The Snowy River (Douriango in the Ngarigo language) is a major river in south-eastern Australia. It originates on the slopes of Mount Kosciuszko, Australia's highest mainland peak, draining the eastern slopes of the Snowy Mountains in New South Wales, before flowing through the Alpine National Park and the Snowy River National Park in Victoria and emptying into Bass Strait.
While the river's course and surroundings have remained almost entirely unchanged, the majority of it being protected by the Snowy River National Park, its flow was drastically reduced in the mid-20th century, to less than 1% (as measured at Jindabyne), after the construction of four large dams (Guthega, Island Bend, Eucumbene, and Jindabyne) and many smaller diversion structures in its headwaters in New South Wales, as part of the Snowy Mountains Scheme.
The river has been immortalised in cultural folklore through the poem The Man from Snowy River, written by Banjo Paterson in 1890, which formed the basis of many subsequent works in film, TV and music theatre.
Geography
The main headwaters of the Snowy River, which include the Eucumbene, Gungarlin and Thredbo rivers and many smaller alpine watercourses, are predominantly located in Kosciuszko National Park and meet near Jindabyne. From this point, the river winds southwards through inaccessible country, comprising private lands and the Snowy River National Park, eventually reaching the sea in the Snowy Inlet, at Marlo, near Orbost.
In New South Wales, the river runs through the Snowy Monaro Regional Council. The tributaries of the Snowy River below Jindabyne include: the Mowamba, Wullwye Creek, Maclaughlin, Delegate, Jacobs, Pinch, Suggan Buggan, Deddick, Buchan, Rodger and Brodribb rivers. At a pinch point named Hutchings pass, water flows uphill.
In 1986, Jennings and Mabbutt mapped four geomorphic classes in the Snowy River Basin; (i) Australian Alps; (ii) the Monaro Tablelands; (iii) the East Victorian Uplands and (iv) the Gippsland Plains. Each class is physically distinct from the others.
Rainfall The general distribution of rainfall over the Snowy River drainage basin (catchment) is controlled by orographic effects. There is a strong rainfall gradient across the basin.
The highest average annual rainfall is recorded in the higher alpine reaches of the Snowy Catchment, with recorded in areas above . The lowest average rainfall is recorded in the rain shadow affected north eastern catchment on the Monaro Plains around Dalgety, with average rain below . The lower eastern sub-catchments are more strongly influenced by coastal rainfall patterns. For example, peak rainfall in the Delegate catchment is strongly influenced by east coast lows, rather than the alpine dominated precipitation patterns in the upper Snowy River catchment. These local variations in rainfall result in distinctly different hydrology in the rivers across the Snowy River catchment.
Hydrology The snow melt derived rivers in the Snowy Mountains typically have the lowest average stream flow in the months from November to June, with October having the largest monthly flows of the year, e.g., mean monthly flow for October at Dalgety was prior to the Snowy Scheme. The large flows in September and October are derived from snowmelt and hydrologically it is one of the key aspects that defines these mountain waterways. Typically, Australian rivers can be defined as having highly variable river flows, with frequent zero flows even in humid areas, due to the extreme age of soils and consequent extremely high water absorption, which allows plants to absorb minimal phosphorus via proteoid and similar root types. The mixed snowmelt-rainfall rivers of the Snowy Mountains can be defined by strong seasonal patterns and remain permanent throughout the year, with no record of zero flow ever observed in the Lower Snowy. Prolonged base flows over the summer months are another feature of these types of rivers, driven by snowmelt derived groundwater.
In the lower reaches of the Snowy River catchment, the larger tributaries have a flow regime that is distinctly different from the snowmelt rivers of the Alps. These tributaries are typically dominated by the winter rainfall and often have peak monthly flows a few months earlier than the snow melt tributaries. The peak monthly flows for these lower Snowy River tributaries occur in June through July. Additionally, the flow regime in the lower tributaries is far more variable and unpredictable.
Waterfalls The Snowy River below Jindabyne Dam contains four major waterfalls; Stone Bridge Falls, Corrowong Falls, Snowy Falls and Pinch Falls. Potentially, many of these waterfalls act as barriers for the large scale movement of aquatic species in the main stem of the Snowy River. The flows required to drown out the largest barrier, Snowy Falls, are potentially larger than the environmental water releases to the river via Jindabyne Dam.
Parklands and protected areas Around 70–80% of the Snowy River's length is protected by national parks, these include, from upstream to downstream: Kosciuszko National Park — New South Wales Alpine National Park — Victoria Snowy River National Park — Victoria
River ecology The aquatic flora and fauna of the snowy mountain snow melt rivers have evolved with the predictable seasonal hydrological snow melt peaks and constant summer base flow conditions. Many of these flora and fauna are coldwater specialists.
River habitat The instream habitat of the Snowy River below Jindabyne has changed.Seddon, G. S. 1999. Saving the throwaway river. Australian Geographical Studies, 37(3), 314–321 Many of the in-stream features of a large upland river are not evident today. The substrate was previously typified by a clean cobble stone substrate. Today, the river channel has contracted and the substrate has a heavy cover of sediment, overlying much of the cobble stone riverbed.
