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Water and Life WONDROUS WATER Life arose in water and there began its evolution from the simple plants and animals that were virtually all water to humans, who by weight are approximately two-thirds water. The average human contains nearly 50 liters of water and must replace about 5 percent of it daily for vital bodily functions. Water has unique physical and chemical properties that enable it to play key roles in regulating the metabolism of our living planet. · Elixir of life The peculiar molecular structure of water makes it an almost universal solvent; no other liquid can dissolve such a wide variety of compounds. Because cell membranes are permeable only to certain dissolved substances, water is the elixir of life, essential- as blood and lymph both for the nourishment of cells and for the removal of their wastes. It plays this same role at all higher levels of life's organization: for the individual plant or animal, the household, the city, civilization, and, apparently, for the earth itself. · Climatic thermostatA gram of water can absorb more heat for each degree of temperature rise than can most other substances. This high specific heat gives water a correspondingly large thermal inertia, making it the flywheel of the global heat engine. Because of water's special character, oceans and large lakes fluctuate little in temperature, and the heat-sensitive proteins within plant and animal cells are insulated by their aqueous baths. · Global heat exchanger When changing among its liquid, vapor, and solid states (at constant temperature), a gram of water absorbs or 17
18 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES yields more heat than do most other substances. The phase changes of water on the earth are powered by the sun. Solar energy stored in water vapor as latent heat during evaporation travels with the vapor in the atmospheric circulation until it is released when the vanor condenses into precipitation. redistributed globally. In this way both water and heat are The range of surface temperatures and pressures on the earth is such that water is plentiful in its life-supporting liquid state and yet moves freely and vigorously to its vapor and solid states as well. The more we learn about our desiccated, and apparently barren, neighboring planets, the more we wonder if our good fortune is not a result as well as the cause of life on the earth. ROUND AND ROUND AND ROUND IT GOES The pathway of water as it moves in its various phases through the atmosphere, to the earth, over and through the land, to the ocean, and back to the atmosphere is known as the hydrologic cycle (Figure 1.1~. 1 Precipitation on land Moisture over land Evaporation from land Precipitation on ocean Infiltration ~`,` Moisture Water ~ table Go Evaporation and evapotranspiration KIWI lUWdlUl IIUW _ Evaporation from ocean Surface outflow Groundwater outflow FIGURE 1.1 Elements of the hydrologic cycle. SOURCE: Reprinted, by permission, from Chow et al. (1988). Copyright @) 1988 by McGraw-Hill, Inc.
WATER AND LIFE 19 In one round trip through this cycle a single water molecule may assume various roles: dissolving minerals from the soil and carrying them to nourish plants, quenching the thirst of humans, acting as a coolant, and serving as a solvent or chemical reactant in industrial processes. In any of these roles this water molecule may return to its hydrologic pathway in new chemical compounds or, along with its associates, it may be mixed with various solid and liquid substances. Thus the hydrologic cycle is not defined solely by the quantity of water moving through it but also by that water's quality. Furthermore, many things affected by water in its relentlessly re- petitive cycle have their own effects on that cycle. Prime examples are plants, which regulate the rate at which a land surface returns water vapor to the atmosphere, and humans, who alter nearly all aspects of water on land. Such interactions are not limited to living things, however, if we consider longer time scales. For example, alluvial aquifers, formed over geological time through erosion and sedimentation by glaciers and streams, form a dynamic component of the contemporary hydrologic system. Our water-based environ- ment has arrived at its present state through eons of convolution of climate, life, and the solid earth. WATER AS ENABLER AND SUSTAINER OF CIVILIZATION Water, so fundamental to maintaining life, was also critical to the development of civilization. In fact, it is not an exaggeration to state that civilization was born of water. Without access to and some degree of control over water, the coming of civilization would have been impossible. Water quenches people's thirst, supports their crops, and provides transportation and power. Water has long been essen- tial to trade and to communication as well. Water and Agriculture The great early civilizations blossomed in the valleys of important river systems: the Nile of Egypt, the Tigris-Euphrates of Mesopotamia, the Indus of northern India (in what is now Pakistan), and the Hwang Ho of China. Generally, the Neolithic civilizations came into promi- nence some 10,000 years ago, when humans began mastering the skills and tools that gave them a measure of control over their environment. A critical step was the beginning of agriculture. As long as the efforts of virtually all the populace were required for subsistence food production, there was little time or energy for civilization to develop. However, as agriculture evolved and became more reliable and efficient, some
