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Snowy River Benchmarking and Environmental Flow Response Monitoring

Flow management

Joint government agreement on flow releases, Premiers Carr and Bracks with then chair Australian Conservation Foundation Peter Garrett, and independent MP Craig Ingram. Source: Teresa Rose, DNR

Three water storages were constructed on the Snowy River between 1955 and 1967 as part of the Snowy Mountains Scheme – an integrated water and hydro-electric power scheme in southern NSW. The Scheme collects and stores water from the Snowy River that would normally flow east to the coast and diverts it inland through trans-mountain tunnels and power stations. The water is then released into the Murray and Murrumbidgee Rivers for irrigation.

As a result of the scheme, the flow in the Snowy River below Jindabyne Dam was reduced to only 1% of the mean annual natural flow of the river severely impacting on the river and its ecology. In 2000 the NSW, Victorian and Commonwealth Governments agreed to return 21% of the natural flow to the Snowy River in stages over ten years (see Table 1) increasing to 28% depending on water savings in the Murray-Darling Basin. The first environmental flow was released in August 2002 bringing flows to 6% of natural.

Table1: Stages for release of environmental flows to the Snowy River

Stage	Timeframe for release	% of mean annual natural flow
1	1 st year	6
2	2 nd to 7 th year	15
3	8 th to 10 th year	21
4	> 10 years	28

Flow Response Monitoring

This project is one of the most comprehensive environmental monitoring programs in Australia. It will determine the changes attributable to the new flow regime across a range of river attributes (i.e. hydrology, water quality, geomorphology, riparian and littoral vegetation, macro–algae, aquatic macroinvertebrates and fish).

The program has been developed in two stages.

In 1997, the initial project was commissioned to assess the status of the "health" of the Snowy River, with the view of measuring changes in condition through time.
In 1999, the project was reviewed and the monitoring design improved to ensure that it guides the adaptive management of environmental flow releases. This is the current monitoring design.

The project is managed by the Department of Natural Resources South Coast Science Unit, but receives significant support from the Victorian Government, via the Department of Sustainability and Environment, and the NSW Premiers Department.

First flow release from the Mowamba Weir to the Snowy River, 28 August 2002. Source: Robyn Diamond

Project aims

Monitor the ecological effects of a more natural flow regime by quantitatively measuring appropriate environmental indicators; and,
Advise flow managers on the adequacy of the flow release regime to rehabilitate the ecology of the Snowy River.

Outline of monitoring design

The design for the monitoring program has the following components:

Hypothesis based (ie., specific flow related responses are defined);
Generally Before-After, Control–Impact (BACI monitoring design);
Snowy River test sites in NSW and Victoria (shown in Figure 1) compared with reference and control sites (defined in Table 2), and pre– Scheme data where available;
Test sites chosen within a spatial and temporal hierarchical framework; and
Habitat based sampling.

Figure 1.The Snowy River catchment and study sites.

Enlarge the Snowy River catchment and study sites image (1000px X 1413px)

Table 2. Definition of test, control and reference sites.

Test sites	Control sites	Reference sites
Sites in the Snowy River that will receive the environmental flow releases.	Sites that are impacted by flow regulation and will not receive an environmental flow release. A hydrological condition to move away from.	Sites that experience little or no flow regulation. A hydrological condition to aim towards.

Environmental attributes monitored

Hydrology

Impact of the Scheme

Flow records for the Snowy River at the Dalgety gauging station show that all aspects of the flow regime have been modified due to the operation of the Snowy Mountains Scheme.

There have been significant reductions in flow volume as shown in Figure 2. For example, the minimum summer base flow has been reduced to less than the 200 ML per day. Before the Scheme, base flows greater than 200 ML/d occurred 99% of the time, but now have a probability of occurring only 10% of the time.

The frequency of channel maintenance floods (greater than 20,000 ML/d) that naturally occurred around 80% of the time, now have a probability of occurring only 25% of the time, and the period between flood events is now much longer.

