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Alafia River Minimum Flows and Levels - Southwest Florida Water ...

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head differences indicating breaches in the clay confining unit between aquifers.<br />

South of the <strong>Alafia</strong>, head differences are generally larger, ranging from 23 feet to<br />

128 feet, <strong>and</strong> indicating a greater degree of confinement between the aquifers.<br />

For the most part, water levels in the SAS are consistently higher than levels in the<br />

IAS <strong>and</strong> UFA, indicating a downward flow gradient. Along the coast, this downward<br />

gradient is typically reversed with water from the UFA being discharged upward into<br />

the overlying aquifers. However, for much of southern coastal Hillsborough County,<br />

water levels in the UFA have declined due to groundwater withdrawals. This has<br />

resulted in a seasonal reversal of the vertical gradient between the aquifers. During<br />

the drier periods of the year (typically the spring months) water levels decrease with<br />

depth along the coast <strong>and</strong> water moves downward from the surficial aquifer. During<br />

the remainder of the year, water levels in the UFA are higher <strong>and</strong> the vertical<br />

movement of water resumes in an upward direction.<br />

Figure 2-6. Average observed head difference between the surficial aquifer <strong>and</strong> the Upper<br />

<strong>Florida</strong>n aquifer water levels (feet) in the vicinity of the <strong>Alafia</strong> <strong>River</strong>, based on period-of-record<br />

data.<br />

2-12

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