Using Simulated Data and the Range of Variability Approach to Assess Changes to the Flow Regime of the River Murray at the South Australian Border

Abstract

Indicators of hydrologic alteration and the range of variability approach were used to assess the effects of river regulation on the hydrology of the River Murray in South Australia. Two simulated data sets derived from the Murray-Darling Basin Authority's MSM-Bigmod model were compared for the period of 1895–2009. The first scenario assumed that levels of extraction and diversion as of July 2009 (present) were applicable for the entire period. The second assumed that there were no water extractions or regulatory structures and the system was natural. Whilst the natural cycle of a single yearly high flow pulse was largely preserved, lower flow pulses were more prevalent and of longer duration under present conditions, whilst high pulses were less frequent and of shorter duration. Flow variability had increased during times of high flow, and decreased during times of low flow. The difference between natural and present conditions was more severe in the summer and autumn than the winter and spring. Under the present scenario low flows occurred around two months later in the year, whilst high flows occurred slightly less than one month earlier than under natural conditions. These results can guide the design of environmental flows for the river.