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The Role of Science in Groundwater Management in Arizona Rita P. Maguire, Think AZ Introduction There is increasing conflict between population growth and limited water supplies in Arizona. For the past decade, Arizona and Maricopa County, home to Phoenix, have been consistently ranked among the fastest growing states and counties in the United States. For example, Arizona’s total population in 1990 was under 3 million people; today the state’s population exceeds 5.5 million. The state’s surface and groundwater supplies remain essentially unchanged, however, the Central Arizona Project provided a significant increase in access to Colorado River water during this time period. This increase is central to the implementation of Arizona’s groundwater management program, a major provision of which is the substitution of renewable supplies for mined groundwater. Arizona’s water supply comes from two major surface water systems, the Gila River Basin, the Colorado River Basin and groundwater. Annual statewide demand for water is approximately 7 million acre feet. Groundwater pumping supplies about one-half of the demand, the remaining demand is met with supplies from the Colorado and Gila River systems. About 70% of the state’s water supply goes for agricultural use; down from 90% at the turn of the 20th Century. Regulation of Water Use In Arizona, like the rest of the United States, water is considered a public resource regulated by the state through the Arizona Department of Water Resources (ADWR)1. ADWR issues water rights and permits to use surface water on land in accordance with the Prior Appropriation Doctrine which recognizes the senior rights of water right holders before junior right holders in times of shortage2 This becomes particularly important because of the frequent drought periods that dramatically affect the state’s surface water supplies. The legal doctrine of prior appropriation does not apply to the state’s Colorado River supplies which are governed by federal law developed pursuant to interstate compacts, federal law and judicial rulings that apply to the seven states that share the Colorado River. Arizona is located in the Lower Basin of the Colorado River and has rights to 2.8 maf from the 7.5 maf delivered annually to the three Lower Basin states: Arizona, 1 http://www.azwater.gov/dwr/ 2 This doctrine implies that the first person to obtain a water right on a stream is the last to be shut off. When stream flow is low, the water right holder with the oldest date of priority (the most senior right holder) can demand the water specified as their water right regardless of the needs of junior users (those gaining access to water at a later date). If there is additional water, the person with the next oldest water right can take as much as necessary continuing down the line of water right holders until the surplus is exhausted. 69
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California and Nevada (CRWUA 2005). In exchange for federal funding of the construction of the Central Arizona Project which delivers Colorado River water to the central and southern parts of the state, Arizona agreed to accept reduced deliveries when shortages occurred in the Colorado River Basin. Access and use of the state’s groundwater supplies are also regulated by the ADWR in accordance with the Groundwater Management Act (GMA) adopted in 1980. However, the GMA only applies to the use of groundwater in certain parts of the state known as Active Management Areas (AMAs). Eighty percent of the state’s population resides in the state’s five AMAs. The primary goal of the GMA is to assure sustainable use of the groundwater supplies in the AMA’s. This is done by replacing groundwater pumping with surface water. “Safe- Yield” refers to the goal of maintaining a long-term balance between the annual amount of groundwater withdrawn in an AMA and the annual amount of natural and artificial recharge. It does not account for impacts on surface water due to diversions, drought or excessive groundwater pumping. Key provisions of the GMA include the restriction of any new irrigation in the AMAs after 1980, and the prohibition of residential development on land without an “assured water” supply. The Assured Water Supply program requires all new subdivisions in AMAs to demonstrate that sufficient water supplies of adequate quality are physically, continuously and legally available for 100 years. The new subdivision’s water provider must also prove the financial capability to construct water delivery and treatment systems to serve the proposed development. The entire focus of the Assured Water Supply program is to promote the use of renewable supplies such as effluent and Central Arizona Project water. Groundwater is used as a last resort after exhausting all available renewable supplies. Even when groundwater is the only reasonable option for supplying water to a new community, the developer is required to purchase and store surface water in one of the recharge basins located within the AMA to compensate the aquifer for the withdrawn groundwater. In addition to the Assured Water Supply Program, the ADWR administers an extensive conservation program for municipal, industrial and agricultural water uses. Starting in 1980 and each succeeding decade through 2025, per capita or per acre water use is reduced in a continuous effort to achieve Safe Yield in the five AMAs by 2025. The Department is authorized to impose civil penalties for failure to comply with the prescribed water duties for each use sector. Future Sources of Municipal Water Supplies in Arizona It is projected that municipal and agricultural demand will exceed the state’s surface water supply by 2030 although droughts on the Colorado River System could hasten the shortfall. In fact, if all groundwater pumps were turned off today, the state would experience a shortfall of approximately 2maf annually. As a result, Arizona is actively engaged in recharging Colorado River supplies in aquifers within the CAP service area. 70
