Water Management

Land-based life on Earth revolves around sweet (nonsalty) water. Domesticated plants require a regular and sufficient supply of sweet water. People must manage this water supply. People also must manage the supply of sweet water for humans, for our domesticated animals, and for manufacturing. However, since the invention of agriculture these latter goals often have been met while people manage the water supply for domesticated plants.

Most of the surface of our planet is water, but most of that water is too salty for use by organisms living on land. However, the hydrological cycle (the sequence of conditions by which water passes from vapor in the atmosphere through precipitation onto land or water surfaces and back into the atmosphere) provides a continuous supply of sweet water in the form of rain and snow. After precipitation hits the ground it either runs off on the surface, as rivers and other streams, or soaks into the soil. From the point of view of a farmer cultivating fields in a fixed place, the water environment is sweet, with water running on the surface, water in the top layer of the soil (soil water), and water deeper underground (groundwater).

As is true for most life processes, an ideal amount of water exists for the farmer. However, the environmental supply of water is variable, fluctuating from place to place and from time to time on daily, monthly, and yearly schedules. Combining the need for an ideal amount of water with the unending fluctuation yields three kinds of conditions: about right, too much, and too little. “About right” rarely occurs.

Water has several physical characteristics that are relevant for managing a farm. First, water is liquid and flows easily. Thus, all water responds to gravity and naturally flows downhill. It always takes the shortest possible route. Water is easy to move if a downhill path can be found. However, because water is a liquid, if a person wants to lift it, a sealed container must be used. Second, water is heavy. Lifting it requires not only a sealed container, but also considerable energy. Third, water is an excellent solvent. One of the major functions of water in the life of the green plant is to dissolve nutrients (from the soil) and transport them into the plant. However, water can also dissolve poisons (including salts). Fourth, water can carry many solid particles in suspension. Erosion of the landscape by running water transports such solid particles downstream.

The farmer wants sweet water for his plants in the right amounts, at the right times, moving at the right speeds, and containing the right components (dissolved, suspended). Irrigation is the technology that increases the water supply to plants, and drainage is the technology that reduces the water supply to plants.

The major energy sources for moving water are gravity, human muscle, animal muscle, wind, and heat engines (mechanisms, such as internal combustion engines, that convert heat energy into mechanical or electrical energy). For irrigation we supply water at a high point, and for drainage we remove it at a low point.

Irrigation

The elements of a canal irrigation system are an intake, where ditches tap into a water source; a main canal (sometimes many kilometers long); and a series of branch canals that delivers water to the farmer’s fields. Movable gates may control water flow into the branch canals, or the system may be designed so that water flows in every channel simultaneously.

The ditches move the water from the source to the fields. The technology for digging these ditches is simple and has been invented virtually everywhere. People use digging sticks, shovels made of wood, and hoes made of stone to loosen the dirt. Such tools are old and widespread. People use baskets to move the loosened dirt. Because water responds so quickly to gravity, people can easily test whether a ditch has the right slope and change the slope if they have made errors.

Most irrigation systems are what are called “run of the river,” meaning that the water available to them is what is in the river (the source) at the time.The construction problems are obvious (water must flow downhill, dirt must be moved) and the solutions have been invented many times. A significant problem with irrigation systems is variation in environmental moisture. For example, a drought can reduce a river’s water supply to a trickle, posing a threat to crops.

One solution to such variation is to store water in a reservoir. However, water storage was quite rare in early world history. The city of Jawa in the Jordanian desert had a storage dam by about 4000 BCE. Tank irrigation systems that stored water behind a small dam were widespread in southern and southeastern Asia by the first millennium BCE. Roman engineers built many small storage dams of masonry, but these dams may have been meant for domestic use rather than for irrigation. An early dam in the New World was the Purron Dam in Mexico, dated to about 800 BCE. That dam was made of earth and at its maximum was 19 meters tall. The dam was in operation for approximately one thousand years and could store more than 3 million cubic meters of water. Purron was one of only two storage dams known to have existed in the highland area of Mexico. Beginning during the late nineteenth century people have built many massive storage dams in most parts of the world. Machinery and modern materials—and a plentiful supply of money—have been central to these efforts.

