Water security

This is about why and when infrastructure was built along the River Murray.

Students read the Student infrastructure history resource (see downloads) and view the video ‘A brief history of water use in the Murray–Darling Basin’. The soldier settlement scheme (see point 3 right) was introduced both to give ‘occupation’ to returning soldiers and also to provide a pool of people ‘willing’ to settle remote from the cities to expand agriculture (and economies). The student resource contains links to the National Museum of Australia with more information.

Re question 4: Higher river flow has changed from winter/spring (following natural rainfall cycle) to summer/autumn as water is stored then sent downriver from dams to support irrigation.

Re question 7: deeper knowledge may be demonstrated by answers ‘to supplement Hume dam’ or to ‘provide additional water for irrigation’. Question 11 is an assessment opportunity.

(If there is a less advanced group in the class, this is the more suitable activity for them.)

1. Alfred Deakin, George and William Chaffey.
2. Beat drought, grow more food, make land more productive or similar.
3. Soldier settlement – after WW1 and 2 returning soldiers given cheap loans/land in small holdings pushing into western New South Wales and Victoria. Must make ‘improvements’.
4. False – flow has changed from winter/spring (following natural rainfall cycle) to summer/autumn as water is sent downriver from dams to support irrigation.
5. The barrages were built to prevent salt water entering the lower lakes and to guarantee that these lakes would always be fresh (as a drinking and stock supply for Adelaide).
6. Murrumbidgee and Murray.
7. Dartmouth was built to ‘drought proof the Murray’.
8. 1 year.
9. Hume was 1% full (of capacity 3,005 GL), so there was about 30 GL of water remaining.
10. 6,200 GL / 500 = 13 Sydney harbours worth.
11. Answer should demonstrate awareness that irrigation demand can always outstrip storage if there is insufficient rain for a few years.

Here students are identifying the extent of area in Victoria managed by Goulburn–Murray Irrigation that is fed by water from the dams, where each of the 7 districts’ water comes from, and the different types of infrastructure to get it where it is needed.

Ideally, the interactive map (bottom) should be used, however it requires Flash. If this is not available, the top (static) map can be downloaded and printed.

They also investigate the New South Wales side of the River Murray (where the infrastructure is managed by Murray Irrigation Ltd.).

Students should discover just how extensive the dams, weirs, channels and pipeline network is, how the water gets to farms, and that it is also used for hydropower generation.

Note. Correctly identifying where the water for Torrumbarry weir comes from is more difficult, and can show evidence of more advanced research skills. Question 5 is an assessment opportunity.

1. 68,000 sq. km. area, 70% of Victoria’s water storage, 7 river basins.

2a. Central Goulburn – Goulburn weir and Lake Eildon (primary)

2b. Murray Valley – Yarrawonga weir and Hume dam (primary)

2c. Torrumbarry weir (pumped via National Channel) and Hume Dam primary.

3. Dartmouth, Lake William Hovell, Yarrawonga and Eildon.

4a. 326,618 ML

4b. 556,913 ML

4c. 535,621 ML

4d.i. stock grazing pasture – lucerne/cereals (166,286 ML)

4d.ii. cereals for grain or seed – wheat, oats, maize (129,558 ML)

4d.iii. grapes (51,850 ML)

4d.iiii. pastures for hay – wheat, oats, maize (33,830 ML).

4e. stock grazing (evidenced by lots of annual crops, Lucerne, stock feed). Grazing is firstly dryland and secondly irrigated.

5. Students should demonstrate evidence of understanding of dams holding water for the primary purpose of supplying it to farmers, water delivery (by private companies) from the dam passing along rivers (generating hydropower in some cases) then into irrigation networks that get ever smaller ending up on farms. A higher level of understanding could show water being ordered, water moving seasonally (mostly spring-summer), evidence of understanding water-hungry crops or land-use, or the highly-regulated nature of water in this part of the Murray–Darling Basin.

Give the students a printout of the Basin storage report for 22 April 2009.

Students need to understand the total storage capacity (22,256 gigalitres [GL]). Tell them that this is only for government-managed storages.

There is other water captured on farms and in private reservoirs, so the total storage capacity of the Basin is 23,162 GL* (if all the storages were full).

Discover that we can store all of the inflow most years.

*Bureau of Meteorology, 2016 National Water Account

Almost 3/4 of the total storage for the Basin is in the southern system (River Murray and tributaries).

Answers h. and i. are an assessment opportunity (for higher-level of understanding).

Activity 1

1. 22,256 GL
2. 16,294
3. Dartmouth (3433 GL); Hume (3005 GL); Eildon (3334 GL). Hume and Dartmouth are in Upper Murray (New South Wales) and Eildon in Goulburn catchment (Victoria).
4. Dartmouth 21%; Hume 2.1%; Eildon 12%.
5. 3,807 GL.

Activity 2

1. It is rarely ‘average’. Inflows are variable. It is quite likely to be ‘below average’, and we are likely to have much less than the average in storage.
2. We can store all of it in most years (except exceptionally wet).
3. Students should demonstrate understanding that an enormous amount of water can be captured in storages (44.5 Sydney harbours!), that current storages can already capture all the inflow in many years, and that unless it is unusually wet, we can use up most of the water that is stored in 1 year.
4. Students should show understanding that an additional dam would only fill in exceptional years (or would likely ‘rob Peter to pay Paul’ – holding water that would otherwise have filled another storage, or being used as a resource by other farmers, towns or the environment).

According to the ABS, water applied for irrigation in the MDB during the 2016–17 water year was 6,377,014 megalitres (6,377 GL). An additional 285,497 ML of water was taken from rivers and streams for agriculture (285.5 GL). In total 6,623 GL of water was used for agriculture in the Murray–Darling Basin.

The ‘all Australia’ usage was 9969 GL. Therefore 66% of all usage was in the MDB.

Total irrigation percentage (question b) = 6,377/9,104 = 70%

2016–17 was a very wet year, inflow was 14,800 GL.

2015–16 was, in contrast, very dry. Basin total inflows for 2015–16 were 3,040 GL.

In this year, total agricultural water use was 5,209.9 GL, and irrigation used 4,938.4 GL.

The amount of water allocated to farmers’ (and indeed the environments’) water ‘rights’ is a function of the amount in storage and rainfall. It is changed each year depending on conditions.

Answer 4 is an assessment opportunity.

1. 1. 67%
   2. 70%
   3. 43%
2. 4,938.4 GL
3. Students should demonstrate understanding that:
   • 2015 was a dry year
   • The storages were only about 20% full at the start
   • 5,560 GL (35%) more water was taken out than was ‘recharged’ from inflow
   • The year ended with less stored water than it started as a consequence.
4. Graph example shown below. Students should demonstrate understanding that actual inflow is not well represented by ‘long-term averages’. We cannot count on ‘average flows’. Regardless irrigation needs a certain amount of water. In low inflow years, this can be significantly above ‘sustainable’ levels. The amount used does vary though. (This is because of the water allocation system – see left.)