Editor's Note: This is part 4 and the final portion of a multi-part series of articles on an Interstate Stream Commission staff quarterly public meeting held at Western New Mexico University on Monday evening. It will cover the presentation by hydrologist Deborah Hathaway of S.S. Papadopolus and Associates consulting firm.
"I am not advocating for anything," hydrologist Deborah Hathaway of S.S. Papadopolus and Associates consulting firm began her talk. "In 2009 and 20010, we initiated data collection, including land evaluation surveys, well transects, and seepage runs. We have coordinated this study with The Nature Conservancy and the New Mexico Department of Game and Fish."
The study consisted of developing the model tools in 2010-2011, and in 2011-12, applying the groundwater model. "We have no simulations, we are just describing a tool."
The past few months, Hathaway said the group has used the Indicators of Hydrologic Alteration developed by The Nature Conservancy to do analysis of surface water and groundwater interaction, along with riparian groundwater models. She described the computer model and how it looks different if the water is a trickle or if it overflows its banks.
She said the model considers canal seepage, irrigation water use and recharge, stream gains and losses, and riparian/wetlands water use.
"The point is to show how surface water affects groundwater and vice versa," Hathaway said. "For demonstration runs of the model, we picked a baseline condition."
The illustrative scenarios were three for comparison. Scenario 1 was a Consumptive Use and Forbearance Agreement diversion of 13,500 acre-feet simulated. Scenario 2 used the CUFA and a 30 percent increase in agricultural irrigation, and Scenario 3 included the CUFA withdrawal and a 30 percent increase in riparian vegetation. The graphs and the report are viewable at nmawsa.org.
"We picked two time points of a hypothetical year—the end of February, which should be the highest runoff from snowpack after CUFA diversions and the end of July for the low flow," Hathaway said. "Scenario 1 showed a small difference in the winter groundwater elevations, which ranged from a few inches to two feet, but were short-lived. In the summer, there was little change."
Scenario 2 showed no change in the winter, and a small change in the summer, depending on the location of irrigated areas.
Scenario 3 showed no change in the winter, when the vegetation was dormant, and in the summer a small change depending on the location of the riparian communities.
She stated, that although the CUFA diversions caused little to no impact to the hydrology of the stream, its impact on sensitive riparian or animal ecosystems remained to be determined.
In order to evaluate the ecosystem response, several steps would be required, including characterizing the altered hydrograph and articulating the flow-ecology relationships by identifying the physical changed to the hydrologic environment and by characterizing the eco-response to physical change.
Hathaway showed several graphs comparing the past 60 years of hydrologic data on the Gila River to a simulation of the same 60 years, if CUFA had been in place. She pointed out that the Indicators of Hydrologic Alteration would not deliver a value judgment. "You have to look at where things are changing."
She said the CUFA does not get rid of the high flows, "so it is not drying up the river. The largest difference in high-flow pulses with the CUFA diversions is about 20 cfs. In the small floods, with a CUFA diversion, the median actually goes up. We are showing March as the only month of the year over the past 60, where the median flow changes significantly. It is the most significant seasonal change, because the snowpack runoff has finished."
"What does IHA tell us about the CUFA diversions?" Hathaway asked and answered. "There is no change to extreme low flows of 150 cfs and no change to low flows 75 percent of the time. The CUFA," she reiterated, "does not dry up the river. There is no change to median monthly flows, except in March. The high-pulse events median peak is 221 cfs down a little to 205 cfs with CUFA. Small flood median peak change goes up from 2850 cfs to 3072 cfs. The large flood median peak change is from 12,100 cfs slightly down to 11,930 cfs.
"The impacts are relatively subtle, and it is helpful to examine the full range of statistics to identify focus areas for ecological evaluation," Hathaway said.
She described the next steps for consideration in the model as:
1) refine/recalibrate the riparian groundwater models with data collected over the past two years;
2) set up the model scenarios and recalibrate them; and
3) continue to monitor the data.
Helen Sobien, ISC engineer, gave a short report on the assessments with which she has been tasked.
"They include the Mimbres Valley projects," Sobien said. "The Deming effluent reuse report should be ready by July. I hope to have all the reports to Mary Reece at (the U.S. Bureau of) Reclamation by September."
The Grant County Airport well field project will include a 16-mile pipeline to provide water to Hurley. A consultant has been hired to do the work.
The Bayard effluent reuse project for watering the parks in Bayard has a competing proposal from Grant County to take the same effluent to water some of Bayard's parks, and to create a reservoir on Twin Sisters or Cameron creeks. "We are doing the preliminary work on these."
An audience member asked Hathaway about the use of the hydrologic model. "You mentioned a CUFA diversion of 13,500 acre-feet. I would like to see the different values per year. The Arizona Water Settlements Act allocates 140,000 acre-feet of water over a 10-year period. I would like to see what it does to the river if more water is taken in a given year."
Hathaway said the model could be used to run a variety of scenarios.
ISC Gila Project Manager Craig Roepke said the ISC really appreciated the turnout, and asked if those present would like a special meeting just to answer questions. To an overwhelmingly positive response, he said the agency would try to set up such a meeting.
Martha Cooper of The Nature Conservancy pointed out small floods do not overbank the river but feed water into the wetlands.
Hathaway said it is done incrementally.
A questioner said a concern is communication about how the reports are generated, and there are so many factors. "I need to know how to home in on what's important and what people hear."
Hathaway said it has been discussed to do two analyses. The preliminary groundwater models need to be taken to the next stage.
"We are not modeling a 30-foot drop in groundwater," Hathaway said. "The drop ranges from a couple of inches to two feet."
She said the IHA analysis was done with no secondary analysis that included climate change projections.
An audience member asked if the ISC was planning on modeling into the future.
Roepke said: "Yes, the ISC is going to model lots of things. The advantage to the IHA is that it is specific. In really bad years, there will be no CUFA diversions. We can find in the 60-year record a time like what we think a given year will be."
Todd Schulke of the Center for Biological Diversity said his concern was that the future might be unprecedented.
Editor's footnote: This editor/reporter left at this point due to exhaustion. The meeting continued for a short time, but was not covered.