20 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES people were freed from its burdens. They had time to make bricks and pottery, weave wool, cotton, and flax into fabrics, or work with metal. Trade developed. People congregated in villages and towns. In turn, other achievements ensued, such as the development of mathematics and writing. Egypt provides a clear illustration of the relationship between a river and the development of an agricultural society. In late June, like clockwork, the lower Nile began to rise. By late September, the whole floodplain was covered. Then, as the waters receded, shrinking back to the main channel by October, they left behind a soil-building layer of silt, and a great agricultural potential. "Egypt," Herodotus said some 2,400 years ago, "is the gift of the river." The Egyptians used their hydraulic engineering skills to make the most of this al- ready beneficial relationship: they built simple canals, dikes, and reservoirs to help manage the water and increase crop production. Measurements of the Nile's water level were made at the second cataract as early as 1800 B.C. Two thousand years ago the Romans began to make regular measurements of the river's stages at Cairo, thus initiating the longest hydrologic record in the world. This "Nilometer" water-level gage was calibrated by the Roman naturalist Pliny the Elder (A.D. 23-79) in subjective terms that dramatically reveal the importance of the river to Egyptian life (Figure 1.2~. As is often FIGURE 1.2 Pliny the Elder's calibration of the Nile River's stages. SOURCE: Reprinted, by permission, from Dooge (1988). Copy- right @) 1988 by Blackwell Scientific Publishers Ltd. 20 18 CD ~ 16 <5 11 LU 14 - LL o A 12 10 Disaster Abundance Security Happiness Suffering Hunger 20 18 16 14 12 10
WATER AND LIFE 21 the case along uncontrolled rivers, social disaster accompanied both low stage (i.e., drought) and high stage (i.e., flood). Mesopotamia, part of a region often called the Fertile Crescent by archaeologists, consisted roughly of what is today Iraq and parts of Iran. Although millennia of climate change and human neglect have caused the region to become arid and inhospitable, this area that separates the valleys of the Tigris and the Euphrates rivers was once rich and productive. From 4000 B.C. the Sumerian civilization in the Tigris-Euphrates valley created an impressive irrigation system, including a great canalthe Nahrwan, about 120 m wide and over 320 km long that fed smaller canals and channels throughout the valley. They also invented the water wheel to help transfer this water into ditches and furrows. By 2400 B.C., however, the Sumerian culture was in decline, apparently for reasons directly related to the failure of its irrigated agriculture. The Sumerians had no drainage system to carry off excess water, and the salts left behind by evaporation of the irrigation water accumulated on the fields, rendering them unsuitable for growing crops. Water and Climate Change Climate is the fundamental determinant of water availability and hence of where humans have migrated and settled. Defined as the average local weather (i.e., temperature, pressure, precipitation, cloud cover, wind speed, and so on) over a long period of time (say, 30 years), climate is not a constant. It fluctuates with periodicities of 100,000, 41,000, and 21,000 years because of predictable variations in the earth's orbit, and it changes irregularly, for unknown reasons, on all time scales. These fluctuations influence both the amount and distribution of precipitation. A culture tied closely to a particular climate will be in jeopardy when its water supplies are reduced. Water and the City Whether village, town, or city, few human habitations have ex- isted whose founding did not depend on the proximity of water. Often it was water for agriculture and drinking that pinpointed the exact spot for a settlement. The sites of villages are not typically fortuitous; people (either deliberately or spontaneously) choose sites with natural advantages, often water-related, such as defensibility or ease of transportation and communication. Towns often have been founded at some junction of physically contrasted zones. For instance, many coastal cities occur where goods are transferred from seagoing
22 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES ships to land transport or river craft. For similar reasons cities are often found at the junctions of mountain and plain. Cities are born to take advantage of beneficial geography. Ancient seaports, for ex- ample, declined or were moved when effective access to the water was cut off by siltation, and modern seaports may disappear or be moved as a result of rising ocean levels. WATER AS A HAZARD Floods and droughts plagued humans even before they adoptec. an agricultural lifestyle.
