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Water availability in Australia

The mouth of the Murray

Outcomes

By the end of this resource, students will understand:

  • the factors that influence water availability in Australia
  • the effects of limited water availability
  • management options for some water availability issues.

Curriculum focus

  • ACHGK039 The quantity and variability of Australia’s water resources compared with other continents
  • ACHGK040 The nature of water scarcity and ways of overcoming it, including studies drawn from Australia
  • ACHASSK190 The influence of environmental quality on the liveability of places.

How to use this resource

This resource builds on the MDBA’s ‘Influences on water cycles’ unit. Although it can be done separately, students will gain a greater insight if the two are used together as a unit of work.

Understanding of the Murray–Darling Basin’s climatic zones and size can be enhanced by viewing the Amazing Discovery video if this has not been covered through another MDBA unit.

Following on from this resource is the Water use and distribution unit. If the Influences on water cycles unit has been completed, step 1a below (engage with the topic) can be omitted, or used as review.

Preparation

  • The poster map of the Murray–Darling Basin (above) may be ordered in hardcopy in advance of the lesson.
  • Students need computers, access to Excel and the provided Excel spreadsheets.
  • Draw up the table at point 2 below on the board.
  • Print the student worksheets.

Engage with the topic

2.  Explore the following data and discuss the amount of water available for human use:

Type of water % of Earth’s water
Water vapour 0.001
Fresh – on the surface (rivers, lakes, swamps) 0.025
Fresh – under the ground 0.615
Fresh – frozen in icecaps, glaciers, snow 2.15
Salty - under the ground 0.93
Salty - oceans 97.2

3.  Discuss these interesting facts:

  • Two towns in the Meghalaya region of India are the world wettest places with over 11,000 mm of rain per year – almost all during the monsoon season between June and September.
    • In one year (Aug 1860 to July 1861), one of these towns (Cherrapunji) received 26,461mm!
  • South America is the wettest continent, averaging 933 mm/yr.
  • The driest continent is Antarctica (average of 166 mm/yr).
  • Australia (whole continent) receives an average of 419 mm/yr – making us the driest inhabited continent on Earth.

Explore the topic

 

4.  World discharge comparison

Have students investigate the following world river comparison data (see the Excel spreadsheet in downloads). Ask them to:

  • first create individual bar charts for Basin/river length or Basin/discharge etc.
  • then to Next, select columns A, C & E and create a clustered column graph (Insert > Recommended Charts > All charts)
  • format the Y-axis, changing the maximum to 100,000. (This will cut off the top of the Amazon bar, but that does not matter). 
  • use the chart tools Design > Quick Layout and select ‘Layout 7’ (this will also help make comparisons easier).

River basin

Area (km2)

Main river length (km)*

World length ranking*

Long-term average discharge (m3/second)

Amazon

7,000,000

6,750

1

209,000

Congo

3,680,000

4,667

9

41,200

Nile

3,400,000

6,695

2

2,830

Mississippi

3,200,000

3,734

4

16,792

Murray–Darling

1,059,000

2,508

15

400

St. Lawrence

1,030,000

3,058

25

16,800

Mekong

811,000

4,023

12

16,000

Danube

801,463

2,857

30

7,130

The result should look like this:

Ask the students to use the data/charts and the provided images and facts on their student worksheet and write their conclusions at point 1.

Students should conclude that although the Murray (which is connected to the Darling) is comparable in size to the Danube, and its catchment is bigger, its discharge is tiny (meaning it has very low flow for its size). The drainage area of the St. Lawrence in North America is about the same size as the Murray-Darling, but the St. Lawrence’s discharge is much (42 times) greater. The Murray/Darling have many more tributaries than the Nile, and though is 1/3 as long, its discharge is much less than 1/3 that of the Nile.

5.  Murray–Darling Basin catchments and rivers

If students have already completed the previous unit Influences on the water cycle, they have learned that 94% of Australia’s rainfall, on average, evaporates, drains into groundwater or is transpired by plants. We are now going to explore the remaining 6%.

The Murray–Darling Basin is a good case study for water availability in Australia because:

  • The south-eastern states hold around 66% of the population
  • It contains our three largest rivers
  • Its river system supplies water to around 3 million Australians 
  • It has the largest concentration of water storage and management structures (over 3,000)
  • It contains 40% of Australia’s farms, producing a large proportion of national revenue and food supply.

Discuss these interesting facts:

  • the Murray–Darling Basin is equivalent in size to France plus Spain (over 1,000,000 sq. km).
  • The Murray–Darling’s discharge does not even make Wikipedia’s top 139 ‘rivers by discharge’ list. One major reason for this is low rainfall:

River Basin

Area (Km2)

Average annual rainfall (mm)

Amazon

7,000,000

2300

Nile

3,400,000

650

Murray–Darling

1,059,000

471

Mekong (lowland portion)

811,000

1500

Then students work (in groups or individually) through the following activities and answer the corresponding questions on their worksheet.

