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Water resources - Overview - Tasmania

Specify a region: -- select region -- Arthur River Coal River Derwent River East Coast Flinders - Cape Barren Islands Forth River Gordon River Huon River King-Henty Rivers King Island Kingston Coast Mersey River Pieman River Piper-Ringarooma Rivers Rubicon River Sandy Cape Coast Smithton-Burnie Coast South-West Coast Tamar River Tasmania (13SF2) Tasmania (13SF3) Tasmania 1

Basin & Surface Water Management Area: Tamar River

Introduction

The Tamar SWMA covers 11670 square kilometeetres and is located in the northwest part of Tasmania. The area has 5 reasonably distinct areas. These are:

• Rivers and streams downstream of the South Esk at Launceston
• The section regulated by Hydro Electric Corporation which includes, the South Esk below Macquarie, the Macquarie below Lake River, Lake River, Brumbys Creek to Poatina Power Station.
• South Esk River above Macquaire
• Macquarie above Lake River
• Meander River

The topography of the SWMA is quite varied. The major river systems consist of a flood plain, adjacent rolling hills and mountains towards the headwaters.

Rainfall over the SWMA is quite variable ranging from as low as 510 mm at Ross in the Macquarie (middle reaches of 4 above) to 1200 mm at Gray (upper reaches of 3 above). .

The estimated average annual rainfall for major rivers in the SWMA range from 600 mm to 900 mm.

The SWMA consists of a mixture of perenial and non perenial streams. The major rivers such as the South Esk, North Esk, Macquarie, Lake and Meander flow all year. Many of the smaller river and creek systems generally stop flowing during dry summers. Most of the Macquarie River above Lake River (supplied from lakes Tooms and Leake), the Lake River and Macquarie above Brumbys Creek (supplied from Woods Lake), Macquarie below Brumbys and South Esk below the Macquarie (supplied from Great Lake) are regulated rivers.

The Meander, North Esk, and South Esk above Macquarie rely on base flows to provide continuous flow through out the year. There is a high demand on these flows which has resulted in the capping of water extractions over the period December through to April. In dry time, to protect this flow, water restrictions have become necessary, particularly in theMeander Catchment.

Landuse in the SWMA is mainly agriculture, forestry with limited mining for coal and metals in the upper South Esk catchment. The major agriculture activities in both the South Esk and Macquarie catchments are sheep and beef farming. However there are a growing number of propertiues becoming involved in irrigation such as poppies and potatoes.

Near Cressy and Longford is a small State irrigation scheme that uses water from Poatina Power Station. This reliable water supply has allowed more intensive cultivation of vegetable crops both in and outside the scheme. Water released from Woods Lake by the HEC also has provided for reliable irrigation of crops and pastures in the Lake River and Macquarie below Lake River.

Apart form providing water for irrigating crops and pastures in the SWMA, water is also used extensively for power generation. The Great Lake - South Esk power system is the largest power generating development in the State. The main power stations are are Poatina Power Station (which gets water from Great Lake) and Trevallyn Power Station at Launceston (which get its water from the bottom of the South Esk River.

Another significant user of water in the basin is the city of Launceston. Launceston gets its water form the North Esk mand St Patricks Rivers.

A growing landuse in the SWMA is grape growing for wine. This industry is located mainly around the Tamar valley downstream of Launceston.

There are a number of water resource issues in the SWMA that have arisen due intense competition for water. This competion includes that between irrigators and power generation, irrigation and town water supply and irrigation generally (due to limited reliable water available in some areas during summer.

Vital Statistics:

Area:	11,670 Km2
Total storage volume:	3,809
Total surface water use:	91,188 ML/yr
Development category:	HIGH DEVELOPMENT
Mean annual run-off:	3,585,819 ML/yr

A four-class classification system was developed to provide a simple method to communicate the status of the use and allocation of Australia's water resources in relation to sustainable water management.

It is important to recognise that adequately quantifying a sustainable flow regime or sustainable yield and consequent operating rules is a complex matter. State, Territory and scientific agencies continue to develop and apply methods and measures for determining sustainable flow regimes and sustainable yields.

This categorisation provides a general guide only. Please refer to the State and Territory Overview and Technical reports for detail on the analysis methods used.

	Category	Development status
1	<30%	Low development
2	30 - 70%	Moderate development
3	70 - 100%	Highly developed
4	100%	Overdeveloped

* Water use as a percentage of sustainable flow regime (surface water) and sustainable yield (groundwater)

PLEASE NOTE:

Sustainable Yield:

Sustainable yield was calculated by taking the difference between the annual median flow and the estimated environmental flow. The method of determing the environmental flow is set out belo

The NLWRA Tas Environmental Flows Method (for Use in The National Land and Water Resources Audit only)

The following method has been developed for application in the Tasmanian section of the National Land and Water Resources Audit (NLWRA) only. While the method is broadly based upon that of Tennant (Tennant, 1976; also known as the Montana Method) it is only being used as an expedient means of assessing environmental water requirements for the Audit. The estimates should not be taken to represent true environmental water requirements.

