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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 thermostat—A 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
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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.
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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
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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
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Disaster
Abundance
Security
Happiness
Suffering
Hunger
20
18
16
14
12
10
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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 canal—the 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
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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.
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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
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it
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— '1 , ~ 1
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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.
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OPPORTUNITIES IN THE HYDROLOGIC SCIENCES
2.8
2.6
en 2.4
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1.6
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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
-
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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.
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25
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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
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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 - - ~ -
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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
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WATER AND LIFE
29
1~*
1 ~
Ah'
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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.
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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.
Representative terms from entire chapter:
hydrologic cycle
