EFFECTS OF REGULATION ON THE FLOW REGIME OF THE RIVER MURRAY, AUSTRALIA

The flow regime of the River Murray has changed markedly over the last century, and especially the last 50 years, through increased diversio ns, construction of dams, weirs and levees and changes in operational procedures. A model developed by the Murray-Darling Basin Commission i s used to compare simulated natural (unregulated) flows at eight stati ons with those at seven consecutive stages in the development of regul ation. Monthly and annual average flows and coefficients of variation and skewness were computed, and the flow-duration, peak-flow and low-f low characteristics curves plotted. The results confirm that average m onthly and annual flows are now considerably lower than those which pr evailed under natural conditions. The seasonal distribution of flows h as changed in the upper Murray, owing to the influence of dams. Flow-d uration characteristics now vary considerably along the river, whereas there was little change under natural conditions. The effect of regul ation on flow-duration characteristics is minimal at Albury and become s more pronounced downstream; it is most apparent in regard to flows e xceeded 20-80% of the time. The magnitude of average annual hoods (ann ual exceedance probability 50%) has been reduced by over 50% at all st ations, but big floods (average recurrence interval 20 years or more) are little affected. Further, the low flows for a given annual non-exc eedance probability are higher under regulated conditions than those u nder natural conditions. These changes have profound implications for communities of native plants and animals in both riverine and floodpla in environments, and also for the long-term utility of the river as a resource.