A fragile oasis is in danger of vanishing
The San Pedro is one of Arizona’s most precious rivers. But hundreds of new wells may leave it running dry
A flash of red streaked through the trees: a vermilion flycatcher. The brightly colored bird chirped and trilled, adding to a chorus that rang from the towering trees.
Beneath the shady canopy of cottonwoods and willows, the San Pedro River flowed shin-deep, gurgling through smooth rocks.
This green artery, which snakes north from the Mexican border into southeastern Arizona, nourishes an astoundingly rich variety of life, including more than 350 species of birds, many of which stop here during migration. The forests and wetlands along the river teem with animals from frogs to bobcats to butterflies.
The ecosystem depends on the river, and the river itself depends on an un
seen source. Much of its flow is fed by groundwater, emerging from the aquifer in springs and seeps, sustaining the river.
Over decades, as more wells have been drilled across the river valley, pumping has lowered the water table in many areas, drawing away water that would otherwise replenish the river’s underground sources.
For the past 24 years, activist Tricia Gerrodette has immersed herself in court cases, written letters and spoken at government meetings to advocate for protecting the river. She said this oasis is fragile and could rapidly be destroyed if groundwater levels continue to decline.
“In a dry place, water is life,” Gerrodette said, looking out over a pond beside the river in the San Pedro Riparian National Conservation Area. Though the aquifer still feeds the river here, she said, “it’s at risk because we continue to pump from that aquifer and drop the level.”
Decades ago, water diversions and heavy groundwater pumping dried up other rivers across Arizona, from the Santa Cruz in Tucson to long stretches of the Salt and the Gila around Phoenix, leaving parched riverbeds.
The San Pedro has survived as one of the last free-flowing rivers in the Southwest. But many segments of it have suffered long-term declines as pumping has pulled down groundwater levels. Some stretches that once flowed yearround have been transformed into dry sand, running aboveground only when rainstorms bring bursts of runoff.
The river’s connection to groundwater is visible in the way it flows, running aboveground for one segment, dropping underground through a dry stretch, and reemerging farther downstream, where the aquifer’s levels or different geology push the water out of the ground again.
But the connection between surface water and groundwater isn’t recognized in the law. In Arizona, as in other western states, different rules apply to surface water and groundwater. While diversions from streams and rivers require a water right based on historical use, state law allows unlimited groundwater pumping in unregulated parts of the state, including the San Pedro River Valley.
The law doesn’t require anyone to consider rivers when they’re drilling new wells. The only legal requirement is that the groundwater be put to “reasonable use.” As more wells have been drilled to supply growing towns along the river, the lack of restrictions on pumping has left the San Pedro closer to drying up.
An analysis by The Arizona Republic shows significant and widespread declines in groundwater levels near the river. Average water levels in wells monitored by the state in the river’s watershed dropped from 47 feet in the early 1950s to 208 feet during the past four years.
The number of wells drilled in the watershed has increased. In the Sierra Vista subbasin of the upper San Pedro, where the most development along the river has occurred, 871 wells have been drilled from 2015 to late 2019. That is on track to be the highest five-year period since the data collecting began in the early 1970s.
The same is true for the Mammoth subbasin to the north, in the lower San Pedro.
And the wells are being drilled to much deeper levels. The average depth of new wells drilled since 2010 in the Sierra Vista subbasin is about 150 feet deeper than wells drilled in the 1970s.
Gerrodette described what she sees as a worst-case scenario: If the aquifer falls too much, she said, the river would dry up and eventually trees would wither when their roots could no longer reach the water table. Over a period of years, the green corridor would wither, and the birds and animals would vanish.
Gerrodette said the river is now “hanging on by a thread” — threatened not only by pumping that occurs today, but also by pumping that happened decades ago. Over the years, wells in the Sierra Vista area pulled down the aquifer and left what hydrologists call a “cone of depression,” a drawn-down portion of the water table that continues to expand toward the river.
Despite conservation efforts, communities near the river still use more groundwater than they did in the mid-1990s, Gerrodette said, and now developers plan to build thousands of new homes, all of which would rely on the same groundwater that supplies the river.
“That’s my greatest fear, is that the river will be overcome,” Gerrodette said, “and that we would lose this treasure.”
