San Pedro River–the thin fragile line

The San Pedro River

Threading its way north from the mountains of northern Mexico, the San Pedro River meanders to the Gila River, then westward to join the Colorado River on its way back to Mexico.  It is one of the few remaining undammed rivers (in the desert, they call any flowing water a “river”) in the US.  It forms a lush, green corridor along it’s length, creating vital habitat and a critical migration corridor for millions of birds and other species.  More than 300 species of birds use its cottonwood and willow canopy to guide their annual migrations, and some 200 species of butterflies and 80 species of mammals call it home at some point in their lives.  In recognition of the importance of this rare oasis in the desert, the Bureau of Land Management protects the first 40 miles north of the US-Mexico border within the San Pedro Riparian National Conservation Area.  The Nature Conservancy protects a few plots further north, before the confluence with the Gila River.  The BLM, TNC and other organizations have put a lot of effort into habitat restoration along the river, first removing cattle from the riparian area, then reintroducing beaver, removing exotic vegetation,  and performing occasional controlled burns to thin the brush.

The river remains a relatively healthy ecosystem.  The river itself is very dynamic – reduced to a mere trickle during the dry pre-summer period, and becoming a raging torrent during the summer rainy season – and annual flows are strongly impacted by both summer and winter precipitation patterns.  The beaver dams help ameliorate this, but it’s a tough environment for beavers, whose dams are often blown out by summer floods.  The water pooled up behind their dams help recharge the aquifer that supports nearby human settlements.

I took a hike along the river last week.  I like to check on the river a couple of times a year, looking for tracks and trying to record the birds and bugs.  One of my first recordings of the river became a runner-up in the Most Beautiful Sound in the World contest, and has become my most played recording on Soundcloud.   But its been difficult to replicate that recording due to the increasing air craft noise over the river – more military flights in and out of Fort Huachuca, more light aircraft flying over the river corridor, and a huge increase in Border Patrol drones.

My recent day on the river was beautiful, as Shadow and I hiked the San Pedro trail north of the historic ruins of Fairbank to Willow Wash and returned via the cool, shaded river.  Along the way we ran across a Gila Monster, a rare sighting, and the first time I’ve ever seen one along the river.

A Gila Monster along the San Pedro Trail.
A Gila Monster along the San Pedro Trail.

The gentle gurgle of the stream under the whispering cottonwoods and willows provided a lovely backdrop to a riot of singing warblers, towhees, doves, and hawks.

But there were only a few scattered moments here and there when the river corridor was quiet enough to let the natural sounds settle in and relax me.  Mostly it was aircraft noise, especially before 10 am, sometimes so loud it drowned out all of the other sounds.  I felt bad for the birds, biologically compelled to vocalize to attract mates, defend territories, and warn their relatives and neighbors of danger.  They didn’t ask for all this noise, but were being forced to adapt to it.  The birds of the San Pedro are not too bad off, compared with birds that live in big cities, where studies have shown that they’ve had to change the pitch at which they sing to be heard over the traffic noises.  But the noise also impacts human visitors, and diminishes the experience of quiet nature that many of us seek between the river’s banks.

The San Pedro River provides vital wildlife habitat in the desert.
The San Pedro River provides vital wildlife habitat in the desert.

But the biggest threats to the wildlife of the San Pedro come from outside of the river corridor.  Ground water pumping by the small cities closest to the river are slowly lowering the aquifer the feeds the river outside of the rainy season.  In an effort to minimize threats to the aquifer, Cochise County (home of the southernmost portion of the river) passed regulations requiring that developers provide evidence of a 100-year-water supply for any new developments.  However, two recently proposed large developments appeared to come up short on those requirements, prompting state legislators to propose a bill that would allow municipalities to waive the 100-year requirement.  The bill passed, but was vetoed by the governor.   The southernmost proposed development, the 7,000 home Tribute development slated to be built east of Sierra Vista, was stopped when a judge ruled their claims of little impact on the river to be inadequate, and the governor’s veto of overriding legislation may stop that development for the foreseeable future.  The estimated water use by that development alone was roughly equal to the remaining flow of the San Pedro.  The other development, Villages at Vigneto, would add 28,000 homes and some 70,000 residents to the small burb of Benson (how does a town of 5,000 people ramp up to provide services for 70,000 in just 20 years?).  It, too, could have a major impact on the river, effectively wiping out the riparian area for 40 miles or more downstream.  Recent modeling has shown that it might severely impact the St. David Cienega, one of the last remaining cienegas (marshes) on a river that used to be more marsh than stream.

The San Pedro River is a true oasis in the desert, a vital wildlife corridor and habitat, a recreational destination that pumps millions of dollars into the local economies, and a critical water supply for nearby residents (wild and not).  Global climate change is predicted to result in more droughts for this region, meaning any future withdrawals from the river need to be done very cautiously.  It would truly be a shame if greed slowly killed the San Pedro River, benefiting a few while the rest of us watch it die.


For more about the potential impacts of the Villages at Vigneto’s impact on the river, see “Killing the San Pedro: Arizona’s last free-flowing river at risk.”

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