The Goulburn River flows for 570 km from the Great Dividing Range upstream of Woods Point to the River Murray east of Echuca.
The construction and operation of Lake Eildon and Goulburn Weir have significantly altered the Goulburn River's natural flow pattern. Water harvesting during naturally wet periods and regulated releases to meet irrigation and other consumptive demand during dry periods mean flow downstream of these structures is typically low in winter and spring and high in summer and autumn. This effectively reverses the natural seasonal flow pattern. Land-use changes and the construction of small dams and drainage schemes have further modified the Goulburn River's flow regime. Levees and other structures prevent water inundating the floodplain.
The regulated flow regime in the Goulburn River is partly ameliorated by inflows from tributaries (such as Seven Creek and the Broken River) that provide some natural flows downstream of Lake Eildon and Goulburn Weir. Large floods that cause these to fill and spill are also important for the flow regime.
Environmental water in the Goulburn system is held by the VEWH, CEWH and MDBA as part of the Living Murray program. The CEWH is the largest holder of environmental water in the Goulburn system. The availability and use of Commonwealth environmental water is essential to achieve environmental outcomes in the Goulburn River. Environmental water held on behalf of the Living Murray program may also help meet environmental objectives in the Goulburn system en route to icon sites in the Murray system (see Table 1.4.2).
Environmental water may need to be delivered through the Goulburn system to meet a downstream environmental objective. Where possible, these releases are managed to achieve outcomes in the Goulburn system before being reused downstream.
Environmental targets can also be met by water delivered from Lake Eildon to meet downstream consumptive demands in the River Murray (known as inter-valley transfers). Goulburn inter-valley transfers occur at times during the irrigation season, from spring to autumn. These flows may help achieve the desired environmental objectives without the need to release environmental water.
The priority environmental flow reaches in the Goulburn River are downstream of Goulburn Weir (reaches 4 and 5) as they are the most flow-stressed sections of the river and support more-abundant and diverse native fish communities. These two reaches are collectively referred to as the lower Goulburn River. Delivering environmental water to the lower Goulburn River also provides benefits to the mid Goulburn River between Lake Eildon and Goulburn Weir (reaches 1 to 3). Environmental water releases from Lake Eildon that target the mid Goulburn River (reach 1 in particular) are most beneficial between late autumn and early spring, when low river flows can occur. For most of the year (early spring to late autumn), transfers of consumptive water from Lake Eildon that are diverted out of the river at Goulburn Weir result in the flow exceeding the environmental flow targets for reaches 1 to 3.