Thresholds Database > Dryland salinity, south-western Western Australia

Background

It has been estimated that salt, carried in rainfall has been deposited in the Western Australian soil over a period of 7000 to 13000 years and stored in the groundwater and the underlying regolith. The deep-rooted native perennial trees and shrubs prior to European settlement would use the groundwater throughout the year keeping the groundwater-table at depth.

Alternate Regimes

1. Productive, non-saline soils with deep-rooted perennial vegetation,

2. Unproductive salt and waterlogged soils with shallow-rooted vegetation.

Mechanism

Since European settlement, much the native perennial vegetation was replaced by shallow-rooted, annual agricultural plants which transpire only in winter and spring and whose root system is too shallow to intercept the water-table (Clarke, 2002). This reduction in evapotranspiration has led to the water-table rising, bringing the stored salt to the surface.



A threshold occurs in relation to the level of clearing of the deep-rooted native vegetation, particularly in the upper catchment, before the water-table rises to the point where the water and salt are carried to the surface via capillary action. The position of the threshold varies with soil type.

Management Decisions in Each Regime

State 1:

Early 1900s - Low gold prices and the need for an alternative export income fuelled land release for wheat farming (Beresford et al 2001).

1910s - The Commonwealth/State Soldier Settlement Agreement purchased land for over 5,000 soldiers returning from WW1. The railways were extended and cheap land and cheap loans were made available to others.

1920s - expenditure on railways and agricultural expansion accounted for approximately 60% of State Government expenditure. The link between salinity and land clearing was established (Wood 1924) yet despite criticism from scientific experts, The Group settlement scheme was established to attract British settlers, giving them 160 acres with bush cleared and 10 shillings a day.

1950s - Despite salinity problems occurring in many regions, the War Service Settlement Scheme (following WW2) provided farms to soldiers returning from WW2, two thirds of the bush cleared, a house, shed, dams, water tanks, fencing and crops sown.

1960s - New Farm Lands and Million Acres a Year schemes.

1970's - Crash in wheat prices limited further expansion.



State 2:

1970s - Establishment of the Environmental Protection Authority. From 1979, a licence was required to clear land.

1980s - More land released to appease farmers

2000s - Salinity Strategy released, money made available, largely to landholders to address salinity problems.
Funding by the Federal and State government made available to tackle salinity in Australia. In areas not yet crusted with salt, trials were conducted where rows of trees were interspersed with agriculture (Clarke 2002), and investigations into deep-rooted pastures and the use of pumps and drains to physically lower the water table.