Where monsoon water goes after heavy rains

Published: Aug. 31, 2021 at 6:34 PM MST
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It feeds our aquifer and ground water supply, which is good news for Pinal County agricultural users who now have to pump ground water. Evans said while it may seem like a lot of water, heading into the aquafer below, more moisture is needed during the winter to raise ground water levels substantially.

Any washes and rivers are left with whatever water there may be, trickling to a dry stop. Daniel Evans, with the U.S. Geological Survey and Arizona Water Science Center, said the water goes many places, but mostly just below our feet.

“Some of it goes to evaporation, some of it goes to the plants the trees drinking it, but the vast majority simply comes down because of gravity and goes into the ground,” said Evans

Typically, he said, flows from monsoons typically don’t have a lot of volume. It’s the winter flows that make an impact, such as the ones that occur after snow packs onto Mount Lemmon.

The rest of the water not seeping below ground has a long trip ahead of it.

“It hits the Santa Cruz River, flows north to the Gila River, just West of Phoenix,” said Evans. “Almost always, it does not make it to the Gila River West of Phoenix.”

If it does, the water will link up with the Colorado and head down to the Sea of Cortez. But Evans said mostly, the water just stays under your feet, soaked up easily by the sandy wash bottoms.

“In the desert southwest, it usually flows down,” he said.

Experts say there is a small layer of ash in many washes and rivers which slows the water draining into the ground.

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