Salinity Risk in the Corangamite Region, Australia

Author: Peter Gerald Dahlhaus

Dahlhaus, Peter Gerald, 2010 Salinity Risk in the Corangamite Region, Australia, Flinders University, School of the Environment

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Abstract

Classic hydrogeological science, in which observations, measurements and experiments are used to deduce theories, has resulted is a deep understanding of many aspects of salinity processes. The outcome of this approach in Australian dryland salinity studies has been a vast body of scientific work that has resulted in the widespread adoption of two paradigms: 1) that dryland salinity is caused by rising groundwater tables as a result of broad-scale clearing of native vegetation; and 2) that dryland salinity is a threatening process that is a risk to assets. The Corangamite region in south west Victoria, Australia, has proven to be an ideal landscape in which to test these paradigms using a systems thinking approach to complement traditional scientific methods. The variation in the region's biophysical landscape provides a diverse milieu; the environmental history of landscape changes is well documented; a record of groundwater and salinity monitoring exists; detailed scientific studies have been undertaken; and social policies based on salinity risk have been implemented. Using this broad range of evidence, this research project has shown that salinity is a permanent and inseparable attribute of the Corangamite region. Primary salinity has episodically existed throughout the Quaternary as evidenced by the landscape record of saline lakes and drainage lines, which were supported by shallow saline groundwater tables. The earliest written historical records noted hydrological changes and attributed them to anthropogenic causes that were contrary to the current axiom. From these records there is no evidence found which supports significant rises in groundwater following widespread land-use change. Detailed investigations in one landscape reveal that the area of salinised land has continued to expand and new saline discharge areas have emerged, despite the efforts of active salinity management, a decade of below average rainfall, and a general trend of falling watertables. Investigations of the increasing stream salinity in another catchment shows that there has been little discernable effect on groundwater levels following land clearing over the past 150 years. These findings question the validity of the commonly accepted cause (rising watertables) and effect (land and stream salinisation) model. Alternative salinity models are proposed based on the broad range of data available. In contemporary risk assessment studies, salinity is universally viewed as a threat to assets. However, salinity risk has both negative and positive impacts, and risk assessment needs to also consider salinity as critical in sustaining the region's internationally important environmental assets. Hence, a systematic, disciplined and rigorous framework for salinity risk management has been developed to protect all classes of assets which are threatened by changes to salinity processes, even those where the salinity itself is the asset. Since it is based on the generic international and national risk management standards it is broadly applicable to all salinity risk management policies. The recurring theme in this thesis has been to challenge the current salinity process theories, salinity risk assessment methods and salinity risk management dogma in Australia. Testing the current paradigms using evidence from a broad range of disciplines has resulted in new perspectives.

Keywords: Salinity,groundwater,risk,wetlands,Corangamite
Subject: Environmental management thesis, Environmental Science thesis

Thesis type: Doctor of Philosophy
Completed: 2010
School: School of the Environment
Supervisor: Professor Craig Simmons