The nature of rivers
Rivers form when rain or melting snow runs down the side of a mountain to form streams. Eventually, streams catch more water or join other streams to form a river. Smaller streams that flow into rivers are called tributaries.
It can take millions of years for rivers to form. Rivers carve a path through the land as they pass from their headwaters (the place where a river starts) in the mountains to their mouth (the place where a river empties into the ocean).
Most Australian rivers are located near the coast. The largest and longest Australian rivers can be found in the eastern part of the country. They pass through various kinds of environment on their journey to the sea: mountain forests, wetlands, farmlands, and even cities and towns.
Many different animals live in and around Australian rivers. Fish, frogs, crayfish, mussels, platypuses, swans, ducks, pelicans, kangaroos, lizards, snakes and tortoises can all be found living in river environments.
The dry continent
Less than one-fifth of the rain that falls in Australia ends up in its rivers. Most of the rainwater evaporates, is used by trees and plants or, ends up in lakes, wetlands or the ocean. Because of this, Australian rivers have very irregular flow patterns. This means that sometimes a river is wider, deeper and faster flowing, and sometimes it is shallower, narrower and slower.
Use of rivers
Aboriginal people who lived along the banks of rivers used them for many purposes. They fished and hunted and ate the plants that grew in the area. The land beside the rivers was used as campsites. Rivers were also used for transport and recreation.
There is evidence of aboriginal use along the banks of many Australian rivers: burial sites, scarred trees whose bark was used to make canoes, and campsites.
The European settlers also used rivers as a transportation system. They used paddle steamers to transport people and essential supplies as settlements were established. Rivers were the inland highways of Australia until the introduction of railways in the 1850s.
Many Australian rivers have had their flows regulated with dams and weirs. This provides water for use in farming, industry and day-to-day urban living. This has affected the plants and wildlife that have evolved in response to the traditionally irregular flows of Australian rivers.
The introduction of European farming and water management techniques has had a dramatic effect on the Australian environment. Salinity is one of the most serious causes of water degradation facing Australia’s rivers today.
Another problem is that more water is being taken out of Australian rivers than is going into them. Because Australia is so dry, there is only a limited amount of water available. A river needs a certain amount of water to flow properly, to provide the right living conditions for animals and fish, and to provide enough water for plants.
Sediment and nutrients
The waters of Australian rivers are also being affected by the addition of certain substances, like sediment and nutrients.
Sediment occurs when dust and dirt resulting from erosion gets into the river water. Erosion is the natural wearing down of land caused by the weather. Removing trees and plants from an area can greatly increase the rate of erosion. So can grazing large numbers of animals like sheep and cows. More erosion means more sediment and rivers with high amounts of sediment can kill the plants and animals that live in them.
Nutrients are substances, such as fertilisers that are used on crops, that make plants grow quickly. Sometimes nutrients can leak into a river system. Sometimes when there are too many nutrients in a river, an algal bloom will occur. An algal bloom is a large growth of a kind of microscopic plant called algae. When the algae in algal blooms eventually dies it can kill the other kinds of plants and animals that live in the river.
Rivers of Australia
The Murray River and its main tributary, the Darling River, are the two main rivers in the Murray-Darling River Basin. A river basin is the area of land that surrounds a river and all of its tributaries, from the headwaters to the mouth. The Murray-Darling Basin measures over one million square kilometres, which is almost one-seventh of all the land in Australia. When measured from its source in Queensland to its mouth in South Australia, the Murray is over 2,500 kilometres long.
The first Europeans to encounter the Murray were Hamilton Hume and William Hovell, who explored the rivers west of the Great Dividing Range to see if they flowed into the ocean, or into a great inland sea. They named the river the Hume. But six years later, Captain Charles Sturt came upon the river and named it after Sir George Murray, not realising that it was the same river that Hume and Hovell had already named.
The Snowy River starts in the Australian Alps in New South Wales. It runs south until it reaches the ocean at Marlo in eastern Victoria. Along the way, it passes through the Snowy River National Park.
Only half of the Snowy’s water reaches the ocean. The other half is diverted by the Snowy Mountains Hydro-electric Scheme through a series of tunnels and pipes so that it flows into the Murray and Murrumbidgee rivers instead. This diverted water is used mainly for irrigation. As it flows toward the Murray and the Murrumbidgee, the water passes through a series of hydro-electric power stations, which generate electricity.
The Snowy River is probably Australia’s most famous river, known through Banjo Patterson’s poem The Man from Snowy River. The poem tells the story of a man whose skill as a horse-rider allows him to ride through mountainside country to recapture an escaped horse.
Murrumbidgee means ‘big river’ in the local Aboriginal language. It flows for over one and a half thousand kilometres through New South Wales, from the Australian Alps to the point where it enters the Murray River. This makes it one of the largest and most significant tributaries of the Murray.
The Murrumbidgee passes through the Riverina region of New South Wales, one of Australia’s most productive farming and agricultural areas. The farms in the Riverina area are reliant on the Murrumbidgee as a water source.
Other major river systems in Australia include the Fitzroy in Queensland, the Fitzroy, Ord and Swan Rivers in Western Australia, the Derwent and Tamar Rivers in Tasmania, and the Hawkesbury in New South Wales.