In an average year, 2 million tonnes of salt flows down the Murray–Darling. It is important for the health of the Basin to flush out this salt. They are flushed out naturally through the mouth of the river. A closed river mouth means less salt is taken out from the Basin. Over the last decade the Murray Mouth has been closed for 4 of 10 years.
Having too much salt in the water in the Basin can:
- damage agricultural production
- affect the quality of drinking water
- increase costs for infrastructure and industry.
Increased river flows will ensure that the River Murray can export salt through its mouth 9 years out of 10.
Natural river flows
The Basin is important for biodiversity. It supports a large number of plants, animals and ecosystems.
The volume of water that flows through Basin rivers is naturally low and varies more than major international rivers. For example, the average annual volume of water flowing through the River Murray is less than the average daily flow of the Amazon River.
Low levels of rainfall, slow river flows and a flat landscape can cause high evaporation. It also means that storing water is more difficult.
Farmers, communities and governments in the Basin have made significant progress in using water more wisely. This includes changing to world-class irrigation practices and technology. However, too much water is being removed from the Basin's rivers, wetlands and floodplains. This has resulted in long-term environmental decline.
Natural river flows result in regular medium floods and seasonal dry periods. The system would flush during high flow periods. Low flow periods in summer support other important environmental processes.
Development in the Basin has reduced these natural changes stream flows. For example, development has meant that some areas did not go through the small to medium floods as often as they should.
Both the reduced availability of water and changes to river flow has resulted in environmental decline. This has caused:
- lower numbers of native birds and fish
- an increase in algal blooms
- reduction in pollination
- reduction in fish breeding
- reduction in nutrient recycling and replenishment of soils.
For example, during the last drought the Basin experienced the world's largest recorded outbreak of acid sulfate soils.
Restoring regular flows to the Basin will improve its environmental health. It will also deliver benefits economic and social benefits to all users.