The hydrology of the Catchment is also highly variable. The Catchment's average rainfall is 726 mm per year. Seventy percent of rain falls in the summer months from October to March. Rainfall it is highly variable in timing and amount in any one year. Few streams have permanent flow.

There are 2,787 licensed production bores and 12,000 stock and domestic bores in the catchment. In addition there are around 235 authorised water-harvesting diversions upstream of Chinchilla, with diversion rates generally between 43.2 and 86.4 megalitres (ML) per day. The maximum diversion allowable is 86.4 ML/day for most properties. Irrigation represents, by far, the major category of use, estimated to consume 80 - 90% of all supplies taken. Many groundwater developments throughout the Catchment have annual allocations in excess of sustainable annual supplies.

The Condamine River at Chinchilla Weir has a mean natural flow of 550,000 ML/year. The mean annual diversion above Chinchilla is around 185,000ML/year. This is made up of a mean annual water-harvesting diversion of around 67,000 ML; a mean annual diversion from area "hectare" licences, of around 31,200 ML; regulated supplies in the Upper Condamine Irrigation Project and the Chinchilla Weir irrigation Project are on average around 33,500ML, and other demands such as industrial, stock and domestic and overland flow make up the remainder. This diversion represents around 30-35% of the mean natural flow.
Overland flows are a significant component of the water resource within the basin. Overland flow development has increased considerably in recent times. Competing interests and concerns about impacts to river flows has brought about new legislation to introduce Government regulation of water in the floodplain areas. The Condamine-Balonne Water Resource Plans will introduce regulation in the Condamine-Balonne basin.

The assessment made for environmental flows for the Condamine system as undertaken by the WAMP Technical Advisory Panel has indicated the Upper Condamine is in fair to good condition but with an increase in occasions when there are no flows.

The environment flow objectives are aimed to provide an improvement in flow regimes at various flows eg no flows, low flows, etc. A broad indicator that is commonly discussed is the change from natural median flows. The science has suggested that around 62% median annual flow remaining in the system is the limit. However it is important that maintenance or improvement to all the stages of river flow is achieved to limit ecological degradation.

Source: Condamine-Balonne WAMP Current Condition and Trend Report, 2000