Should the San Pedro River get federal water rights? A ruling might not be the last word

About 35 years ago, Congress created a federal conservation area along the San Pedro River to protect one of the most important riparian areas in the Southwest.

The designation entitled the 40-mile segment of river with water rights to make sure it could sustain key habitat.

A judge has now quantified how much water the San Pedro Riparian National Conservation Area is entitled to, but it's unlikely the legal process ends with this ruling and activists fear for the fate of the river.

"This case would create a water right if it were never appealed. But that's not going to happen," said Rhett Larson, a professor of water law and senior research fellow with the Kyl Center for Water Policy at Arizona State University. An objection would send the case to the Arizona Court of Appeals.

In late August, Maricopa County Superior Court Judge Mark Brain quantified the amount of water sufficient to fulfill the purpose of the 57,000-acre conservation area, which is managed by the Bureau of Land Management.

His ruling examined decades of data and determined the sufficient amount of water that would be monitored through four stream gauges and nine monitoring wells.

The decree would reduce the amount of groundwater that owners of 2,400 wells in the southwest corner of Cochise County are allowed to pump, said Robin Silver, co-founder of the Center for Biological Diversity. All of them were drilled after the conservation area was declared.

That is an early, and contested, interpretation of the ruling.

The judge's order could also be challenged by people who have been using the water for longer than the conservation area, said Larson. Seniority, when it comes to water rights, is one of the main lines of defense.

Users who started pumping water after the 1988 declaration of the conservation area have less priority, but it's still unclear how and by whom the federal water rights could be enforced.

First in time, first in right

There are other users who have been pumping groundwater long before the conservation area was established. The U.S. Army's Fort Huachuca, one of the largest water users on the upper San Pedro River, was established in 1877. This base could argue its water rights supersede those of the riparian corridor.

Users outside of the basin could also appeal the ruling. The deadline for objections is Jan. 22.

Even with a formal decree for the conservation area, there is a higher court case that could change the fate of water on the San Pedro River, said Larson.

The August ruling is part of a much larger legal process that began in 1974 to settle the water rights of the Gila River system. The San Pedro River is one of many tributaries, along with the Verde and Salt Rivers, that are part of that case.

"Every water right that is held by anyone, including federal and tribal water rights, are all included in this one large judicial process," Larson explained.

In that basin, there are many more users whose water rights have higher priority.

The Gila River General Stream Adjudication, which will likely continue for years, is lining up all the people who hold water rights throughout the greater basin, tributaries included, from oldest to youngest, Larson said. The court will quantify each of those rights.

Even after the process ends, the San Pedro River will remain "in the middle of a kind of long-term uncertainty about the overall priority and use" of its waters, Larson said.

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ADWR issued permits with a pending adjudication

Groundwater pumping within the conservation area has caused what hydrologists call a "cone of depression," in which the water table drops where pumping is occurring and then slowly expands around it.

Some wells showing a higher water level could drop when that "cone" flattens out.

Even with whatever conservation measures are in place, that "cone of depression" is deepening and will continue to expand, according to studies by USGS hydrologists.

"The river cannot recover if we don't stop pumping," said Silver, who has been litigating for decades to protect the riparian area.

After 1988, the Arizona Department of Water Resources issued about 2,400 well permits near the San Pedro Riparian National Conservation Area and extended 66 certificates of a 100-year adequate water supply to public water systems.

All of them are junior water users, compared to the conservation area, and groundwater pumping from these wells has a direct impact on the aquifer that also sustains the river.

Silver said the agency owes an apology to residents.

In 1992, the water department certified a water right for the San Pedro River conservation area: 11,028 acre-feet per year for the Charleston gauge, one of the four stream gauges that are considered in the adjudication.

Estimates were not far off.

Brain ruled the monthly flow coming from the gauges should be determined with "the median rate of the mean daily flow for that month from 1981 to 2015." A hydrologist working with the Center for Biological Diversity analyzed the U.S. Geological Survey data and concluded that the amount is about 12,300 acre-feet per year for the Charleston gauge.

The water agency "knew from 1992 how much water the adjudication was going to assign. None of this is a surprise, yet they still issued these permits and certificates," said Silver. About 22,000 people depend, to some level, on that water supply.

"This is the scam. This is how people were not treated fairly."

