Australian Natural Resources Atlas

Natural Resource Topics

Water resources - Management and Development - Queensland

Location map of Mt. Larcom

Groundwater Management Unit: Mt. Larcom

Introduction

Management Context:

Declining groundwater levels, due to the combined influence of drought conditions and extraction, are a priority issue in the Mt Larcom groundwater management unit. Karst activity appears to diminish with depth in the limestone aquifer, becoming much less pronounced at approximately 15 m AHD. Consequently, storativity and yield are greatly reduced in the deeper, more basal section of the limestone deposit. Extraction bores located in the basal section will therefore have a lower probability of encountering 'good' supplies of groundwater.

Mine dewatering operations have resulted in both a lowering of the water table, by up to 20 m at the mine, and a reversal in the seepage direction, to the SSE, in adjacent northern catchments. Depletions that may be attributed to mine dewatering, as opposed to purely drought effects, are estimated to extend from 6 to 7 km to the north of the mine. Effects are constrained in other directons due to geological boundaries.

Priority issues

Declining Water Levels

 YES

Salt Water Intrusion

 NO

SALINISATION

 

Dryland

 NO

Irrigation

 NO

Groundwater

 NO

Surface Water

 NO

Urban

 NO

Point Source Pollution

 NO

Diffuse Source Pollution

 NO

Subsidence

 NO

Artificial Recharge (ML/yr)

 no data

Ecosystems Protection

 NO

Surface Water Interaction

 NO

Management Plans

 NO

Defined Minimum Water Level

 NO

Comment: Groundwater quality is another limiting factor in the development and use of groundwater resources in the Mt Larcom GMU, as the groundwater obtained from the limestone deposits is usually very hard.

Comments on Management Responses

2020 Management Response:

An estimate of 1250 Ml/yr for the forecast use for the year 2020 is based upon the GMU's assessed sustainable yield, develoment potential and the desired level of resource management.

2050 Management Response:

An estimate of 2000 Ml/yr for the forecast use for the year 2050 is based upon the GMU's assessed sustainable yield, develoment potential and the desired level of resource management.

See QLD Water Resources Assessment 2000 Technical Report for a review of management responses.

Assessment of monitoring in Mt. Larcom

Efficacy of the network:

The current monitoring network for the Mt Larcom groundwater mangement unit consists of 139 observation bores, with a proposed quarterly monitoring frequency.

The Queensland Cement and Lime Company (QCL) mines limestone in the Mt Larcom groundwater management unit and is required to monitor the groundwater levels. The QCL monitoring program commenced prior to the initiation of mining and monitors changes in the characteristics of the groundwater supplies of local residents. Water levels in only a few bores within a one kilometre radius around the mine are directly affected by interference effects due to the relatively steep cone of depression, indicative of a relatively low transmissivity (T) value, resulting from the mine dewatering operations. However, impacts are felt over a larger area due to the pumping from the mine which exceeds sustainable levels at the local level.

Data management requirements:

Queensland groundwater monitoring data, both water level and water quality, is stored within the Groundwater Database (GWDB) system. The new system is based on web technology and is available through the Department's intranet. Allocation and use data is obtained through the Water Entitlements Registration Database (WERD) which is an electronic database for water license details. Both databases are managed locally at district level, with respect to the collection and entering of water monitoring, allocation and use data; and are accessed statewide.

Protective management:

Water pumped from the mine is presently discharged into the local creek system. A recharge system is being investigated to recirculate the pumped water, which currently is lost from the local area, so that impacts on local groundwater users can be minimised. Injection bores have been drilled and pump tested. It is proposed to inject groundwater from the mine back into the limestones at a point about 2 km north of the mine to try to reverse the water level trends.

Options for monitoring:

Data and information gaps are the responsibility of the mine.

See QLD Water Resources Assessment 2000 Technical Report for a review of monitoring.

What is the estimated demand for groundwater?

Sustainable Yield

Comment about sustainable yield figure: 

An assessment of 2000 Ml/yr for sustainable yield was made in 1999.

Sustainable yield:

ML/yr

Threshold year for sustainable year:

2,050 

Abstraction Volume 1996/1997:

1,250 ML 

Current Resource development categorisation:

 

Estimated Use in 2020

Comment:

 

Estimated use in 2020:

1,250 ML 

% change from 1996/1997:

0 

Resource development categorisation:

 

Estimated in 2050

Comment:

 

Estimated use in 2050:

2,000 ML 

% change from 1996/1997:

60 

Resource development categorisation:

 

What assumptions were used in this assessment

Development Potential:

In 1982, water quality was noted as a limiting factor in the development and use of groundwater resources in the Mt Larcom groundwater management unit. The groundwater obtained from the limestone deposits is usually very hard, rendering supplies as mostly unsuitable for drinking and other domestic purposes. However, the groundwater quality is generally suitable for irrigation of medium to high salt tolerant crops in addition to stockwatering. Stockwatering is the main usage of groundwater in this area. Local mining activities were reported, in 1993, to have had no significant influence on the water quality in the groundwater management unit. A numerical model was developed in 1995 to assess the impact of the mine on groundwater levels in the area. The numerical model has been used to forecast potential impacts to 2012.

Estimate of Use:

An estimate of 2000 Ml/yr for the forecast use for the years 2020 and 2050 is based upon the GMU's assessed sustainable yield, develoment potential and the desired level of resource management.

Data Availability,Gaps and Recommendations

Data Availablility:

In excess of 250 observation bores, both private and State owned, are located within the Mt Larcom GMU. The availability of water level data is high, with continuous water level monitoring in 175 observation bores from 1977 to the present. Comprehensive water quality data exists for 175 observation bores within the GMU, with recent analyses to 1998. In addition to observation bores, there are 7 gauging stations and 4 weather station in the GMU.

Current Gaps and Recommendations:

Data Gaps: Formal use and allocation data is not available for the Mt Larcom GMU, as it is not located within a declared sub-artesian or irrigation area.

Recommendations: Data and information gaps are the responsibility of the mine.

Future Gaps:

Data and information gaps are the responsibility of the mine.

Further information

Key

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