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1 The Future of Irrigation Irrigated agriculture has played a critical role in the economic and social development of the United States. In terms of crop production, irrigated farms contribute proportionally more than nonirrigated farms: irrigated lands make up only about 15 percent of all harvested cropland yet they produce nearly 38 per- cent of the total crop value from the nation's agricultural lands (Bajwa et al., 1992~. From a social perspective, irrigation served as the engine that drove western settlement, and today it supports local rural economies in the arid West and in wetter regions as well. But the future of irrigation, and particularly the future of irrigated agricul- ture, in the United States is probably less clear today than at any other time during the past 50 years. The reasons for the uncertainties facing the practitioners of irrigation are neither surprising nor mysterious. Intense competition for water among an increasingly wide range of users, changing economics, increased envi- ronmental concerns, changing public values, and other trends in modern times are putting new pressures on irrigation. No individual or group, regardless of wisdom and experience, can predict with assurance how, where, and when irrigation will be practiced in years to come, but it is imperative to at least consider these issues. In the best of worlds, it is better to anticipate problems than to react to crises and better to be proactive than simply to follow the path of least resistance. This is the rationale behind all efforts to anticipate the future, including this report. Irrigation is an old art, probably one of the earliest agricultural practices. It arose out of necessity first in arid areas of the world, where irrigation was essen- tial to ensure plant survival in the absence of timely precipitation. Archeological 8
THE FUTURE OF IRRIGATION 9 sites around the world provide ample evidence of centuries of irrigation and of highly successful economic and social systems built on the productivity that it enabled. History also bears record of irrigation-related problems and failures, and whether these are due to technological or political causes we can only sur- mise. While it is not for this document to revisit the history of irrigated agriculture in the United States, some historical perspective is necessary to understand the present-day context of irrigation. The special place of irrigation today is a result of a long and complex history of federal policies, individual entrepreneurial spirit and creativity, natural disasters, economics, and trade. In part, the future of irrigation depends on what society learns from these experiences. In the United States, irrigation was first practiced by the indigenous people in the Salt River valley, on the Colorado Plateau, and along many river courses throughout the West. The ancestors of the present-day Pima, Hopi, Tohono O'odham, Hualapai, Havasupai, Yaqui, Pomo, and other American Indians grew corn, peaches, beans, squash, melons, and other crops through an intricate net- work of ditches and canals. In many instances, today's irrigation canals follow the same general layout of prehistoric canals, such as in the Salt River valley in central Arizona. Some of the immigrants arriving in North America, particularly from the Mediterranean, brought with them ages-old heritages of watering the land as part of farming. Spanish colonists irrigated extensive gardens at the string of missions established on the Pacific Coast beginning in the 1760s. Spanish water rights are still a part of California water law. However, Northern European colonists had no background in irrigation and found no need for this in the humid East until the population began to push into the arid West. The history of modern irrigation in the United States can be dated to July 1847, when an advance party of Mormons preceded Brigham Young into Utah's Salt Lake valley and immediately diverted water onto a patch of land to soften the soil so they could plant potatoes. Over time, irrigation became a central component of the federal government' s strategy to encourage settlement of the West and build a nation that stretched from coast to coast. Irrigation was extolled as the solution to a range of problems, including overcrowding in eastern cities and debt resulting from the Civil War and earlier wars. Through a series of Executive Orders and Acts of Congress, legislation was enacted that provided for the division of land, the estab- lishment of reservations and allotment and sale of Indian lands, and the settlement and sale of "excess public land." Not by coincidence, one of the major federal water resource development agencies, the U.S. Bureau of Reclamation, was formed dur- ing this time, and it provided significant engineering and financial capital to develop irrigation on newly acquired lands in the West. Even as the push to irrigate was at its peak, however, some people recog- nized irrigation as a mixed blessing. T. S. Van Dyke (1904) writing in the magazine Irrigation Age, put it very well:
