The clearing of native perennial vegetation for the development of agricultural systems based on annual crops and self-regenerating annual pastures is acknowledged as the primary cause of water logging and secondary salinisation of many of the cat chments in southern Australia, particularly in southwestern Australia. Estimates by McFarlane and Williamson (2002) put the current area of cleared land in Western Australia affected by water logging and salinity at about 1.8 million hectares, or 10% of the area cleared for agriculture. Across southern Australia the total area estimated by McFarlane and Williamson (2002) to be at risk from secondary salinity is about 15.5 million hectares