The main items of business at the Gila Basin Irrigation Commission meeting, held Sept. 11 in Gila, were reports from Craig Roepke, Interstate Stream Commission Deputy Director, and Mary Reece, recently promoted to Bureau of Reclamation Phoenix Office Manager of Development, overseeing projects in the Phoenix and Tucson areas in Arizona, as well as the Arizona Water Settlements Act projects in southwestern New Mexico.

Roepke began with a short history of the Arizona Water Settlements Act.

"The Arizona Water Settlements Act was signed on Dec. 4, 2004, but before the act was signed, the Interstate Stream Commission came up with a policy to address the opportunity to gain 14,000 average annual acre-feet of water for the area and up to $128 million for a New Mexico Unit," Roepke said.

The two major tenets of the policy are 1) to recognize the unique and valuable ecology of the Gila Basin, while applying the best available science and 2) while considering the historic uses of and future demands for water in the Basin and the traditions, cultures and customs affecting those uses.

"The ISC chairman at the time told me they seemed like contradictory elements," Roepke said. "My reply was to please approve it, as we were going to look for projects to fit both needs."

He showed a photo of a dry 2011 Gila River and a March 13, 2012 photo of the river running at 129 cubic feet per second.

"That is an adequate flow for the ecology," Roepke said. "We don't need to touch any water until the flow is at 150 cfs."

He also showed photos of a dry Gila River on May 29, 2013, and another taken in June showing a dry river with some ponds.

"We went to Mogollon Creek and everything was green," Roepke said. "Below the diversions there is a lot of dead riparian vegetation, but when you get below the return flow ditches, everything is green. We have a problem."

He showed a sample schematic with only one diversion.

"If there is plenty of water, it floats agriculture," he said. "The problem is when the river gets low and water is diverted to water the fields. One choice is drying the fields and leaving water in the river to keep the riparian areas happy.

"How can we keep both?" Roepke asked rhetorically.

"The Gila Basin Irrigation Commission proposed diverting and storing water in ponds adjacent to the valley or farther away," Roepke said. "Dave (Ogilvie) had, in his developed riparian area, more southwest willow flycatchers during the recent bird survey than anyone else."

"More than 10 times as many," Dave Ogilvie of the UBar Ranch, serving as GBIC chairman, said.

"When the river gets low, the GBIC project proposes taking water out of the ponds," Roepke said. "Then you have water for ag and for the river. You take water out (of the river) when you have a whole bunch of water, store it and let it go. It benefits both the environment and agriculture.

"People say the ISC wants to dry up the river," he continued. "That's the last thing we want to do."

"This hydrograph shows the flows in the river, high and low," Roepke said. "If you deduct what we could take, you can see it in the graph as the little red tips of the tall blue columns.

"Other times when there is a lot of water in the river, it cannot be taken because of Consumptive Use and Forbearance Agreement (CUFA) constraints," he said. "These are based on the historical record."

Ogilvie asked about the constraints.

"I would like to save that to the end, because we have a model," Roepke answered. "This is a histogram of the flows from 1937-April 2013. There were 18,000 occurrences when we had flows below 101 cfs. If we add the CUFA, the blue bars are when we did nothing, and the red bars show the number of times water was diverted. If you are taking water out, why is the red bar higher?"

He said the ISC has set a baseline of not taking water below 150 cfs. That is double the median flow.

"You get more water with diversion 87.4 percent of the time," Roepke said. "In some instances, there may be an impact. For instance, every spring the ecology may need a flushing flow of 600-700 cfs.

"Other than that, there is only around an overall 1 percent difference in flows. It would be a stretch that it would have any ecological impact."

The Indicator of Hydrologic Alteration, which The Nature Conservancy developed, was used in a study. IHA is a statistical analysis.

"Using the IHA, we saw no change to extreme flows or low flows, with the CUFA diversions," Roepke said. "No significant  change at all, except in March median flows, when it went from 189 cfs down to 159 cfs. The high pulse median peak flow change was from 221 cfs to 201 cfs. Small floods showed a median peak change from 2850 cfs to 3071—an increase— with the CUFA. Large floods had a change of 12,100 cfs to 11,930 cfs. Remember we never leave less than 150 cfs in the river.

"The seven-day maximum drops a little bit," he continued. "The high flow pulses are about 60 cfs, so that should not hurt the ecology. Add it all up—for every peak that gets touched, two do not get touched.

"Small floods are probably more critical for the riparian habitat, and we found they actually increase if you divert," he said.

