[Originally published in 1998 as Kansas Geological Survey Bulletin 239. This is, in general, the original text as published. The information has not been updated.]
In the 1980's, much of the American environmental community rallied around the concept of "sustainable development," the idea of limiting resource use to levels that could be sustained over the long term. As a guiding philosophy, sustainable development quickly became popular, seen as something of a litmus test to judge the way resources should be exploited: any use that could be undertaken indefinitely met with approval under this concept, while those uses that could not be sustained were suspect.
It all seemed easy enough. Then people began grappling with the meaning of the phrase and came to realize the difficulties inherent in defining and adopting sustainability. Exactly what do people mean when they talk about sustainability? Is it possible to have a meaningful conversation about sustainable development of a nonrenewable resource? And how long can a resource be used before that use is considered "sustainable"? Ten years, a hundred years, geologic time? Do those amounts of time mean anything to most of us? Scientists realized that it might prove dauntingly difficult to quantify resources in order to determine how long their use could be sustained and to analyze the impact of resource use. In the essay The Shaky Ground of Sustainable Development, historian Donald Worster discusses sustainable development as it is applied to the science of ecology, writing that sustainable development "depends on the assumption that we can easily determine the carrying capacity of local and regional ecosystems" (Worster, 1993). Making those determinations is anything but easy in ecology, and apparently not much easier in many other scientific disciplines.
Shortly after the concept of sustainable development arrived in the environmental community, water-policy-makers in the ground-water management district of northwestern Kansas began discussing the concept of "zero depletion." This was the idea that water should be pumped from the aquifer at the same rate that it was replenished. If such a policy were enacted, depletion in parts of the Ogallala would go from the rate of several feet per year to zero, at least in theory. However, because recharge rates in western Kansas are low, a policy of zero depletion would require a drastic reduction in irrigation in the most seriously depleted portions of the Ogallala. Other ground-water management districts in the state were already applying standards of sustainability when they made judgments about allowing new wells to be drilled in their parts of the state. But this was the first time that an agency considered regulating existing water rights-wells that were already in place-with the goal of long-term, sustainable use of an aquifer. Zero depletion aroused considerable analysis, reaction, and discussion in northwestern Kansas and was applied eventually only to new wells.
Today the concepts of zero depletion or sustainable development are generally referred to in the hydrologic community as "safe yield." Safe yield has traditionally been defined as "the attainment and maintenance of a long-term balance between the amount of ground water withdrawn annually and the annual amount of recharge" (Sophocleous, 1997). While that definition seems simple enough, the following chapters demonstrate that, even when it comes to a renewable resource such as water, such a definition is fraught with difficulties and complexities. The definition does not explicitly recognize some of the inherent connections between ground water and surface water. It does not attempt to take into account the impact that pumping in one part of the hydrologic system may have on other parts of the system. Nor does it suitably address the question of time, the way yields change over long periods. It makes no mention of the complexities of characterizing the hydrologic system, or how the concept of sustainability might change in different hydrologic settings.
Just as the concept of sustainability required more subtle and detailed analysis in order to be meaningful, the concept of safe yield must be examined more carefully if it is to have any applicability to water issues. In organizing the following volume, and in writing several of the chapters, Survey hydrogeologist Marios Sophocleous is attempting to raise the level of discussions about the application of safe yield to water resources in Kansas. To do that he brought together ten of the state's water scientists, asking each to write about the issues of safe yield as applied to their particular scientific specialty. He then coordinated their efforts, constantly encouraging and cajoling. At times, working with these authors must have seemed a little like making water flow uphill--it can be done, but it takes time, energy, and constant maintenance.
Like any conversation, discussions about safe yield must be set in a context, and Sophocleous provides much of the necessary background, beginning the book with a description of hydrologic systems and water management in Kansas. Sophocleous and the other authors then discuss the concept of safe yield and its applicability in a variety of geologic and hydrologic settings and circumstances, such as confined aquifers and interconnected streams and aquifers. Other authors have contributed chapters that consider safe yield and surface water, water chemistry, and climate change. Two of the later chapters describe the complexity of hydrologic systems and the impact of agriculture on those systems.
