Inland Waters
Page 179
Groundwater
Introduction
Groundwater is the world's largest source of fresh water. It is estimated that the
amount of groundwater is 400 times greater than all the surface water in lakes,
reservoirs, streams, and rivers. Groundwater is a key part of the planet’s water
cycle. When precipitation falls on land, some water evaporates, some flows to
streams and rivers, and some seeps into the soil and is absorbed by plants.
Excess water in the soil may percolate further down until it reaches a level
known as the water table where all the pores or openings in the soil or rock are
saturated with water. Water in the saturated zone below the water table is called
groundwater.
Groundwater supplies approximately 65% of all irrigation water demand in
South Australia. Whilst mainly surface water resources service the Adelaide
metropolitan area, there are important and significant local users of
groundwater. Most of the commercial spring and mineral water supplies are
obtained from groundwater resources of the Piccadilly Valley in the Mount Lofty
Ranges. Soft drink and beer manufacturers pump high quality water from the
deep Tertiary aquifer beneath Adelaide. Groundwater is also pumped for
industrial applications and for irrigation of recreational and sports fields
throughout the metropolitan area. Irrigation for horticultural production was
undertaken early in Adelaide's development and still operates in regions around
Adelaide. Over-use of resources may create inequitable conditions and
unfavourable long term availability (SoE, 2007).
Groundwater availability is generally controlled by the physical characteristics of
the host aquifer and the rate of recharge or replenishment. Large-scale
groundwater extraction can result in significant detrimental impacts, including
lowering of water tables, salt-water intrusion, land subsidence and lowered base
flow in streams, resulting in ecological damage. Pollution can also affect
groundwater quality - examples include septic tank effluent, soil contamination
infiltrating into the watertable, and wastes being pumped into bores (SoE,
2007).
Generally deteriorating ground water has consequential impacts on horticultural
and agricultural industries where use of high salinity irrigation water can affect
plant and soil health, and is evident in the Northern Adelaide Plains. Ecological
communities reliant on groundwater rather than surface water can also be
affected (EPA, 2000).
The risk of rising water tables causing dry land salinity requires effective
management to prevent large scale and often irreversible impacts to flora and
fauna ecosystems, soil health and land based industry (SoE, 2007).
A potential effect of coastal sea level rise and higher tides due to climate
change is the effect on coastal groundwater levels. These effects may include
