Australian Natural Resources Atlas

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Water resources - Management and Development - Queensland

Location map of Bribie Island

Groundwater Management Unit: Bribie Island

Introduction

Management Context:

It has been requested as part of a major groundwater management initiative that Bribie Island become a declared groundwater area under the Water Resources Act 1989. Until the island is declared, production bores do not require licensing and consequently, allocation and abstraction of the resource cannot be managed.

Deforrestation of the pine plantation located in the middle of the island is of major concern. In 1998, groundwater investigations resulted in a model predicting the effects that increased evapotranspiration, due to tree clearing, would have on groundwater levels. South of the plantations, the rises are expected to be insignificant. Groundwater levels in the immediate pine plantation area are predicted to rise by up to 800 mm. Continual observation of groundwater levels are of priority in monitoring this effect.

Groundwater quality is another issue of concern. The chemical analyses of samples taken from monitoring bores revealed readings of levels higher than the standard for nitrates, manganese, iron and alluminium.

Saltwater intrusion is another water quality problem, mainly along the northern part of the island. This area is under tidal influence and is prone to inundation during high tide. The saltwater intruding the aquifer has resulted in deteriorating groundwater water in the northern tidal estuary and around the island fringes.

Priority issues

Declining Water Levels

 NO

Salt Water Intrusion

 YES

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

 YES

Defined Minimum Water Level

 NO

Comment: Clearing of the pine plantation in the centre of the island has prompted concern about the possibility of groundwater level rises. There is continual monitoring of groundwater levels to observe these predicted rises.

Comments on Management Responses

2020 Management Response:

The development potential of the Bribie Island GMU is high with current abstraction levels at less than 5 % of the sustainable yield. It is forecast for 2020 that increased abstraction on the island by the Caboolture Shire Council will be in the order of 5 Ml/d. Projected over a year, the forecast use at the desired level of resource management is estimated to be 1825 Ml/yr. This is pending the approval of the Enviromental Impact Statement currently being prepared.

2050 Management Response:

The development potential of the Bribie Island GMU is high with current abstraction levels at less than 5 % of the sustainable yield. It is forecast for 2050 that increased abstraction on the island by the Caboolture Shire Council will be in the order of 8 Ml/d. Projected over a year, the forecast use at the desired level of resource management is estimated to be 2920 Ml/yr. This is pending the approval of the Enviromental Impact Statement currently being prepared.

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

Assessment of monitoring in Bribie Island

Efficacy of the network:

The current monitoring network for the Bribie Island GMU consists of forty-two observation bores.

The majority of water levels monitoring has occurred since 1992 to the present with measurements taken every 2 months. The monitoring of the groundwater levels assists in the interpretation of aquifer performance and provides an indication of aquifer storage. It is recommended that measurements remain at this frequency, allowing for the observation of the predicted groundwater level rises due to large-scale tree clearing.

Data management requirements:

Queensland groundwater monitoring data, both 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 licence 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:

Management of the groundwater resource of the Bribie Island Groundwater Management Unit aims at monitoring groundwater level and quality fluctuations. The requirement that the GMU be declared a sub-artesian area would enable management to further protect the resource through the introduction of licensing and the subsequent control on allocations and abstractions.

To protect the groundwater resource from saltwater intrusion, it is required that a suitable saltwater intrusion monitoring network be established. There are monitoring bores located in the north of the island monitoring saltwater intrusion at the tidal inlet. This network needs to be expanded to include the island fringes that are also prone to this effect.

Options for monitoring:

The Bribie Island Groundwater Management Unit needs to be declared as a sub-artesian area. Declaration would be the basis for the implementation of future management strategies within the GMU.

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: 

In 1992, an investigation was conducted into the groundwater resources of the Bribie Island and Pumicestone Passage area. Part of this investigation involved quantifying the annual recharge to the Bribie Island aquifer system.

Inputs into the estimation were the specific yield of the aquifer, the area of the island, rainfall data and variations in groundwater levels. Initially, the recharge was reported to be 15 000 Ml/yr. This figure was based on limited water level data of less than a year of groundwater level record.