Still an oasis, but changed by pumping
Humans have lived along the San Pedro River since prehistoric times. Archaeologists have found bones of bison and mammoths at sites where they say Clovis people hunted and killed the animals about 11,000 years ago, after the end of the last Ice Age.
Over the centuries, other groups of indigenous people made their homes near the river, leaving rocks adorned with petroglyphs.
When fur trappers rode through in the early 1800s, the beavers were so plentiful that they called it the Beaver River, a name that faded as the beavers vanished.
In the early 1900s, wells were drilled along the river, and they proliferated over the years to supply farms, the Fort Huachuca Army base, Sierra Vista and other communities.
In a 1970 article in Arizona Highways, Eulalia “Sister” Bourne wrote about her observations of the San Pedro starting in the ’30s, saying it was “really rich in water” and had long hindered travel, leaving wagons and cars stranded in its waters.
Decades of pumping have weakened the river’s flows. The portions of the San Pedro that flow year-round have shrunk. In some places where only a thin ribbon of water remains, you can step across and barely get your shoes wet.
This change has occurred as the number of wells has skyrocketed in the upper San Pedro River basin to supply a growing population, more than doubling from 3,592 wells in 1987 to 8,765 wells in 2017, according to state data.
It only takes a small decline in groundwater levels to affect the surface flow.
The ecosystems along streams harbor all sorts of creatures, from salamanders to bats, and their gradual desiccation is helping push species toward extinction at an accelerating rate.
Across the United States, scientists have documented major declines in bird populations over the past 50 years, and they point to habitat loss as a primary cause. Wetlands have been drained and creeks have been sucked dry. The Colorado River delta in Mexico, which a century ago was filled with lagoons and wildlife, has been transformed into a dusty expanse of desert, while the water has been siphoned off to farmlands and cities.
The heating of the planet, unleashed by the burning of fossil fuels, is contributing to the stresses on species that are already struggling to survive. In the desert Southwest, research has shown that hotter temperatures are intensifying years of drought and shrinking the flow of streams.
With so many streams in decline, the San Pedro stands out as sanctuary for biodiversity.
Stretching 140 miles from its headwaters in Mexico to its end in Winkelman, where it joins the Gila River, the river forms a green pathway through arid grasslands, a lush corridor that resembles a tropical forest and bustles with life.
Clumps of Huachuca water umbel, an endangered plant with slender leaves, grow in wetlands by the river — one of more than 600 species of plants found along the San Pedro.
Millions of migrating birds stop to feed during their journeys from Central America and Mexico to the rest of North America.
The American Bird Conservancy has named the San Pedro a “globally important bird area.” Birders come from across the country with their binoculars and scopes to search for rare species such as southwestern willow flycatchers and yellow-billed cuckoos.
An expanding ‘cone of depression’
Researchers with the U.S. Geological Survey have studied the hydrology, water-use trends, and groundwater levels in the river’s upper basin. They found some improvements in the watershed between 2002 and 2012, including the retirement of wells that previously irrigated farmland, and the use of treated effluent from Sierra Vista’s wastewater plant to replenish groundwater near the river.
But they pointed out even with these positive steps, “groundwater levels across much of the subwatershed are declining” because of the current pumping for the more than 80,000 residents and the effects of pumping years ago.
The “cone of depression” between Sierra Vista and Fort Huachuca has continued to deepen, they wrote in their report, and stream gauges at Palominas, Charleston and Tombstone show the river’s base flow has decreased.
Stabilizing the amount of groundwater that’s discharging into the river would be challenging, the researchers concluded, and if achieved would represent a “major groundwater-management success.”
“If pumping across the subwatershed were to completely stop tomorrow,” the scientists wrote, “the cone of depression would continue to spread and its effects, including decreases in natural discharge to the riparian area and river, would continue for decades.”
The cumulative effects of pumping decades ago are still playing out underground. Even if pumping were to stop, the drawdown would continue to spread.
Thomas Meixner, a University of Arizona hydrology professor, said the expanding depression in the aquifer beneath Sierra Vista will eventually reach the river and consume the groundwater that sustains it — unless increases in recharge or decreases in pumping make a significant dent.
“This groundwater cone of depression has grown for the last 70 years, and it has to be filled in somehow,” Meixner said. “That debt ultimately has to be paid back, or it will eventually have impacts on the surface water system.”
