/L as Mg||29.0||34.7||35.0||45.8||88||1992−2010|
|Nitrate + nitrite, total, mg/L as N||0.02||0.05||0.05||0.38||92||1984−2010|
|Orthophosphate, total, mg/L as P||0.01||0.02||0.02||0.05||64||1972−2010|
|Phosphorus, total, mg/L as P||0.01||0.03||0.03||0.03||50||1972−2010|
|Potassium, total, mg/L as K||7.0||8.6||8.5||12.3||88||1992−2010|
|Sodium, total, mg/L as Na||214.0||246.9||248.3||287.0||87||1992−2010|
|Specific conductance, field, µmhos/cm at 25°C||1202||1858||1890||2184||85||1984−2010|
|Specific conductance, lab, µmhos/cm at 25°C||1540||1910||1930||2400||87||1972−2010|
|Sulfate, total, mg/L as SO4||150.0||175.2||174.0||214.0||97||1972−2010|
|Total dissolved solids, mg/L||854||1062||1060||1250||91||1981−2010|
|Water temperature, °C||20.5||23.2||23.1||26.0||119||1972−2010|
mg/L = milligrams per liter
cfs = cubic feet per second
Age of discharge water
Large cave at Silver Glen Springs
The age of water discharging from Silver Glen Springs was determined by measuring the concentration of tritium, delta carbon-13, and carbon-14 in the spring discharge, which was measured in April 1996, and the concentration of tritium and helium-3 in the discharge, as measured in March 2001. Silver Glen Springs had a tritium concentration of 2.4 tritium units, which suggests that the water is less than 43 years old. The tritium/helium-3 age was 26 years. Silver Glen Springs had a delta carbon-13 value of −7.70 parts per thousand and a carbon-14 concentration of 20% modern carbon, which results from the mixing of Upper and Lower Floridan aquifer water. The adjusted carbon-14 age is recent.