Importance of environmental flows in the Wimmera catchment, Southeast Australia

Abstract In this paper the environment, climate, vegetation, indigenous and European settlement history, stream flow patterns, water quality and water resources development in western Victoria, Australia are studied. The last part of the paper focuses on the MacKenzie River, a tributary of the Wimmera River located on the northern slopes of the Grampians Ranges in western Victoria, Australia. Water release along the MacKenzie River was regulated to improve water quality, stream condition and river health especially in the downstream reaches. The upstream section tends to receive water most days of the year due to releases to secure the requirements of water supply for the city of Horsham and its recreational and conservation values, which is diverted into Mt Zero Channel. Below this the middle and downstream sections receive a more intermittent supply. Annually, a total of 10,000 dam3 of water is released from Wartook Reservoir into the MacKenzie River. Of this volume, only about 4,000 dam3 was released explicitly for environmental purposes. The remaining 6,000 dam3 was released to meet consumptive demands and to transfer water to downstream reservoirs. The empirical data and models showed the lower reaches of the river to be in poor condition under low flows, but this condition improved under flows of 35 dam3 per day, as indicated. The results are presented to tailor discharge and duration of the river flows by amalgamation of consumptive and environmental flows to improve the condition of the stream, thereby supplementing the flows dedicated to environmental outcomes. Ultimately the findings can be used by management to configure consumptive flows that would enhance the ecological condition of the MacKenzie River.