Throughout the book, the authors analyze safe authors yield by using examples mainly from Kansas hydrologic settings. While this book will be of primary benefit to water users and policy-makers in the state, the Kansas case studies should prove instructive for areas throughout the Great Plains and the nation. Even more important, rather than limit these discussions to technical, sometimes mathematical examinations of the questions about safe yield, the authors have striven to make these chapters more accessible to water users, water regulators, and water-policy experts. For discussions about safe yield to have long-term impact, they must reach the people who are making, enforcing, and carrying out water policy. That is what this book attempts to do.
Regardless of what these concepts are called--sustainable development, zero depletion, or safe yield--they all attempt to address the feasibility of a long-term approach to resource use. The work of Sophocleous and the other authors is a first step in the process of analyzing these concepts as they apply to Kansas. This book will certainly not be the final comment about these issues, but it is an important contribution to discussions, and will undoubtedly inform future debates over water policy in Kansas. That is why the following chapters deserve a wide reading. And for attempting to bridge the gap between the scientific community and water users and policy-makers, Sophocleous and his fellow deserve the thanks of both groups.
Sophocleous, M., 1997, Managing water resources systems--Why "safe yield" is not sustainable: Groundwater. v. 35, no. 4, p. 561
Worster, D., 1993, The shaky ground of sustainable development; in, The Wealth of Nature, D. Worster, ed.: Oxford Press, p. 154
Kansas Geological Survey
Water resources are essential to both economic development and the maintenance of natural systems. While water technically does not disappear but only changes form, the quality and quantity of water resources in anyone place can be degraded or improved by a variety of human activities. Population growth, intensified land use, economic demands, and environmental degradation are exerting mounting pressures on the earth's soil, water, and other natural systems. The specter of possible changes in climate can only add to these pressures. Few areas of public policy are as contentious as the issues surrounding water management. Misconceptions and deficiencies in the dissemination of research findings to the local and regional levels add to these contentions.
The purpose of this volume is to contribute in educating Kansans and other people about waterresources sustainability issues so as to promote a better understanding of water resources in Kansas and more enlightened management of these resources. Knowing what we have, understanding how natural ecosystems work, and effectively communicating to decision-makers about environmentally sustainable practices are crucial if we are to ensure that the natural goods and services that we have enjoyed will continue to be available for both present and future generations. Although this effort has a Kansas focus with existing Kansas and U.S. Great Plains examples, it also stresses the universally applicable concepts on sustainability of waterresources systems. We attempted to make this work comprehensive within the hydrologic (scientific) realm of water-sustainability issues, and also cross-disciplinary with other scientific fields, but by design we do not specifically address socio-economic, political, legal, and ethical issues. This work is semi-technical, addressed to the educated layperson with a bachelor's level of education. We particularly aim at personnel in state and local management units who deal with water-resources issues on a regular basis. Each chapter stands by itself with no firm rigid formats, but with cross references and interconnections to other chapters. Boxed sections provide supplemental or more technical aspects, and a glossary provides easy-to-understand definitions.
Thus, Chapter 1 addresses the issue of "what we have" and the factors that control water resources in Kansas. It also covers how water is used in Kansas, what institutions are managing its water resources, and how they are managed. It also identifies the major water-related problems we face in Kansas. Chapter 2 addresses the hydrologic principles underlying the concept of safe yield, identifies its weaknesses, and outlines several examples of its use. This basic chapter was the catalyst for developing this entire volume. Chapter 3 expands on more recent developments of the evolving sustainability concepts, emphasizing the ecosystem management approach, and outlining the Kansas water-management experience. Chapter 4 addresses sustainability issues related to confined aquifers, with emphasis on the Dakota and Ozark aquifers of Kansas. Chapter 5 provides water-chemistry background and reviews pollutant pathways to aquifers as a basis for understanding the impacts of chemical compounds and processes on sustainable yield of aquifers. Chapter 6 addresses surface-water yield issues with emphasis on Kansas reservoirs. Chapter 7 presents an assessment of the effects of agricultural development on water yield in Kansas. Chapter 8 addresses the issue of climate change and its possible impact on sustainable water yield. Chapter 9 stresses the importance of recognizing and evaluating uncertainty in developing yield estimates. Chapter 10 is a concluding overview explaining why "safe yield" as traditionally defined is not sustainable and how to improve waterresources management. Finally, Chapter 11 presents a selective but rather comprehensive glossary of hydrology and sustainability-related terms in nontechnical language.
