During the early establishment of the Mallee region, irrigation, and agricultural practises like land clearing and flood irrigation, led to excess water draining beyond the root zone of crops and causing a rise in groundwater levels, creating groundwater mounds.
This agricultural development, paired with things like high evaporation rates and free draining soils, means in the Mallee most groundwater systems are as salty as seawater. In short, salinity affects production in crops, pastures, and trees by interfering with nitrogen uptake, reducing growth and stopping plant reproduction.
An increase in salinity levels found in groundwater, rivers, and waterways can have a detrimental impact on irrigated crops, town water supplies and infrastructure such as hot water systems and evaporative coolers.
The Mallee Region is a wind-driven landscape and lacks the surface drainage that other areas might have, meaning it’s important to monitor and manage salinity levels found in groundwater and our rivers, and waterways.
Since the 1990’s, irrigation induced salinity has been managed through the modernisation and implementation of efficient irrigation practices, and the development of groundwater salinity catchment systems to divert salt to inland catchment areas for harvest and disposal.
These mitigating processes have been made possible by the introduction of the Salinity Impact Zone levies linked to irrigation development in the Nyah to SA Border region of Victoria post 1994.
Since then, improvements in the salinity levels in the Murray River have been reported, however salt remains in floodplains and drainage basins.
There has also been a significant increase in irrigation development since 1994, meaning there’s a large area of land that we need to expand our monitoring program for.
Like many other irrigated areas, the Mallee region contains saline aquifers beneath the surface of the land. Saline aquifers are made up of porous rock formations, that contain saline dense water as salty as the sea.
These aquifers can be connected to the Murray River and its floodplains throughout the Mallee region, so when additional water is applied to the surface – whether through rain events or irrigation practices – the water enters the aquifer from above and pushes the saline groundwater out into low lying areas such as rivers and floodplains.
Increase in river salinity is costly to both agriculture, and the environment in the local and downstream areas. That’s why managing the impacts of salinity is crucial to the long-term sustainability of irrigation in the region.
Mallee Catchment Management Authority (Mallee CMA) is responsible for managing salinity throughout the Mallee region as part of our regulatory obligation under the Basin Salinity Management 2030 Strategy.
Mallee CMA’s role is to identify, implement and manage salinity impacts through delivering on Victoria’s Sustainable Irrigation Program and identified mitigation programs and procedures in the Salinity Management Framework.
While Mallee CMA continues to implement mitigation processes from earlier salinity management models such as the Victorian Mallee Irrigation Region Land and Water Management Plan, the threat remains.
Highly saline groundwater is still prevalent above river levels and other low spots in the landscape, continuing to drive groundwater and salt towards the river, floodplains and wetlands, which continues to present a risk of causing ecological impacts to water quality and agricultural productivity.
The first step in effectively managing salinity is gaining a clear insight into the salinity levels in our groundwater, river systems, and floodplains.
Airborne Electromagnetic Surveying, or AEM, is an accurate and cost-effective way to determine the levels of salinity in specific areas of concern, and to collect the necessary data to inform ways to better manage salinity.
AEM, as opposed to ground drilling, is a non-invasive way to gain insight into the salinity levels. The AEM system, consists of a transmitter and receiver coil suspended from a low-flying helicopter, providing vital information on salinity in riverbeds, soil, floodplains, and groundwater. The information obtained through a groundwater modelling survey such as an AEM, can inform management of salinity throughout regions like the Mallee.
Since 1988 the States of New South Wales, Victoria and South Australia, together with the Australian Government, have funded the construction of salt interception schemes. These schemes prevent approximately half a million tonnes of salt per year from reaching the River Murray.
Salt interception schemes are large-scale pumping schemes that divert saline groundwater and drainage water before entering rivers. In most cases, a bore and pump system extract the groundwater and pumps it to a salt management basin some distance from the river.
Salt interception schemes, together with other actions such as improved irrigation practices and river dilution flows, have reduced the salinity in the River Murray by approximately 200 EC per year at Morgan in South Australia.
Salinity has been noted as one of Victoria’s greatest environmental threats and an ongoing problem for the Murray River that could take generations to fix.
In the 1990’s a plan was developed to improve irrigation practises that would offset the impact of irrigation on salinity levels and in the generation since we’ve seen the modernisation and sophistication of irrigation methods improve dramatically to align with best practise models.
Salt inception schemes have been implemented, capturing saline groundwater before it enters the Murray River and divert it inland for harvesting and disposal.
Since the last salinity survey was conducted, the irrigation and agricultural area has expanded by 42%.