Groundwater threat to rivers worse than suspected
Excessive groundwater development represents a greater threat to nearby rivers and streams during dry periods (low flows) than previously thought, according to research released today by CSIRO.
In an address to the Groundwater 2010 Conference in Canberra, CSIRO Water for a Healthy Country Flagship scientist, Dr. David Rassam, said land-use practices that reduce groundwater recharge into rivers and streams could significantly reduce low flows in nearby rivers and streams.
鈥淢any rivers are highly dependent on 鈥榖ase-flow鈥� from groundwater to keep running through dry times and traditional ways of managing groundwater pumping follow a 鈥榮afe yield鈥� approach which balances the amount of water extracted with the amount known to be 鈥榬echarging鈥� the aquifer,鈥� Dr. Rassam said.
However, the study, conducted at Tarcutta in NSW, showed that application of this 鈥榮afe yield鈥� approach in times of low-flow can reduce recharge much more severe than previously thought.
鈥淭he yield of an aquifer must be considerably less than recharge to ensure sufficient water to maintain the quantity and quality of low flows in streams, springs, wetlands and other groundwater-dependent ecosystems,鈥� Dr. Rassam said.
鈥淢any people don鈥檛 realise that groundwater discharge from shallow aquifers to surface water systems represents an environmentally critical component of the flow in most rivers.
鈥淚t鈥檚 the groundwater discharging into the channel through the bed and banks of the stream that keeps it flowing during the dry period. Most rivers are basically sustained by groundwater during the dry season.
鈥淲hat we found was that the impact on base-flow of reducing recharge might be small at first, but that each subsequent reduction of recharge has a disproportionately large impact on base-flow in the stream.
鈥淚n this stream in Tarcutta we found that increasing groundwater pumping by 40 per cent caused a 93 per cent reduction in base-flow in the river 鈥� it鈥檚 not a linear relationship at all.
鈥淭his demonstrates that preventing water entering aquifers, or pumping too much groundwater out, may lead to complete drying of nearby streams during the dry period.
鈥淭his can happen much more easily than we previously thought. The impacts on local water ecosystems could be dire.鈥�
More information: The Groundwater 2010 conference runs from 31 October to 4 November at the National Convention Centre, Canberra.
Provided by CSIRO
