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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: Coal River

Introduction

The Coal River Basin water management area covers 736 square kilometres and occupies and area of the south east of the State north east of Hobart.

The Coal is located in arguably the driest part of the State with a catchment rainfall of about 600 mm.

The principal source of water for the region is Craigbourne Dam. This dam supplies the South East Irrigation Scheme which suports a very viable and developing horticulture and grape growing area. The Scheme has two stages. In the first of these, called Stage 1, landholders obtain their water by pumping directly from the River. In Stage 2, a high pressure pump scheme supplies all landholders with water at a pressure satisfactory to run a travelling irrigator.

Apart from Craigbourne Dam, other sources of water for parts of the area come from farm dams and the Hobart Water Authority town water supply system.

The Coal River would cease to flow for considerable periods of time if not for Craigbourne Dam. With the exceptions of the Coal River and a few spring fed creeks, the majority of streams in the area do not flow for long periods of the year.

Apart from river flats, topography for the basin is generally hilly.

Major landuse consists of irrigated agriculture (including vineyards poppies and vegetables), sheep grazing and pasture cultivation.

Water resource issues include the need to find further water to meet the needs of irrigation expansion and improve reliability of supply. This supply has to be of a very high security due to the permanent nature of the irrigation (eg vineyards and fruit trees) planned.

Additional water for area is planned to come from pumping water from the Hobart Water Authority system into a proposed holding dam and then distribution under gravity to the Stage 2 of the Scheme. Water from the Hobart Water Authority for use in the south east area generally comes from the nearby Derwent River catchment (SWMA 304).

Vital Statistics:

Area:	736 Km2
Total storage volume:	13,500
Total surface water use:	3,231 ML/yr
Development category:	LOW DEVELOPMENT
Mean annual run-off:	54,102 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 determininong the environmental flow is set out belo

The NLWRA's 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's 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's 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 environmenal flow estimate was then deducted from it.

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

Table: Surface water resource by salinity class.

	Total Volume, Divertible Yield (ML/Yr)
Total volume (ML/yr), DIVERSION	10,000
<500 mg/l (ML/yr)	no data
500 mg/l (ML/yr) - 1500 mg/l (ML/yr)	no data
1500 mg/l (ML/yr) - 5000 mg/l (ML/yr)	10,000
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)
Craigbourne Dam	12,500
Richmond Pump Station	1,000
Total	13,500

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