This volume represents different perspectives on water-sustainability issues in Kansas by ten experienced scientists working in this state. We hope that these perspectives on sustainable development of water resources in Kansas will enhance public education and discourse, and enlighten managers and policy makers to making more informed and thus better decisions. The editor would appreciate feedback from the readers on any aspect covered in this volume, especially by pointing out errors, inaccuracies, and significant omissions so that these could be rectified in future editions of this or similar volumes. Figures throughout the book are used with permission of the publishers.
I would like to thank all participants in this volume for their willing cooperation and patience through the long process of multi-author coordination, review, and revision. I am particularly indebted to the Kansas Geological Survey (KGS) Associate Director Rex Buchanan for his continued support and participation in this project, as well as the KGS editor Marla Adkins-Heljeson for handling the editing and review processes. The chapters in this volume have undergone a double review process. The KGS internal review members consisted of (in alphabetical order) Marla Adkins-Heljeson, Rex Buchanan, Robert Buddemeier, and Marios Sophocleous. The external review members consisted of (in alphabetical order) Ernest Angino (University of Kansas, Lawrence, KS), Stanley Davis (University of Arizona, Tucson, AZ), Edwin Gutentag (Downey and Gutentag, LLC, Lakewood, CO), John Helgesen (U.S. Geological Survey-Lawrence, KS, office), Les Lampe (Black & Veatch Engineers-Architects, Kansas City, MO), William Mullican (Bureau of Economic Geology, Austin, TX), David Pope (Division of Water Resources, Kansas Department of Agriculture), and Adrian Visocki (Illinois State Water Survey, Champaign, IL). To all these and their staff, a note of gratitude is due for their volunteered, yet essential, service.
Senior Scientist, Editor
[Note: The editor would like to thank Robert Sawin of the Kansas Geological Survey and the author-participants for their contributions in drafting this summary.]
Few issues of public policy are as contentious as those surrounding management of our environment and natural resources, such as water. This book analyzes the management concept of sustainable water development from a variety of hydrologic perspectives and describes its application to different hydrologic settings. The following summary is divided into four major sections-Kansas water resources, characterization of hydrologic systems, management of water-resources systems, and hydrologic impacts of agricultural development and climate change on water resources. Selected key conclusions and recommendations are highlighted in boldface italic type.
A prerequisite for managing a region's water resources is knowing the quantity of suitable-quality water that can be developed. A hydrologic inventory or budget is needed to evaluate existing and potential development of dependable water supplies.
More than 98% of the water available for use enters the state of Kansas as precipitation. The statewide average annual precipitation is about 27 inches (68.5 cm). Evapotranspiration returns about 23.2 inches (59 cm) back to the atmosphere. Aquifer recharge uses approximately 0.9 inches (2.3 cm), Runoff to rivers that originate within the state represents approximately 2.6 inches (6.5 cm), and when combined with streamflow into the state from Nebraska and Colorado (equivalent to less than 0.4 inches or 1 cm), surface-water outflows to Missouri and Oklahoma account for almost 3 inches (7.5 cm). Annually, Kansans use about 1.6 inches (4 cm) of water. Groundwater use represents approximately 1.2 inches (3 cm) of that total (92% is used for irrigation), and surface-water use equals approximately 0.4 inches or 1 cm (75% is used by power plants).
Although the precipitation, evapotranspiration, and other factors in the water budget vary widely from year to year, the averages over several decades remain nearly constant. The evidence to date shows that the main water supply for Kansas-precipitation that falls on the state has changed little in the last 150 years. What has changed is how water is used.
In western Kansas, ground water provides almost all the water, but at the present level of water use, groundwater resources are being depleted. Although the demand for water is continuously increasing, many areas in western and central Kansas are closed to further appropriations. In eastern Kansas, surface water is the principal water source; however, large withdrawals of ground water, which is closely coupled to the surface-water system, are obtained primarily from the alluvium of the Kansas River valley.
Kansas faces a number of water-availability and water-quality problems. Ground-water-level declines and streamflow reductions are especially significant in western Kansas. Saline-water intrusion, both natural and human-induced, affects surface- and ground-water systems. Pollution from non-point sources (mainly pesticides, fertilizers, and livestock), from point sources (waste-disposal sites), and from mining activities are other water-quality problems that affect water resources in the state.
