By Teri Walker–
Editor’s note: This is the first of a three-part series on groundwater usage in Arizona. The first article in the series focuses on a new study tool to manage groundwater usage in the state’s most populous regions. The second article will report on the status and operations of the Coconino aquifer, which is the primary groundwater source for northern Arizona. The third article will explore typical water usage for potash mining operations and concerns of landowners near potential potash mining in the Holbrook Basin.
Since 1940, groundwater in Arizona’s alluvial basins has been depleted by more than 74.5 million acre-feet, or about three times the maximum storage of Lake Powell, according to a study unveiled by the U.S. Geological Survey (USGS) last week.
The draw on this groundwater source, which is located south of the Colorado Plateau and provides water to the most populous areas of Arizona, equates to about 2.4 million acre-feet per year, a rate that researchers say outpaces the level at which water is being returned to, or recharging, the alluvial basins.
The new USGS study evaluates groundwater availability and use for all of Arizona’s alluvial basins from 1940 to 2007, and provides a tool planners can use to model the interconnected nature of adjoining basins and assess how changes to groundwater supplies in one area might affect flow to or from adjacent areas.
Arizona’s alluvial basins are aquifers composed of sand, silt and clay material that has eroded from mountains surrounding the basins.
These basins supply 95 percent of the state’s groundwater use, according to USGS. Groundwater provides about 45 percent of the entire state’s water supply.
“Arizona is one of the fastest growing states in the nation, and groundwater supplies will undergo increased demand as water needs for a growing population are balanced with Arizona’s agricultural sector,” said USGS hydrologist Fred Tillman, who led the study. “This report is intended to aid state and local agencies by providing them information about groundwater to help better plan for the future.”
Arizona’s alluvial basins, which cover 65 percent of the state’s total land area, provide water in areas of the state below the Colorado Plateau, where more than 85 percent of the state’s population resides.
In Navajo County, groundwater is housed in the Coconino aquifer, where demand outstripping recharge of groundwater is not currently a problem.
Tom Whitmer, manager of regional strategic planning and tribal liaison for Arizona Department of Water Resources (ADWR), says the demand on the Coconino aquifer is more than readily met by the supply.
The Coconino aquifer holds about 500 million acre-feet of groundwater, and more than 300,000 acre-feet are recharged into the aquifer every year, according to studies conducted by ADWR. The demand on the aquifer is significantly less than what is recharged through rainfall, snowmelt and other sources.
In a study completed recently, ADWR found that in 2005 and 2006 (the latest years for which complete information is known), the total municipal, industrial and agricultural demand on the Coconino aquifer was about 105,000 acre-feet, or roughly one-third of the amount sent back into the aquifer each year.
The Coconino aquifer is found under most of northern Arizona, stretching essentially from Utah to the Mogollon Rim, and from New Mexico to Flagstaff. Draws on the aquifer come from Page, Flagstaff, Heber, Winslow, Holbrook, the Navajo Nation, the Hopi Reservation, and all communities, industrial and agricultural operations in between.
While groundwater supply and availability isn’t presently a pressing problem in northern Arizona, continued drought conditions and potential development are elements that can effect changes in water supply in the future, and require municipalities to consider the impact on the aquifer of planned developments and industrial or agricultural activities.
It is in the regions of the state served by the alluvial basins where groundwater supplies are expected to undergo further stress as an increasing population competes with the state’s agricultural interests. According to the U.S. Census Bureau, population in Arizona surpassed 6.5 million people in 2008, an increase of 140 percent since 1980, when the last regional USGS groundwater study was conducted.
According to the study, groundwater withdrawals are mainly for agriculture use and secondarily for municipal use. The primary source of groundwater recharge, or replenishment, comes from mountain runoff that flows into the groundwater basins. Groundwater in these basins has been depleted because the amount of withdrawal has outpaced aquifer recharge.
The new report includes updated groundwater budget information for each of the 45 individual basins or management areas, as well as a new groundwater-flow model to test an approach for evaluating groundwater basins.
“The new USGS report on groundwater availability and use in Arizona is a valuable compilation of information and dates,” said Frank Corkhill, chief hydrologist of ADWR. “The report provides a significant analysis of recent water-level data and long-term trends, and provides a well-balanced assessment of the strengths and weaknesses of various methods used to estimate groundwater budget components.”
The results of the USGS study troubles the newly formed think tank The Grand Canyon Institute, which has issued a water policy report titled “Arizona at the Crossroads: Water Scarcity or Water Sustainability?”
“There are credible scenarios for a very dry Arizona over the next 100 years that would have a dramatic effect on our economy,” said Karen Smith, Ph.D., former deputy director of the ADWR, now a fellow of the Grand Canyon Institute and author of the group’s report.
“We have grappled with, talked about, studied and measured our state’s water supply challenges for too long; we must take action now,” said Carolyn Allen, a former state senator and chair of the House Environment Committee, who is the current vice chair of the Grand Canyon Institute. “We must aggressively take the appropriate steps today to protect the future for our children; the alternative, given the consequences, is not acceptable.”
The institute issued five recommendations to the Arizona Legislature in its report, including:
“* Arizona needs to maximize its sustainable water resources, especially reclaimed water. The legislature should direct Arizona’s water agencies that reclaimed water be used for all purposes for which ADEQ (Arizona Department of Environmental Quality) believes it safe and where it is physically possible to do so.
“* Arizona’s water customers need better information on water use and pricing of wasteful water consumption. The legislature should require Arizona water providers to issue detailed information to customers on water use….
“* Arizona needs to simplify its surface water laws for environmental purposes. The legislature should create a commission to investigate Arizona’s surface water legal framework, and provide recommendations for any changes that will provide greater flexibility in securing instream flow and riparian water rights….
“* Arizona needs innovative, market-based approaches to water management. The legislature should create a commission to investigate market-based approaches to water allocation within the state and make recommendations concerning any needed changes in Arizona law.
“* Arizona needs a statewide financing mechanism for water acquisition and infrastructure…. The legislature should consider authorizing a new and sufficient revenue stream to fund water resources infrastructure, including acquisition costs.”
The full USGS report is available online at pubs.usgs.gov.sir/2011/5071. The Grand Canyon Institute background report can be found at www.grandcanyoninstitute.org.