Effects Of Groundwater Pumping On Saltwater Intrusion In The Lower Burdekin Delta, North Queensland

Abstract: The Burdekin Delta is situated in the dry tropics of North Queensland and provides a major water resource for the irrigation of sugarcane. The Delta is unique in that it overlies a shallow groundwater system and is close to the Great Barrier Reef. Aquifer management practices include large recharge pits to assist with artificial replenishment of groundwater. Artificial recharge can be used to maintain groundwater levels and subsequently control seawater intrusion. This technique, however, is often costly and ineffective in areas where excessive groundwater pumping occurs. In the lower Burdekin Delta more than 1800 groundwater pumps are used for irrigation purposes and excessive pumping has resulted in seawater intrusion near the coastline. In this paper we describe the use of a variable density flow and solute transport model, SUTRA, to define the current and potential extent of saltwater intrusion in the Burdekin Delta aquifer under various pumping and recharge conditions. A 2-D vertical cross-section model has been developed for the area, which accounts for groundwater pumping and various artificial recharge sites currently being used in the delta. The Burdekin Delta aquifer consists mainly of sand and clay with granitic bedrock. The model domain uses vertical cross sections along the direction of groundwater flow. The initial conditions were based on the land use prior to agricultural development in the area when the seawater interface was in its assumed natural state. The results address the effects of variations in pumping and artificial and natural recharge rates on the dynamics of saltwater intrusion. The simulation has been carried out for a range of recharge, pumping rates and hydraulic conductivity values. The results show that the saltwater intrusion is far more sensitive to pumping rates and recharge than aquifer properties such as hydraulic conductivity. The impacts of possible management scenarios on groundwater quality have also been investigated