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Background
The Lower Lachlan Groundwater Management Area covers
an agricultural region that is extremely important economically,
with major irrigation projects and townships increasingly
utilising its groundwater resources. These resources are
regulated under the Lower Lachlan water-sharing plan, whereby
overall groundwater use is limited to the estimated sustainable
yield. In the drought period of 2002-03, groundwater usage
exceeded the sustainable yield estimate, and concerns were
raised regarding the veracity of the sustainable yield estimate.
Lachlan Valley Water Inc. commissioned C. M. Jewell &
Associates Pty Ltd to undertake an independent review of
the Lower Lachlan Groundwater resources, which was to include
a review of the recharge estimates and a review of the groundwater-dependent
ecosystem requirements.
Hydrogeological Environment
The region's geological history included the deposition
of alluvial sediments - for over 40 million years - onto
what is now the floodplain of the Lachlan River and its
effluent creeks. The thick sequences of deposition include
productive aquifers such as the Calivil and Upper Renmark
aquifers. Groundwater recharge is identified by the low-salinity
groundwater plume that it generates; outside this plume,
groundwater salinities are generally higher, owing to the
longer residence times and the more saline host rock conditions.
However, lower quality groundwater may also be found within
the low-salinity plume region, because of localised saline
zones and (for example) the presence of pyritic lignite.
Objectives and Scope
The objectives of the assessment were:
- to review Department of Infrastructure, Planning and
Natural Resources (DIPNR's) estimate of the annual recharge
within the study region (including a review of the data
used, and a review of the interpretation methods and conclusions);
- to review the environmental water requirements of groundwater-dependent
ecosystems; and
- to identify any information gaps critical to an accurate
assessment of the recharge and the environmental requirements
of the aquifer.
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Projects
