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Water Availability for the Western United States--Key Scientific Challenges

By Mark T. Anderson and Lloyd H. Woosley, Jr.

U.S. Geological Survey Circular 1261

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The citation for this report, in USGS format, is as follows:
Anderson, Mark T., and Woosley, Lloyd H., Jr., 2005, Water availability for the Western United States--Key scientific challenges: U.S. Geological Survey Circular 1261, 85 p.


In the Western United States, the availability of water has become a serious concern for many communities and rural areas. Near population centers, surface-water supplies are fully appropriated, and many communities are dependent upon ground water drawn from storage, which is an unsustainable strategy. Water of acceptable quality is increasingly hard to find because local sources are allocated to prior uses, depleted by overpumping, or diminished by drought stress. Some of the inherent characteristics of the West add complexity to the task of securing water supplies. The Western States, including the arid Southwest, have the most rapid population growth in the United States. The climate varies widely in the West, but it is best known for its low precipitation, aridity, and drought. There is evidence that the climate is warming, which will have consequences for Western water supplies, such as increased minimum streamflow and earlier snowmelt events in snow-dominated basins. The potential for departures from average climatic conditions threatens to disrupt society and local to regional economies. The appropriative rights doctrine governs the management of water in most Western States, although some aspects of the riparian doctrine are being incorporated. The "use it or lose it" provisions of Western water law discourage conservation and make the reallocation of water to instream environmental uses more difficult. The hydrologic sciences have defined the interconnectedness of ground water and surface water, yet these resources are still administered separately by most States. The definition of water availability has been expanded to include sustaining riparian ecosystems and individual endangered species, which are disproportionately represented in the Western States. Federal reserved rights, common in the West because of the large amount of Federal land, exist with quite senior priority dates whether or not water is currently being used. A major challenge for water users in the West is that these reserved rights may supersede other existing users. The minimum amount of water required, however, to sustain native peoples, a riparian system, or an endangered species eventually will need to be known in order to manage the available water supply. Periodic inventory and assessment of the amounts and trends of water available in surface water and ground water are needed to support water management. There is a widespread perception that the amount of available water is diminishing with time. This and other perceptions about water availability should be replaced by objective data and analysis. Some data are presented here for the major Western rivers that show that flows are not decreasing in most streams and rivers in the West. Systematic information is lacking to make broad assessments of ground-water availability, but available data for specific aquifers indicate that these aquifers are being depleted, especially near population centers.

The complexity added to the issue of Western water availability by these and other factors gives rise to a significant role of science. Science has played a role in support of Western water development from the beginning, and the role has evolved and changed over time as society's values have changed. In this report, the role of science is discussed in three phases: (1) development and construction, (2) consequences and environmental awareness, and (3) sustainability. The development and construction phase includes some historical accounting of water development in the West and shows how some precedents set in those early days are still applied today. Science has played an important role in the second phase by objectively pointing out the consequences of this development and construction phase, such as the effects from converting rivers to reservoirs, the effects of ground-water pumping on surface water in streams, land-surface subsidence, and the changes in water quality brought about by the disposal of wastewater and manmade chemicals into the Nation's waterways and aquifers. The sustainability phase reflects the present efforts of water managers and other natural-resource managers to sustain water supplies beyond the present generation. Sustainability, as presently interpreted, goes beyond mere water availability for water supply, and includes ecosystems and even individual species. Sustainability by this definition is superficially appealing, but is and will continue to be a significant challenge for science to translate into measurable water-management strategies. A sustainable water supply for a community ideally would provide enough water to support a growing population and economy, even during protracted periods of drought a tall order. There are many scientific challenges surrounding a sustainable use of water resources, but five key challenges are discussed in this report: (1) the determination of a sustainable level of ground-water use that meets identified management needs, (2) artificial recharge in the long-term, (3) selected water-use strategies such as desalination and water reuse, (4) sustaining valued ecosystems, and (5) sustaining individual endangered species. These key challenges will demand scientific attention in the coming decades and are examined here in detail, including the following case examples: (1) the Middle Rio Grande Basin, New Mexico; (2) artificial recharge in the Greater Los Angeles, California, area; (3) selected water-use strategies (no location); (4) San Pedro Riparian National Conservation area, Arizona; and (5) Upper Klamath Lake, Oregon. The case examples illustrate the technical and scientific complexity of the issues and explain the scientific approaches taken to address these issues, including the types and amounts of data collected. To support society's demand for sustainability, scientists, managers, policymakers and water users at large will need to develop, communicate, and use scientific information in more effective ways. New collaborative ways of conducting monitoring and research across disciplinary lines will be needed to develop quantitative habitat requirements for ecosystems and endangered species. The new role of science will be to support environmental decisionmaking to achieve some new level of sustainable use that will provide an assured supply of good-quality water for humans and for stream and riparian ecosystems.

Table of Contents





Purpose and Scope

Previous Work

Characteristics of the American West

Population Growth and Demographic Change

Climate and Climate Change

Water Availability and Patterns

Surface Water

Ground Water

Water-Use Patterns and Distribution

Western Water Law and Federal Reserved Water Rights

Water Quality

Naturally Occurring Constituents

Effects from Irrigation Return Flows

Effects from Mining

Effects from Urbanization

Biodiversity and Habitat Change

Evolving Role of Science

Development and Construction Phase

Consequences and Environmental-Awareness Phase

Conversion of Rivers to Reservoirs

Ground-Water/Surface-Water Interactions

Land-Surface Subsidence

Changes in Water Quality

Sustainability Phase

Determination of Sustainable Ground-Water Use

Scientific Information

Case Example--Middle Rio Grande Basin, New Mexico

Long-Term Artificial Recharge

Scientific Information

Case Example--Recharge in the Greater Los Angelos, California, Area

Selected Water-Use Strategies

Sustaining Valued Ecosystems

Scientific Information

Case Example--San Pedro Riparian National Conservation Area, Arizona

Sustaining Individual Endangered Species

Scientific Information

Case Example--Upper Klamath Lake, Oregon, Lost River and Shortnose Suckers




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