Indicator: Environmental flows
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What the results tell us for Tumut
The streams for which hydrological stress ratings have been determined within the Stressed Rivers Report (DLWC 1999) include:
- Hillas
- Adelong
- Tarcutta
- Gilmore–Sandy
- Talbingo–Jounama–Blowering
- Upper Tumut
- Goobarragandra
Information on stress ratings, extractions, primary risk factors and future risks are provided in Table 1. It is clear from these tabulated data that the hydrologic status of rivers across the Shire, in terms of environmental flows, is highly stressed.
The eleven inland River Flow Objectives (RFOs) include:
- protect pools in dry times
- protect natural low flows
- protect important rises in water levels
- maintain wetland and floodplain inundation
- maintain natural flow variability
- maintain natural rates of change of water levels
- mimic natural drying in temporary waterways
- manage groundwater for ecosystems
- minimise effects of weirs and other structures
- minimise effects of dams on water quality
- make water available for unforeseen events
The Interim River Flow Objectives (EPA 2000) provide further information as follows:
Town water supply subcatchments
- protect pools in dry times
- protect natural low flows
- manage groundwater for ecosystems
- minimise effects of weirs and other structures
- local factors to be considered within a catchment area in determining how best to protect pools in periods of no flow, to share low flows and to manage the catchment include:
- maintaining natural flows to springs;
- the needs of ecosystems and people within the area and downstream;
- reliability of town water supplies; and
- managing effects of land use on volumes and times of runoff, particularly in droughts.
- Protecting medium to high flows in streams feeding into the dam is essential for town water reliability and ecosystems health. This is not listed as an objective for priority action because it is currently being achieved.
Uncontrolled streams
For groundwater areas that feed into streams, are naturally shallow enough to supply trees or have rising watertables:
- manage groundwater for ecosystems
Streams affected by the Snowy Scheme
All eleven RFOs apply but no targets or priorities for action have been recommended until the separate State and Commonwealth Governments have decided on which changes will be made to flow diversions to or from streams affected by the Snowy Scheme.
This category applies to the Murrumbidgee above Burrinjuck Dam and the Tumut River above Blowering Dam. Diversions from the Murrumbidgee River reduce the flows available to share between the environment and extractive users downstream. Flows in the Tumut River have increased in volume and changed in variability Appropriate actions to manage flows in the upper Murrumbidgee will be determined as an outcome of the Snowy Water Inquiry.Action plans need to be further developed in the context of flow management decisions associated with the Snowy Water Inquiry for nominated reaches of the Upper Murrumbidgee, and Tumut Rivers (EPA, 2000).
Table 1. Summary of hydrologic stress and water use as a proportion of river flow for streams within Tumut Shire.
| Sub-catchment | Water extracted to 50th percentile (%) | Water extracted to 80th percentile (%) | Hydrologic stress | Primary stress factors | Future risk(s) |
|---|
| Present estimate | Full development estimate |
|---|
| Adelong | 40–49.9 | 80–89.9 | high | high | Horticultural development | Subcatchment is already subject to high extraction, current pressure to expand horticultural industry |
| Hillas | 10–19.9 | 30–39.9 | medium | high | Extraction | Full development scenario indicates potential for increase in hydrologic stress to warrant higher management category (S1) |
| Tarcutta | 10–19.9 | 30–39.9 | medium | high | Sediment slug and softwood development | Full development scenario indicates potential for increase in hydrologic stress to warrant higher management category (S1) |
| Gilmore/Sandy | | | unresolved | unresolved | Plantation areas | Modelled full water use development classification remains unresolved at this stage |
Bombowlee/Brungle/
Adjungbilly | | | unresolved | unresolved | | Modelled full water use development classification remains unresolved at this stage |
| Goobarragandra | 10–19.9 | 10–19.9 | | | Plantation forests, trout farm | Modelled full water use development does not indicate sufficient added extraction pressures to warrant higher full development management classification |
About the data
Data were obtained from the following sources:
- Environment Protection Authority of NSW (EPA) - website address: www.epa.nsw.gov.au/
- NSW Department of Land and Water Conservation (DLWC). 'Stressed Rivers Assessment Reports' for the following catchments: Bega; Murrumbidgee; Snowy/Genoa; Towamba and Tuross. The reports were published by the DLWC, in Sydney, 1999.
- Murrumbidgee Catchment Action plan (DLWC, 1998)
- State of the Rivers Report - Murrumbidgee Catchment, 1994-95 (DLWC).
Description: What does 'environmental flows' measure?
Which data are collected?
- number and proportion of waterways for which environmental flow guidelines have been established and are being met (expressed as 1st, 2nd, 3rd order streams)
Why do we report this indicator?
Environmental flows are the amount of water that is needed in streams (rivers, lakes and marshes) to meet the requirements of aquatic flora and fauna. Insufficient water, or water at the wrong time, can result in a loss of habitat, breeding failure and even death for some species.
The need for developing environmental flow guidelines has arisen as both rural and urban communities have developed and utilised the water resource. Establishing and meeting guidelines for environmental flows in the streams of the Australian Capital Region is necessary to prevent further decline in stream health.
Ideally all streams would have environmental flow guidelines. Until that occurs, the number and proportion of streams for which environmental flow guidelines have been established and are being met is an indicator of the response by our community to the threat to aquatic ecosystems caused by our use of the water.
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