10 A NEW ERA FOR IRRIGATION That perversity of human nature that leads us to take hold of so many new subjects by the wrong end seems to rejoice especially in misleading the begin- ner in irrigation.... this perversity may mislead him into thinking he is accom- plishing wonders when he is losing money by the day.... One may be injuring the land without suspecting it, and about the time he has lost considerable money may conclude that irrigation is a heartless hoax. Despite the significant contributions that irrigated agriculture makes to soci- ety in terms of food and fiber production, society entertains an ambivalent feeling toward irrigated agriculture, with some reason. First, because irrigation is prac- ticed largely in arid regions, although it is increasingly used in subhumid and humid regions to ensure timely availability of water, it is increasingly coming into competition with other sectors of society for a scarce resource water. Sec- ond, although irrigated agriculture surely is not alone in causing negative envi- ronmental impacts, irrigation can degrade water quality, deplete streamflows, reduce ground water levels, and alter stream channel morphology and local hy- drologic regimes. The nation's sensitivity to such environmental harm has deep- ened over time. The remarkable early development of irrigation was fueled by an enormous level of federal involvement, including engineering and financial assistance, but this role has diminished greatly in recent years. Growth no longer needs encour- agement. And the role of agriculture in the nation's economy has changed. Only a small percentage of the population now makes its living by producing agricul- tural products, and memories of the family farm no longer are part of most people's experience. Corporate farms are now common. At the same time, some of the nation' s priorities have shifted, with increased concern for environmental issues, an increasingly global economy, and tremendous pressures from popula- tion growth and urbanization. Parks, nurseries, urban landscaping, suburban lawns, and golf courses have been added as bona fide users of large quantities of water. Instream uses such as fishing, boating, and preservation of fish and wild- life habitats have greater standing today than they did in the past. THE COMMITTEE'S CHARGE AND APPROACH The National Research Council's Committee on the Future of Irrigation in the Face of Competing Demands was formed to study the changing availability of water for irrigation and to identify ways to facilitate irrigation's transition to a world where there are increasing and, in some cases, conflicting needs for water. The committee was asked to draw lessons from past experience, examine current and foreseeable advances in science, and identify examples of change and re- sponses to change that appear to be underway at this time that might tell us something about the future direction of irrigation. Specifically, the committee was asked to
THE FUTURE OF IRRIGATION 11 · describe some of the short-term and long-term issues associated with irrigation in both the western and the eastern United States, including, for ex- ample, impacts on water quality, soil quality, and environmental values, as well as physical, biological, social, and economic impacts; · identify the range of pressures affecting the availability of water for irriga- tion and the impacts of these pressures for major regions of the United States; · explore the role of technology in helping the nation adapt to changing conditions and identify gaps in the knowledge base; and · identify and evaluate economic, institutional, and policy changes that might facilitate the transition of irrigation to a world of increasing water scarcity. The committee used a variety of mechanisms to gather information for this study. The committee's members, selected to represent a diversity of skills, knowl- edge, and experience, augmented their own knowledge by hosting a workshop with some 40 invited guests, conducting in-depth case studies of different regions in the nation, and visiting Arkansas, California, and Oregon to talk with represen- tatives from agriculture and related fields. In addition, the committee conducted an extensive review of the literature to gain understanding of both the forces of change affecting irrigation and the responses to that change. The committee focused particular attention on the forces behind current changes in the availabil- ity of water for irrigation and the types of responses needed to adapt to these different circumstances. Special effort was made to hear from people in different parts of the country, particularly from farmers and others closely involved with agriculture and possessing hands-on experience in water management. Efforts were also made to obtain insights from those representing some of the key com- petitors for water or concerns for environmental quality. As the committee's work progressed, it became apparent that the report would have a heavy emphasis on the West because that is still where most irrigation occurs 91 percent of all irrigated acreage lies in just 20 states: the 17 states west of the Mississippi River, plus Arkansas, Florida, and Louisiana. Many ecological, technological, economic, institutional, and social factors affect the future of irrigation. Three broad approaches may be used to group these factors and assess how they might operate in combination with one another over time: I. Appraise the current situation (i.e., emerging problems, technologies, and policies that raise concerns or offer promise); 2. Develop historical and geographical analogies from past irrigation expe- rience that might have practical value for future decisions; and 3. Examine and extrapolate from recent trends (e.g., in irrigated acreage, production patterns, and problems in the latter part of this century).
