Pounding monsoon rains do little to replenish the area’s aquifers

Southern Arizona’s summer monsoon, which features spectacular lightning shows and pounding downpours, doesn’t really do much to replenish the area’s aquifer, a University of Arizona water expert said Friday.

It quickly flows off and runs down the arroyos and rivers.

Winter’s gentler rains of longer duration do a better job, said Kristine Uhlman, a university Water Research Center staff member.

More than a dozen members of the Green Valley Citizens’ Water Action Coalition heard Uhlman explain the dynamics of water in arid lands, such as the Sonoran Desert.

And there’s lot evidence that water is being withdrawn from the local aquifer faster than is being replenished.

But she said much has been learned over the years about the water here.

She said there has been a water monitoring station on the San Pedro River near Sierra Vista for more than 50 years, the oldest such station on earth.

Arizona started getting serious about managing its water in 1980 when it adopted the Groundwater Management Code.

From that code have come organizations that act to preserve the water, to require that users of the groundwater put back as much as they take out and that developers must guarantee that there’s enough water to sustain their projects for at least 100 years.

The code also addressed water rights, trying to make sure those who were first in time are first in line to get the water.

But Uhlman said, partly in jest, that “if you have the deepest well and the biggest pump, you have the right to the water.”

Overpumping the aquifer, taking more water out than is being replenished, can have negative consequences beyond wells drying up.

Subsidence, or a settling of the ground, is one of the problems. Fissures sometimes appear. Settling ground can break buried utility lines and even leave buildings uninhabitable.

She showed a slide taken in the San Joaquin Valley, Calif., were subsidence caused the Earth’s surface to fall 39 feet in the last century.

Only 4 percent of Arizona’s rivers are perennial, flowing year around.

The beds of those rivers lie below the area’s water table.

Intermittent rivers and streams that lie above the water table flow only after heavy rains or when natures fills the aquifer to a level higher than the stream bed.

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