The histogram of March medians shows a range of 300 cfs to 700 cfs, "where you might have a problem, but over 70 years of data, we're talking about only six occurrences.

"The lesson is you have to be careful with statistics," Ropeke pointed out. "Even in this IHA model, there could be a significant impact one year, and another year no impact. If you can establish with the CUFA, where there would be hydrologic change, you have to make the case for the differences."

It is important to understand that even if the he IHA analysis of alternatives identifies a change in flows, it says nothing about the nature or degree of ecological impact, he said.

The Nature Conservancy is conducting a study on hydrologic impacts on the ecology. The group will compile the data, analyze the data, and predict the Gila flow with climate change and CUFA diversions. Then they will have have an expert panel create a background report, hold flow ecology workshops and then develop the final report.

"I wrote a letter supporting the proposal, because the work needs to be done," Roepke said. "I asked that an ISC hydrologist be part of the expert panel, but we were turned down."

"We are concerned that the TNC study will rely on the opinions of a hand-picked expert panel."  He quoted Bill Hume, who used to work for Gov. Bill Richardson: "The laws of physics and the natural functions of ecology are not susceptible to amendment by consensus."

"In other words, nature has it own rules and laws that have little relationship to human opinion," Roepke said.

"The Commission has asked us to use the best available science," he continued. "We are applying money to ecologic studies."

Completed are studies on low water use crops; drip irrigation, which the study found uses more water; geomorphic evaluations; climate change; a groundwater/surface water model; an IHA comparison; and ecological data compilation.

Beginning or ongoing are continuing studies on groundwater/surface water interactions; wetlands; further IHA statistical analyses; biological resource surveys; physical habitat simulation for birds, fish, and macro-invertebrates; population viability analysis for fish and birds; riparian flow correlations; and flow/macro-invertebrate correlations.

Some will be completed by the end of the year; some by next summer, according to Roepke. "Staff's job is to bring the data and results from all these studies to the Commission, so they can make an informed decision."

The complete groundwater/surface water model used three scenarios to show the effect of surface water diversions and flows on groundwater levels. The first is CUFA diversions of 13,500 acre-feet of water being removed completely from the river as if hauled out on a truck; scenario 2 is the CUFA diversions plus a 30 percent increase in irrigation; and the last is CUFA diversions plus a 30 percent increase in vegetation.

A baseline groundwater level was determined. The largest drop during spring runoff with scenario 1 was 1.6 feet. "Ninety-nine percent of the valley shows less than six inches. If you add in the irrigation from scenaior 2, the drop is one or two inches, because the water comes back as return flow from the fields. In the summer, you take water out and the drop may be up to .04 of a foot, with the irrigation increase, it would be a drop of .04 to .08 of a foot."

"What this is saying is that diversions are not making any noticeble difference," Roepke said.

Scenario 3, with increased riparian vegetation, shows a drop at the most of .2 of a foot, according to the model. "Models do predict; they do not prove," he said.

"Was the same substrate used for the comparisons?" Michael O'Connor, Gila Valley resident, asked.

"We have some piesometers along the river," Roepke said. "The modelers used that data, as well as information from the geologic surveys and other data.

"The modelers used the data they had to calibrate the model," he said.

He explained a piesometer is like a monitoring well to measure the water level or water quality. The ISC has five transects and The Nature Conservancy has four or five.

"I am experienced geologist, with my expertise in sedimentation," O'Connor said. "I have a lot of knowledge of streams moving back and forth. For the past 15 years, I've been studying a section of Bear Creek and have learned a lot. I do know that when it migrates back and forth, the range of sediments varies widely. In the old channels are the fine sediments, which can block flows. The placement of data points can be critical."

"From a hydrologic point of view, the fines can be dropped out and clays can develop, but I don't think they will have a huge impact except locally," Roepke said.

He continued with a discussion of the studies. "On climate change studies, we contracted with Dave Gutzler of the University of New Mexico. By his best estimate, the Gila River will have a reduction of flows of approximately 8 percent by 2050. A pronounced multidecadal natural variability will be superimposed on the projected decrease. That included the the El Niño, La Niña effects of the Pacific Ocean. Third, the timing of peak streamflow will show earlier spring flows and fourth, he says the effect on monsoons are difficult to assess."

"I asked him if the predicted glacier melt and hotter temperatures wouldn't cause more evaporation and put more water in the atmosphere," Roepke said. "I also asked him what the precipitation models are based on, and those projections were not very robust."

The rest of the meeting will be covered in a subsequent article.

Live from Silver City

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