Salinity Risk Mapping


South West Catchments Council (SWCC) engaged the services of Department of Agriculture and Food WA (DAFWA) to produce salinity guidelines to assist with the assessment of tree planting proposals for Carbon Farming Initiative (CFI) eligibility under the salinity guidelines (Department of Climate Change and Energy Efficiency-CFI Act 2011). DAFWA produced a series of salinity maps as part of the Resource Condition Report.

The full report “Salinity risk mapping for assessing Carbon Farming Initiative proposals: Decision support & data requirements” (DAFWA, 2014) can be found here.

The following data layers that can be displayed in the below map browser have been provided by DAFWA as a part of this report. Further information on each of the layers is provided below the browser.

 

Salinity Risk

To understand these layers, one should first appreciate the difference between salinity hazard and salinity risk.

Areas of salinity hazard are those for which the potential exists for salinity to occur, they are generally valley floors and other low-lying areas. Salinity hazard is intrinsic to many Australian landscapes. The hydrozones used by DAFWA to report salinity hazard and risk are based on soil-landscape zones, which are areas defined on landform and geological criteria that reflect state-scaled regions with similar hydrogeological and farming system attributes. The proportion of each of the hydrozones occupied by areas of salinity hazard depends on its physical characteristics (landform and hydrogeology).

Salinity risk combines the likelihood of a salinity hazard being realised and the consequence. Climate and land management as well as the intrinsic properties of the landscape influence salinity risk. This map shows the salinity risk to agricultural land based on the likelihood of the salt-affected area expanding beyond its current extent and the consequence of that expansion. The consequence is based on the actual area expected to be affected and the economic, environmental and social impacts of that expansion.

Dominant groundwater trends

Dryland salinity occurs when rising groundwater brings salts, stored deep in soil profiles, close to the ground surface where it interferes with plant growth. Groundwater trends, therefore, have a significant impact on whether areas of salinity hazard actually become salt-affected.

Time to hydrological equilibrium

The clearing of native vegetation caused a change in the water balance of the Australian landscape and recharge to groundwater increased. Groundwater levels will continue to rise until discharge balances the increased recharge and a new hydrological equilibrium is established. Groundwater discharge may be active, via flow to rivers, springs or the ocean; or passive, by evaporation from shallow water tables.

It’s the area of passive discharge that determines the salt-affected area. It may take many years after a new hydrological equilibrium is established for the areal extent of dryland salinity to reach a maximum because salts will continue to accumulate in the topsoil long after a shallow groundwater has reached equilibrium.

The time-frames used in this map of time to equilibrium are shown in the following table:

Category Time (years)
Short term <20
Medium term 20–75
Long term >75