Ground-water management and management of surface waters must be conceived as a combined system. Because of the interdependence of surface and ground water, changes to any part of the system have consequences for the other parts.
Under natural conditions (prior to development by wells), aquifers are in a state of approximate dynamic equilibrium: over hundreds of years, wet times (in which recharge exceeds discharge) offset dry times (when discharge exceeds recharge). Discharge from wells disturbs this equilibrium by producing a loss of water from aquifer storage. The decline of ground-water levels around pumping wells located near streams captures some of the ground-water flow that would have, without pumping, discharged to the streams. In fact, at sufficiently large pumping rates, these ground-water-level declines can induce flow out of a body of surface water into the aquifer (a process known as induced recharge). The sum of these two effects leads to streamflow depletion. A new state of dynamic equilibrium can be reached with continued pumping only by an increase in recharge (induced recharge), a decrease in natural discharge, a loss of storage in the aquifer, or a combination of these.
Ground water pumped from the aquifer comes from two sources: aquifer storage and induced recharge of surface water. Storage refers to water that is naturally retained in the aquifer. Induced recharge is surface water that is added to the ground-water system mainly as a result of ground-water-level declines below the surface-water level. Initially, ground water pumped from the aquifer comes from storage, but ultimately it comes from induced recharge. The timing of the change from storage depletion to induced recharge is a key factor in developing water-use policies. Distinguishing between natural recharge and induced recharge to ascertain possible sustained yield is exceedingly difficult and is an area that needs further research.
Permanent streamflow or baseflow is usually a result of ground-water discharge. Thus, if ground-water pumping lowers the elevation of the water table below that of the stream bed, streamflow will be reduced or interrupted. On the other hand, streamflow may be the major source of recharge to some alluvial aquifers, so that streamflow regulation or diversion may alter the recharge characteristics, and therefore the sustainable yield, of the ground water in the area. Stream-aquifer interactions also are important in situations of ground-water contamination by polluted surface water and of degradation of surface water by discharge of low-quality ground water. Coordinated, combined use of surface- and ground-water resource (conjunctive use) and management are required to improve the reliability and value of both resources.
A confined aquifer is a porous and permeable geologic unit that is sandwiched between two relatively low-permeability layers (unconfined aquifers are only bounded by a low-permeability layer below). Because the confining layers above and below these aquifer systems are usually regionally extensive, the recharge and discharge areas for these systems may be hundreds of miles apart. Confined aquifer systems are more sensitive to development than unconfined systems because of their hydrogeologic properties, such as their much lower storativity.
The issues surrounding the sustainability of water resources in confined systems are complex and involve both the quantity and the quality of ground water. These systems will not respond to development in the same manner as unconfined systems because of differences in the sources and amounts of recharge, and in the mechanisms that release ground water to pumping wells. Because of their greater average depth below the surface, confined systems are more likely to contain (or be connected to other aquifers that contain) unusable ground water. As a result, water quality can be a very important factor in determining the usability of the aquifer.
Sustainability of a confined aquifer system may be possible only in regions that are close to either the regional recharge/discharge areas or to areas of hydraulic connection with other aquifer systems. Management on the basis of sustainable yield may be more realistic in this part of the confined system for planning horizons on the order of a few decades. Ultimately, however, sustainability may not be a viable management concept for confined aquifers.
The primary management tools to control declines in confined aquifers are well spacing, restrictions on the rates of withdrawal from the aquifer, and artificial recharge. Depletion of the aquifer will occur if production wells are too close together, or the rates of withdrawal from the aquifer are unregulated.
An essential consideration in development of an aquifer is the chemical quality of water produced because the quality of water limits its use. In an undeveloped aquifer, ground water is, for the most part, at a chemical equilibrium with its surroundings because ground-water flow is generally very slow. Ground-water movement induced by pumping may change the ground-water chemistry. One of the ways that ground-water chemistry may be affected is by recharge of contaminated surface water into unconfined aquifers: surface water may contain incompletely processed sewage effluent, residual agricultural chemicals, or other undesirable chemicals. Another way is through mixing of poor-quality (for example, saline) water into unconfined or confined aquifers: an aquifer containing good-quality water in hydraulic continuity with an aquifer containing poor-quality water may be affected by the poor-quality water.
