Frequently Asked Questions: About water movement
questions about the groundwater itself, its movement, amount, recharge, flow, mixing, and discharge.
- Is there an underground stream from Toowoomba to Stradbroke island?
No, they are not connected hydrologically. The groundwater in the massive sand dunes on Stradbroke is from local rainfall. - Where does the groundwater come from?
The groundwater that is used for irrigation is mainly from the alluvial aquifers. This water mostly comes from the surrounding ranges, by surface flows and groundwater seepage into the Lockyer catchment streams. It then recharges the alluvium. There is only minor direct recharge to alluvium by rainfall in the valley. - Does water from irrigation soak back into the aquifers?
This seems to vary quite a bit in the valley, but studies show that most of the central valley has silts and clays at shallow depth. Here vertical infiltration is restricted at around 60 to 100 cm (0.6 to 1.0 m) by these fine-grained layers. This is probably the case for most of the wider parts of the alluvium, but may decrease in the subcatchments. - Is there plenty of water left in the alluvial aquifers?
Not at the moment. The amount of available, usable groundwater depends on (1)recharge from rainfall, (2) how much is extracted, and (3) how much is lost by ET (evapotranspiration). - Do the aquifers recharge from the Downs?
The alluvial aquifers seem to mainly recharge from nearby ranges. There is slow recharge of much older water to the sandstone bedrock, and this is no doubt sourced partly from the Downs. - Do some parts of the valley get better recharge than others?
Yes. This can vary quite a bit, and is usually associated with the valley morphology (shape and height of hills) which does influence the amount of rainfall. - If there was no irrigation, where would groundwater move into the valley, and where would it flow to?
Under natural conditions water from the ranges would flow into the network of streams around the catchment, and flow along them to the main central creek system. This water would recharge the alluvium as it flowed. If there was enough water the creeks would continue flowing. By nature, however, the Lockyer is an ephemeral drainage system, i.e. only flows after rainfall. Under conditions of no extraction, it is likely that there would be continual groundwater flow within alluvium, into the Brisbane River. A lot of water would be lost along the way by evaporation, and transpiration by vegetation. A natural system develops is own balance.