Meixner said conservation efforts by Fort Huachuca, such as letting grass dry up, have helped cut water use. He said these types of water-saving efforts must continue, along with initiatives to recharge the aquifer with treated wastewater or stormwater.
Other academic experts suggest that regulating how much water is extracted from the ground would make sense to protect the San Pedro.
“The river, as I see it, is on life support right now,” said Juliet Stromberg, a plant ecologist and botanist. “We need to do everything we can to make sure water is still flowing into that aquifer to support the river and its ecosystem.”
The rate of groundwater pumping isn’t sustainable, Stromberg said, and if the watershed isn’t managed more carefully, more of the river will vanish.
River not protected in state law
At a basic level, the San Pedro River faces a legal problem: Even though groundwater and surface water are intertwined, they fall under different rules. And because the San Pedro isn’t part of a state-established “active-management area,” well owners can pump without restrictions.
This system has allowed for unchecked pumping to dry up rivers in many parts of the state, from the Rillito in Tucson to the Gila River in Maricopa, said Robert Glennon, a law professor and water expert at the University of Arizona. He called it Arizona’s “crazy, bifurcated system.”
State law also recognizes a category of water called “subflow,” which is treated as surface water and requires a permit to use. In practice, though, thousands of individual household wells have been drilled in this “subflow” zone, Glennon said, and are taking a toll on nearby streams, including the San Pedro.
“Riparian areas are so special, and we’ve lost so many of them,” Glennon said. “We need to protect every one that’s left.”
State water regulators have continued granting permits for wells to be drilled and have cleared the way for thousands of new homes near the river by issuing certificates stating there is an adequate water supply.
Plans for two giant developments have sparked lawsuits. One case ended last year at the Arizona Supreme Court, with a majority of justices backing a determination by state water regulators for a Sierra Vista development with nearly 7,000 homes.
In another case, environmental groups sued the Trump administration over its granting of a permit for a proposed development in Benson called Villages at Vigneto. Opponents argue that the pumping for 28,000 homes — along with a Tuscan-themed resort and golf courses — would threaten the river, and that federal officials have an obligation to thoroughly analyze the environmental consequences.
Developer Mike Reinbold has dismissed those concerns, insisting the development won’t significantly affect the river. He has said the development will incorporate water-saving practices and use recycled water for outdoor irrigation, and will also support efforts to capture stormwater and use it to recharge groundwater.
Robin Silver of the Center for Biological Diversity, one of the groups that is suing, said an underlying problem is that officials at the state Department of Water Resources don’t consider how groundwater pumping will affect surface flows when signing off on certificates of adequate water supplies.
“That’s one of the reasons why we’re losing the San Pedro. That’s one of the reasons why we’re going to lose the Verde. Because they keep permitting all these wells, knowing they’re connected to the surface water, but they don’t consider it,” Silver said. “This is the quandary that we’re having in Arizona right now, is we have no protection for our surface waters. Unless there is a direct diversion, our surface waters are screwed. And we have almost none left.”
Scientists share these concerns and say the state’s remaining riparian areas are at risk. Katharine Jacobs, director of the University of Arizona’s Center for Climate Adaptation Science and Solutions, said aquifers should be managed to protect riparian areas that depend on groundwater.
“There actually is very little protection for water-dependent natural environments in Arizona,” Jacobs said. “Arizona is really behind other states in that regard.”
Conservation groups have repeatedly advocated for legislation that would add protection for “ecological water” in streams, but for the past two years, these bills have died without being heard.
One court case that could have farreaching effects focuses on the San Pedro Riparian National Conservation Area, which was established by Congress in 1988 and includes about 40 miles of the river from the U.S.-Mexico border to St. David.
Lawyers for the federal Bureau of Land Management are seeking a set quantity of groundwater and surface water that they say is needed for the conservation area. A Maricopa County Superior Court judge could issue a decision on these federal water rights sometime next year.
Mapping wet and dry portions
In June, more than 100 volunteers fanned out along the river, walking the banks and wading through the shallow water. Using handheld GPS devices, they recorded whether each section of river was wet or dry.
This census of the San Pedro has taken place every June for the past 21 years. This year the river had a bit more water in it because of winter rains.
The survey, which is organized by the Nature Conservancy, takes the pulse of the river by capturing a snapshot during the driest time of year.
