GEOS2105: THE GEOGRAPHY OF AUSTRALIA

WATER RESOURCES IN THE MURRAY‐DARLING BASIN (MDB)

Objectives:

1. To gain an understanding of the main drivers of water use in the MDB and the impacts of over allocation of water resources;

2. Recognise the changes to seasonal flows in SW and SE Australia as attributed to flow diversions;

3. Become familiar with some of the strategies which are associated with restoring connectivity between the river and the floodplain and why this is important.

Weekly Questions for Workbook 2

1. Using Figure 1 and thinking about the water uses within the basin over the last 100 years (agriculture, dams etc.):

a. How the seasonal flow regime in SW Australia has shifted from its natural condition (2 marks) (2 sentences);

b. Name at least 2 benefits and 2 negative aspects of this changed flow regime and describe why they have a positive or negative impact (1‐2 sentences for each idea) (4 marks).

2. Outline in 2‐3 sentences, 1 major shortcoming and 1 major benefit of using environmental watering strategies to temporarily restore connectivity to the floodplain (5 marks)

3. What form. of agriculture and/or horticulture do you believe has the most impact on the MDB in terms of the amount of water used to ensure productivity? (3 marks)

Introduction

The Murray‐Darling Basin (MDB) is the catchment of two major rivers in SE Australia: the Murray and the Darling Rivers. The MDB drains approximately 14 % of the Australian landmass and is a very important region for agriculture and horticulture. As the MDB experiences high inter annual variability in rainfall and river flow and is considered a semi‐arid region in some parts, human modification of natural flows and fluvial setting can have a widespread effect. For instance, as a lot of flow is diverted through dams, weirs and taken out for crop and pasture irrigation, the environmental flows of the river have decreased greatly from their pre‐European levels over the last 100 years. The over allocation of water resources within the MDB has detrimental effects on ecology and biodiversity as well as presenting an ongoing challenge for future management.

Instructions

Dams and water diversions play a large role in altering the natural hydrology of rivers. In SE and SW Australia, rivers typically experience peak flows occurring in winter and spring, dams however can change this seasonal flow regime and shift it to a different state. This is evident on the Murray and Darling Rivers due to the occurrence of multiple dams and weirs along stream.

1. Using Figure 1 and thinking about the water uses within the basin over the last 100 years (agriculture, dams etc.) describe in 1 paragraph:

a. How the seasonal flow regime in SW Australia has shifted from its natural condition;

b. Name at least 2 benefits of this changed flow regime and 2 negative aspects and describe why this is so in 1 ‐ 2 sentences for each idea.

Figure 1: Modelled median monthly flow volumes (in GL) immediately downstream of Yarrawonga weir (Yarrawonga weir is located by Albury, Southern NSW) on the Murray River under natural and 1988 development conditions (www.dpi.nsw.gov.au).

Environmental Watering

‘Environmental Watering’ (shown in Figure 2) is used as management option to restore connectivity between the floodplain and river. Environmental watering involves pumping water from the river onto the floodplain and letting it then move naturally through the water table and back to the river over time. This is important as due to the current high amount of water diversions, flow from the rivers ‐ even during floods ‐ cannot now reach a level to inundate the floodplain for a prolonged period of time. This strategy is required to ensure that riparian vegetation and wetland/floodplain habitats have sufficient flow and do not dry out and die. Pumping can however require millions of dollars to set in place, takes many weeks to deliver the required amount of flow onto the floodplain, and also diverts that water from the river. Ideally the pump would use the natural elevation or siphoning as a process to deliver flow, but often times, pumps and generators are needed to delivery sufficient flow.

Figure 2: Environmental watering of the Murray floodplain near Swan Hill, Victoria (abc.news).

2. Outline in a short paragraph 2 major shortcomings of using the environmental watering strategy to temporarily restore connectivity to the floodplain.

Agricultural and horticultural (crops) land use is extremely prevalent in the MDB and some forms of land use are more widespread than others (Figure 3; 4). In turn, some forms of land use tend to use more water (Figure 5) than others and deliver less or more returns per unit of water used.

3. Using the data in Figures 3 ‐ 5 to back up your ideas, what form. of agriculture and/or horticulture do you believe has the most impact on the MDB in terms of the amount of water used to ensure productivity?

4. What are some strategies that may be used to reduce this amount of water use for this sector? (not assessed but something to think about)

NB. You can read more about the MDB Plan here:

https://www.mdba.gov.au/water-management/basin-plan

Figure 3: Percentage of revenue per agricultural land use in the MDB (MDBA, 2005).

Figure 4: Extent of land use in the MDB (MDBA, 2005).

Figure 5: The amount of water used by different irrigators and return per mega litre of water used.