All aquifers contain water that is chemically stratified. Pumping a well causes mixing of the stratified ground water, which may result in dissolution (corrosion) or precipitation (encrustation) of solids, sorption or desorption of metals or organics, ion exchange of cations or anions, and oxidation or reduction of redox elements that affect their mobility in ground water. In addition, fluctuation of the water table that results from pumping or pumping in concert with irrigation can change conditions in the unsaturated (soil) zone, the gateway to an aquifer. The unsaturated zone is an important chemical-buffer zone to aquifers, the importance of which geochemists are only beginning to understand.
Ground-water use that results in deterioration of water quality may cause irreversible damage to an aquifer. Consideration of water-quality effects in sustainable yield assessments represents not just one more test of the "sustainability" of aquifer development, but an essential part of the evaluation.
To protect ground-water supplies from overexploitation, some state and local agencies have enacted regulations and laws based on the concept of "safe yield." Safe yield is defined as the attainment and maintenance of a long-term balance between the amount of ground water withdrawn annually and the annual amount of recharge. Safe yield is a management concept that allows water users to pump only the amount of ground water that is replenished naturally through precipitation and surface-water seepage. As defined, safe yield ignores discharge from the system.
Under long-term equilibrium conditions, the amount of recharge to an aquifer equals the amount of water discharged into a stream, spring, or seep. Consequently, if pumping equals recharge, the streams, marshes, and springs eventually dry up. Continued pumping in excess of recharge eventually depletes the aquifer (e.g., the Ogallala aquifer in parts of Kansas, Texas, and New Mexico). Thus, natural recharge should not be part of the well-field water budget unless natural discharge is also factored into the formula.
Policymakers are primarily concerned about aquifer drawdown and surface-water depletion; both are related to the rate and duration of pumping, location of the well, and aquifer properties. Natural recharge is unrelated to these parameters and is irrelevant to ground-water and surface-water depletion. Despite its irrelevance, natural recharge is often used in ground-water policy to balance ground-water use under the banner of safe yield. It is a misconception that the natural rate of recharge represents a safe rate of yield.
Use of the traditional concept of "safe yield" of ground water persists today despite being repeatedly discredited in the scientific literature. Misconceptions about safe yield and its use in ground-water management lead to continued ground-water depletion, stream dewatering, and loss of wetland and riparian ecosystems.
Safe yield has often been used as a guide for the sustainable use of a single product--the number of trees that can be cut, the number of fish that can be caught, the volume of water that can be pumped from the ground or river, year after year, without destroying the resource base. However, experience has repeatedly shown that a single- product goal is too narrow a definition of the resource, because other resources inevitably depend on, or interact with, or flow from the exploited product. We can maximize our safe yield of water by drying up our streams, but when we do, we learn that the streams were more than jus containers of usable water.
A better approach would address the sustainability of the "system" and its water yield-not just the trees, but the whole forest; not just the fish, but the marine food chain; not just the ground water, but the running streams, wetlands, and all the plants and animals that depend on them. Such a holistic approach, however, is fraught with difficulty. We cannot use a natural system without altering it, and the more intensive and efficient the use, the greater the alteration.
Sustainable development of water resources refers to a holistic approach to development, conservation, and management of water resources, an approach that considers all components of the hydrologic system. It is inherently intergenerational because it implies that we must use the water resources in ways that are compatible with maintaining them for future generations. This intergenerational perspective constrains our management of water. The mechanisms to bring about these changes are not clear-cut and are still a matter of debate. The concept is a dynamic one and will be continually refined.
Although the ideas of sustainable yield have been around for many years, a quantitative methodology for the estimation of such yield has not yet been perfected. Since the 1980's, three-dimensional numerical models of the complete stream-aquifer hydrogeologic system have been employed to provide a predictive tool explaining the connection between well-field withdrawal and surface-water depletion.
In view of persistent declines in ground-water levels, especially in western Kansas, the Kansas Legislature in 1972 passed the Kansas Groundwater Act authorizing the formation of local groundwater management districts (GMD's) to help control and direct the development and use of ground-water resources. As a result of these ground-water level declines, especially since the mid-1970's, streamflows of western and central Kansas streams have been decreasing. In response to these streamflow declines, the Kansas Legislature passed the minimum instream flow law in 1982, which requires that minimum desirable stream flows (MDS) be maintained in different streams in Kansas.