2 A NEW ERA FOR IRRIGATION This report reflects some of each approach. This chapter introduces the issues and sets the stage for understanding the problems faced. Chapter 2 provides a cultural and historical perspective on how societies adapt to change and how we might best help irrigation evolve in the future. Chapter 3 appraises the status of irrigation today. Chapter 4 highlights the forces of changes that are at work. Chapter 5 provides specific examples of how different states or regions are being affected by change in water availability and cost and the approaches used in response. Chapter 6 draws conclusions from the committee' s deliberations. DEFINING OR DIVINING THE FUTURE? There is a large body of practical wisdom embedded in North American irrigation experience. The continent has some 2,000 years of irrigation practice, accumulated in a wide range of environmental, cultural, political, and economic contexts. It includes myriad trials, errors, failures, and successes. Some irriga- tion systems spread over large regions, while others were adapted to local micro- environments and communities. Some lasted centuries; others barely a season or two. This diversity of experience has several implications. First, it should fore- warn us to guard against overgeneralizations about the nature of irrigation sys- tems and their futures. There are always limits to the lessons drawn from anal- ogy. Second, it helps define the range of possible adjustments available to respond to future problems. It is useful to recall the comment of Gilbert Levine (1985): Irrigation systems are as much behavioral as technical. They require daily in- teractions within the irrigation bureaucracies, among farmers, and between the bureaucracies and the farmers.... Yet the thought, time, and effort devoted to understanding and dealing with behavioral questions are infinitesimal by com- parison to that devoted to the technical issues. Indeed, one of the biggest limitations on making analogies based on current or past experience lies in our inability to quantify or measure behavioral and cultural factors. There is also uncertainty inherent in extrapolation that limits what this committee can and cannot say about the future of irrigation. Modern irrigation systems in the United States are less than 100 years old. Some have existed for only a few decades, but during this time they have changed frequently and significantly. Assessing the future thus depends on analyzing many short-term experiments as well as long-term trends. Because long-term data on irrigation exist for relatively small areas and may not be transferable from region to region, it is important to guard against errors made by large-scale regional generalizations based on short-term local evidence. Also, long-term trends, of the time scale of
THE FUTURE OF IRRIGATION 13 decades to centuries, may shed light on the sustainability of irrigation, but they may also have little immediate relevance for irrigators making decisions on time scales of days, months, seasons, or years. The challenge is to draw analogies from long-term experience that are relevant for short-term decision making (Wescoat, 1991~. This challenge underscores the need to identify relevant time frames and spatial scales. Sustainable development implies a relatively long time period-decades to centuries during which time short-term problems and crises must also be met. Irrigation planning, by contrast, uses time frames of several years to several decades. Irrigators, in further contrast, may focus on periods of several hours to several years. When addressing the future of irrigation, it is necessary to consider several time frames simultaneously. Short-term decisions may lead toward, or away from, sus- tainable irrigation development. They may facilitate, or eliminate, long-term water management alternatives. Long-term decisions, such as reservoir construction or indefinite water rights, facilitate some short-term flexibility and options while im- peding others. Such decisions may increase vulnerability to low-frequency but high- magnitude natural hazards. It is also important to work at multiple spatial scales- from the household to the globe. Although this report has a national focus, it recognizes that the nation consists of varied regional irrigation patterns, that those patterns vary locally, and that they are influenced by global and international mar- kets and pressures. In any locale, irrigation evolves its own culture, or set of behaviors, in relation to these influences. Another challenge is our inability to define what constitutes an irrigation "success" or "failure." Success is defined in the present in terms of desired or foreseeable outcomes. In the context of present-day discussions of sustainable development, irrigation success might be defined as the ability to continue farm- ing and to improve the management and productivity of an irrigation system, and at the same time to show resilience to internal or external environmental and economic variability. In earlier decades, however, success was defined more in terms of profitability, uniformity, and economies of scale. Still earlier, subsis- tence, sufficiency, cooperation, and conflict resolution may have served as the key criteria for successful irrigation. Times and priorities change, and these changes in turn drive policies and institutions in new directions. Can we judge what will be successful in the future if we do not know what the evaluation criteria will be? We suspect that they will not be the criteria of the past, but in what direction and how far will they change? Divining the future will require defining the criteria for success for the point in time being considered. Defining such criteria will be difficult because there are multiple objectives in play, and the criteria for success will vary among parties with different objectives. Given increasing demand for water and demands from new users, finding balance will be key: balance among users and balance among profit, productivity, and environmental protection.