WATER AND LIFE 23 Floods A flood is an overflowing of water onto land not usually sub- merged. For scientific purposes the size of a flood is usually measured in terms of the maximum flow rate (cubic meters per second) of the flooding stream and depends on the rate, duration, and areal extent of the rainfall as well as on the nature and condition of the land on which it falls. For purposes of public safety the maximum water- surface elevation relative to the elevation of the bank is of prime concern, because what may be a flood at one place along a stream may be a well-controlled flow at another place. Floods are a natural phenomenon important to the life cycle of many biota, not the least of which is mankind. Floods became a problem only as humans established farms and cities in the bottom- lands of streams and rivers. In so doing they not only exposed their lives and property to the ravages of floods, but also exacerbated floods by paving the soil and constricting the stream channels. Over time continued urbanization of natural floodplains has caused great annual losses of both wealth (Figure 1.3) and human life (Figure 1.4~. The Hwang Ho, for example, is sometimes known as China's Sorrow, a LLJ 1 00,000 c: In o 1 0,000 - ~n is o - - 69 - ' 100 o o it 10 lid '1 , ~ 1 A butt 1 1 1 1 1 1 1 1 1 1900 1910 1920 1930 1940 1950 YEAR 1960 1970 1980 (a) Trend in Flood Damages (in 1983 dollars) FIGURE 1.3 Historical trend in annual U.S. losses due to flood damage. SOURCE: Reprinted from Hudlow et al. (1984) courtesy of the National Weather Service.
24 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES 2.8 2.6 en 2.4 o o 2.2 2.0 1.8 1.6 1.4 1.2 1.0 .8 In I ~ 6 ' LU - .4 .2 o 1 941 1946 1 951 1956 1961 1966 1971 1 976 to to to to to to to to 1945 1950 1955 1960 1965 1970 1975 1980 YEAR _ Lightning I c~rnac~oes ~ Floods >_ _ ~ \ _1 1 - - \ ~'\\ Tropical Cyclone - FIGURE 1.4 Population-adjusted death rates in the United States from four storm hazards, 1941 to 1980. SOURCE: STORM DATA, published monthly by the National Climatic Data Center. National Environmental Satellite, Data, and Information Series. National Oceanic and Atmospheric Administration, Asheville, N.C. river so erratic and dangerous that a single flood reportedly has caused a million deaths. As early as the eighth century B.C., the Chinese were building dikes in attempts to confine the Hwang Ho's shifting channel and control its great destructive power. The Hwang Ho is also called the Mother of China because of the fresh topsoil the floods bring to the land. The major scientific challenge with respect to floods here lies with improved short-range forecasting, but the principal hope for reduction of the losses lies with public policy that regulates development in the floodplain.
WATER AND LIFE 25
26 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES Droughts Like beauty, drought is in the eye of the beholder (or the water user). It is commonly agreed that "drought" signifies an extended shortage of water, but there the agreement stops. The intended use defines what constitutes a "shortage," and the meaning of "extended" is subjective. A water shortage arises when tropospheric circulation, which controls storm tracks, shifts in a way that makes rainstorms less likely at the location in question. A persistent lack of rainfall results presumably from inertia in the phenomena causing the shift in atmospheric circu- lation and may continue for several years or for a decade or more. Little is really known about the causes and persistence of drought, however, and this is a fruitful area for research. Toxicity The by-products of human activities must be disposed of as either liquid, solid, or gas within one of the compartments of the earth system. Many of these waste materials are harmful to human health, and traditionally, humans have disposed of them in streams, rivers, and lakes (from which they are ultimately transported to the oceans). Because these freshwater bodies have also served as prime sources for water supplies, they were the first to be protected by legislation mandating particular treatment of point sources of wastes before allowing their return to the hydrologic cycle. We now realize that many of the waste materials thought to be "out of sight, out of mind" when disposed of within the earth are dissolved in ground water and hence reenter the hydrologic cycle as these waters rejoin the rivers. Regulatory action to control this practice is in its infancy, and cleanup of past damage is a difficult and costly task. Other residuals are discharged to the atmosphere, from which many return to the land either in rainfall or snowfall or as dry deposition, and then go into aqueous solution. Regulation of this activity has yet to be effective. WATER AS A RESOURCE TO BE MANAGED History of Water Management in the United States The management of water has proven to be critically important throughout the history of civilization, but the sophistication of these
