1.1.5 Surface water hydrology and water quality


Surface water of the Gwydir subregion is based on the Gwydir, Macintyre and Barwon river basins (part of the Border Rivers river basin). Areas drained by the Gwydir River and its distributaries west of Pallamallawa in the Gwydir river basin and by the Macintyre River west of Texas, and catchment areas south of the Macintyre-Barwon River including those of Ottleys, Wallan and Gil Gil creeks are within the subregion. The Gwydir subregion excludes all parts of the Barwon river basin that are on and beyond the right (north) banks of the Barwon and Macintyre rivers, which are instead part of the Maranoa-Balonne-Condamine subregion.

The Gwydir River forms a delta-like structure downstream of Moree resulting in the river flows being diverted into several of its distributaries including the Mehi River, Carole and Gil Gil creeks, and two main channels of the Gwydir River, namely the Lower Gwydir and Gingham watercourses. Mehi River and Gil Gil Creek flow into the Barwon River while both the Gwydir River channels terminate in the Gwydir Wetlands. Since the construction of Copeton Dam (outside of the subregion), there has been a substantial reduction in the extent of the Gwydir Wetlands. The Gwydir is a highly regulated river. The Copeton Dam, which is the only major public water storage in the Gwydir river basin, and several weirs regulate flow within the subregion.

There are about 150 agricultural businesses dealing with irrigation. Most irrigation diversions occur below Pallamallawa through a network of weirs and regulators on the Gwydir River and its distributaries. The total capacity of private on-farm dams and weirs used for collection and diversion of mainly irrigation water is 451 GL. The Mehi River has a long history of flooding with significant flood events occurring roughly every ten years.

The general water quality assessments of both the Border Rivers and Gwydir river basins for total phosphorus and total nitrogen are rated as ‘very poor’. The assessment for turbidity is rated as ‘fair’ for both river basins while salinity is rated as ‘fair’ for the Border Rivers river basin and as ‘poor’ for the Gwydir river basin. Within the subregion, the median of mean monthly electrical conductivity values in the Macintyre River and the Mehi River were 275 and 445 µS/cm, respectively. The overall ecosystem health of both the Gwydir and Border Rivers river basins as reported by the Sustainable Rivers Audit was rated as ‘poor’ for both the 2004 to 2007 and 2008 to 2010 periods.

There are about 16 and 33 stream gauging stations in the Macintyre-Barwon and Gwydir river basins, respectively, that are within the subregion. Streamflow data length varies from a few years to more than 100 years. Modelling using climate change projections for 2030 conditions indicates a likely decrease in future runoff.

Last updated:
5 January 2018