CoHeSion - Edith Cowan University

The consequences of unsympathetic groundwater
abstraction on groundwater-dependent
(phreatophytic) vegetation has been observed
throughout Australia. With increasing demand for
water and a changing climate regime, the need to
mitigate the environmental impacts of groundwater
development is increasing. Current bore operation
practices in Australia are largely responsive to
consumption demand and often in conflict with
peak environmental needs for groundwater
during summer, resulting in drought stress and
sometimes death of phreatophytic vegetation. With
community and industry demand for groundwater
highest during the dry period of each year (up to
3 times the winter demand), the risk of impact on
ecosystems dependent on shallow groundwater is
high.
In Western Australia, the single largest source
supplying drinking water to the city of Perth
is the Gnangara Groundwater Mound located
within and to the north of the metropolitan area
on the Swan Coastal Plain. Overlying much of the
Mound is phreatophytic native Banksia woodland
that is susceptible to prolonged separation from
the unconfined aquifer during Perth’s hot, dry
Mediterranean summer. During the last 30 years,
a drying climate coupled with altered land use
and increased abstraction for public and private
water supply has contributed to a general decline
in groundwater levels across the Gnangara
Mound, resulting in heightened ecosystem impact.
Sustainable use of this important water resource
is therefore imperative as Banksia woodlands are
considered functionally important features of the
Swan Coastal Plain landscape.
Previous research by Associate Professor
Ray Froend on phreatophytic vegetation, has
revealed seasonal variability in both the quantity
of groundwater used and the relative importance
of groundwater as a water source. Use of
groundwater by phreatophytes is highest during
the driest season of the year when alternative
water sources become depleted and demand is
highest. It follows therefore, that phreatophytic
vegetation is most vulnerable to lowering of the
water table during the dry summer months and
that a more sympathetic groundwater abstraction
practice would avoid pumping during this period.
Whilst a precautionary approach is valid given
the absence of information on phreatophyte
adaptability and tolerance to drawdown, further
research is required to determine the potential, if
any, for operating bores whilst minimizing impacts
on vegetation. An Australian Research Council
Linkage project led by Associate Professor Ray
Froend is designed to assess the response of
vegetation to operating bores during periods of
low environmental demand and at lower pumping
rates. Modifying pumping to be sympathetic to,
rather than in competition with environmental
demand, offers benefits for sustainable operation
of bores, especially large bore fields. Low
magnitude and rates of change in groundwater
levels as opposed to rapid drawdown, may also
allow intra- and inter-generational adaptation and
persistence of phreatophytes.
The project represents a significant contribution
to Australian and international research on
ecosystem dependency on groundwater. It
is particularly innovative as it aims to use
phreatophyte groundwater requirements and
adaptability to formulate sustainable bore field
operations. The project represents a long-term
commitment by the Chief Investigators and partner
organizations to research that leads to sustainable
water resource development and management.
With the paucity of research on sustainable
groundwater resource development in Australia,
this project represents a significant contribution
to improved management of the resource and the
environment in general.
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