4 A NEW ERA FOR IRRIGATION THE HISTORICAL CONTEXT To understand the current condition of irrigated agriculture in relation to water supply in the United States, some understanding of the setting in the nine- teenth century is essential. As the country expanded westward in the early days of settlement, demand for water was small in relation to supplies, and thus oppor- tunity costs of using water for irrigation were low. Our ability to control flows was very limited either too much or too little water was an obstacle to the development of about one-third of the area of the original 48 states. Natural supplies were critical factors in shaping the development of the nation: rivers provided the principal paths for exploration and transportation, and consequently cities grew around major rivers and harbors. Agriculture, too, was oriented to water supplies: farmers gravitated to places where precipitation and soil was adequate or where streams could be easily diverted for use on crops. Social pressures exerted influences as well. Federal policies encouraged settlement of semiarid and arid areas, and irrigation became the fundamental cornerstone of the development of the western United States during the latter part of the nineteenth century. To supply an expanding population with food, and to make acquired lands productive, water was harnessed for use in irrigation. While the supply of water in relation to demand was large at this time in most instances, the need to secure a permanent source of water gave rise to water laws, such as the prior appropriation doctrine, which established the principle of "first in time, first in right." The development of the prior appropriation doctrine provided strong incentives for farmers to "use it or lose it" where water was concerned. The prior appropriation doctrine also codified a widely held perception at the time that water left flowing in streams was a "waste." Beneficial use became a condition for securing a water right. Another important historical element is the relationship between the United States government and Indian tribes. Treaties signed between Indian tribes and the United States in exchange for the former ceding vast territories provided for the reservation of land and an amount of water "sufficient to fulfill the purposes of the reservation" (United States v. Winters, 1908~. In the latter half of the nineteenth century, the expected use was agriculture, and because irrigation formed the cornerstone of U.S. Indian policy, practicably irrigated acreage be- came the standard measure of Indian water rights. Although relatively little was done then to secure and develop water supplies for Indian irrigation projects, the dedication of significant quantities of water to tribal use now, as treaties are enacted, has enormous implications for future irrigation in the United States. At the turn of the century, the welfare and survival of countless people living in arid, semiarid, and flood-prone areas were at risk from year-to-year variation in weather and precipitation patterns. Many irrigators and irrigation projects were hopelessly in debt. Also, with the more easily irrigated lands already developed, the expansion of irrigation depended on storage and conveyance systems to increase
THE FUTURE OF IRRIGATION 15 dependable water supplies and on technological improvements to pump ground water. Thus a new era began what might be called the construction era (1900 to 1970) a period of rapid growth in water use and development of infrastructure. In this period, withdrawals rose from 40.2 to 370 billion gallons per day. Irrigation use of water increased from 20 to 130 billion gallons per day. The number of dams in the nation rose from 3,000 to more than 50,000, and as a result water storage capacity increased from 10 to 753 million acre-feet (Frederick, 1991~. Many factors contributed to this pattern of growth. Technology improved dramatically (e.g., mechanization of earth moving, vertical turbine pumps, large- scale dam construction techniques). Federal policy evolved to reflect the view that it was in the national interest to develop water resources where they were capable of producing crops, power, or other outputs of economic value to the nation. The successes of technology built a national optimism that inspired other achievements. Dams, canals, pumps, and other engineered infrastructure compo- nents became the accepted solution to virtually any water problem. Planners were always ready to provide offstream users with virtually unlimited supplies at low cost, with the impacts on streamflows basically ignored. Few people had the vision to give much consideration to long-term impacts. The significance of the federal role in the development of irrigation should not be underestimated. Federal laws and policies provided the land base, capital, and incentives to settle arid and semiarid western lands. The Desert Lands Act, the Homestead Act, and the Dawes Allotment Act provided the necessary frame- work for land acquisition and settlement. The Reclamation Service (currently the Bureau of Reclamation) was established specifically for the purpose of "reclaim- ing" arid and semiarid lands for use in irrigated agriculture and, in general, for the development of the West. Western promoters turned to irrigation as a necessary means to sustain western development. Every reclamation project authorized by Congress between 1902 and 1945 provided that the primary purpose was for development of irrigation. The construction era ended as the result of many converging factors. Three of the most important factors were the high cost of developing new supplies, the lack of federal funding brought on by increasing federal budget deficits, and environmental and health concerns expressed through public opposition, legal challenges, and environmental legislation. A look at recent changes in water use, development patterns, and federal policy confirms that there has been a shift in the nation' s approach to water use. Per capita water withdrawals peaked in 1975, and total withdrawals peaked in 1980. The construction of water projects peaked in the late 1960s. Related to those trends, federal policies evolved to provide less funding, impose higher interest charges, and require cost sharing for irrigation projects. At the same time, public interest in environmental protection increased, as evidenced in envi- ronmental legislation such as the Wild and Scenic Rivers Act of 1968, the Na- tional Environmental Policy Act of 1969, the Coastal Zone Management Act of
