Rio Grande Basin unconfined aquifer
drops below September measurement


SOMETHING even more out-of-the-ordinary and disconcerting happened to the Rio Grande Basin’s unconfined aquifer in October. It dropped below its September acre-feet measurement – and that’s never happened before.

Rio Grande Water Conservation District General Manager Cleave Simpson and staff were stunned by the October reading. Now they’re worried about November’s and December’s readings, particularly given the dryness of the past six months. The Colorado Climate Center reported this week that Alamosa had its hottest June-through-November stretch on record.

Typically, once the summer irrigation season ends in the San Luis Valley and farmers are using less water from the Rio Grande Basin in the late fall, the unconfined aquifer will recharge and the flow levels will naturally go up in October and into January.

their conservation efforts were working. But then the October reading on the unconfined aquifer came into the picture and concern took over.

“To see the aquifer still take another monthly drop in October is scary,” said Marisa Fricke, program manager for Subdistrict 1. “Now what else is happening?”

Her theory is that the very dry soils are still soaking up any surface water. But she’s not a soil scientist and she’s talking to Colorado State University and their experts to better understand the October decline.

The lack of any summer monsoon in 2021 adds to the equation, but the overall precipitation levels in 2021 were up slightly from the even drier 2020 and so that also has water managers scratching their heads on why October’s unconfined aquifer reading fell below September.

The November and December readings will be telltale signs of how difficult the 2022 irrigation season will be. 

Crop producers used less water to record their lowest pumping, the Valley had a slightly wetter 2021 than 2020, and yet the unconfined aquifer fell in acre feet in October from September, a time it would naturally recharge higher.

“The aquifer is such a mystery below us,” Fricke said.

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