Geology Reference
In-Depth Information
h.
Search online to determine the current status of the irri-
gation project and any economic and environmental
changes that have occurred since 2006 in this area that has
been aware of groundwater overdraft for more than 100
years.
Although geologic and hydrologic conditions may
be exceedingly complex, the mechanics of saltwater
intrusion may be visualized in the following manner.
Assume that an aquifer crops out on the continental
shelf and is hydrologically connected to the ocean. Nor-
mally, fresh water discharges from a coastal aquifer into
the ocean along seepage faces or through springs
(Figure 16.4A). As fresh water is pumped from the
aquifer, the water pressure in the aquifer is lowered,
reversing the hydraulic gradient (Figure 16.4B). With a
reversal in gradient, sea water migrates inland and may
eventually contaminate pumping wells.
Occurrences of saltwater intrusion are relatively
common in coastal areas. Problem areas include much
of the Atlantic coast from Florida to New England and
many regions of the west coast where there are large
withdrawals of groundwater.
Several techniques have been used to control salt-
water intrusion. These include reducing the amount of
pumping; constructing physical barriers, such as
pumping cement into the rocks (Figure 16.4C); pump-
ing wells nearer to the coast and allowing the water to
flow back into the ocean (Figure 16.4D); and artificial
recharge (Figure 16.4E). The simplest solution is to
reduce pumping, but commonly this is not feasible
PART B. OVERUSE OF A GROUNDWATER
RESOURCE: SALTWATER INTRUSION
IN A COASTAL AQUIFER
The intrusion of saltwater into a fresh groundwater
reservoir is surprisingly common throughout the
world. Saltwater intrusion is generally caused by
excessive pumping of groundwater and leads to dete-
rioration of water quality. In inland areas it is caused
by the upward movement of the fresh- and saltwater
interface; in coastal regions it is commonly caused by
both vertical and horizontal migration of sea water
into a coastal aquifer. For example, during the Dec 26,
2004, tsunami in the Indian Ocean, coastal areas were
flooded by seawater. Some wells were filled with salt-
water; some freshwater aquifers were contaminated
by saltwater infiltrating the land surface.
