Page 355 - Laboratory Manual in Physical Geology

A CTIVIT Y 12.3 Floridan Limestone Aquifer

Name: ______________________________________ Course/Section: ______________________ Date: ___________

Refer to FIGURE 12.6 (Sulphur Springs Quadrangle) and the “sketch map” on page 326 .

A. On the sketch map, mark the elevations of water levels in the lakes (obtain this information from FIGURE 12.6 ). The

elevations of Lake Magdalene and some lakes beyond the boundaries of the topographic map already are marked for you.

B. Contour the water table surface (use a 5-foot contour interval) on the sketch map. Draw only contour lines representing
whole fives (40, 45, and so on). Do this in the same manner that you contoured land surfaces in the topographic maps lab.

C. The flow of shallow groundwater in the sketch map is at right angles to the contour lines. The groundwater flows from high
elevations of the hydraulic gradient to lower elevations, just like a stream. Draw three or four flow lines with arrows on the
sketch map to indicate the direction of shallow groundwater flow in this part of Tampa. The southeastern part of FIGURE 12.6

shows numerous closed depressions but very few lakes. What does this indicate about the level of the water table in this region?

D. Note the Poinsettia Sinks, a pair of sinkholes with water in them in the southeast corner of the topographic map (see

FIGURE 12.6 ). Note their closely spaced hachured contour lines. Next, find the cluster of five similar sinkholes, called Blue
Sinks, about 1 mile northwest of Poinsettia Sinks (just west of the WHBO radio tower). Use asterisks (*) to mark their

locations on FIGURE 12.8 , and label them “Blue Sinks.”

E. On the sketch map, draw a straight arrow (vector) along the shortest path between Blue Sinks and Poinsettia Sinks. The

water level in Blue Sinks is 15 feet above sea level, and the water level in Poinsettia Sinks is 10 feet above sea level. Calculate
the hydraulic gradient (in ft/mi: show your work below) along this arrow and write it next to the arrow on the sketch map.
(Refer to the hydraulic gradient in FIGURE 12.1 if needed.)

F. On FIGURE 12.6 , note the stream and valley north of Blue Sinks. This is a fairly typical disappearing stream. Draw its

approximate course onto the sketch map. Make an arrowhead on one end of your drawing of the stream to indicate the
direction that water flows in this stream. How does this direction compare to the general slope of the water table?

G. In March 1958, fluorescent dye was injected into the northernmost of the Blue Sinks. It was detected 28 hours later in
Sulphur Springs, on the Hillsborough River to the south (see sketch map). Use these data to calculate (show your work)
the approximate velocity of flow in this portion of the Floridan Aquifer:
1. in feet per hour: ____________ 2. in miles per hour: ____________ 3. in meters per hour: ____________

H. The velocities you just calculated are quite high, even for the Floridan Aquifer. But this portion of Tampa seems to be riddled

with solution channels and caves in the underlying limestone. Sulphur Springs has an average discharge of approximately
44 cubic feet per second (cfs), and its maximum recorded discharge was 165 cfs (it once was a famous spa). During recent
years, the discharge at Sulphur Springs has decreased. Water quality has also worsened substantially.

1. Examine the human-made structures on FIGURE 12.6 . Note especially those in red, the color used to indicate new

structures. Why do you think the discharge of Sulphur Springs has decreased in recent years?

2. Why do you think the water quality has decreased in recent years?

I. REFLECT & DISCUSS Name two potential groundwater-related hazards to homes and homeowners in the area that you
can think of.

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