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GSFWC meeting 052113, Roepke presentation

Gila/San Francisco Water Commission members at their meeting in Deming on Tuesday, May 21, heard Craig Roepke, Interstate Stream Commission deputy director, give a presentation on results that can be determined using a model developed the ISC to determine effects of diversions on the Gila River.

"This was updated to the end of March and includes 27,900 days of historical data," Roepke said. "It take flows in different streams and also indicates how much New Mexico has to bypass because of the Consumptive Use and Forbearance Agreement of the Arizona Water Settlements Act."

The model shows the months and the flows that have to remain in the river before a diversion can be made.  "The median flow in the river is only 73 cubic feet a second. Under the CUFA parameters, there is a minimum flow that has to be bypassed. We wanted a good buffer, so for the model we chose 150 cfs.  With the net annual average over the past 80 years, including minimum flows, the annual limit to what we can pre-bank, and the 10-year average of 140,000 acre-feet, that is a reasonable amount.  We don't have to hold to the 150 cfs, but we always have and want to continue to do so."

With the constraints of the CUFA, "we figured we could get 12,113 acre-feet of water a year. We want to take 10,000 acre-feet a year from the Gila River, and allow the San Francisco 4,000 acre-feet a year. Always ensuring the river has a flow of at least 150 cfs, we still get the 12, 113 acre-feet. That's more water than we need by 20 percent."

"Won't that alleviate environmental concerns?" Javier Diaz, GSFWC member representing Luna County, asked.

"That's why we set it at 150 cfs – for ecological concerns," Roepke said. "If we cut the 150 down to 75, the amount goes up, but only slightly. It's just noise. We would never want to leave no water in the river, and no water user would allow that. If we raise the 150 to 175, we don't see that much change in the amount of water we can divert. You do see a change if it is raised to 250 cfs. 150 cfs is the inflection point where the change occurs."

Referring to a previous presentation on The Nature Conservancy's planned study (http://www.grantcountybeat.com/index.php/news/news-articles/10652-gsfwc-meeting-052113-tnc-presentation), Roepke said he hoped The Nature Conservancy utilizes the 150 cfs in its model. "It helps protect the environment and gets us the water we need."

"One of the big concerns is climate change," Roepke said. "There are flows that would be affected by climate change. Say we had a 9 percent reduction. That is what the U.S. Bureau of Reclamation is using as its average of a whole bunch of drought models."

Making the changes on the model on the screen in front of participants at the meeting, Roepke showed the results would lower the amount of water that could be taken from the Gila River to an average 11,832 acre-feet.

"Talking to some, they think the reduction in flows may be closer to 15 percent," Roepke said. "It still gives us more than we need. If we go down 30 percent, it's still where we need to be. However, if the drought to the Colorado Basin increases by 30 percent, we're all basically toast.

"There would not be enough water for agriculture, and we need to keep getting water to people," he continued. "Some think if water gets too expensive, people from Phoenix will move. My worry is where they will move."

Roepke said he has spoken with David Gutzler, University of New Mexico climatologist, and a climatologist from from Arizona. "All the climate change models are based on an old concept that most of the evaporation into the atmosphere occurs from oceans near the equator," he said, "and that the water rises up to where it gets cool and falls on the northernmost and southernmost latitudes. If that happens, precipitation will bypass New Mexico, which is on the tipping point. The models are based on a certain amount of moisture in the atmosphere. If we have a great increase in temperature, which melts the ice caps and glaciers, we will have not just a 30 percent reduction in precipitation, but there will be 30 percent more water in the atmosphere. What's it going to cause? That's a fact nobody knows."

He hypothesized that if the drought increases by 30 percent, there will be a major upset, culturally, economically and with migration. "I suspect that even at 30 percent, we would still have water to divert," he said.

When Roepke reiterated that the data was from the past 80 years, Diaz replied: "That's all?" Roepke said tree ring data shows a major drought going back to 1400-1500 AD.

Martha Cooper of The Nature Conservancy commented that people moved away from the area.

Roepke said if water in the Colorado River Basin goes down 30 percent, Arizona would get the first hit. "It wouldn't have much water. It could take water legally for its population, and it would get adjusted. But even if it were adjusted, New Mexico's exchange water has first priority on the Central Arizona Project, so until they are willing to shut Phoenix off, New Mexico gets its water to exchange for a Gila River diversion. Mootz and Reynolds assured that back in 1968."

He showed a graph of flows on the Gila River showing from zero water to floods. "If you overlay current Gila diversions, what's left are red tips on the graph, which are what New Mexico can divert. There is not much impact. It's not measurable. The thing I want to point out is that with a lot of floods, we don't take anything at all. Because of the constraints, there is plenty in the river to divert. A farmer in Virden might want to divert, but couldn't do it because of constraints. We're talking about taking 7 percent of the water on 10 percent of the days. That's not doing a whole lot. That's what we thought when we did this."

Roepke said Cooper mentioned one of the ISC modelers used software by The Nature Conservancy, which shows statistical impacts. "Our modeler found no change to extreme low flows because of the 150 cfs. If we maintain 150 cfs, we are not touching water in about 90 percent of the flows. That's to our way of thinking critical to the ecological habitat. With no change to low flows and using the CUFA, diversions do not dry up the river. There is no change to median flows except in March."