Catchments and rivers of the Basin

Teaching notes Worksheet answers

Students investigate:

The MDBA’s Murray–Darling Basin map poster

The 23 catchments in the MDB

The Bureau of Meteorology’s rainfall map

The Bureau of Meteorology’s climate classification map

The Bureau of Meteorology’s Australian landscape water balance map

The Murray–Darling Basin is Australia’s largest water resource. The three largest rivers are interconnected, and are fed by many tributaries.

Each of these catchments contains a river that connects to either the Darling or the Murray Rivers.

The Murray–Darling river basin contains Australia’s three largest rivers – the Murray, Darling and Murrumbidgee. The Murray and Darling two join at Wentworth, NSW and then flow down through SA and out to sea at the Coorong (a Ramsar wetland).

The Basin’s river system is spoken about as ‘north’ or ‘south’ connected systems. This is because while many tributaries join on to the Darling, and the same for the Murray, the parts only connect to each other where these two mighty rivers join.

This remainder drains into the catchments and ends up in the Basin’s rivers – this is known as inflow. We measure with gauges – these measure how much water is flowing past that point on a river at any one time. 

At the point where a major river meets the sea (in this case the Murray) the water leaving the river system is called discharge.

Inflow is not the same in every river valley in the Basin (catchments). The Basin covers a number of climate zones from sub-tropical in the far north-east to semi-arid in the west and alpine in the far south-east.

Students discover this by reviewing the Bureau of Meteorology’s rainfall map and making predictions. (They can also click on the drop-down ‘Area’

Referring to the Basin map poster, the class could discuss why it is that most of the inflow comes from the Alps area in the bottom south-east corner of the Basin.
  1. The Nile delta is about 260 km wide; the Amazon delta is approx. 133 km wide, while the Murray outlet to the sea is only 0.26 km wide. Despite having 87 tributaries, and some of them quite long, the Murray doesn’t contain a lot of water. More advanced students may note that despite having a similar sized catchment area and length, the St. Lawrence has 42x the discharge of the Murray-Darling.

2a. The three largest rivers are the Darling, Murray and Murrumbidgee.

2b. They join at Wentworth, NSW.

2c. They flow out to sea via the Coorong estuary in South Australia.

  1. The students should predict that catchments containing or just downstream of higher altitude areas will have the most inflow, e.g. upper Murray, Mitta Mitta, Ovens, higher parts of the Murrumbidgee.
  2. The water flows from the high rainfall areas downhill. Considering where the tributaries to the Murray are on the Basin map poster, and where the mouth is (near Adelaide), the students should conclude western slopes of the Great Dividing Range in the south-east are likely to have more water. West of Mildura and Bourke rainfall is low, and there also are not many rivers, so there’s unlikely to be much water.
  3. Students should be able to explain where they were correct or incorrect.

Elaborate: understanding inflow variability

6.  Students create a one-year inflow graph

Using the provided Excel spreadsheet, ask students to create a River Murray inflows graph for 2013–14 and answer question 6 on their worksheet.

Advise students to use chart type ‘Combo’ – available in the 'All Charts' tab. They may need to be taught how to label chart axes or change default colours in Excel to better understand the data.

Their graph should look like this:

Note: 5-day average means each bar is the inflow for five days added, then divided by 5. The solid line gives an idea of what is ‘average’ over a much longer period (using about 115 years of data).

Worksheet answers:

  • 6.a. August, September.
  • 6.b. June, July, August, 1 Sept, Dec & April.
  • 6.c. January to April (4 months).
  • 6.d. A generally dry year with all flow months below average, except for August. A dry summer.

Conclude

7. Students interpret a longer-term (more than a century) inflow graph

Explain that on the Basin map poster the inflow graph (bottom left) shows inflow for more than a century. It is separated and shown as different shades of blue for the northern and southern parts of the Basin’s river system.

From this graph it can be seen that inflow goes up and down a lot over time (known as ‘highly variable annual inflow’). When it is down, we are in drought and this is a regular feature of the Basin’s climate. Drought occurs on average every decade and can last up to ten years (as seen during the recent 2000—2009 ‘Millennium’ drought).

Students answer question 7 on their worksheet.

Building on all their learning, students should be able to explain that people can’t rely on a steady amount of rain appearing in any one month or year. That there will be droughts and floods. More advanced students may mention that we must be able to store water against the dry times and make arrangements to prevent flooding – both purposes of dams. However, regardless of dams, if we use more water than we receive (and have stored) there will be water shortages – water is a finite resource.

Continue to Water use and distribution

Updated: 30 Aug 2018