Why the Murray–Darling Basin matters The Basin is home to 2.2 million Australians, internationally significant wetlands, First Nations and is Australia’s food bowl.
Where is the Basin? Water in the Basin is managed across four states and a territory covering one million square kilometres.
How the Basin was formed The Basin is hundreds of millions years old, with landforms seen today taking shape over the last 60 million years.
Environmental importance The Murray–Darling Basin is home to a huge range of species, including many that are rare and endangered, and some that can only be found in Australia.
Plants and animals The rivers and lakes of the Basin support unique habitats critical to waterbirds, native fish, reptiles and protected wetlands.
Water for First Nations Water is vital to Australia’s First Nations and is essential for spiritual and cultural wellbeing.
Catchments Discover more about the Basin in your region by exploring the catchments in the Basin.
Infrastructure managed by the MDBA Dams, barrages and weirs in the River Murray regulate water flows and help deliver of water to communities, irrigators and the environment.
Water markets and trade Trade is vital for irrigators by allowing flexibility in response to water availability.
Why don't we close the Murray river mouth? The mouth of the River Murray is the only point in the Basin where the river system connects to the sea, creating a unique environment.
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Get involved Learn more about our current projects and contribute to our common goal of achieving a healthy working Basin for the benefit of the Australian community.
Webinars Learn more about water management and river operations by joining our regular webinars.
River reflections conference River reflections is an annual regional conference hosted by the MDBA. Learn more about the annual conference and how to attend.
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Regional community forums The MDBA has established 6 regional forums to represent local communities across the Basin. Find out more about a regional community forum near you.
The water cycle operates at different scales in different places. It is strongly influenced by location, temperature and topography. Australia is the driest inhabited continent on earth – and large parts of it are unsuitable for agriculture. The largest, most productive agricultural areas are in the south-east through a combination of suitable temperatures, rainfall, groundwater and soils.
These activities guide students as they investigate and discover which parts of the world, and of Australia, receive the most reliable rainfall. They also learn how much of the water becomes accessible, and predict issues this causes (see the next unit, availability of water).
Outcomes
By the end of this resource, students will:
understand factors that influence the water cycle in nature
understand that Australia has a limited and variable water supply.
Curriculum focus
ACSSU116 – Some of the Earth's resources are renewable, including water that cycles through the environment.
ACHGK037 – Classification of environmental resources and the forms that water takes as a resource
ACHGK038 – The way that flows of water connects places as it moves through the environment and the way this affects places
ACHGK039 – The quantity and variability of Australia's water resources compared with other continents
This animation shows 1 molecule of water completing the hydrologic cycle. Heat from the sun causes the molecule to evaporate from the ocean's surface. Once it evaporates, it is transported high in the atmosphere and condenses to form clouds. Clouds can move great distances and eventually the water molecule will fall as rain or snow. Ultimately, the water molecule arrives back where it started – at the ocean.
Do: Small groups of students each investigate and each produce a 5 minute presentation to the class on 1 of the 5 factors influencing water availability globally and in Australia: location, topography, seasonality, variability and evaporation. To assist them, the following questions (per topic) are provided on their worksheet.
Where is it most/least cloudy throughout the year?
Where is the most water in the atmosphere? Do they line up?
Where is it consistently hottest? Coldest?
What conclusions can you draw from all this data?
The dry regions are roughly at 30 degrees north or south of the equator. At these latitudes, there are belts of high pressure in the atmosphere. These are caused as trade winds collide and storms around the equator cause the air to rise very high and cool, causing most of the rain to fall nearby in the tropics. As the remaining drier air moves away from the equator and sinks it becomes denser and warmer. In these latitudes, winds may also be less strong and don’t blow as much moisture from the oceans onto land. The warm dry air at these latitudes then increases evaporation, which leaves the land underneath even drier.
Where are the highest mountains? The lowest areas? Why do you think Australia is so flat?
Compare Australia’s highest mountain to Mt Everest and some others in the world.
How do the topography and climate zones match up with the rainfall? (Is the rainfall higher in the tropics? Is it lower in the arid zones?)
What about rainfall on either side of a mountain range? Can you see areas where this is obvious?
Which zone do you live in?
Australia is a very flat country. Mt Everest is 8,846 metres. Europe's 10 highest mountains range between 4,545 and 5,642m. Our highest mountain is 2,228 m. This is because our mountains are much older and have eroded away.
Why does this matter? Because as rain-carrying winds cross land, they rise when encountering a mountain. As air rises, it cools. Cooler air condenses more easily, forming droplets (or if even colder, crystals). Note that most of this rain will fall on the 'catching' side of the mountain – the other side (rain shadow side) generally gets much less. Because our mountains are low, the air doesn’t rise, or cool, as much. There is more rainfall east of the Great Dividing Range (the west is in rain shadow).
In the south-east (where much of Australia’s population lives) west of the divide is the Murray–Darling Basin. 45% of all the water that runs into rivers comes from rain falling on just 11% of its land area)
Compare this effect in the north and in the south.
How likely is it that the area west of the Great Dividing Range in south-east Australia will receive rainfall above 300 mm in May to July?
What part of this area does get rainfall above 300 mm at any time during the year?
When and where do you think most rain falls in south-east Australia?
In the north (tropics) most rain is in summer, while in the south it is winter-spring. The tropics are around the widest part of the earth, and as the earth tilts, as it rotates the sun warms the area more in summer and less in winter. Along with the heat shifting, so does the tropical rain belt.
In the north and south of the earth (narrower) bits, this effect is intensified. The bits of land we are on are either hot, less hot, colder, or cold. In these zones, most rain forms as air rises and cools. So as we are so flat, this cooling is mostly only happening in the colder months.
In the south-east it’s rare to get rainfall above 300 mm. This is particularly so west of the Great Dividing Range, apart from the Alps (which is where most rain falls).
Which places have moderate to high soil moisture? (roughly)
How do things change year to year?
Looking at 2007, and west of the Great Dividing Range in the south-east, what could you say about conditions for growing things?
Look at Actual evapotranspiration. Click through the months of a year. When is it highest and lowest?
Thinking about Australia's places, what things do you think are adding to evaporation rates?
The combination of heat and flatness in Australia leads to very high evaporation.
Because our rivers are mostly travelling over fairly low topography, they move relatively slowly. This allows the heat of the sun to more easily suck up water.
The flat places west of the divide have lowest soil moisture, the tropics, coastal areas on the east and higher areas have more.
2007 was a drought year. In the Murray–Darling Basin (a major food growing area) there was very low soil moisture.
Evapotranspiration is highest in the hotter months.
In Australia on average, 94% of rainfall evaporates or is transpired by plants!
3. Elaborate
Do: Students analyse the following data (provided on their worksheet) and create a pie or bar chart.
Type of water
% of Earth’s water
Water vapour
0.001
Fresh – on the surface (rivers, lakes, swamps)
0.025
Fresh – under the ground
0.76
Fresh – frozen in icecaps, glaciers, snow
1.76
Salty – under the ground
0.93
Salty – oceans
96.54
Students can use Excel if available, and may need to adjust the x-axis scale to be easily able to determine the huge difference between ocean sources and all others.
Write: Students write their analysis of the data.
4. Conclude
In Australia, only 4% of annual rainfall (on average) becomes a water resource for people and nature. Because Australia is drier than many other countries, we have relatively low surface water reserves. About 17% of our fresh water reserves are under the ground, and in an average year, about 30% of our water is drawn from this source.