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Why interpreting the ruling is not easy

Everybody, including the BLM, is still trying to sort out the implications of the judge's order, said Sierra Vista City Manager Charles Potucek.

Whether a federal water rights adjudication could translate into any form of water use restriction on local development is not a given, he said.

"Who is going to impose that on us?" he asked.

The city, Cochise County, the BLM and Fort Huachuca, signed a memorandum of understanding in 2021 establishing shared goals to balance the water needs of the conservation area and the nearby communities.

Brain's ruling adjudicated less water than what the BLM was expecting and more than the City of Sierra Vista wanted, Potucek said.

Weighing that memorandum with the ruling will bring clarity to what the city needs to do "to protect the river and also protect all the people that live between the river and the fort," he added.

'Obviously, they can't all go away'

Developers are likely to face challenges proving there is an adequate supply of water. Castle and Crooke Arizona backed out of a plan to develop about 7,000 homes in the Sierra Vista area soon after Brain's ruling. Planning for the project began nearly two decades ago but no development had occurred.

Only five years ago Arizona's Supreme Court cleared way for the development, arguing the state's water department didn't need to consider the federal rights of the conservation area. That ruling advised that developers notified potential homebuyers about the risk. Such a warning is not required by law.

Water needs are well-studied

The ruling looked at decades of records from gauges and monitoring wells along the conservation area, as well as a "Water Needs Report" published by USGS in 2005, which analyzed the relationship between hydrology and vegetation in the area.

The conservation area, which is two miles wide and runs from the U.S-Mexico border almost to the town of St. David, has a mix of grasslands, mesquite woodland and cottonwood-willow forest.

Knowing how much water those plants use is a key piece of the puzzle to measure the water needs of the San Pedro River.

Researchers use a variety of techniques to measure the amount of water vapor leaving the plants over a long time span, said Russel Scott, a hydrologist with the USDA's Agriculture Research Service, who did evapotranspiration studies in the upper San Pedro River.

After taking measurements in different vegetation types, hydrologists translate the results to a whole area by looking at vegetation maps, quantifying the area each vegetation type covers and extrapolating the measurements, he added.

These and ongoing scientific studies are key to informed decisions and "adaptive management," said Holly Richter, a hydrologist and founding member of the Upper San Pedro Partnership.

Richter and Scott both help advise the partnership, a consortium of agencies and organizations working "to meet the long-term water needs of the Sierra Vista Subwatershed."

"For me, the real story here is kind of what's been accomplished during this long waiting period of the adjudication process and how far we've come during that time," said Richter, adding the adjudication was a milestone from a legal perspective.

Studies on the San Pedro have helped hydrologists understand which areas are the most critical for the health of the riparian habitat, she said. There is a good amount of research to make strategic decisions on where water is recharged or extracted. There are ongoing aquifer recharge projects in lands "where it could do the most good," she said.

The Upper San Pedro Partnership had the goal to balance the water deficit in the area.

A 2020 report from USGS found a deficit of 3,800 acre-feet of water per year. It is the smallest deficit since 2002, when the partnership began tracking the subwatershed water budget, the agency said.

Yet aquifer overdraft is still happening. Two of the nine wells included in the water rights adjudication are still below their minimum levels.

The Cochise Conservation and Recharge Network, which manages a series of projects with the aim of increasing water availability in the conservation area, reports about 6,000 acre-feet of water savings a year, either from recharge or from retired groundwater pumping.

About 80% of that total comes from the Sierra Vista wastewater treatment plant and from a 480-acre agricultural plot that stopped pumping groundwater in 2005.

More litigation awaits

Last month, the Center for Biological Diversity and allies at the San Pedro 100 petitioned the Department of Water Resources to declare an Active Management Area in the Upper San Pedro River basin.

It was the third request made to ADWR; the first was by the Sierra Club in 1984, and the second by the San Pedro Alliance in 2000. Both were denied.

The center may ask the court to re-examine all the 100-year water adequacy certificates issued by the Arizona Department of Water Resources in the Sierra Vista area after 1988, based on the San Pedro River water rights adjudication.

In the same way that the Department of Water issued those certificates, it could revoke them and reassess them, Silver said.

Clara Migoya covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to clara.migoya@arizonarepublic.com.

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This article originally appeared on Arizona Republic: Part of the San Pedro River has federal water rights. Now what?