Tennants method is based upon a consideration of annual average flow, basically allocating proportions of this flow to a summer and a winter period as average flow requirements for habitat maintenance. Various categories of narrative description (or habitat protection) have been used by Tennant to determine the appropriate proportion for a given purpose. His categories include Outstanding, Excellent, Good, Fair or Degrading, Poor or Minimum and Severe Degradation.

The method appears to provide elevated summer flows compared with those which might be expected in Australia possibly as a result of snow-melt dominance in America. These discrepancies appear to occur as the result of the application of proportions to annual average flows to estimate summer flow requirements.

In Tasmania the method has been used in a variety of modified forms including application of proportions to monthly or seasonal flow regimes. Results from these analyses have also been compared with more detailed estimates based upon the Instream Flow Incremental Methodology (Bovee, 1982). However, at this time there is insufficient information to adopt a particular narrative description category for common use. Indications are that an Excellent category may be suitable.

Under the NLWRA it is necessary to consider both an annual period of flows as well as a critical period. In Tasmania, the critical period for most purposes occurs over summer and has been adopted as December 1st to April 30th inclusive.

Issues in the adoption of a modified method are therefore:

• What habitat protection category should be adopted?
• Can we account for apparent summer flow discrepancies?
• How can we make use of the results?

Habitat Protection Category

For the purposes of the NLWRA Tas Method the Good category has been adopted. This category has been adopted as a conservative means of identifying stressed river systems. While comparison of Tennant method estimates with IFIM estimates at a few sites indicates that an Excellent category could be chosen it is important to recognise the transient nature of the method adopted here.

Summer Flow Discrepancies

The apparent over-estimates of summer flow requirements using Tennants Method appear to arise as a result of the use of a proportion of annual average flow. The easiest way to overcome this is to utilise Tennants proportions on the relevant critical period flow. Since we are interested in the typical critical period flow, a median flow has been adopted rather than the mean. In many cases these figures will be similar, however, in stream subject to significant variations in flow median flows would always be preferred.

Use of the Results

The NLWRA Tas Method has been developed only for the purposes of the National Land and Water Resources Audit. Nevertheless, the estimates could also be used as a simple means of assessing the stress that river systems are under in Tasmania as an aid in the prioritising more detailed environmental flows work.

Summary of the Method

• Identify the median critical period and annual flows for the area in question.
• Adopt 30% of the annual flow as the recommended environmental water requirement to maintain good habitat.
• Adopt 40% of the summer flow (Dec Apr) as the recommended environmental water requirement for that period.
• Adopt 20% of the winter flow (May Nov) as the recommended environmental water requirement for that period.
• If the critical period is different from summer or winter then adopt a weighted average of the relevant flows.

References

Bovee, K.D., 1982 A guide to instream habitat analysis using the instream flow incremental methodlogy U.S. Fish and Wildlife Service Biological Services Program FWS/OBS-82/26, Instream flow information paper 12. 248 p.

Tennant, D., 1976 Fisheries, Vol. 1, Issue 4 pp359 373

PLEASE NOTE:

Categorisation:

To determine sustainable yield for the basin the median annual flow to the basin outlet was determined and the environmental flow estimate was then deducted from it.

How saline are the surface water resources in the Tamar River surface water management area?

Table: Surface water resource by salinity class.

	Total Volume, Divertible Yield (ML/Yr)
Total volume (ML/yr), DIVERSION	350,000
<500 mg/l (ML/yr)	350,000
500 mg/l (ML/yr) - 1500 mg/l (ML/yr)	no data
1500 mg/l (ML/yr) - 5000 mg/l (ML/yr)	no data
5000 mg/l (ML/yr) - 14000 mg/l (ML/yr)	no data
> 14000 mg/l (ML/yr)	no data

Major water storages

Table: Major water storage areas:

Storage name:	Capacity (ML)
Trevallyn Dam (West Tamar)	2,706
Trevallyn Dam (Sth Esk)	1,103
Total	3,809

Further Information

• View the Tasmania Water Resources Assessment 2000 Report
• View the Tasmania Water Resources Assessment 2000 Technical Report
• Link to data available for download on the:
• Surface Water Management Areas
• Data from the 1985 Review of Australia's Water Resources and Water Use
• Link to the Map Maker to make a map using this information.
• For more information about water and other natural resource issues link to www.dpiwe.tas.gov.au.