Causes and Consequences of Unutilised Irrigation Orders in the Central River Murray Area

Abstract

Regulation of river systems has led to the development of irrigated agriculture and other uses of this engineered additional water supply. One of the main environmental drawbacks from regulation of river systems has been a shift in the seasonality of flow of these rivers. One such river is the River Murray, Australia. A common concern for the River Murray is a decreased incidence of winter and spring flooding of floodplains. A lesser known problem is the increased incidence of unseasonal flooding of the Barmah-Millewa Forest (B-MF) around the Barmah Choke on the River Murray. These flood events have often been said to be created by ‘rain rejection events’. Rain rejection events are the rejection of advanced irrigation orders by irrigators due to rainfall on their properties meaning this previously requested water goes unutilised. This paper investigates the causes of unutilised irrigation orders (UIO) and takes a holistic view to investigate the variables affecting unseasonal flooding of the B-MF. It is concluded from this research that unseasonal flooding of the B-MF can be linked to UIO but there are other more significant factors; inflow from Ovens River particularly during December, River Murray flow at Albury and the available airspace in the River Murray at Tocumwal. UIO were found to be linked to the previous day’s UIO, rainfall and the advanced order volume placed four days prior.