Geology Reference
In-Depth Information
of potential saltwater intrusion, methods that could be
used to halt the intrusion, and community plans for
future water needs.
3.
Starting at the southwest and northwest corners of Figure
16.6, and at Parris Island, construct flowlines showing the
general direction of groundwater movement in 1961. In what
general direction was the water moving
Potential Saltwater Intrusion
in the Savannah Area
a.
in the southwest corner?
Large quantities of groundwater are used in the
Savannah, Georgia, area for industrial, municipal, and
domestic purposes. The first water well in the Upper
Floridan Aquifer was drilled in 1885; between 1900
and 2000, the pumping rate increased from 10 million
gal/d to 300 million gal/d. Over the years, water lev-
els in wells have declined to more than 120 feet below
sea level. This has caused concern that the water sup-
ply might become seriously depleted or contaminated.
Most of the groundwater used in the Savannah area is
pumped from a confined, limestone aquifer that lies
about 100 feet (northeast) to 350 feet (southwest)
below land surface.
Although groundwater in the Savannah area has
not yet become salty, the supply at Parris Island, about
25 miles northeast, has deteriorated due to saltwater
intrusion. The pumping of groundwater in the Savan-
nah area will no doubt increase and, as a result, intrud-
ing saltwater may eventually reach the pumping
center and contaminate the water supply.
The Savannah River, which flows through the
area, has been used as a partial source of water, but
locally it is contaminated by industrial and municipal
wastes. Furthermore, water can only be withdrawn
from it at certain times because the river is influenced
by tidal waters of high salinity.
In addition to these impacts on the local ground
water supplies, rising sea levels will further increase
the salinity and decrease storage space in some coastal
aquifers.
b.
in the northwest corner?
c.
at Parris Island?
4.
Study Figure 16.7 and describe the changes from 1961 to
1984 at Hilton Head Island, Savannah, Georgia, and 25 miles
up the Savannah River from the center of the cone of
depression.
5.
How much has the water-pressure surface been lowered at
Savannah between 1880 and 1984?
6.
From what area do you expect the fresh water/saltwater
interface to first reach the Savannah area? SW or NE (cir-
cle one) Why? (Hint: Examine the water-level contours,
and the variation in depth of the aquifer described in the
introduction.)
7. Figure 16.8 is a cross section extending into Port Royal
Sound from the NE end of Hilton Head Island showing sim-
ulated changes in the brackish and salt water zones for the
years 2000,2016, and 2032. The model assumes no change in
the rates of groundwater withdrawals on Hilton Head Island
or inland near Savannah.
QUESTIONS (16, PART B)
1.
A water-level map of the Savannah area representing
conditions that existed in 1880 is shown in Figure 16.5.
Construct four equally spaced flowlines showing the direc-
tion of groundwater movement in 1880. Remember that
flowlines cross the water-pressure contours at right angles.
What was the general direction of flow? Was groundwater
at Parris Island likely to have been salty in 1880? Why or
why not?
a.
What value is used as the transition between freshwa-
ter and brackish water?
b.
In the period between 2000 and 2032, how many meters
will the brackish/freshwater interface have moved?
c.
What is the average annual rate of projected advance of
this interface between 2000 and 2032?
2.
Using Figure 16.6, construct a water-level map showing
the conditions that existed in 1961. Use a contour interval
of 10 feet down to the —40 feet level, then use an interval of
d.
About when will the interface reach the edge of the
20 feet.
island?
