Water
resources caps
Capping of resource extraction volumes is an accepted way to manage
overexploitation of surface waters and groundwaters. Around Australia, some 50
per cent of surface water management areas and 75 per cent of groundwater
management units have some form of cap operating. However, AWR 2005 has shown
that there is inconsistency in terms of what is included under a water resource
cap, and that each jurisdiction has a different approach to the use of caps as a
management tool.
Water resource caps can be defined as an 'upper limit for the volume of water
available for use from a waterway, catchment, basin or aquifer'. Capping of
water use is a primary management measure that is used to promote the sustainable
use of water and prevent over allocation of the resource and therefore to meeting
Objective (iv) of the National Water Initiative (NWI):
To complete the return of all currently overallocated or overused systems
to environmentally sustainable levels of extraction.
Grapes are one of the many irrigated crops whose water use comes under a cap
Image by Arthur Mostead, sourced from the MDBC
The level at which a cap is designated can be set in a number of different
ways, including the level of development at the time of implementation, or
the sustainable yield for the resource. An understanding of the current use
of caps in Australia is needed for the Commission to implement the National
Water Initiative (NWI).
Water resource caps are not set in the same way in all water management areas
because a simple upper limiting volume is not an appropriate limit in all cases.
For example, in groundwater resource management, a designated water level or
water pressure may be a more appropriate way of limiting extractions than applying
a specific cap on extraction volumes. Caps on water entitlements may also be
applied.
For this report, the states and territories provided information on use of
caps on extraction, the form of the cap, the administrator of the cap, and
water usage that does not fall under the cap.
One of the best-known caps in Australia , and the first inter-jurisdictional
cap introduced, is the Murray-Darling
Basin Cap (the Cap) on surface water diversions. It was introduced as a result of concerns about
water availability in the Murray-Darling Basin during the early 1990s and in
response to An Audit of Water Use in the Murray-Darling Basin (June
2005). After an interim Cap in 1995, the upper limit on the amount of water
that could be taken from the Murray-Darling Basin river system was defined
in 1997 as:
The volume of water that would have been diverted under 199394 levels of
development.
Irrigation area along the Lower River Murray
Image by Arthur Mostead, sourced from the MDBC
A permanent Cap is in place in all the river valleys in the Murray-Darling
Basin except the NSW Border Rivers, Murray-Darling Basin subcatchments in Queensland
and the Australian Capital Territory . Queensland is in the process of determining
its capped level of diversions. The NSW Border River cap is subject to the
conclusion of an intergovernmental agreement between New South Wales and Queensland
. The Australian Capital Territory cap is being developed.
The Cap of 1993-94 levels of development is defined in terms of the infrastructure
(pumps, dams, channels, areas developed for irrigation, management rules) that
was in place in 1993-94; it does not limit water use to the actual volume of
water that was used in 1993-94. For example, the Cap in the 2004-05 water year
was calculated by using climate data for that year to predict how much water
could have been diverted if 1993-94 management rules and infrastructure were
still in place. Further information
on the MDBC cap. The Murray-Darling Basin Cap does not currently include groundwater, return
flows or floodplain diversions.
There has been an increase in groundwater extractions in the Murray-Darling
Basin since the Murray-Darling Basin Cap on surface water diversions was introduced.
The expected continuation of this trend poses a serious threat to the long-term
availability of surface water in the Murray-Darling Basin . In response, the
Murray-Darling Basin Commission is examining methods of either incorporating
groundwater extractions into the current Cap or implementing a separate groundwater
cap for the Murray-Darling Basin.
Related links
Water resources caps are discussed in more detail in the following sections:
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