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This water will be withdrawn in the future when shortages occur due to excessive demand or drought. Future municipal demand is expected to be satisfied by the purchase and retirement of water rights on farmland. Arizona is fortunate to have substantial amounts of agricultural land surrounding Phoenix and Tucson, the state’s major metropolitan areas. In addition, extensive Native American water rights on Indian reservations throughout the state are expected to be available for lease to non-Indian cities and towns in the future. The expectation in the management plans is a combination of reduction in per capita use of groundwater and an increase in use of renewable supplies. Working towards the safe- yield goal in an iterative fashion allows for adjustments in supply enhancement and demand management over time, in response to changing conditions. What are the most important water issues that Arizona faces in the next 10-15 years? As we continue to guide development and management of the state’s water resources, we will be required to: 1. meet water demands that will grow and shift among water use sectors; 2. analyze and prepare for the potential impacts of global climate changes; 3. identify and compensate for groundwater contamination due to runoff and recharge of surface water into the groundwater basins; 4. respond to the complexities of protecting species and managing water in an ecosystem with extreme wet/dry cycles; and, 5. analyze and mitigate the environmental impacts of new or expanded water development projects. What kind of research is most helpful in providing the knowledge and technology needed to address long-term needs? Groundwater Modeling Because of the tension between growth and limited water supplies, there is a need for increasingly sophisticated numeric models such as “Modflow” produced by the United States Geological Survey (USGS) to analyze the relationships between surface water and groundwater in basins where rapid growth is occurring. Hydrologists and geologists at the ADWR have refined these models to anticipate the impacts of projected pumping and recharge on aquifers. The Department is also refining the model’s grids for the purpose of better understanding the impacts of groundwater pumping near streambeds on surface water flows. 71
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Land Subsidence An ever increasing problem in Arizona is land subsidence wherever significant groundwater pumping is taking place. ADWR has been working with the USGS and National Air and Space Administration (NASA) to develop and monitor changes in surface elevations in areas where little or no development has occurred. Using Infarometric Synthetic Aperture Radar (INSAR), the federal government has provided satellite imagery to measure the changes in surface elevations. This information can be very helpful in anticipating and preventing structural problems in structures within the impact zone. In addition, subsidence studies have been conducted using extensometers (to measure compaction), global positioning system information (to measure changes in elevation of the earth surface), as well as radar interferometry. The USGS has also been pioneering the use of gravity meters in Arizona to assess the relationship between changes of volume in storage and rates of subsidence. Availability of the interferometry data has substantially changed perceptions of the seriousness of subsidence within the urban parts of the state. Mapping the Connection between Groundwater and Surface Water Little is know about the interconnection between groundwater and surface water in the rural areas of the state, the location for much of the state’s future population growth. Understanding these relationships will help determine how federal land management policies impact water supplies on federal lands that are often at the headwaters of the state’s surface water supplies. For example, the federal forest and land management policies adopted by the Bureau of Land Management and the U.S. Forest Service affect runoff and percolation. But little research is available to tell us how. There appears to be growing interest in modifying the management of the Ponderosa Pine forests in Arizona due to the recent forest fires that have occurred. Before new management practices are adopted, consideration will be given to the impact on water supplies, both surface and groundwater. Improving Decision-making in Water Management Water managers throughout the state are continually seeking to improve the scientific input to improve real-time water management decision-making and minimize the environmental impacts of water operations. In particular, information generated from stream-gauges, well monitoring, and snow pack evaluation at the higher elevations is very useful to water managers throughout the Colorado River watershed. Partnerships have been developed with the USGS, Bureau of Reclamation, universities and state agencies to maximize the availability of real-time water information across the state and throughout the West. Water Quality Effects of Recharging Surface Water into Groundwater Basins Throughout the western United States, communities are actively engaged in recharging effluent in depleted groundwater aquifers. Little is known about the long-term effects of 72
