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
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Water bodies, watersheds and storm water
Crescent Beach Submarine Spring main view

Crescent Beach Submarine Spring main view

Crescent Beach Submarine Spring

St. Johns County

Description

Crescent Beach Submarine Spring is at least a second-magnitude spring. The spring is situated 59 feet below the surface of the Atlantic Ocean, and the spring boil can be seen at the sea surface on a calm day. The sea floor around the spring is level. However, numerous subsurface structures appear around the area of the spring (Kindinger 2000).

The interpreted seismic reflection profile reveals a well-defined vent feature that appears to have been developed and maintained from submarine discharge of artesian water (Swarzemski et al. 2001).

Crescent Beach Submarine Spring Geologic Profile A-A’

Profile A – A’ (courtesy USGS)

Crescent Beach Submarine Spring Geologic Profile B-B’

Profile B – B’ (courtesy USGS)

The profile also reveals multiple large collapse features directly adjacent to the Crescent Beach spring vent, as indicated by the presence of a series of fractures. The density difference between the freshwater discharges from the spring and seawater can be seen in the seismic reflection profile of the water column. The spring appears to be a recent, incised spring vent rather than a collapse structure. The northern side of the vent is higher than the southern side. For a more complete discussion of the seismic profiling and the visual scuba observations, the reader is directed to Brooks (1961) and Kindinger (2000).

Discharge

No actual discharge measurements have been done at Crescent Beach Submarine Spring. Brooks (1961) estimated the discharge by two methods. Based upon the estimated volume of water rising to the surface, a maximum possible discharge of 1,500 cubic feet per second (cfs) was estimated. Based upon the mixing ratio of spring water to seawater, a discharge of 40 cfs was estimated. All in all, Brooks estimated that “true discharge is certainly between 10 cfs and 300 cfs.”

Water quality

Crescent Beach Submarine Spring was sampled by St. Johns River Water Management District in 1995. Divers from the Jacksonville Reef Research Team, Continental Shelf Associates, and the U.S. Geological Survey assisted in the sampling of the spring. A sand point was attached to a weighted, vinyl tubing. Divers inserted the sand point into the sediment at the bottom of the spring, and the water was pumped through tubing for sample collection. The water quality data for selected variables are shown in the table below.

Summary statistics of water quality data at
Crescent Beach Submarine Spring

Crescent Beach Submarine Spring Value Period
Alkalinity, total, mg/L as CaCO3 129.0 1995
Calcium, dissolved, mg/L as Ca 296.0 1995
Chloride, total, mg/L as Cl 3630.0 1995
Fluoride, total, mg/L as F 0.77 1995
Magnesium, dissolved, mg/L as Mg 252.00 1995
pH, field 7.13 1995
Potassium, dissolved, mg/L as K 64.10 1995
Sodium, dissolved, mg/L as Na 2040.00 1995
Specific conductance, field, µmhos/cm at 25°C 13010 1995
Specific conductance, lab, µmhos/cm at 25°C 11920 1995
Sulfate, total, mg/L as SO4 816.0 1995
Total dissolved solids, mg/L 7460 1995
Water temperature, °C 28.7 1995
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 Crescent Beach Submarine Spring was determined by measuring the concentrations of delta carbon-13 and carbon-14 in the spring discharge in August 1995. Crescent Beach Submarine Spring had a delta carbon-13 value of –5.22 parts per thousand and a carbon-14 concentration of 14% modern carbon, which suggests that the water is approximately 10,450 years old. The age of the water suggests that Crescent Beach Submarine Spring has a deep flow system and a regional area of influence.

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