Murray River

Factfile

Length: 2,508 km
Sources: Cowombat Flat
Key Tributaries: Darling, Murrumbidgee, Mitta Mitta, Ovens, Goulburn, Campaspe & Loddon
Basin area: 1.061 million km²

Located in Australia Spanning: New South Wales, Victoria & Southern Australia
population: 2 million
Discharge: 767 m³/s

Physical Geography

As Australia’s largest fluvial system the Murray River flows 2,508 km from its source on the Cowombat Flat of the Australian Alps westward to its mouth 10km southeast of Goolwa and 75 km SSE of Adelaide. The catchment area of the Murray River covers 1.061 million km² as such the system goes through many changes along the course in both regional climatic settings and also the geomorphological setting. As such below the overall setting of the Murray River will be analysed to develop an understanding of the physical setting of this fluvial system.

Formation/Geology

Following Australia’s separation from Antarctica around 85 million years ago, the Murray River Basin was formed by slowly subsiding over time. The Murray River Basin was then filled with 600 m of sediments approximately 65 million years ago during the Cenozoic Era. The Murray Basin was then inundated multiple times by the sea, before retreating, during the Paleocene and Eocene Epochs with the deposition of Warina sand, silt and the formation of clay throughout the basin. The mudstone and limestone that is found across the basin was formed later during the Miocene with the production of clay in the shallow waters, following a period of sea level rise. With sea level beginning to fall following the mid-Miocene the clays that were produced were deposited on top of the mudstone and limestone that had formed. Following on from the Miocene to the Pliocene, sea level continued to increase and decrease multiple times leading to the further deposition of sands, silts and the formation of clay and mudstone.

Preceding the formation of the underlying geology of the murray basin the region was dammed off as a result of 250 m of uplift in the Grampians around 2.5 million years ago forming a 40,000 km² waterbody called Lake Bungunnia. The Murray river then formed a channel to the sea draining the river, with the lake being gone approximately 0.7 million years ago.

The Murray River drains the majority of inland Victoria, New South Wales (NSW) and southern Queensland, however, the river itself has characteristics of an ephemeral fluvial system with no flow along its course during periods of extreme drought, which has been noted on 3 occasions. The upper course of the river is located in the mountains of NSW, Australia flowing through Mt. Pilot from the Cowombat Flat. The river flows west-northwest, passing through Hume Reservoir, acting as the natural boundary between NSW and Victoria. The river continues on this course until Morgan, South Australia where the river bends southward flowing through Lake Alexandria to Murray Mouth. Murray Mouth itself is a position that changes over time with the formation of a sandbar that encloses the region from the Southern Ocean. The mouth itself is located in a coastal dune system that extends for 145 km Goolwa in a Southeastern direction.

Geomorphology

Murray Darling Depression - The Murray River Basin itself is a geomorphological landform created over 85 million years with the region being a depression that was filled multiple times by coastal inundation. The basin is filled with a wide variety of different geology mixing both terrestrial and Marine sediments to form its current setting.

Cowombat flat - The mountainous region of the Upper Murray catchment provides the source of the Murray river located along the Cowombat Flat this region has been formed over millions of years with the Cowombat Flat itself being a small region of flat ground where the snow melt and precipitation of the region combines to form the headwaters of the Murray river

Murray Mouth - One of the most unique geomorphological landforms of the whole catchment with a 145 km coastal dune system providing a natural divide between the fluvial system of the Murray river and the Southern Ocean. The positioning of the mouth of the river changes as a result of erosion of the coastal dunes meaning that the coastal environment is in a constant state of change. In this location the dune system is divided into two with the western Sir Richard Peninsula, with a Spit that runs along the coast, and the easten Younghusband Peninsula.

Climate

The catchment area of the Murray river experiences a climate that can be compared to that of the mediterranian with hot,dry summers and mild winters, the basin itself is located in a semi-arid region with the northeast of the basin experiencing arid conditions. The average temperature during the catchments summer months is 28°C while the winter average reduces down to 15°C. In terms of precipitation the region is one of the most reliable rainfall regions in australia with a range in annual precipitation across the basin from 450 mm in the mid/lower to 800 mm in the upper course.

Ecosystems

As with much of Australia, the Murray River Basin contains a wide array of different species holding both a high biodiversity throughout the basin but also a high density of different flora and fauna species that support the natural function of the environment. Below the many different species of Flora and Fauna will be examined to provide an overview of the diverse life in this basin.

Flora

A key feature of the Murray river system is the expansive collection of different bioregions that consist of different assemblages of flora species, one of the most synonymous flora species of the Murray river basin is the Red Gum trees that can be located along the banks of the Murray river throughout its course. Below the different assemblages within the basin will be outlined showing the diverse species that make up the flora of the Murray Basin.

