Ecohydrology and Environmental Change to Lake Albacutya and Wyperfeld Park in North-Western Victoria, Australia

Lake Albacutya is a well-known intermittent lake in north-western Victoria. The lake is near the termination of the Wimmera River. From time-to-time the lake fills and flow passes down Outlet Creek into Wyperfeld National Park. The wetlands associated with the lake have a high biodiversity value and are named in international treaties. This paper examines the hydrologic factors associated with lake filling and flow into Wyperfeld. The lake has filled approximately six times since 1880 and has partially filled on other occasions. Examination of rainfall data from 1875 at Horsham gave no indication of long term rainfall decline, and showed that rainfall at Horsham can be viewed as representative of rainfall in the Wimmera River catchment. However a double-mass analysis showed that the relationship between the Wimmera River flow and rainfall has varied from 1890 to the present. Examination of data associated with six fillings of Lake Albacutya suggested that filling is a two-year event requiring at least 550 GL of flow passing Horsham over the two years immediately associated with the flood. A simple model based on rainfall and this threshold reproduced observed characteristics of the data reasonably well. This suggested that the flooding frequency of Lake Albacutya has dropped from about one in 25 years in the natural state to a substantially lower frequency under current river conditions. The results also suggested that because of changes in the Wimmera River the last filling and flood into Wyperfeld in 1976 was far smaller than it would otherwise have been. This is consistent with field mapping of the flood in relation to River Red Gum (Eucalyptus camaldulensis Dehnh.) stands. Analysis of the health of these stands showed major dieback with the severity of this being roughly proportional to the distance from the 1976 flood boundaries. An examination of values associated with the lake and adjoining Wyperfeld National Park suggested that biodiversity and economic values are and will be compromised by the reduction in flooding. In particular, an internationally-known provenance of Red Gum is at risk, and bird-breeding opportunities have diminished.