WATER AND LIFE 27 efforts and the pace of change have increased dramatically in the past few centuries. During the first 100 years of the European colonization of North America, each colonial household met its own needs for water and waste disposal. However, with increasing population growth in the early 1700s, the responsibility for some of these functions shifted to villages and then to cities, and the first water control structures were built to impound water for sawmills and gristmills and to di- vert water for municipal supplies. Still, water development was hy- drolozicallY, hydraulically, and structurally unsophisticated. The science V J ' J J ' and the engineering of water structures were based on short-term observations, trial and error, and rules of thumb. These early efforts may have been small scale and intended for local services only, but they provided water for consumption and power for the mills that were central to the economy of the colonies. Beginning in the early 1800s, as the eastern United States was becoming more urbanized and as the West was beginning to be settled, the concept of larger, regionally oriented water projects took root. The nation built several major water reservoirs in the mid-1800s to supply eastern cities and to support western irrigation and hydraulic mining. The stage had been set for a federal role in river-basin-scale water development when in 1824 the Congress provided its first appropriations to the U.S. Army Corps of Engineers for clearing snags and sandbars from the Mississippi and Ohio rivers. In the late 1800s, the U.S. Geological Survey was established to gather and develop the hydro- logic information needed to complement the nation's water manage- ment efforts. By 1902, the U.S. Bureau of Reclamation had been established with a mission of developing irrigation water to help small farmers in their efforts to settle the West. Subsequent decades found more and more roles for the federal government with respect to water resources. Beginning with the New Deal legislation of the 1930s, river basin water development was seen as a device for achieving social objectives such as the regional transfer of capital and people. The Army Corps of Engineers, the Bureau of Reclamation, the Soil Conservation Service, and other agencies engaged in a period of intense water resources management in response to various pieces of legislation intended to control floods, irrigate 17 western states, conserve soil and water, and provide navigable streams, hydroelectric power, water supplies, recreation, drainage, and other functions. The accomplishments during this extremely active period of development are impressive indeed. However, the environmental damage resulting from these projects is now also understood. For example, dams have interfered with the environment and life cycle of aquatic organisms and with the transport of river-borne supplies of -on ~ r - - ~ -
28 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES sediments to replenish eroding beaches; irrigation has led to salination of agricultural land and to pollution of wetlands by leachates. Many factors (such as increased environmental consciousness, shifted political priorities, and increased expectations of economic efficiency) contributed to ending this era of large-scale development, but there is no denying the significance of the period to the evolution of the science of hydrology and of related science and engineering disci- plines. Efforts to manage water resources helped create a new, human- modified national landscape and, in the process, established humans as an inseparable part of the hydrologic cycle. The design, construc- tion, and operation of these large water projects have furthered the development of many practical disciplines such as hydrologic engineering and water resources management. They have also stimulated increased interest in an understanding of the hydrologic science underlying these river-basin-scale projects. Provision of Safe Drinking Water The management of water resources throughout the nation and the world has had as a goal the availability of clean water for human consumption. It is the single greatest requirement for public health and a condition that is generally taken for granted in the United States and other industrialized nations. In the United States, water quality problems were recognized early in the twentieth century and were tackled by sanitary engineers, who devised treatment methods such as the simple addition of chlorine to kill infectious organisms. But in developing countries, nearly 2 billion people (of a world population of approximately 5 billion) lack safe drinking water. Most of these people have no public water supply or wastewater disposal service; water-borne diseases are commonplace. Continued progress in providing safe drinking water will allow countries to focus on other water issues, such as irrigation for sustainable agriculture, and environmental problems, such as soil erosion, deforestation, and hazardous waste management. Contemoorarv Water Resources Management Problems Efforts to provide for the water-related needs of the world's popu- lations have been impressive, but population growth and the chang- ing demands of increasingly sophisticated societies have put unparalleled pressures on water resources. Today in the United States, and perhaps throughout the world, it seems that nearly every community faces some type of water crisis and that these crises are more technically, politically, and socially complex than those faced in the past. The
