Australian Natural Resources Atlas

Natural Resource Topics

Water resources - Management and Development - Queensland

Location map of North Stradbroke Island

Groundwater Management Unit: North Stradbroke Island

Introduction

Management Context:

The main area of concern for Stradbroke Island pertains to the potential lowering of water level in Eighteen Mile Swamp and Herring Lagoon. These have however remained constant between 1991, when it was reported that levels had dropped, and 1994. The lack of change to water level between 1991 and 1994 therefore suggests that there is equilibrium between inflow from high sand dune hill water storage, outflow to the ocean and volumes pumped from Herring Lagoon. Maintaining this water level has also been aided by implementation of a maximum withdrawal limit of 50 Ml/d from Herring Lagoon, which is recommended to continue in a 1998 report.

Water quality monitoring in the GMU shows no significant change in groundwater quality due to water withdrawl. Nine bores tested across the island support this view and indicate that salt water intrusion has not occurred.

Management strategies to maintain the quality and quantity of water resources on Stradbroke Island include: (1)Maintaining the maximum rate of withdrawal from Herring Lagoon, (2) Continuing water quality monitoring and, (3) Continuing environmental reporting.

Priority issues

Declining Water Levels

 NO

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

 YES

Surface Water Interaction

 NO

Management Plans

 NO

Defined Minimum Water Level

 YES

Comment: Monitoring of water quality thus far indicates that saltwater intrusion has not occured on North Stradbroke Island. Defined minimum water level in lakes are monitored to ensure safe levels of withdrawal.

Comments on Management Responses

2020 Management Response:

A forecast use estimate of 30000 Ml/yr by 2020 is made by the Redland Shire Council based upon historical growth trends in the shire. This does not include potential increase in demand from within Stradbroke Island, where consumpive use is currently 1290 Ml/yr.

2050 Management Response:

Forecast use estimates have not beeen projected to 2050 however the maximum potential use of 100000 Ml/yr is unlikely to be reached. Environmental concerns may also prevent the full sustainable yield from being reached.

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

Assessment of monitoring in North Stradbroke Island

Efficacy of the network:

Water level monitoring commenced in 1968 and is ongoing in the GMU. Water quality data exists for 38 bores with post 1990 sampling. The current monitoring network for the Stradbroke Island groundwater management unit consists of 32 observation bores with a proposed bi- annual to monthly monitoring frequency.

Data management requirements:

Queensland groundwater monitoring data, including water level and water quality, is stored within the Groundwater Database (GWDB) system. The new GWDB 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 licences.

Both databases are managed at a district level, with respect to the collection and entering of water monitoring, allocation and use data; and are accessed statewide. Collection of monitoring data on the island is however carried out by Redland Shire Council and the mining companies.

Protective management:

The main areas of concern for the North Stradbroke Island GMU are the effects of withdrawal rates of groundwater, and lake water, on water levels in the swamp and environment of the swamp, and the potential threat of saltwater intrusion. In response to these concerns, the following recommendations are made:

- Withdrawal from Herring Lagoon should continue to be limited to 50 Ml/d

- Environmental reporting should be continued

- Water quality monitoring should be continued.

Environmental monitoring of Eighteen Mile Swamp is currently conducted by CRL in association with the University of New England, Grafton.

Options for monitoring:

Installation of at least four automatic data recorders, for continuous daily water level and rainfall data, would enable better calibration and refinement of groundwater computer models.

Comprehensive quality monitoring every two years, as a precautionary measure, would ensure integrity of the resource. In special cases, (eg. pollutant spill) monitoring frequency would be increased.

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 annual supply of 122500 Ml was calculated for the GMU by water balance calculation and recharge estimates. For environmental concerns a conservative amount of 100000Ml/yr was adopted as the annual sustainable yield.

Sustainable yield:

ML/yr

Threshold year for sustainable year:

2,100 

Abstraction Volume 1996/1997:

14,552 ML 

Current Resource development categorisation:

 

Estimated Use in 2020

Comment:

 

Estimated use in 2020:

31,000 ML 

% change from 1996/1997:

114 

Resource development categorisation:

 

Estimated in 2050

Comment:

 

Estimated use in 2050:

31,000 ML 

% change from 1996/1997:

114 

Resource development categorisation:

 

What assumptions were used in this assessment

Development Potential:

Groundwater allocations within the North Stradbroke Island GMU, indicate that about 58572 Ml/yr is committed, although only about 20362 Ml/yr is for consumptive use. Currently use is estimated to be about 45000 Ml/yr. Hence there is still control, through licensing and metering, to develop the resource. Environmental concerns may however prevent development of the groundwater resource to its total sustainable yield.

Estimate of Use:

Forecast use in 2020 is based upon growth trends in Redland Shire and does not consider increased demand from Stradbroke Island. No projection has been made for groundwater use in 2050.

Data Availability,Gaps and Recommendations

Data Availablility:

Water level monitoring in the GMU commenced in 1968, and is ongoing in the current monitoring network of 32 bores. Good water quality data exists for 38 bores with analyses from 1990 onward. Use data is stored by CRL and Redland Shire Council and is available on request. Allocations are set by license and are on file with the Department.

Current Gaps and Recommendations:

Data Gaps: Data gaps in past data are not considered to have any limitations on the current management or practices regarding the resource.

Recommendations: Water quality monitoring and environmental reporting by Redland Shire Council and Consolidated Rutile Limited should continue in the GMU.

Future Gaps:

The North Stradbroke Island GMU is currently managed at a high level. Although there are no significant needs or gaps in the available data, the folowing recommendations are made for future monitoring:

- Regular running of the groundwater computer model, with the changing management circumstances, would allow for groundwater extraction effects to be gauged.

- Observation bores may need to be appropriately re-sited to check for seawater intrusion if extraction points alter significantly.

- Regular conductivity logging by geophysical tools, would provide a monitoring and management control.

Further information

Key

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