16 A NEW ERA FOR IRRIGATION 1972, Federal Water Pollution Control Act Amendments of 1972, and the Endan- gered Species Act of 1973. The courts and the legislative process became the battleground for major changes in water project development. Concomitant with these changes came changes in the balance between water supplies and demands. Water demands increased with population growth, in- creased incomes, increased leisure time and interest in outdoor recreation, and rising environmental values. Supply, on the other hand, was not keeping pace- depletion and degradation of supplies became factors, and the high costs of water treatment and recycling limited the adoption of those supply-enhancing options. Rising water project costs became inevitable because the best reservoir and dam sites were developed first, and the provision of new storage facilities is eventually subject to diminishing returns. Moreover, the opportunity costs of storing and diverting additional water became unacceptable. Overall, the magnitude and nature of future increases in water costs among users will depend in large part on how existing supplies are managed and allocated. There are clear implications associated with how water is priced. If water is underpriced and supplies are locked into traditional uses, then more of society' s costs will take the form of deteriorating aquatic ecosystems, loss of instream values, restrictions on development resulting from the inability to secure ad- equate supplies, more frequent interruptions in service, and impediments to ur- ban, industrial, and economic growth. In addition, agriculture will continue to consume a large quantity of scarce water in relatively low value uses, and there will be inadequate economic and institutional incentive to adopt more efficient irrigation techniques and strategies. On the other hand, if the costs of water are borne by users who have incen- tives to conserve and opportunities to sell water, then there will be benefits to society as water is used more efficiently, the highest-value uses (determined either by market forces or societal goals) are assured of adequate supplies, and the nation derives greater overall net benefits from its water resources. In addition, irrigators would benefit from the increased value of their water rights, would have increased incentives to conserve water or take land out of production, and would have more capital to invest in water conservation technologies. IRRIGATION: INDUSTRY OR CULTURE? This study considered many questions, but there was one overriding issue that, while difficult to articulate, seemed recurrent. Agriculture is viewed by the public in two not necessarily consistent ways. The first is that agriculture, includ- ing irrigated agriculture, is a business, an industry, albeit an industry essential to human existence. Competing with this pragmatic view is one that sees irrigated agriculture as a complex system, one that has spawned an individual culture. If society takes the position that irrigated agriculture is an industry, it would logically move toward a situation where the user bears all the costs of production.
THE FUTURE OF IRRIGATION 17 In turn, the producer passes those costs along to the customer. On the other hand, if society accepts that irrigation is more a culture the way people live and part of the national identity it is then logical for the public to absorb a significant share of the responsibility for the activity in the name of the national interest. Thus society shares in the costs and uncertainties of farming by providing various subsidies to farmers, which in turn subsidize the costs of food and fiber to con sumers. Both models have strengths and weaknesses. Since the 1930s, the United States has favored the agriculture-as-culture model, but the trend in recent years is changing. More and more, agriculture, including irrigated agriculture, is seen as a business that must compete in a global economy. This new emphasis stresses the entrepreneurial side of farming, but it may diminish the cultural assets associ- ated with the irrigated agriculture community. The United States is not alone in this dilemma it is playing out throughout the world. This committee met with many people during the course of the study, and it was clear that many of those most active in irrigation and its associated industries view irrigated agriculture as a business. The farmers, in particular, held this view; they are all sophisticated industrialists operating relatively large enter- prises, and they see themselves as business people. Even the Bureau of Reclama- tion, once charged to promote irrigated agriculture as a social goal, now seems to see irrigated agriculture as an industry as well and is seeking to evolve into a new role in water management. From an historical perspective, this is a radical idea. It flies in the face of the nation's history, which soundly supported the subsidiz- ing of irrigated agriculture as critical to the national interest the settlement and regional development of the West. It is still possible to argue that water is "different" from other commodities and thus should be exempt from the harsh discipline of the market. Although the committee believes that the more success- ful farmers are moving away from that view, their shift in attitude may not be shared by those engaged in smaller farming operations who struggle to make a living, even with water and crop subsidies. In considering the cultural issue, a critical dimension is geographic scale. The national scale is an important one to look at with respect to the pressures on irrigated agriculture. These pressures are many and mounting: environmental quality, salinity, urbanization, energy prices, subsidy withdrawal, opportunity costs, and even the uncertainty of climate change these all play a role in forcing change on the irrigation sector. Among these, the environment has only been a factor of any influence for 25 years, a relatively short period of time. As an issue, environmental concerns emerged from a stage of nonrecognition to a stage of widespread public recognition, and environmental needs are now competing for water with more traditional users. It is difficult to forecast the ultimate impact of environmental concerns on the availability of water for irrigation, but these con- cerns are likely to remain among the factors to be resolved.
