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Logging in the Thompson Catchment

logging of thompson

Logging is having a dramatic effect on our domestic water supply - but the only people paying for it are the tax payers.

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The Thomson Reservoir is situated along the eastern escarpments of Mount Baw Baw and carries approximately 60 percent of Melbourne’s water storage capacity (Howe et al 2005). It is surrounded by 48,700 hectares of forested catchment that includes the northern and eastern slopes of Mount Baw Baw, the southern slopes of Mount Matlock on the Great Dividing Range and the western slopes of the Aberfeldy Range.

After clear fell logging water run off is reduced by up to 50% and does not return to pre logged volumes for up to 150 years

kuczera curve

The Thomson is the largest of four major water supply catchments for Melbourne, with the others being Maroondah, Upper Yarra and O’Shannassy. All are located within the Central Highlands of Victoria (Howe et al 2005). The Thomson is a major water supply catchment upon which logging is permitted. The forest industry considers the Mountain Ash, Alpine Ash and Shining Gum forests within the catchment as highly valuable for timber and pulp and targets these for logging. These forests cover 33.5 percent of the Thomson Catchment (Alaouze 2004) and occur within the high rainfall areas, mostly along the escarpments of Mount Baw Baw. When regenerating after logging, these species have been observed to double their use of water through having a higher Leaf Area Index (LAI) (Peel et al 2000, Vertessy et al 1998). The Strategy Directions Report stated that if logging were to be phased out of the Thomson Catchment by 2020, it is estimated that it will provide an additional volume of water in the order of 20,000ML (Water Resources Strategy Committee 2002). This chapter provides an overview of the issues concerning logging in the Thomson Catchment and implications for future management. These are covered in the following

sections:
• Annual Rainfall within the Thomson Catchment (Section 10.2)
• Forests and Water Use (Section 10.3)
• Predicting Impacts on Water Yield within the Thomson Catchment (Section 10.4)
• Logging within the Thomson Catchment (Section 10.5)
• Global Warming and the Thomson (Section 10.6)
• Implications for Future Management (Section 10.7)

This chapter reveals significant problems with past and continued logging within the Thomson Catchment. It reveals that logging Ash Forests results in the greatest water yield loss for any forest type in the catchment. 67 percent of the Ash forest area within the Thomson Catchment has been or will be logged. This exceeds the minimum of 20 percent for changes in the water yield to be detected.

Logging of Melbournes Water Supply the Thompson Catchment