From Guidance for groundwater storage utilisation in water planning - Water Report Series No. 81, June 2012:
(A series of works commissioned by the National Water Commission on key water issues)
From section 2.3 Unconfined, semi-confined and confined aquifers (p. 6):
Whilst there is a significant distinction between completely confined and unconfined aquifers, there is a continuum of properties between them that is the domain of the more common ‘semi-confined’ (or ‘leaky’) aquifers. These are neither completely confined nor unconfined, but are generally fully saturated, and overlain by ‘leaky’ strata through which recharge and discharge can occur illustrates potential relationships between common aquifer types (SKM 2011) and the unconfined, semi-confined and confined classification.
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environmental objectives for
groundwater systems are likely to include: overall long-term system extraction limits to ensure
water levels/pressures do not continue to decline (i.e. that there is no long-term ‘mining’ of the
resource); water level/pressure thresholds that must be maintained (at all
times or from time to time) to protect base flows and other dependent
ecosystems (these will be particularly important in unconfined groundwater
systems); possibly maximum or other rates of water level/pressure change to
protect GDEs; and water quality objectives and associated water level targets
that ensure the beneficial use of the resource is not compromised (this is also
important for supply sustainability).
interception. Allowing utilisation of groundwater storage
will result in greater groundwater extraction. In most confined systems, this
water will come largely from elastic storage. Recharge from adjacent aquifers
and/or surface water systems will occur, but is unlikely to be increased appreciably. Discharge will be reduced; however, in many of these deep confined systems this discharge is to more
saline systems, which themselves may take hundreds, if not thousands, of years to reach surface water bodies as saline water. In many unconfined
systems, however, taking from storage will result in both induced recharge from
surface systems, and reduced discharge to adjacent groundwater systems and
surface systems. This ‘interception’ may have impacts not only on environmental
values, but also on the rights of existing water entitlement holders in those
connected surface water or groundwater systems. This is particularly an issue
for connected systems that are already fully committed, and even more so in the
Murray-Darling Basin, where surface water use is capped.
In reality, most ‘confined’ systems are actually semi-confined, and to varying degrees are connected to aquifers above them. Changes in deeper aquifers will often manifest as declines in overlying unconfined aquifers, sometimes quickly and sometimes over several years. In such cases, the impact on objectives of overlying systems, and of surface systems connected to these, also must be taken into account.
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From section 4.3.5 Developing groundwater management strategies and undertaking risk assessment (p. 40):
Social risk assessment considerations might include:
· the social impacts of the proposed options and alternatives for
groundwater storage utilisation
· the equity issues associated with the groundwater storage utilisation
options and alternatives
· the adjustment costs to satisfy the equity principles of reform.
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Published by the National Water Commission
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Canberra ACT 2600
Tel: 02 6102 6000
Email: enquiries@nwc.gov.au
Date of publication: May 2012
