In 2011 parched soils in Texas caused agricultural losses of around $8 billion in one of the worst droughts the state has ever seen. 2017 saw the opposite extreme when Hurricane Harvey dumped 150 cm of rain over south-eastern Texas in six days, resulting in extensive flooding, 68 fatalities and economic losses of over $100 billion. Whilst we can’t control the rain, we can control the water. A new study demonstrates the potential of the “managed aquifer recharge” technique for capturing flood water in Texas and injecting it into aquifers.
This technique, which already helps Texas manage its water supply, diverts floodwater, reducing its impact. It temporarily stores the water at the surface, before treating it and gradually injecting it into depleted aquifers beneath. This tops up groundwater supplies ready for the next drought.
To investigate this approach in Texas, Qian Yang and Bridget Scanlon from the University of Texas at Austin, quantified how much water could be captured and stored from the ten major rivers that discharge into the Gulf of Mexico.
Between 2015 and 2017 around 37 cubic km of water could have been captured from these ten rivers during high magnitude flow events, the scientists found. The excess water from these three wet years is equivalent to around twice the annual water demand in Texas in 2016 and would have been enough to replenish the depleted Texas Gulf Coast Aquifer system.
“Compared to traditional surface reservoirs such as lakes, depleted aquifers provide much greater storage capacity,” says Yang, whose findings are published in Environmental Research Letters (ERL).
By studying rainfall and river flow records over the last 50 years, Yang and Scanlon also show that small numbers of long duration events – longer than a week – contribute most to the large flow volumes.
Such schemes are more cost-effective than expanding surface water storage. Texas already has three operational managed aquifer recharge systems in place — at El Paso, Kerrville and San Antonio. Other parts of the world, particularly areas where aquifers have been depleted and flash floods are common, are also taking advantage of this way of balancing water supply and demand. To date there are over 1000 schemes in operation worldwide.
Climate change is projected to increase weather extremes, with floods and droughts anticipated to become more frequent and severe in many regions. Yang and Scanlon believe that managed aquifer recharge is likely to become a serious mitigation tool.
“I think managed aquifer recharge will become very prevalent in the future as a way of better managing water resources, especially in those regions that suffer from floods, droughts, and groundwater depletion,” says Yang.
