Diversion plans for the Gila would have major impact, critics say

Small and medium-sized flows could be most affected.

 

The Interstream Commission, whose nine members were appointed by New Mexico Governor Susana Martínez, must decide whether it will pursue a diversion along the Gila River that would provide more water for southwest New Mexico, or whether to serve regional water needs through non-diversion alternatives, such as conservation and watershed restoration.

The deliberation comes under the 2004 Arizona Water Settlements Act, which gave New Mexico the right to develop up to 14,000 acre feet of additional water on the Gila — enough to supply a city the size of Santa Fe for a year.

On Aug. 26, the commission delayed voting on options for the river until the results of further feasibility studies come out later this fall. It will hold two more meetings — one scheduled for Sept. 22 and the other in October — before making a final decision in November.

For 10 years, the commission has weighed in on various proposals for the Gila. All of them are designed to improve the water supply for the dry southwestern corner of the state. But debate over how to do that has created one of American West’s most contentious water battles, pitting proponents of a diversion against those advocating for less costly conservation alternatives.

Craig Roepke, deputy director of the commission, says it is evaluating all 15 proposals, and not just those for a diversion and is “applying the best science” before making a decision. But environmental groups like the Nature Conservancy and the Gila Conservation Coalition say the commission is silently pushing for a diversion — and selling flawed science to the public in an effort to win support for that agenda. These critics say the commission is unlikely to choose options that forgo grabbing more water for the state, no matter the cost. At stake are a $46 million federal subsidy reserved for a diversion project, and the rare chance to bolster shrinking water supplies for drought-prone New Mexico, before thirsty Arizona takes it.

“There’s been a successful campaign of misinformation about which flows will be diverted,” says Martha Cooper, the Southwest New Mexico Field Representative for the Nature Conservancy.

The Gila is a capricious river, ranging from a roaring deluge during early spring snowmelt and late summer monsoon to barely a trickle during drier times of the year. The floods range in size, with the largest coming in like a tsunami and the smallest barely noticeable, but they all play a critical role in the ecology of the Gila by spreading nutrients around the floodplain and re-charging the groundwater reserves that keep the riparian forests flush with life.

“It’s like a sponge,” says Cooper, who’s lived and worked at the Conservancy’s research station in the Cliff-Gila Valley for nine years. “I’m always stumbling into small wetlands I didn’t know existed.”

Under the complicated terms of the Arizona Water Settlement Act, New Mexico can only divert up to 350 cubic feet per second of water at any given time. That’s the equivalent of 350 basketballs whizzing by each second, which isn’t a lot on the mighty Colorado, but on the Gila — which can look more like a creek at certain times of year — it’s significant.  For that reason, the commission said a diversion would only be allowed to draw water when the Gila is flowing at a minimum 150 cubic feet per second to keep from “de-watering” the river. The idea, says Roepke is to just shave the peaks off major flooding events.

The Nature Conservancy disagrees. Its own report, called “The Gila River Flow Needs Assessment,” looks at how the river’s fluctuating flows shape its ecosystem and how that relationship would be affected by a diversion. The study shows that contrary to the commission’s message, a diversion would have the greatest effect on the small- and medium-sized floods by reducing their frequency and magnitude. This would lead to rapid groundwater declines and set off a chain of harmful ecosystem changes. 

An earlier report written by S.S. Papadopulos & Associates, environmental consultants hired by the Interstream Commission, also found that the small- and medium-sized flooding events will be altered most by a diversion, but opponents of the diversion say those findings have not been well publicized. In public presentations, the commission maintains that a diversion will have minimal impact on the Gila’s flows and will actually improve the ecology of the river.

But that doesn’t jive with the science, says Cooper. The really big floods only occur every five to ten years, so if those were the only times a diversion were drawing from the river, it wouldn’t capture much water. Not only that, she says, “if a 30,000 cubic foot per second flood becomes a 29,650 cfs flood, that obviously doesn’t really matter, but if you take 350 cfs from a 600 cfs flood, you’ve just taken more than half of its flow.”

When that happens, the river won’t move out of the main channel and into the secondary streams snaking through the floodplain. That would hurt the cottonwoods, since their seeds need a bed of wet mud in which to germinate, and numerous species that depend on the trees, including the endangered southwestern willow flycatcher and yellow-billed cuckoo.

“One thing I’ve learned from all this is that general averages don’t tell the whole story,” says Cooper. “They’re [the ISC] saying groundwater levels would decline a foot but then bounce back but the trouble with averages is they mask the actual effects in any particular year.”

Roepke, however, claims that first diverting and then storing water will help prevent the river from drying out during the peak irrigation season before the late summer monsoons hit. “If you can store some of the flood water and keep the river flowing, you’ll do some really nice things for the species in the river and the riparian habitat,” he says. 

That may help some fish and aquatic macro-invertebrates, says Mike Fugagli, a local ornithologist, “but it’s a classic example of robbing Peter to pay Paul.” In other words the diversion would potentially improve the river’s base flow, slightly, but could destroy the crucial small- to medium-sized flooding events.

“The ISC has made no effort, as far as I can tell, to acknowledge this tradeoff,” Fugagli says.

As the debate over the Gila enters its final stretch, no side is backing down. The commission has until the end of the year to decide whether New Mexico will build a diversion — and receive the federal subsidy reserved for that purpose. Meanwhile, everyone is wondering: how much is the Gila’s water worth?

Sarah Tory is an editorial intern at High Country News.