The bushfires of 2002–03 added to this problem, as large amounts of sediment and organic matter were deposited in the river via tributary inflows. This input of sediment lead to the substrate becoming finer.Rose T. (2010) Geomorphic changes in the Snowy River following the stage environmental release. Snowy River Flow Response Monitoring and Modelling. NSW Office of Water This pattern of increased silt in the pools of rivers and streams has been observed across the Snowy Mountains following the bushfires. These bushfires are likely to have a long lasting influence on these waterways.
Larger events are required to start to improve the condition of the river bed. Events of per day will start to move the unconsolidated fine particles of the riverbed.Reinfelds I. and Williams, S. (2008). Hydraulic modelling to estimate threshold discharges for sediment entrainment in the Snowy River, Australia. Snowy River Recovery: Snowy River Flow Response Monitoring, NSW Department of Water and Energy Events between per day are important for conditioning the riffle habitats (i.e., a type of flowing water habitat).
The current poor condition of the river bed is one of the key factors inhibiting the aquatic fauna typical in a snow melt river.
Water quality The mountain streams and rivers are typically low in nutrients and electrical conductivity. Conductivity is generally below 50 μS/cm.Bowling, L., Acaba, Z. and Whalley, P. (1993) Water quality in the Snowy River catchment area, 1992/93. Technical Services Division, NSW Department of Water Resources, December 1993Bevitt, R. and Jones H. (2008). Water quality in the Snowy River before and after the first environmental flow release from the Mowamba River. Snowy River Flow Response Monitoring. NSW Department of Water and Energy. Sydney, NSW
Large dams can essentially influence downstream water quality via two key mechanisms, either by poor water quality released from the waters of the dam itselfGrowns, I., Reinfelds, I., Williams, S., and Coade, G. (2009).Longitudinal effects of a water supply reservoir (Tallowa Dam) on downstream water quality, substrate and riffle macroinvertebrate assemblages in the Shoalhaven River, Australia. Marine and Freshwater Research 60, 594–606 and reduced mixing of the river water column attributable to lower water velocities leading to anoxic conditions at the bottom of deep river pools.Turner, L. and Erskine, W. D. (2005) Variability in the development, persistence and breakdown of thermal, oxygen and salt stratification on regulated rivers of Southeastern Australia. River Res. Applic. 21: 151–168
Influence of Jindabyne Dam on water quality Possibly the main influence on downstream water quality from Jindabyne Dam, is the influence on water temperature. Unlike many other dams where coldwater pollution is a concern, where water is released from the below the thermocline in the reservoir (i.e. the bottom water of the lake), the water is released from the surface waters of Lake Jindabyne. The water temperature of the Snowy River downstream can reach temperatures of in summer.
The Snowy River is on average 4 °C (7 °F) warmer than the surrounding unregulated snow melt rivers, with a peak difference of up to 8 °C (14 °F). The water temperature in spring appears to be the greatly warmer than the surrounding snow melt rivers.
Thermal stratification Thermal stratification in the river reaches below Jindabyne is typically restricted to a few of the larger or deeper pools. In general thermal stratification is spatially restricted to the pools that are typically greater than deep. Pools shallower than have not displayed any thermal stratification.
Stratification can occur between October and March, but typically does not persist for very long in the Snowy River in the Jindabyne Gorge. Breakdown of thermal stratification is frequently driven by the cooling overnight air temperature. This region experiences a very large temperature range between day and night (i.e. diurnal temperature range).
Algae Algae is present in the water column and on the bed of the Snowy River. The water column algae is called phytoplankton, whereas the riverbed algae is defined as periphyton (attached algae).
Riverbed algae Much of the bed of the Snowy River below Jindabyne contains high levels of attached algae. These taxa are typically filamentous algae. In the snowy mountains rivers unaffected by water diversions, large stands of filamentous algae are uncommon.
Water column algae During 2008–09, the river pools of Jindabyne Gorge and the Dalgety uplands were typically dominated by blue green algae. Two blue green algae Aphanotheca spp. and Aphanocaspa spp. comprise about 25% of the total abundance. However, these abundances are still under the guidelines and its unclear if this is solely related to river regulation, but also reflects other catchment inputs.
The composition of algae in the free flowing snow melt rivers are typically defined by diatoms. Over 58% of taxa are diatoms, with Fragilaria spp. being the most numerically abundant taxa.
Water bugs The water bugs in the Snowy River differ from the bugs of the snowmelt rivers.Brooks, A., Russell, M. and Bevitt, R. (2007). Response to aquatic macroinvertebrates to the first environmental flow regime in the Snowy River. Snowy River Recovery: Snowy River Flow Response Monitoring, NSW Department of Water and Energy. Dams have been shown to have an adverse impact on the water bugs of rivers.Marchant R. and Hehir G. (2002). The use of AUSRIVAS predictive models to assess the response of lotic macroinvertebrates to dams in south-east Australia. Freshwater Biology 47, 1033–1050.