Quantifying Submarine Groundwater Discharge to Indian River Lagoon, Florida

Hydrogeology:

Chart of hydrostratigraphy of Northeastern Florida

The hydrogeology along the northeastern coast of Florida can be broadly divided into two aquifer systems – the Surficial and the Floridan aquifer system (Fig. 4). Sand, silt and clays of the Intermediate confining unit, which constitutes most of the Hawthorn Formation, separates these two aquifer systems (Leve, 1970; Spechler, 1994).

The Surficial aquifer system consists of Miocene to Holocene interbedded sand, shell, silt, clay and dolomitic limestone strata. The Surficial aquifer system is mostly unconfined, although the hydrogeology can be very heterogeneous.

Figure 5. Hydrograph of a Titusville well (adapted from St. John's Water Management District, 2000)
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Four clastic, highly regional surficial aquifers border the Indian River Lagoon including Terrace, Atlantic Coastal Ridge, Ten-mile Ridge, and Inter-ridge aquifers. Terrace aquifer occurs on the barrier islands separating Indian River Lagoon from the Atlantic Ocean. The Atlantic Coastal Ridge aquifer occurs in the northwestern region of Indian River Lagoon. This aquifer is composed of the Pleistocene Anastasia Formation, and provides most of the water supply for towns on the western edge of the northern Indian River Lagoon (Mims and Titusville).

The Floridan aquifer system can be further divided into two water-bearing aquifers (Upper and Lower Floridan), separated by less permeable semi-confining units. The Upper Floridan aquifer in the study area corresponds to the Ocala Limestone and in some parts, the Avon Park Formation (Fig. 4). The Ocala Limestone is characterized by high permeabilities that can be enhanced along bedding planes, fractures and conduits.

Figure 6. Potentiometric change map
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Significant variations in ground-water levels occur seasonally (Fig. 5). Superimposed on such seasonal variations is a long-term decrease in the potentiometric surface that is largely attributed to increased groundwater withdrawals (Fig. 6). Nonetheless, recent potentiometric surface maps of the Upper Floridan aquifer indicate elevations that are above sea level for the entire length of Indian River Lagoon.

Such potentiometric surface elevations increase from north to south, where the Hawthorn Formation increases in thickness. The elevated potentiometric surface of the Upper Floridan, combined with the general lack of a confining unit in the vicinity of the study area makes much of upper Indian River Lagoon a potential zone of submarine groundwater discharge.