Understanding Salt Mobilisation in the Barr Creek Catchment, Northern Victoria

The Barr Creek catchment in northern Victoria has been recognised as a major contributor of salt load to the Murray River. The dominant land use is surface irrigated pasture. The catchment is characterised by a 1-2 m deep saline groundwater table which intersects the 2.5 m deep surface drainage network. Groundwater seepage into drains in autumn, winter and spring is considered to be the dominant process mobilising salt into Barr Creek. During the last decade salt load in Barr Creek has dramatically reduced. Simultaneously, significant changes in water use, climatic conditions and the deep regional groundwater pressure have occurred, which may have caused the salt load reductions. However the contribution of these different factors to the reduction of salt load in Barr Creek is not yet well understood. In this study, time series of the potential drivers were analysed to better understand the change in salt load. Potential drivers considered were rainfall, evapotranspiration, irrigation water use, Loddon river flood flows and Deep Lead pressure. Linear correlation, classification and regression trees and artificial neural network analyses were applied to assess the importance of the different drivers, their time lag effects and the degree of non-linearity in the salt load response. The statistical methods indicated that short-term rainfall history was the main driver of salt load in Barr Creek. The short-term history of Deep Lead pressure was also a significant driver of salt load. The artificial neural network analysis suggested that differences in importance between all potential drivers except rainfall were very small and that salt load response to the drivers investigated was almost linear.