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Since 2004, an aquifer injection project in San Antonio, Texas, has stored about 190 million m3 of water in the Carrizo-Wilcox Aquifer.

A study has found stormwater that washes to the Gulf could replenish aquifers — if it can be caught and stored

Flooding in Texas has long punctuated the state’s history, even entering into popular culture. But even though Texas may be legendary for getting its share of rain, the volume of Texas stormwater had never actually been quantified before.

A new University of Texas study, however, has cleared up the mystery. The researchers, Qian Yang and Bridget R. Scanlon, estimated the volume of stormwater in major Texas rivers during high magnitude flows (HMFs) and determined that depleted coastal aquifers in Texas offer enough storage capacity to capture the lion’s share of it. The researchers differentiated HMFs from normal flows by considering daily mean water flows from the last half-century; flows that exceed the 95th percentile are considered high magnitude.

The researchers concluded that between 2015 and 2017, 37 km3 of HMF water could have been captured from 10 significant Texas rivers that flow into the Gulf. Because aquifers on the Texas Gulf Coast have been depleted from years of use by agriculture and cities, they have room for 20 million acre-feet of water. That volume is equal to that of Lake Mead, the largest reservoir in the United States. It’s enough space to hold two thirds of the excess stormwater in Texas from the study period. Ideally, the stormwater would simply be used to recharge the aquifers.

Costs of Capturing Stormwater

Although the storage capacity is free and waiting to be used, the infrastructure to tap HMFs is not free. Floods may come in a flash, but injecting water into aquifers takes time. Storage would have to be engineered and built to hold HMF water. The team warned, “Engineering approaches will become increasingly important to manage climate extremes.”

The strategy already is working in the Texas cities of El Paso, Kerrville, and San Antonio, but capturing HMFs at a statewide level would require a massive investment in planning and new infrastructure. Is there enough to justify such an infrastructure push? According to Bridget Scanlon, senior research scientist at UT Austin’s Bureau of Economic Geology at the Jackson School of Geosciences, “This study is the first step, but it looks like the water is worth going after.”

Although the study period between 2015 and 2017 had more than average precipitation, the researchers found that HMFs do happen with regularity on the 10 rivers under study. Each river is as likely as not to experience HMFs in a given year, and 80% of HMFs last a week or more, allowing more time to tap them. Studies on the San Antonio and Brazos rivers also demonstrated that 65% of HMFs could be tapped with no harm to the environment. The researchers also determined that tapping HMFs would not infringe on the water rights of owners.

Paradoxically, while Texas may be well known for flooding, it is equally known for its droughts. The new study offers a viable strategy to mitigate one with the other, recharging drinking water supplies with oversupply from HMFs, which is important since the frequency of extreme droughts and floods is expected to increase with climate change. The study reinforces a Texas water strategy focused on wastewater reuse and groundwater aquifer storage.

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