Models calculate the volume of water that can be sustainably taken from Victorian waterways

Clean and clear river water showing reeds

Image credit: Department of Environment, Land, Water and Planning (DELWP)

The Murray-Darling Basin Plan requires Water Resource Plans to set out the method for determining how much water can be taken from northern Victorian rivers and waterways every year while keeping the rivers and environment healthy.

This is called the 'permitted take'.

The permitted take differs from year to year because it depends on how much water is available and the weather conditions that affect how much water we need.

Without measuring and limiting the amount of water taken from our waterways, water use will continue to increase, and there wouldn't be enough left for the environment. This is the problem that the Murray Darling Basin Plan was created to address.

The question becomes: how much should we be taking from our rivers?

Models help us to answer that question.

First, they consider the weather over the past year and how much water was available to users. Then, they calculate what the sustainable level of use would have been under those weather conditions. This includes the water demands of farms, industries and towns. Finally, the total volume that is used in the model for that year is the permitted take – that is, how much water could be used or diverted away from the waterway at a sustainable level.

This modelled number is then compared with the amount of water that was actually used.

Ultimately, these calculations allow Victoria to track how much water we use over the long-term relative to the sustainable diversion limits.

When assessed as an average over the long-term, the permitted take is referred to as a 'Sustainable Diversion Limit' or 'SDL'. And SDLs are the keyway the Murray-Darling Basin Plan limiting the amount of water taken from waterways, ensuring enough water is left in the system for the environment.

This is the power of hydrological models. Without them, we simply wouldn't have as accurately and clearly understand where our water goes and how much is diverted away from our waterways.

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Page last updated: 05/05/22