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
thumb|Headwaters of the Snowy River, with [[Mount Kosciuszko beyond]]
thumb|right|The Snowy River near Suggan Buggan, in Victoria, 2008
thumb|Snowy River mouth at [[Marlo, Victoria|Marlo in flood, 2012]]
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. 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. 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. 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. 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.
Large dams can essentially influence downstream water quality via two key mechanisms, either by poor water quality released from the waters of the dam itself and reduced mixing of the river water column attributable to lower water velocities leading to anoxic conditions at the bottom of deep river pools.
Influence of Jindabyne Dam on water quality
Possibly the main influence on downstream water quality from Jindabyne Dam, is the influence on water temperature. Dams have been shown to have an adverse impact on the water bugs of rivers.
Caenid mayflies (riffles) and oligochaete worms (pool edges) are generally typical of the upland regulated Snowy River. Other studies have also found greater densities of Caenidae mayflies in regulated rivers compared to unregulated rivers. Reduced high flows and constant low flows in the upper Snowy River are likely to have favoured high densities of worms through the buildup of silt and organic matter in the pools. Nichols et al. (2006) and Petts et al. (1993) also found greater densities of segmented worms associated with soft sediments and coarse organic debris in response to river regulation. Chironomids were also numerically dominant in riffles sampled in the regulated Snowy River. This response has been found in many other studies of regulated rivers and has been attributed to an increase of periphytic growth in riffles that increased overall habitat area and food availability.
Conoesucidae caddisflies (riffles), larval and adult elmids (riffles) and Oniscigastridae (pool edges) distinguished the snow melt rivers from regulated Snowy River. Marchant and Hehir (2002) reported that AUSRIVAS models (>50% probability) predicted Conoesucidae and elmids to be present in the upper Snowy River, but these taxa were not found in their study. The greater density of these taxa in snowmelt rivers compared the Snowy River is consistent with river regulation.
Marchant and Hehir attribute the absence of these taxa to dams acting as a barrier to drift and limiting recolonisation of these taxa and not to flow regulation.thumb|right|Exposed riverbed just south of the NSW/VIC border is a result of the reduction of the river's water flow by 99%
1950–1990s reduced water flow
The Snowy River originally had a huge, often destructive flow during the spring snow-melt which flowed directly into the sea. In the 1950s and 1960s, as part of the Snowy Mountains Scheme, a network of four dams (i.e. Guthega, Island Bend, Eucumebene and Jindabyne) and many smaller water diversion structures were built to collect and divert 99% (as measured at Jindabyne) of the Snowy River's flow through the mountains, to provide more water to the Murray and Murrumbidgee River agricultural basins for irrigation. Several hydro-electric power stations were also constructed to generate electricity. While there was initial public opposition to the diversion of the river's water during the 1950s and '60s, it was largely ignored as the scheme provided agriculture with more water. It generated a large number of jobs in construction initially, then in agriculture and logistics, and added permanent and reliable, on-demand electricity generation to two states.
1990s–2000: Increased awareness
By the 1990s, the reduced flows in the Snowy River became a major environmental concern in Victoria, New South Wales and across Australia. After the scheme was built downstream flows were insufficient to keep the channel clear of vegetation or move sediment in the stream bed. Salt water intrusion extended seven to ten kilometres up the estuary and outdoor recreational activities were curtailed along the lower reaches of the river. The key outcomes of the Snowy Water Inquiry was an initial agreement to increase environmental water releases to the Snowy River below Jindabyne by 15%