The frequency of habitat cleansing flushes (greater than 1,000 ML/d) that naturally occurred around 73% of the time now have a probability of occurring only around 3% of the time.

The flow regime of Australian rivers is naturally highly variable and the aquatic biota have adapted to this variability. Variability in the flow regime ensures that the various lifecycle requirements of biota are met. In the Snowy River, the daily flow variability has been greatly reduced. In particular, flows less than 2,667 ML/month have now become more constant. Additionally, the seasonal variability in flow has been lost as the large spring snowmelts are diverted by the Scheme.

Figure 2: Snowy River annual flow at Dalgetty

What's being measured?

The hydrology hypotheses are based on the expectation that the flow release regime in the Snowy River will become more similar to pre- Scheme hydrologic conditions, albeit smaller than natural. Continuous flow data are collected from telemetered gauging stations across the study area.

Water quality

Impact of the Scheme

The change in the flow regime in the Snowy River has resulted in changes to water quality in the Snowy River. Water temperatures are likely to have greater daily and seasonal variability than natural, and higher summer water temperature as a result of Jindabyne dam, because of the reduced baseflows and shallower habitats. Electrical conductivity (a measure of salinity), is likely to have increased in the Snowy River because of the reduced flows.

What's being measured?

The hypotheses are based on the expectation that environmental flows of greater than 21 % M.A.N.F will reduce daily and seasonal variability in water temperature, as well as lower summer water temperatures and higher winter temperatures from Jindabyne Dam. A decrease in electrical conductivity is also expected with environmental flow releases.

Water temperature and electrical conductivity are monitored at five sites on the Snowy River and five reference sites, either by continuous monitoring at telemetered sites or regular sampling with a multi–probe.

Sampling water temperature at the surface and bottom of pools with a multi-probe to assess thermal stratification. Source: Robyn Bevitt.

Geomorphology (physical characteristics of the river)

Impact of the Scheme

The change in the flow regime in the Snowy River has resulted in the following changes to the physical characteristics of the river:

greatly reduced channel size (as shown in the photo below);
pools in-filled with sand; and,
loss of physical habitat diversity.

Significant re–working of bed material and bank sediment at Sandy Point and Bete Bolong after the June 1998 flood has been recorded, but the larger events that re-work the river do not occur as frequently or as long as before the Scheme.

What's being measured?

The hypotheses for geomorphology are based on the expectations that the channel form will shift from contracting to expanding; the riffle pool sequence and the deeper channel will be re–defined; sediment will become coarser, and fines mobile; and, physical habitat will increase in diversity, quantity and quality. Surveys of permanent cross sections and long sections, particle size analysis of bed and bank sediments, and physical habitat mapping are undertaken.


Mapping the physical habitat. Source: Teresa Rose, DNR	The Snowy River from Jacks Lookout showing the greatly contracted channel.

Vegetation

Impact of the Scheme

The change in the flow regime in the Snowy River has resulted in the following changes to the riverine vegetation:

the vegetation has colonised much of the old river channel;
the lack of flow variability has likely favoured exotic species; and
vegetated chokes and submerged macrophytes as shown in the photos below are common in the Snowy River both typical of still to slow water habitats.

What's being measured?

The hypotheses for vegetation are based on the expectations that vegetated chokes will be removed, cover of submerged vegetation will be reduced, and species composition will change from weedy to native. GIS mapping from aerial photography of the river reach and species census is undertaken every 2 to 3 years, showing change in vegetation cover and relative abundance. Quadrat sampling of vegetation along transects across the river channel in autumn and spring shows change across the channel with change in geomorphology. Change in littoral vegetation (i.e. in pool and run habitats along the river edge) is determined by stratified random quadrat sampling in autumn and spring.


