1.1.5 Surface water hydrology and water quality

Summary

The Maranoa-Balonne-Condamine subregion includes the river basins of the Condamine‑Balonne River (including the Maranoa River), the Moonie River and the portion of the Border Rivers river basin that is located in Queensland. The historical mean annual surface water availability of the subregion is between 1462 and 2670 GL, depending on how much of the surface water from the Border Rivers is included in the Maranoa-Balonne-Condamine subregion. The Murray‑Darling Basin Plan outlines water quality and salinity management issues including key causes of water quality degradation, water quality objectives, and water quality targets for a number of locations in the subregion.

Condamine-Balonne river basin

The Condamine-Balonne and Maranoa are the main rivers of the Condamine-Balonne river basin. The Condamine-Balonne River downstream of St George bifurcates into several distributaries that form the Lower Balonne floodplain system, with heavily dissected channels of various sizes. These channels carry a significant proportion of the surface flow during flood events. The upper reaches of the Condamine-Balonne River are highly prone to flooding (major floods occur every two years on average), which can result in widespread inundation of agricultural land, damage to farming properties and loss of livestock. There are four major public water storages in the basin with a combined storage capacity of 208 GL. In comparison, the numerous private offstream water storages in the lower parts of the river basin have an estimated combined storage volume of 1916 GL.

As water quality measurements are carried out at only a few selected reaches of the Condamine-Balonne River, nutrient and turbidity data are generally deficient along the river. In the upper Condamine river basin, stream nutrients are generally within water quality guidelines, while the electrical conductivity (EC) ranges from 100 to 800 µS/cm, which is greater than those found in other Queensland rivers.

There are 42 operational stream gauging stations within the river basin. The eastern part of the basin has more gauging stations than the western part, and there are no small- or medium-sized gauged catchments in the western half. Results from 60% of the modelling with climate change projections indicate a decrease in future runoff.

Moonie river basin

The Moonie river basin is one of most cleared in southern Queensland and is dependent on surface water for most of its irrigation needs. There is no major public water storage in the basin, but it has a number of off-river private storages with an estimated total volume of 29 GL.

Two water quality sampling sites in the Moonie river basin show high total nitrogen, but no trends for EC or turbidity are detected. There are three stream gauging stations in the basin (two with more than 40 years of flow record); all are in the Moonie River. The flow data indicate loss of streamflow in the middle reaches of the Moonie River. The projected effects of climate change on runoff are similar to those for the Condamine-Balonne river basin.

Border Rivers river basin

The Maranoa-Balonne-Condamine subregion contains only the north-western part of the Border Rivers river basin, which includes the Weir River, Macintyre Brook, Callandoon Creek and the northern flank of the Macintyre-Dumaresq-Barwon river system. Coolmunda Dam in the Macintyre Brook catchment is one of the major public water storage dams in the area with a storage capacity of 69 GL. Surface water sources comprise more than 90% of the water used for irrigation in the Border Rivers river basin.

There are insufficient data to assess the water quality for nutrients, turbidity and EC in most areas. The part of the Border Rivers river basin that is within the Maranoa-Balonne-Condamine subregion has 19 stream gauging stations with varying flow record lengths. The effect of projected climate change on future runoff in the whole of the Border Rivers river basin (including areas that are in the Gwydir subregion) is a likely decrease in runoff by about 9% by 2030.