WATER AND LIFE 29 1~* 1 ~ Ah'
30 OPPORTUNITIES IN THE HYDROLOGIC SCIENCES water system infrastructure that exists in most areas today is aging and is approaching the limits of its capacity to provide the services for which it was designed. The demand for water for many uses is increasing, and the supply may be decreasing in some regions. The introduction into the environment of exotic chemical products exacerbates this problem. Treatment of municipal and industrial wastewater does not assure pollution-free streams. A much more confounding issue is water quality degradation from distributed (i.e., non-point) sources. Non- point pollution includes fertilizer and sediment runoff from agricultural fields, acid deposition from the atmosphere, detergents, oils, metals and fecal material carried in urban storm sewers, and other substances that cannot be identified as coming from a single source. This type of pollution can be particularly difficult to identify, let alone prevent, as is clearly the case at the Chesapeake Bay in the eastern United States. Boston, Massachusetts, provides another example of the growing problem of non-point pollution. For approximately a century, aque- ducts have carried water from reservoirs in central Massachusetts through a system of holding lakes to the Boston metropolitan area for municipal use. Until now the quality of this water has been such that water treatment was unnecessary. Non-point pollution from development on lands tributary to the holding lakes is changing this situation. Traditional challenges in irrigation management have included salinity, streamflow characteristics, storage requirements, and provision of means for conveyance and drainage. More recently, the discovery of toxic trace elements in the irrigation drainage water of the San loaquin Valley of California and the mining of ground water (i.e., its exploitation beyond what is renewed) have had a serious impact on the future of irrigated agriculture in the United States. Ground water mining for irrigation and contamination by trace elements are also occurring in many other parts of the world. These are but a few examples of contemporary water problems and the challenges they are now presenting to hydrologists and water managers. Emerging Water-Related Problems We now understand that the hand of mankind is altering the earth's environment on a global scale by virtue of such widespread activities as deforestation, urbanization, and pollution. Accompanying this environmental change is global-scale change in the hydrologic cycle. Ensuring the security of water supplies and protecting against flood, drought, and toxicity require that we understand these changes.
WATER AND LIFE 31 Humans are introducing into the air, soil, and water of our planet chemicals foreign to the evolutionary process that produced con- temporary plant and animal life. To safeguard life we must under- stand the water pathways and aqueous processes to which these chemicals are subjected as they move through the earth system. To meet these and other emerging challenges we must devote more attention to the hydrologic science underlying water's geophysical and geochemical role in supporting life on the earth. The needed understanding will be built from long-term, large-scale coordinated data sets and, in a departure from current practices, it will be founded on a multidisciplinary education emphasizing the basic sciences. The benefits society will ultimately receive from a thorough scientific understanding of water behavior are many. Advances in the areas of irrigation, drinking water and ground water supplies, improved rec- reational areas and wildlife habitat, and flood and drought forecasting and planning are only a few examples. Improved hydrologic science will provide a foundation for decision making, resulting in protection and improved management of the world's water resources. SOURCES AND SUGGESTED READING Chow, V. T., D. R. Maidment, and L. W. Mays. 1988. Applied Hydrology. McGraw-Hill, New York. Dooge, J. C. I. 1983. On the study of water. Hydrol. Sci. J. 28(1):23-48. Dooge, J. C. I. 1988. Hydrology in perspective. Hydrol. Sci. J. 31(1):61-85. Ford, E. C., W. L. Cowan, and H. N. Holtan. 1955. Floods- and a program to alleviate them. Pp. 171-176 in Water, the Yearbook of Agriculture 1955. U.S. Department of Agriculture. Francko, D. A., and R. G. Wetzel. 1983. To Quench Our Thirst: The Present and Future Status of Freshwater Resources of the United States. The University of Michigan Press, Ann Arbor, 148 pp. Hudlow et al. 1984. HYDRO Tech. Note 4. National Weather Service. Langbein, W. B.1981. A History of Research in the USGS/WAD. Pp.18-27 in Water Resources Division Bulletin (Oct.-Dec.). U.S. Geological Survey. McCullough, David G. 1968. The Johnstown Flood. Simon and Schuster, New York, 302 pp. Schneider, S. H., and R. Londer. 1984. The Co-evolution of Climate and Life. Sierra Club Books, San Francisco, 563 pp.