Typha (cumbungi) choking the Snowy River downstream of the Mowamba River (Site 1). Source: Teresa Rose, DNR	Overgrowth of aquatic plants, mostly weedy species, at the Snowy River downstream of Blackburn Creek (site 4). Source: Teresa Rose, DNR

Macro–algae

Impact of the Scheme

The changes to the riverine macro-algae as a result of the changed flow regime are not as obvious, but at present, the macro-algal flora of the Snowy River is characterised by many warm–adapted macro–algal species that are usually associated with low levels of velocity mediated disturbances. That is, the magnitude, duration and frequency of hydrological scouring and resetting of bio–films are reduced, thus favouring a smaller sub–set of the natural macro-algae flora of the river.

What's being measured?

The hypotheses for macro-algae are based on the expectations that macro-algae will move from warm to cool water species and cover will be reduced through scour. Macro-algae are being sampled in stratified random quadrats annually in autumn and spring in riffle and run habitats.


Macro–algae species Microspora floccosa characteristic of cooler waters. Source: Jason Sonneman.	Macro–algae sampling in 1 metre quadrats in the Snowy River . Source: Teresa Rose, DNR

Aquatic macroinvertebrates

Impact of the Scheme

The changes to the riverine macroinvertebrates as a result of the changed flow regime are not as obvious, but at present, the "water bugs" of the upper Snowy River are characterised by:

the macroinvertebrate fauna of pools and fast water habitats (riffles) in the Snowy River are different to those in the reference rivers (i.e. no dams);
sites in the Snowy River near the dam contain high number of macroinvertebrates typical of slow flowing or still water habitats (eg. worms, midge larvae, snails, mud–eyes), likely because of flow reduction and physical habitat alteration since the Scheme; and

What's being measured?

The hypotheses are based on the expectation that the macroinverterbate community composition of the Snowy River sites will become more similar to the reference sites following a substantial increase in all parts of the flow regime. Sampling is conducted quantitatively in pool and fast water habitats annually in spring and autumn using a suction sampler with identification of samples to family level.


Dragonfly larvae Austrogomphus ochraceus commonly known as “Mudeye” prefers slow water. Source: Peter Serov, DNR	Sampling macroinvertebrates with the suction sampling device at the Buchan River reference site (Site 26). Source: Robyn Bevitt, DNR

Fish

Impact of the Scheme

The changes to the riverine fish as a result of the changed flow regime are not as obvious, but at present, the fish species of the Snowy River are characterised by:

differences in fish species richness, abundance and community composition between the Snowy River and the reference sites, and above and below Snowy Falls;
native fish species richness and abundance increases in the Snowy River with increasing distance from the dam and greater inflows from tributaries; and,
introduced species abundance is relatively high for Snowy River sites above Snowy Falls compared to native species abundance and compared to the reference sites.

What's being measured?

The hypotheses are based on the expectations that native fish species richness and relative abundance will increase and population size structures will expand compared to the pre–flow release period, following an increase in all parts of the flow regime. Fish are sampled annually in summer, with sites above and below a major fish barrier (Snowy Falls). Other short term studies are also being undertaken to assess flow induced fish barriers in the Snowy River.


Native fish species Galaxias maculatus known as “common galaxias”. Source: Brett Mawbey, Tasmanian Inland Fisheries Service.	Fish sampling by electrofishing boat.Source: Robyn Bevitt, DNR

The future

The first stage post–environmental flow release data are currently being analysed to quantify changes in the Snowy River. Additional staged environmental releases will be monitored via this flow response monitoring project.

Future partnerships will be developed between DNR and other research organisations in order to address current knowledge gaps.

Results from this project will become increasingly important as staged flows are released, and guidance is sought from flow managers on the efficacy of the flow release regime to maximise ecological benefit to the Snowy River.

For more information, contact:

Simon Williams
Science Manager, South Coast
Department of Natural Resources
PO Box 867, Wollongong NSW 2520
Simon.Williams@dnr.nsw.gov.au

NSW Department of Natural Resources