"Some of the graphics the software produces you will see a little bit below on the median. That's the 75th percentile and the seven-day maximum. On the high flow pulses, you see some of the pulses went down. That's the 350 cfs maximum. For every one that went down, a whole bunch stayed the same. This is a small flood, and it is actually improving them, according to the TNC software.  Even though the 75th percentile and the median are higher, these could be ecologically critical flows."

Thal asked what was critical about an ecologically critical flow.

Roepke said that was a good question and a key question. "The real work is figuring out how to go from impact to flow to impact to the ecology. Maybe sometimes, when the flow is reduced there is no impact. Sometimes, you might reduce the flow and have a beneficial impact. It might be good for the Apache leopard frog and bad for the spikedace or southwest willow flycatcher. "

"This doesn't factor in humans," Thal said. "It seems to me the ecological model has to include humans."

"Hydrologic alteration alone won't tell you anything," Roepke said. "The tough work is documenting the impact on the species or community specific. One concern we have frankly with The Nature Conservancy study is that they have handpicked their partners and the partners will write the background report. They will also be writing the final report, and it is not required to have other people's input in their report."

Thal said in regards to the TNC methodology, as presented in Cooper's report, it is excluding humans. "I would hope we get a chance to work on models including humans and the trade-offs."

Roepke brought up the report by Deborah Hathaway of Papdopolus & Associates, which used three scenarios in a model similar to the one Roepke was presenting. The three scenarios took a CUFA diversion in an above-average year, a second scenario with a CUFA diversion plus 30 percent increase in irrigated acreage and scenario 3, a CUFA diversion plus a 30 percent in riparian vegetation. The report which Hathaway presented to the GSFWC at a prior meeting showed little to no impact to groundwater levels.

Diaz said he didn't see the second scenario happening economically in one year.

Roepke said the three scenarios were chosen to show extremes to see if there were a real concern.

He then showed a map developed through flying LIDAR (Light Detection and Radar) to show elevations and river channels. "This information is captured in the model, if you're concerned about flooding channels for the leopard frog habitat or the southwest willow flycatcher. We are able to show this because we spent money flying LIDAR."

Roepke pointed out the baseline information post-winter runoff; then information during the summer dry period, when lower groundwater levels start to show up. "This is the decrease in the groundwater level after you put on the CUFA." He compared it to winter and summer when there is no change, except in one wetland. "Effectively there is no change. The maximum drop was 1.9 feet in the whole reach." The summer dry period plus an increase of 30 percent irrigation showed a slight change in groundwater of .12 of a foot. "The reason is when you are irrigating, you get a return flow, which keeps the water table up." The CUFA plus 30 percent increase in riparian vegetation showed a slight change in groundwater of up to three inches drop in the water table. "That's not going to hurt either."

He showed a histogram, which is what was used during the AWSA negotiations between 2000 and 2004. The histogram takes the frequency of flows in a flow range, such as 100-200 cfs, 200-300, 300-400 and so forth. With a normal histogram, and putting in the 150 cfs minimum, almost all flows are within the parameter.  "We thought we were doing a good job protecting most of the flows. There is a lot of flexibility in the CUFA to accommodate environmental issues. To be real frank, someone may be able, I hope they can demonstrate, not just an opinion, whether we need flows at 750 cfs."

"If you wanted to maintain the ecological livelihood of the river, it wouldn't be species specific," Diaz said.

"There might be tradeoffs," Roepke said. "I was told about a meeting where a southwest willow flycatcher biologist and a spikedace biologist were in the same room, and they almost came to blows.

"The hard part is translating the impact on flows to the impact on ecology," Roepke said. "That's one of the big concerns I have with the TNC study. I wrote a letter supporting the grant request. We were a little abashed that The Nature Conservancy would not let the ISC be a member of the panel, be part of the background report or co-author anything using our data and models, so we're going to have to duplicate what they're doing. We plan to spend money on it and have very good scientists working on it, but they tell us it will take two to three years to do rigorously."

Diaz asked what happened to species in the past. "The future doesn't matter if in the past the river was natural."

"Some in The Nature Conservancy say their position is that we should not divert a drop of water," Roepke said. "Everything I've shown today, whether the histogram, or the TNC statistical software, I could change items to make it look worse. Statistics can be treacherous. What the ISC does when it convenes a panel is it invites scientists from different persuasions, so that everybody is involved from the start. What we're doing, we will invite The Nature Conservancy, Fish and Wildlife Services, Game and Fish, all from the start."

Concurrent with all this, Roepke said there are meetings on critical habitat for the spikedace and loach minnow. "I was shocked when somebody asked one of the technical team members, what is the greatest threat to the spikedace. His response was: 'people.' That's not a scientific response. These things can take on a life of their own. The only way to do it is with people of differing viewpoints at the table right from the start."

Vance Lee, GSFWC member representing Hidalgo County, asked if the 150 cfs cutoff were in place, and the river was running at 160 cfs, would it be possible to divert 10 cfs, to which Roepke said yes.

The meeting continued with committee reports and discussions. They will be covered in a subsequent shorter article.

Live from Silver City

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