In 1999, the long-term recharge was recalculated to be 25 000 Ml/yr using a longer period of water level record. This long-term average annual aquifer recharge has been adopted as the sustainable yield for the Bribie Island GMU.

Sustainable yield:

ML/yr

Threshold year for sustainable year:

no data 

Abstraction Volume 1996/1997:

1,610 ML 

Current Resource development categorisation:

Estimated Use in 2020

Comment:

Estimated use in 2020:

1,825 ML 

% change from 1996/1997:

14 

Resource development categorisation:

Estimated in 2050

Comment:

Estimated use in 2050:

2,920 ML 

% change from 1996/1997:

82 

Resource development categorisation:

 

What assumptions were used in this assessment

Development Potential:

The development potential of the Bribie Island GMU is high with current abstraction levels at less than 5 % of the sustainable yield. The main consideration with increased abstraction is the environmental impact on the flora and fauna that inhabit the Bribie Island National Park central to the island. The effect on saltwater intrusion is also of concern, particularly in the north of the island. Increases in abstraction must be planed so as not to induce the inland migration of the saltwater/freshwater interface.

Estimate of Use:

The development potential of the Bribie Island GMU is high with current abstraction levels at less than 5 % of the sustainable yield. The estimate of the forecast use for the years 2020 and 2050 is based upon the GMU's assessed sustainable yield and the desired level of resource management.

The Caboolture Shire Council (CSC) is currently the main consumer of groundwater on the island. Groundwater is extracted from trenches in the south of the island for treatment at the Bribie Island Water Treatment Plant. The CSC is currently preparing an Enviromental Impact Statement (EIS) for a proposed wellfield and the construction of a new treatment plant near the Bribie Island National Park. It is proposed that the wellfield will enable the CSC to extract at a rate between 5 Ml/d and 10 Ml/d. This would increase the yearly abstraction by up to three times the current level, pending EIS approval.

Data Availability,Gaps and Recommendations

Data Availablility:

The Bribie Island GMU monitoring network consists of forty-two monitoring bores. These bores are periodically observed as part of a monitoring network. Groundwater levels have been taken since 1992, although three of the bores have water level measurements from 1987 to the present. Measurements are taken six times a year.

Groundwater samples have been taken from forty- one of the monitoring bores to provide a basic trend of salinity across the GMU. These bores were sampled in 1992 for comprehensive water chemistry analysis. Most bores have been sampled since, as recently as 1996, for conductivity and general water quality.

The Caboolture Shire Council (CSC) records the daily abstraction from the extraction trench. Data of this abstraction is available from 1993 to the present.

There is a good amount of literature available for the Bribie Island GMU. Groundwater flow and groundwater resource investigation studies have been the main source of information into priority issues, aquifer descriptions and groundwater quality for the GMU.

Current Gaps and Recommendations:

Data Gaps: The Bribie Island GMU has a good amount of data available. Data gaps exist with regards to water levels.

Monitoring bores have only been on the island since 1987. The majority of groundwater level records commenced in 1992, which does not give a good indication of the long-term water level trend across the GMU. In several of the bore hydrographs, gaps exist in the records for 1994 and 1995.

Recommendations: It is recommended that the Bribie Island GMU be declared a sub-artesian area under the Water Resources Act 1989. This would allow for better resource management through the introduction of bore licensing and allocation policy.

It is recommended that a suitable saltwater intrusion monitoring network be established. There are monitoring bores located in the north of the island monitoring saltwater intrusion at the tidal inlet. This network needs to be expanded to include the island fringes that are also prone to this effect. Monitoring bore lines currently trend east-west. It is proposed that bores be drilled at both extremes of the bore line, extending out to the coastline.

Future Gaps:

The Bribie Island GMU needs to be declared a sub-artesian area under the Water Resources Act 1989. This would allow for better resource management through the introduction of bore licensing and the resulting allocation policies.

A suitable groundwater quality monitoring programme needs to be established to cater for concerns regarding the previously observed levels of heavy metals and nitrates within the water chemistry. This network could include the monitoring of other water quality concerns such as saltwater intrusion. There are monitoring bores located in the north of the island monitoring saltwater intrusion at the tidal inlet. This network needs to be expanded to include other areas that are prone to this effect.

Further information

Key

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