Floodplain woodlands - located in the northern and southern plains, as well as the floodplains of intermittent rivers of the western basin. These woodlands cover large areas of the floodplains and include flora species such as:

yapunyah
river willow
river cooba
silver wattle
burgan

Shrublands

Located in small areas along the floodplains and semi-arid regions of the catchment. The plants found in shrublands are generally adapted to hot, dry conditions, and grow in areas that are rarely inundated. Within this region there is a wide array of flora including:

nitre goosefoot
dillon bush
golden goosefoot
black roly poly
old man saltbush

Grasslands

Many species of native grasses have evolved or adapted to the different environments in the Basin.

Warrego grass, cane grass and curly Mitchell grass, found throughout the north and west of the Basin.
common reed (phragmites)
water couch & Rat tail couch
spiny mudgrass

Sedgeland & rushland

common spikerush
Cambungi

Fauna

Birds

There are 367 identified species in the basin including 35 endangered species and 98 waterbirds.

Waterbirds include:

Australasian painted snipe (endangered), black-winged stilts, grey teal, hardhead, hoary-headed grebe, little pied cormorant, royal spoonbill, sacred kingfisher, straw-necked ibis, white faced heron, white ibis, yellow-billed spoonbill.

Woodland birds include:

Brown treecreeper, Striated pardalote, Diamond dove, Sacred Kingfisher, Rufous whistler, Diamond firetail, grey crowned babbler, Regent parrot, Superb parrot and Yellow rosella.

Mammals

There are 85 mammalian species identified within the Murray basin however 16 of these are endangered with 20 species from this basin being extinct. The identified species include:

Easter Quolls, Grey Kangaroos, Red Kangaroos, Platypus, Sugar Gliders, wallabies, Koalas. Common ringtail possums, Black flying foxes, Wombats

Fish

There have been 50 native fish species identified along the course of the Murray river

Native fish species include:

Australian smelt, black bream, bony herring, congolli, freshwater catfish, golden perch, Lamprey, Macquarie perch, Murray cod, Murray–Darling rainbowfish, Murray hardyhead, olive perchlet, silver perch, spangled perch, purple-spotted gudgeon, trout cod

Non-native species include:

brown trout
carp
eastern gambusia
goldfish
oriental weatherloach
rainbow trout
redfin perch
roach
tilapia

Amphibians

31 native frog species have been identified in the basin.

Reptiles

There are 149 reptile species identified in the basin with 46 snake species, 100 lizard species and 3 freshwater turtle species.

Turtles (Eastern-snake necked turtle, River Murray short-necked turtle and Saw-shelled turtle
Snakes include tiger snakes, eastern browns and red-bellied black snakes
Lizards include blue tongue lizards, geckos, bearded dragons and earless dragons

Invertebrates

within the Murray catchment there have been 124 families of invertebrates identified.

Human Geography

The Murray river basin has been home to humans since the occupation of the lands of Australia, with very little impact occurring to the natural environment of the region until the European colonisation of the region. Following the introduction of Europeans to this region, the misuse of the land and the natural resources of this region began with unsustainable water usage practices and the exploitation of biota resources in the basin having a detrimental impact on the natural environment of the region.

Pollution

The pollution of the Murray river has many sources including industrial mining, agricultural practices, domestic sources and the salinisation of freshwater resources.

Agricultural activity within the basin has led to an increase in the amounts of pesticides, fertilisers as well as antibiotics entering the natural environment, creating a large threat to the natural environment of the Murray basin. This is combined with the overuse of water resources for the purposes of irrigation meaning that there is an increased concentration of these harmful products in the natural environment, increasing the risk of eutrophication within the basin.

This issues of the basin further exacerbated due to intrusion of naturally saline groundwater resources with the water being filtered through layers of ancient marine sediments and salts that were deposited during the formation of the region. This saline water is causing many problems throughout the catchment for agriculture, domestic and industrial processes throughout the basin presenting an issue for the sustainable usage of water resources through the catchment.

There are also other sources of pollution including that from domestic sources, such as littering that is introduced to the environment during storm events as a result of surface runoff or through direct deposition into the natural environment. This source of pollution increases the number of harmful micropollutants into the environment, including microplastics, that can have a detrimental effect not only on the Flora and Fauna of the basin but also humans, who source their drinking water from this system.

Climate Change

Climate change in the Murray basin is set to lead to increases in temperature while a reduction in the amount of precipitation in the region. This will put a major strain on both the natural environment that is supported by the flow of the Murray river but also those who live within the basin with a reduction in the available freshwater resources for drinking water as well as agriculture and industry throughout the basin. The changes to climatic variables such as temperature and precipitation also has the potential to increase both the frequency and magnitude of extreme events such as droughts that have a severe impact on the natural environment of the basin. As such, in order to reduce the impact of climate change on the region many adaptive processes need to occur to increase the sustainability of the region reducing the pressure that is placed on the environment by those who live within it.

Sea level rise as a result of anthropogenic climate change poses a threat to the river basin with an increase in sea level leading to the inundation of the coastal region of Murray mouth leading to the loss of an expansive coastal dune system while also increasing the salinisation of the Murray water resources. The inundation of Murray mouth would also potentially lead to the loss of one of Australia’s largest freshwater lakes, Lake Alexandria, that is located at the mouth of the Murray River.