Before the Interstate Stream Commission Arizona Water Settlements Act public meeting at the Cliff Schools gymnasium Monday, April 14, the Cliff Schools Family, Career, and Community Leaders of America provided a lasagna dinner for donations. Top photo shows Kylee Rice, Cheyenne Zacharias, Emma McDonald, and Katie Turner, who served the food. Second photo is of Tammy Hooker, the first female president of the Cliff-Gila Farm Bureau, which organized the event, and Rita Larson, chef and helper.
Editor's Note: This is the first in a series of three articles on the Interstate Stream Commission quarterly meeting addressing the Arizona Water Settlements Act planning process.
Photos and article by Mary Alice Murphy
The Interstate Stream Commission hosted a quarterly public meeting Monday, April 14, at the Cliff High School gymnasium.
Reese Fullerton, facilitator, welcomed the crowd to the meeting and said: "We welcome and consider all your input."
The first presentation was by Amber Whittaker, INTERA geologist and GIS specialist, giving a report, Gila River Flow and Riparian Vegetation Health in the Cliff-Gila Valley. "We at INTERA had the goal of comparing vegetative health to river flow."
The hypotheses and test were that riparian vegetative health would increase with increasing flow in the Gila River, she explained. "We wanted to determine and compare health and flows over time. We looked for a positive correlation."
"We separated the valley into five reaches—Reach 1 was from the confluence of Mogollon Creek with the river to the first diversion; Reach 2, from the first diversion to just below the highway 211 bridge; Reach 3, from just below the bridge to the Bill Evans Lake mining diversion; Reach 4 from the mining diversion to the Bird Area; and Reach 5, from the Bird Area to Virden," Whittaker said.
"We also wanted a combination of wet and dry years and wet and dry seasons, along with the best aerial photographs, as well as satellite images we could get from Landsat on clear days," she said. The years chosen were 2005, 2009, 2010, 2011 and 2013.
"We identified vegetation community, estimated the vegetation extent and health and, with the flow estimates, we compared flow and vegetative health," Whittaker said.
National Heritage New Mexico at the University of New Mexico did the general vegetation mapping, with 16 plots and 88 field maps. Most trees in the riparian areas are native, including Freemont's cottonwood, Arizona sycamore, boxelder, Goodding's willow and shrubs.
"With the aerial photos, we see little change from 2005 to 2013 in type or amount," Whittaker said. "Fifty-six percent of the vegetation was mixed trees, with 10 percent mixed trees/shrubs, 11 percent sparse shrubs, and mixed shrubs/trees, mixed shrubs, sparse trees, and sparse trees/shrubs, ranging from 1 percent to 7 percent.
"With the Landsat satellite information, we used the normalized difference vegetation index (NDVI)," she explained. "The NDVI was used for scenes for three dates during the growing season, May-August, determining the average NDVI per reach for each year.
Infrared information on the image reflects the green; the red information absorbs the green, creating a dark red for healthier vegetation; and the two together give a composite image, which makes up the NDVI. The higher the NDVI, the healthier the vegetation is.
"We also did a hydrologic study, with the goal of estimating the river flows in and out of each study reach," Whittaker continued. "The model was based on USGS gages, contributing watershed areas, and diversion reports from the NMISC."
[She presented several graphs and charts of the yearly reaches' average flows from June through August, including one with a goodness-of-fit or R2 value.]
"By comparing the average NDVI and the river flow, we then determined whether the data sets had a relationship," she said.
The interpretations from fieldwork were that the riparian areas are primarily native tree dominated; from the aerial photographs, that the extent of vegetation has not changed significantly since 2005; from satellite imagery that NDVI patterns are complicated, especially in Reach 2; in hydrology that there are consistently lower flow conditions in Reach 2: and vegetation health generally increases with increasing river flow; and the response is rapid, although Reach 2 had poor correlation.
The conclusions were positive significant correlations between NDVI and river flow, which support the hypothesis in most of the reaches, with Reach 2 being different. Further study is needed.
"We want to discover why Reach 2 is different," Whittaker said.
"I live along that reach," Mary Burton Riseley said. "The river goes dry for 4-8 weeks a year. "
Whittaker noted the healthiest vegetation is along the ditches in the reach, likely using groundwater.
David Anderson, ISC environmental scientist, said: "These are draft reports, with the final reports available in June."
"What were the parameters for the study?" a female questioner asked.
"We chose recent times, with wet and dry years, and really needed good aerial photography and satellite imagery," Whittaker said.
"What about the higher R values?" a man asked.
Whittaker noted the vegetation in general absorbs red and reflects infrared. The higher the NDVI, the healthier the plant. "We can't tell the difference between the riparian vegetation and the fields."
"Why this study?" a young female participant asked.
"We saw a cottonwood die off, and within the budget, we wanted to know if there was a correlation between vegetative health and river flow," Anderson replied. "The report is on the website nmawsa.org.
"Did you speak to residents who have observed the river over many years?" a woman wanted to know.
"We spoke to a lot of residents," Whittaker replied. "That is not directly reflected in the report. We could see our vegetation has changed. Talking to residents gives perspective."
To a question about costs, Anderson said it is ongoing work, but the work order on the website would have the cost.
The next article in the series will address two reports—one on potential environmental impacts if water is diverted, and another on biological and cultural surveys in the canyons that might be used for water storage.