“Many reaches are stable. Some definitely are declining,” said Holly Richter,
the conservancy’s Arizona water programs director. She added that some of the declines aren’t yet statistically significant over the 20-year period, but that “a lot of these places have gradual declines.”
The fastest declines in the river have occurred between Highway 92 and the U.S.-Mexico border. Richter said she’s unsure about all the factors behind these declines, but significant drops in the aquifer have also occurred south of the border in Mexico, where the copper mine in Cananea is one of the major pumpers sucking water out of the aquifer.
Just north of Highway 92, a different trend has emerged. Over the past two decades, Richter said, the segment of the river in Palominas has been the only part of the San Pedro that’s shown a significant increase in the stretches that have water.
This shift came about after a land deal in which the conservancy retired agricultural wells and pumps. Fields that were once green with alfalfa have been converted to cattle-ranching lands. Groundwater levels have rebounded.
The conservancy has also bought other farmlands and properties that were slated for development. Using conservation easements, the nonprofit group has ensured that high-volume wells are shut down, and that subdivisions won’t be built on these lands.
Richter said her organization wants to achieve a long-term balance, or “sustainable yield,” in the watershed.
Along with retiring some wells and promoting water-saving, the group has been working with local agencies to boost recharge into the aquifer.
They’ve used a simulation model to pinpoint locations to build recharge facilities, and they’ve teamed up on infrastructure that captures stormwater to replenish the aquifer. They’ve also used treated wastewater from Sierra Vista’s treatment plant, where the effluent soaks into the soil to replenish groundwater.
The effluent has formed a mound of water in the aquifer, Richter said, and the goal is to create a series of these underground water mounds that help buffer the river as the cone of depression around Sierra Vista continues to expand.
Cochise County officials in August signed an agreement that clears the way for using treated wastewater from the city of Bisbee. Richter said the agreement enables work to begin designing a recharge project near the border, including a 12-mile pipeline to bring the treated water.
She said it’s crucial to keep putting more water into the aquifer. The cone of depression “is going to continue to spread until it gets to the river, and it’s going to take years to do that,” Richter said. “But decades from now, even if we don’t pump another drop, the river will see increasing impacts from the historic pumping that has occurred here.”
‘We need to change the groundwater rules’
If you follow the river downstream to Benson, there are stretches that sit bone-dry except when rainstorms bring runoff roiling through.
North of Interstate 10, the river reaches the Narrows, a rock formation that divides the upper and lower San Pedro. For a short stretch passing through ranchlands, the river starts to flow again, forming a shallow stream with algae swaying in the current beneath towering cottonwoods.
In Cascabel, about 30 miles north of Benson, the San Pedro again becomes a parched riverbed snaking along the base of rugged cliffs.
Barbara Clark has lived here since 1970. Her property spans the riverbed and includes shady stands of mesquite trees. She has goats, a garden, and a workshop for making clay pottery.
Clark has seen the river change dramatically. During the past 15 years, she said, the water level in her well has dropped 10 feet. The stream, which used to flow intermittently much of the year, now only rarely has water.
“We’re using our resources too fast. And I see it in my well,” said Clark, who is a board member of the Lower San Pedro Watershed Alliance.
She walked down to the riverbed, where the sounds of chittering birds filled the trees. Many years ago at this spot, she recalled, the water was often shin-deep or waist-deep, depending on the time of the year.
She remembered going tubing and cooling off in shallow pools. She saw schools of longfin dace, a type of a silvery minnows, gliding through the water. As she talked of the frogs and turtles that used to flourish in the river, her eyes teared up.
“I took it for granted,” Clark said. “But what’s happened now, in the last 15 years more or less, is that it doesn’t run 10 months of the year anymore. It runs when it floods.”
Sometimes even the monsoon rains no longer bring back flowing water in this part of the river.
Seeing how this ecosystem has faded makes her feel sad and scared for the future.
“It’s a loss,” Clark said. “We’re supposed to be stewards.”
She wishes everyone along the river could simply learn to “live within our means” and keep the watershed in a balance. But she said Arizona may need legislation that requires leaving some water in rivers.
“I don’t think it’s fair to pump the groundwater so deeply that we dry up all our surface waters,” Clark said. “We need to change the groundwater rules here. And I think we need to recognize that our rivers and our natural systems have a right to exist, and we need them to exist.”
Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.