Comment about sustainable yield figure:

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 below

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

Sustainable yield (ML/yr):

6,153,175

Threshold year for sustainable year:

no data

Diversion Volume 1996 (ML):

300

Current resource development categorisation:

LOW DEVELOPMENT

Estimated use in 2020(ML):

400

% change from 1996:

33

Resource development categorisation:

LOW DEVELOPMENT

Estimated use in 2050(ML):

500

% change from 1996:

67

Resource development categorisation:

LOW DEVELOPMENT

Management information

Scale of allocation planning

STATE/TERITORY

STATE/TERITORY

Inputs to allocation

BROAD RESOURCE INVESTIGATION

BROAD RESOURCE INVESTIGATION

Type of monitoring - quantity

LIMITED OR NONE

LIMITED OR NONE

Type of monitoring - quality

NONE

SALINITY AND OTHER LIMITED PARAMETERS

Distribution efficiency (H,M,L)

HIGH

HIGH

Use efficiency (H,M,L)

MEDIUM

MEDIUM

Resource management efficiency (H,M,L)

LOW

LOW

Degree of licensing

LIMITED

LIMITED

Water trading (None, Limited, Significant)

NONE

LIMITED

Mechanism of trading

Volume traded (ML/yr)

no data

no data

no data

Number of transactions

Inter-basin transfers

NONE

NONE

Volume transferred (ML/yr)

no data

no data

no data

Environmental allocation category:

• None
• <33% of waterways with formal allocations
• between 33% and 66% of waterways with formal allocations
• >66 % of waterways with formal allocations

no data