978-0-00-812422-9 COLLINS CAMBRIDGE AS AND A LEVEL GEOGRAPHY

Groundwater
Human activity has seriously reduced the sustainable potential of groundwater
in some parts of the world.
If the use of groundwater exceeds the recharge of groundwater, the water
table will drop. Many groundwater stores are in a stable state of equilibrium
where recharge and discharge are equal.
One of the main problems of groundwater abstraction is in coastal areas,
namely saltwater intrusion. This is the movement of saltwater into an aquifer
that previously held freshwater. For decades many coastal communities around
the United States have experienced saltwater intrusion.
Overextraction can lead to subsidence. As water is moved from the rock,
sediment particles fill pore spaces previously filled with water. The result is
a compression of the land and a reduction in height of the land. This can be
particularly problematic when occurring under structures and buildings. Railway
lines and pipes can be ruptured.
Industrial usage
Mining
Mining can deplete surface and groundwater supplies. Groundwater withdrawals
may damage or destroy streamside habitat many miles from the actual mine site.
In Nevada, the driest state in the United States of America, the Humboldt River is
being drained to benefit gold mining operations along the Carlin Trend. Mines in
the northeastern Nevada Desert pumped out more than 580 billion gallons of water
between 1986 and 2001 – enough to feed New York City’s taps for more than a year.
Mining can affect water quality in a number of ways, for example heavy metal
contamination, such as arsenic being leached out of the ground, sulphide-rich
rocks reacting with water to create sulphuric acid, chemical agents designed to
separate minerals that leak into nearby water bodies, erosion and sedimentation
from ground disturbance that can clog waterways and smother vegetation and
organisms as well as silting up fresh drinking water.
Energy generation
Hydropower uses the force of water to turn turbines. This has little impact on
the quantity and quality of water as it is largely returned with little change in
state. Less sustainable energy uses involve the use of water for fossil fuel and
nuclear energy production. In each, water is converted to steam that powers
the turbine in order to generate electricity. This water is then returned to
surrounding bodies of water, rivers and lakes with a lower oxygen content at
differing temperatures, threatening fish populations and freshwater habitats.
Structures like dams can
reduce the impact of a flood
in downstream areas.
Tides can add to the height
of flood waters, increasing
the area flooded.
Major cities built on
floodplains also experience
floods.
Floods occur in rural
areas. They can
happen quickly or
slowly.
Floods occur in
urban areas. They
can happen
quickly or
slowly.
figure 1.38 Human influence on the hydrological cycle.
Hydrology and fluvial geomorphology 33