An Ecological Risk Assessment of Irrigation in the Ord River Catchment, a Highly Disturbed and Poorly Understood Area in the Wet-Dry Tropics of Australia
Department of Primary Industries, Water and Environment, Tasmania
Faculty of Computing, Health and Science
School of Natural Sciences / Centre for Ecosystem Management
An ecological risk assessment of the impact of irrigation on the ecological values of the Ord River was undertaken. The Ord River is located in the wet-dry tropics of Western Australia and has been highly disturbed by grazing and irrigation developments. The construction of two dams has changed the river from being seasonally dry to now having permanent flows downstream of the dams. The Ord River irrigation Area (15,000 ha) is fed by waters from the Kununurra Diversion Dam. Approximately 50% of the water is returned to the river downstream mixed with drainage from the farms. Comparatively little is known of the ecology of the Ord River, although recent research efforts are starting to addressd this. The risk assessment focused on the area between the Ord River Dam and upper boundary of the estuary. A mass balance of nutrients, sediments and water for the Lower Ord River clearly demonstrated the irrigation drainage was the principal source of nutrients. The low knowledge base for the system resulted in a qualitative risk assessment largely guided by expert opinion. Priority ecological consequences were identified as loss of biodiversity and biota kills (primarily through biocides), weeds as lastly algal booms and channel infilling. The priorities were used to guide further research. Low stakeholder involvement in the assessment was believed to undermine the sense of ownership of the process. A low knowledge base limited the assessment to being purely qualitalive and dominated by expert opinion. Further research should allow a second iteration of the process to produce more useful outcomes and some quantitative risk assessments.