18 A NEW ERA FOR IRRIGATION The local scale is the appropriate scale for responding to many types of change. The notion that one national set of policies pertaining to irrigation will achieve desired outcomes in all regions simply is not realistic. For example, Nebraska and Florida face very different problems related to ground water and are developing different strategies to solve them. Beyond the local scale is the individual farm, the location where actual responses to the changing availability and cost of water will take place. Most effective action, and acceptable adapta- tion, it appears, will take place at the local and farm levels because the problems irrigators face are in the end site specific. How does this question of irrigation as industry or culture affect policymaking? If the industry view of irrigated agriculture is pursued, one option is to make an even bigger push for markets in water so as to subject the industry to full market discipline. There could be more price pressure on the industry, fewer subsidies, and full-cost pricing of federally supplied water. In return, irrigators might be granted transferrable water rights and limitations on the acreage eligible for federal water might be removed. On the other hand, if irrigation is viewed more as a culture, policy decisions would tend to insulate agriculture from direct mar- ket forces. The prevailing view irrigation as industry or culture varies from region to region and person to person. Rather than imply that one view is more right or wrong, it is the committee's intention to say simply that both views exist and will continue to exist as irrigation evolves into the future. THE FUTURE OF IRRIGATION The history of irrigation in the United States is fundamentally a story about the development of the water resource and the accompanying set of laws, institu- tions and technologies that have enabled the capture and use of water for irriga- tion. The underlying premise of this study is that given the increasing competition for water supplies, changes in how water is managed, allocated, and valued are inevitable. It is not possible to predict the future accurately. Still, change is least disruptive when it is anticipated. Careful thought about the future of irrigation can help the nation as a whole adapt to changing conditions. This report attempts to identify the range of key trends and factors that are likely to influence the future of irrigation. It addresses competition for water resources, especially from relatively "new" users such as golf courses, lawns, and landscaping, as well as from recreation and instream use. It looks at related issues such as soil and water pollution, federal subsidies for crops and for water, the revolution in biological science, and changes in irrigation technology. It also addresses broad issues with potentially far-reaching impacts such as American Indian water rights, the global agricultural economy, and the changing political climate, each with respect to implications for the future of irrigation.
THE FUTURE OF IRRIGATION 19 Irrigated agriculture has played a vital part in the nation's history, and it has served social goals far beyond simply providing food and fiber. Its success spawned a culture and sparked an evolution of technology and myriad supporting institutions. These institutions have served irrigation and the nation well, al- though not without costs to other water users and social programs. The nation, however, is now facing a time of changing public values and new demands. Irrigators feel a combination of pressures today unlike at any time in the past. They are experiencing competition from new directions, and they are finding ways to adapt. The irrigation sector, like the rest of the economy, is in flux. To succeed in the future, it must be innovative, responsive to change, and a leader in attempts to resolve conflicts with other water users. The committee cannot say with any degree of certainty how irrigated agricul- ture will change. It can, however, assert with considerable confidence that irri- gated agriculture will change. Few companies produce the same product in the same way they did 50 years ago, and agriculture is no different. Irrigation attained its present stature because it was part of the nation's vision about how best to meet the needs of its citizenry. Whether one agrees or disagrees with the judgments and values that guided past decision makers, it is impossible not to admire the dedication with which that vision was put into action. REFERENCES Bajwa, R. S., W. M. Crosswhite, J. E. Hostetler, and O. W. Wright. 1992. Agricultural Irrigation and Water Use. ERS/USDA (Agricultural Information Bulletin No. 638). Frederick, K. 1991. Water resources: Increasing demand and scarce supplies. In America's Renew- able Resources: Historic Trends and Current Challenges. K. Frederick and R. Sedjo, eds. Wash- ington, D.C.: Resources for the Future. Levine, G. 1985. Irrigation and development. Water Science and Technology Board Newsletter 2(5):1-2. Washington, D.C.: National Research Council. United States v. Winters 207 U.S. 564 (1908). Van Dyke, T. S. 1904. Irrigation Age 1:16-17. Wescoat, J. L., Jr. 1991. Managing the Indus river basin in light of global climate change: Four conceptual approaches. Global Environmental Change: Human and Policy Dimensions 1:381- 395.
