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Groundwater Salinity Index of indicators

Indicator description

Why is it indicative

What does the data show

Data

Related Indicators

Acknowledgment

Indicator description

Salinity of groundwater aquifers, as a particular measure of water quality.

Why is it indicative

Salinity is a major water quality limitation on the environmental values (including potential beneficial uses) of groundwater. It is influenced by human action such as irrigation, disposal of waste waters, seawater intrusion in response to excessive extraction from coastal aquifers, and the like. Excessive salinity in all groundwaters may limit their use and therefore the productivity of lands reliant on borewater irrigation. Although some groundwater sources are too salty for human use, lower salinity levels can adversely affect vegetation growing in areas of shallow watertables.

Where background (natural) salinities are moderate to high, salinity is a relatively poor indicator of pollution from human activities (except where poor borehole completion results in cross-contamination of aquifers). Other indicators such as petroleum hydrocarbons, nitrates, pesticides and E.Coli may be used where data is available.

What does the data show

  • There is limited historical data to support trend analysis of groundwater salinity in Tasmania.
     
  • Based on limited data, the National Land and Water Resources Audit (NLWRA 2001) estimated that 62.64% of the total sustainable yield of groundwater in Tasmania calculated for 2000, was below the salinity level of <1,500 mg/l (suitable for human consumption and crop irrigation). Of the major useable groundwater resources that occur within the Groundwater Management Units (GMUs), approximately 87% of the sustainable yield fell below a salinity of 1,500 mg/L in 2000.
     
  • The NLWRA indicated that the Llandherne GMU and the North East Unincorporated Area (UA) were the only areas of the State to record brackish average groundwater salinities between 1,500-5,000 mg/L in 2000. The Sorell GMU recorded salinity levels of around 1,458 mg/L, just below this range. The salinity level in Llandherne GMU is of particular concern, because it has a shallow watertable (2 metres deep to the top of the aquifer), which increases the risk of dryland salinity occurring.
     
  • Groundwater salinities for all other GMUs and UAs of the State were below 1,500 mg/L (<500 mg/L is considered to be fresh).
     

Data

There is limited historical data to support trend analysis of groundwater salinity in Tasmania. The compilation of all available groundwater data was undertaken as part of the NLWRA (2000) and was largely drawn from information from Mineral Resources Tasmania. The following tables summarise the results of the NLWRA, which provide an indication of groundwater salinity.

Groundwater resource by salinity class

<1,500 mg/l (ML/yr)

5,000 mg/l (ML/yr)

14,000 mg/l (ML/yr)

>14,000 mg/l (ML/yr)

Total Volume (ML/yr)

Total GMU

270,342

38,322

449

3,039

312,152

Total UA

1,315046

728,383

175,191

2,218,620

GMU = Groundwater Management Units

UA = Unincorporated Areas

Source: NLWRA 2001


Average groundwater salinity for each Groundwater Management Unit and Unincorporated Area

Province

GMU

Area (km 2 )

Depth to top of aquifer (m)

Average salinity (mg/L)

1

Burnie

3,392

8

124

1

Smithton

1,840

6

336

1

West - UA

23,760

6

138

2

Llandherne

24

2

2,340

2

Longford

1,509

6

377

2

Sorell

27

10

1,458

2

Spreyton

96

9

294

2

St Marys

17

10

294

2

Wesley Vale

212

6

240

2

Central South East - UA

27,792

6

870

3

Flinders Island

1,901

1

600

3

Ledgerwood

28

3

500

3

Ringarooma

28

500

3

Scottsdale

403

1

168

3

Tomahawk

212

2

300

3

Winnaleah

28

6

500

3

North East - UA

7,027

5

2,520

GMU = Groundwater Management Unit

UA = Unincorporated Area

Source: NLWRA 2001


Related Indicators

Area of Rising Watertables

Area Affected By Salinity

Acknowledgment

National SoE Key indicator 1.2 (Fairweather and Napier 1998)

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Last Modified: 14 Dec 2006
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