18.3 Discharge to landscape
This process occurs in the Canberra region, but the volume could not be quantified due to the lack of data and a suitable quantification approach. In Canberra the recharge is due largely to rainfall, while discharge generally is to streams and evapotranspiration. Recharge of groundwater and discharge to surface water in fractured rock aquifers is usually localised and as such difficult to calculate. Broad-scale movement of water through an upland fractured system with local flow system is generally limited. The 2011–12 year was considerably a wet year for the Canberra region with a total annual rainfall of 1,115 mm compared to its long term annual average rainfall of 801mm (Figure C3 Graph of total monthly rainfall for the Canberra region). Recharge and discharge from fractured rock aquifers is closely linked to recent rainfall history. As such, it would be expected that the groundwater recharge and consequently discharge from landscape to be larger in 2011–12 than an average year.
The Australian Capital Territory Government, Environment and Sustainable Development Directorate uses an estimate of 74 GL of groundwater recharge each year as a guide when setting limits for ground water extractions; approximately 10% of this recharge is available for abstraction annually.