The three western GMD's (1,3, and 4), which have the least precipitation and the highest rate of ground-water-level declines, adopted a planned ground-water depletion policy (although GMD 4 switched to a zero-depletion policy for new wells in 1990); the two GMD's in central Kansas (2 and 5), which have more precipitation and smaller rates of ground-water-level declines, adopted modified forms of "safe yield" or "sustainable yield" policies, thus attempting to maintain a balance between water-resource inputs and outputs.
Wise management of water resources needs to be approached not only from the standpoint of quantity and quality, but should also take into account the impact of ground-water exploitation on the natural environment, including human, ground-water, surface-water, and riparian ecosystems. This kind of integrated management approach is now taking hold in Kansas. The progressive evolution of Kansas water management from the establishment of local GMD's, and the progression of their policies, to the adoption of integrated resource planning and management by the Kansas Water Office and Division of Water Resources (Kansas Department of Agriculture) bodes well for the sustainable development of water resources in Kansas.
Water-resource management should be based on the best information we have today, but should be flexible enough for change and complexity because natural systems are inherently variable, "patchy," and complex. This also implies managing in a probabilistic and risk-assessment framework that recognizes the inherent unpredictability of nature. Instead of determining a fixed sustainable yield, managers should recognize that yield varies over time as environmental conditions vary.
Our understanding of the basic principles of soil and water systems and processes is fairly good, but our ability to apply this knowledge to solve problems in complex local and cultural settings is relatively weak. Additional lines of communication from the research fields to the water users in the field are required. Communication breakdowns probably account for the persistence of simplistic but misguided concepts such as conventional safe-yield management strategies. A strong public education program is needed to improve understanding of the nature, complexity, and diversity of ground-water resources, and to emphasize how this understanding must form the basis for operating conditions and constraints. This is the only way to positively influence, for the long term, the attitudes of the various stakeholders with water-resource interests.
Yield is used to characterize the capacity of a water resource to serve as a long-term water supply. Yield determinations affect many facets of water policy. In Kansas, a yield estimate places an upper limit on the amount of water supply that can be marketed from a reservoir. This de facto rationing of water resources can have significant implications for entities in search of water supplies. Therefore, it can affect the larger regional water supply. Yield determinations also have corollary implications for policies pertaining to reservoir recreation, reservoir fisheries, and downstream streamflows and riverine habitat.
Reservoir yields depend primarily on inflows and reservoir storage. As such, reservoir yields decrease with time due to reservoir sedimentation. The loss of storage results in a loss of reservoir yield unless compensatory actions are taken. These measures can include augmentation of inflow, increasing the conservation storage capacity via structural or institutional means, or physically removing the accumulated sediments. Except for increasing the conservation storage via institutional means, these approaches (augmentation of inflow, structural increases in storage capacity, removal of bottom sediments) are generally not feasible due to economic, environmental, and political concerns.
Water-resources planners realize that knowledge of the hydrologic system is fraught with uncertainties, but decisions still must be made. Water-yield estimates are the result of a hydrologic-balance calculation, based on the initial stock of water, and all inflows and outflows to the system. These quantities vary with time and location and can only be estimated, and thus may carry significant uncertainty. All sources of uncertainty need to be recognized, and their impact on the variables, such as water yield, need to be evaluated. Because uncertainty and risk are companions, evaluating uncertainty allows the assessment of risks and the management of its consequences. Uncertainty needs to be incorporated into the analysis in a quantitative fashion, by means of probabilities. By doing this, decision makers can set policies that meet acceptable levels of risk.
Natural systems can never be perfectly known. Fortunately, uncertainty can be evaluated and policies adopted that minimize the risk of undesirable consequences, such as depleting an aquifer at a rate faster than desired. By recognizing uncertainty we can make the most of the available information, thus leading to better decisions.
Over the last 150 years, most of the land area of Kansas (over 90%) has been changed by agricultural development. Sustainable crop production without irrigation has been a matter of developing management practices that increase the effectiveness of a limited water supply and protect the soil from excessive erosion. Adoption of conservation practices that decrease runoff and reduce evaporation losses have been important. In much of the state, the effectiveness of these practices has resulted in more efficient use of water for grain and forage production.
