Groundwater is basically all the water that exists under the surface. Rain seeps through the soil and accumulated in spaces between sediments or cracks in the bedrock, which are called ‘aquifers’.
Local Sydney and Hawkesbury land stone create porous aquifers providing a potential, often extractable source of groundwater (see Figures 1 & 2).
Types of Aquifers, Wells and Groundwater Flow
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Some households have access to groundwater onsite (‘urban wells’ in
Fig. 2) but are only allowed to tap into their ‘bore’ water if it is
used for non-drinking purposes.
The Urban Water Cycle
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There are currently trial bores within the Sydney catchment to assess
those aquifers, which will give us a better understanding about
potential water resources in case the current drought continues.
Some groundwater issues on the Central Coast:
- The Kulnura Mangrove Mountain Water Sharing plan:
 kulnura_mangrove_plan 627.92 Kb
A recent report by the Centre for Ground Hydrology (Merrick et al.)
found that groundwater was being extracted at above sustainable yield
levels and that loss of ground water affected the base flow in the
streams that provide our drinking water.
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Extraction from sand beds at Woy Woy Peninsula and along the coast.
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There is considerable concern that this extraction will impact on
vegetation, threatened species and endangered ecological communities.
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Extraction of groundwater via bores and spearpoints is often not
metered or reported. Hence, the actual extraction from groundwater
sources is uncertain.
For more information on this topic -
A lack of understanding about groundwater issues
Prof Ian Acworth from the UNSW recently (May 2006) talked on a
groundwater forum in Sydney about the importance and lack of knowledge
about groundwater issues.
He stressed that groundwater is a larger component of the water cycle
than surface water and that the both systems (ground and surface water)
are one interconnected system which both depend on rainfall - directly
or indirectly. Groundwater provides base-flows for many rivers and visa
versa: rivers discharge into groundwater reservoirs.
This cycling rate of water moving from the surface into the ground
('recharge') and groundwater moving out of the ground in a river or
creek (discharge) creates a water balance in the environment. If ground
water is taken out of the system, water will move in from somewhere
else to restore this balance.
Groundwater extraction (i.e. through bores) will thus always have an
impact somewhere, whether it happens at the actual extracting location,
at the discharge point, the recharge point or somewhere in between.
Extraction will also impact on the speed and direction the water is
moving.
The difference between surface and groundwater is mainly the speed at
which the water moves in it's environment. This is dependant on the
environment it travels in (sand, clay etc.) and the water balance
(saturation) of the environment.
There is a general lack of knowledge of long term impacts of groundwater extraction and a lack of recharge and discharge data.
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