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storing effluent on an aquifer. Do the constituent chemicals, such as pharmaceutical drugs, in effluent breakdown over time? If so, how long does it take? What harm results, if any? In addition, states in the southwestern United States are actively engaged in recharging surface water underground. The benefit is substantial when attempting to restore over drafted aquifers in metropolitan areas. During wet years, the ability to capture excess water and store it underground maximizes its use and provides protection against future droughts. However, surface water supplies such as those delivered to Arizona’s aquifers through the CAP contain high levels of salt. For example, it is estimated that 1 acre-foot of CAP water contains 1 ton of salt. During the last eight years, 1.5 maf of CAP water has been stored in central and southern Arizona groundwater basins, resulting in 1.5 million tons of salt contaminating these groundwater supplies. Today, little is known about the effects of salt-loading on aquifers. The largest source of known contamination at this time is in the Colorado River which is utilized throughout the agricultural and municipal areas of the state. As we become more efficient in the use of available surface water supplies, less runoff will recharge rivers and streambeds. The consequence of less water runoff is higher saline content in our rivers. At the extreme, certain useable water supplies today will be unusable in the future. Questions remain unanswered about whether the brine-stream can be cost-effectively treated to return it to useable status. If not, how can we safely dispose of brine streams when a saltwater body is unavailable for disposal purposes to a community? How can scientific research have greater practical application to water resource management? In recent months several meetings have been held between researchers from Arizona State University and the University of Arizona and water managers from public and private water agencies. These meetings were arranged due to a growing recognition that the research produced at the state’s universities has little value to real world water managers. Typically, the research produced at the universities is too theoretical or untimely for practical application. After one full day session, hosted by several colleges at ASU, the following list of questions was developed for the purpose of improving communication between the university and water managers: How can improvements in the interactions between water providers, both public and private, and academia be improved? • Need to identify the optimal bridging mechanism/institutional arrangement to link science with water management. • Provide information to policy-makers and the public in a way that is understandable. • How do you get research into practice? 73
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• How can the studies completed by the private sector be made more readily available to the academic and public policy-maker to arrive at better decisions for all? • What are the most effective ways of communicating water issues to policy- makers and the public? • What areas of research are most immediately needed by water managers? • Research into institutional barriers with regard to achieving adaptive management in water supply/quality sectors is needed. • A disconnect exists in Arizona between the law and hydrology as it relates to recharge. • Develop future scenarios of water supply-demand given uncertain climatological conditions; demographic/urbanization trends; and institutional arrangements. • Establish a web-based statewide water supply and demand database (current and historic) that can be updated annually. • Develop visualization tools and approaches that can help the public understand the nature of the groundwater system. • Simulate drought in groundwater models. • Develop a more reliable method to model potential contaminant movement in the groundwater. • Develop demand/economics models that are integrated into hydrologic models. • Build a consensus groundwater model for the Greater Phoenix Region. As you can see from the foregoing list, scientists and managers in Arizona are struggling with ways to bridge the communication gap that exists between them. Communication of existing information between scientists and managers is at least as big a hurdle as the inadequacy of the data itself for some parts of the state. Two outcomes resulted from the meeting. Future meetings will be held to strengthen communication between the two groups and a summary of the minutes of the meeting including a list of participants was distributed. 74
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References Colorado River Water Users Association. 2005. Law of the River. Available online: http://www.crwua.org/ [accessed November 23, 2005]. 75
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