Since water use by agriculture is a consumptive use that results in evaporation of water from the land surface, more efficient irrigation practices mean that less water becomes runoff or ground-water recharge. As a result, with the development and adoption of ways to use water for agriculture more efficiently in Kansas, less water is available for non-agricultural uses, especially in the drier regions of the state. In the future, these effects will probably result in further decreases in the amount of water available for appropriation by other users. In the western half of the state in particular, stream flows have been reduced by up to 50% since 1950 by a combination of agricultural practices, including withdrawal of ground water for irrigation along streams. In the eastern half of the state, the effect has been limited because of the difference in climatic conditions.
A rapidly growing body of evidence suggests that we are entering a somewhat warmer and definitely more variable world. Sustainable water yields mayor may not be reduced in the long-term average, but they will almost certainly be less reliable in the short term. Climate warming may increase demand for water at a rate even greater than that predicted on the basis of economic development. Present-day reservoirs, well fields, and water laws and rights are consistent with the climate-as-it-was. These rights and structures--or at least their present mode of operation--can not be expected to yield the same results in the now-and-future climate.
Sustainable yield depends on the assumption of basic stability of the hydrologic cycle: long-term consistency in precipitation and the flow of surface water and ground water, and factors such as temperature, wind, and sunlight that control evaporation and transpiration. Climate is subject to both natural and human-induced changes on scales ranging from local to global.
The local and regional hydrologic effects of global changes cannot be reversed or stabilized at a local level. Adaptation is the only near-term management option. Such adaptation will almost certainly require reconsideration of the concepts, as well as the present water quantities, associated with "safe yield" and ideas of sustainability.
Climate change will have uncomfortable results, but it need not be disastrous if action is taken now to prepare the state and its citizens to mitigate the worst effects of climate change and take advantage of possible benefits. Some of the possible approaches include:
Chapter 1: Water Resources of Kansas--A Comprehensive Outline, by Marios Sophocleous
Chapter 2: On the Elusive Concept of Safe Yield and the Response of Interconnected Stream-aquifer Systems to Development, by Marios Sophocleous
Chapter 3: Evolving Sustainability Concepts--Modern Developments and the Kansas Experience, by Marios Sophocleous, R. W Buddemeier; and R. C. Buchanan
Chapter 4: Is Sustainability a Viable Concept in the Management of Confined Aquifers in Kansas?, by P. Allen Macfarlane
Chapter 5: Water Chemistry and Sustainable Yield, by G. L. Macpherson and M. A. Townsend
Chapter 6: Yield Estimates for Surface-water Sources, by David I. Leib and Thomas C. Stiles
Chapter 7: Effects of Agriculture on Water Yield in Kansas, by James K. Koelliker
Chapter 8: Climate Change and Sustainable Water Yield, by Robert W Buddemeier
Chapter 9: Managing Uncertainty in Yield Estimates, by Hernán A. M. Quinodoz
Chapter 10: Concluding Comments on Managing Water-resources Systems--Why "Safe Yield" is Not Sustainable, by Marios Sophocleous
Chapter 11: Selective Glossary of Hydrology and Environmental Sustainability-related Terms, compiled by Marios Sophocleous
Biographical Sketches of Chapter Contributors
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|microgram (µg)||0.001||milligram (mg)|
|mile (mi)||1.60934||kilometer (km)|
|mile (mi)||5280||feet (ft)|
|million acre-feet (MAF)||1.23348||cubic kilometers (km3)|
|million acre-feet (MAE) per year||892.74||million gallons per day (MGD)|
|million gallons (Mgal)||3,785.41||cubic meters (m3)|
|million gallons per day (MGD)||3.06888||acre-feet per day (ac-ft/d)|
|million gallons per day (MGD)||1,120.14||acre-feet per year (ac-ft/yr)|
|picocurie (pCi)||1x10-12||curie (Ci)|
|square foot (f2)||0.0929||square meter (m2)|
|square mile (mi2)||2.58999||square kilometers (km2)|
|square mile (mi2)||258.9988||hectares (ha)|
|square mile (mi2)||640||acres|
Area of Kansas = 82,276 mi2 = 52,656,640 acres = 213,094 km2
Next--Terminal zone of continental glaciation
Kansas Geological Survey
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Web version placed online May 6. Original publication date 1998.