Early irrigation systems built with simple tools were probably widely distributed. Their existence is difficult to document because all subsequent irrigation systems in the same place used the same routes for the ditches.Thus, researchers have difficulty finding and dating the earliest occurrence. However, scholars think they have evidence of irrigation early in all of the world’s civilizations. Irrigation may have existed during Neolithic times as well. The tools to build such systems were already available, as was the social organization. Only so many effective designs of an irrigation system exist, and they have existed around the world during all time periods.

A dam at Simatai in March 2004, a Great Wall tourist location to the far north of Beijing. A fine example of the Chinese commitment to dambuilding.

The Ganges river near Serampore has long been of major economic and religious significance to Indians.

Drainage

Drainage systems are the reverse of irrigation systems. Irrigation systems move large amounts of water to the top of the fields, then break it down into smaller and smaller packages for distribution to fields. Drainage systems collect small amounts of water at many places high up in the system, combine these small amounts into larger and larger channels, and collect the total at the bottom of the field system.The problem then is where to put the drainage water. If it accumulates it can flood the lower fields. The drainage water so collected is eventually put into a large body of water (a river, the ocean), and often people can use gravity to put it there. Gravity works well as an energy source, and ditches again are used to channel the water. Another technology for draining water is tile pipes. The pipes, with holes in them, are installed in ditches in the fields and then covered up. The lower end of the pipes must drain into something, usually a river bed. Tile pipes are effective and virtually invisible to all but the most discerning eye.

Another way to drain water is to dig dirt out of a swamp and pile it up so that the top is above the water level, producing what are often called “raised fields.” These fields can vary in size from a few square meters at the edge of a swamp to thousands of hectares. Among the earliest water management systems using raised fields were in highland New Guinea, dated to about 5000 BCE.

Lifting Water

Because of water’s weight and liquid nature, people had difficulty lifting water for many millennia. People used human muscle to lift small amounts of water in pots to water individual plants in the Valley of Oaxaca, Mexico, about 2000 BCE. People in Egypt could lift larger amounts with the shadoof (a beam on top of a pole, with a counterweight at one end and a container for the water on the other end). Human muscle powered the shadoof. People have dug wells (vertical shafts from the surface down to the water table) for a long time, but extracting large amounts of water has been difficult. People have used large domesticated animals to power the raising of larger amounts of water, but the output has not been substantial.

In the dry mountain belt from Turkey to western China, horizontal wells (called “qanats” or “foggara”) were widespread. People dug a shaft from the point of use (often an oasis) into a mountain, gently sloping upward, until the shaft met with water-bearing earth. People dug vertical shafts down to the horizontal shaft to remove dirt and to gain access for repairs. Horizontal wells could exceed 60 kilometers in length. They could provide water for centuries if properly maintained.

The first major innovation that increased people’s ability to lift water was the windmill, which became prominent in northwestern Europe during the thirteenth century. The Dutch reclaimed low land from the sea by building protective dikes and then draining the water out of the low land behind the dikes. They ganged together large windmills to lift the water out of the low land and dump it into the sea or a river outside the dikes. However, the height to which water could be raised was limited, and the windmills could operate only when the wind was the right speed.

With the advent of the heat engine during the Industrial Revolution the limits on lifting water were eliminated. One of the first tasks that people gave to steam engines was to drive pumps that drained water from flooded coal mines. Later uses included pumping drainage water out of a basin and lifting water for irrigation. People could lift water from a surface source (such as a river or lake) or from a deep well. Today people acquire a great deal of irrigation water from deep underground, and they could not do this without the heat engine to drive a pump.

With the introduction of the internal combustion engine, small pump and driver (an engine that powers the pump) sets became feasible, even to the point that farmers could own such sets and move them around the farm to where they were needed. However, although such sets save labor, they are expensive in terms of energy.

A modern innovation in irrigation technology is the pressurized system. Two major forms are used: sprinkler systems and drip systems. In sprinkler systems a pump and driver pressurize water, which is then moved through a series of pipes that is above the level of the plants that are to be irrigated.These pipes have multiple nozzles, and the water distribution mimics a light rain. Two major advantages of this system are: (1) Water use is much more efficient (more than 90 percent of the water reaches the crop root zone; by contrast, ditches have efficiency as low as 50 percent), and (2) no need exists to sculpt the surface of the soil, thus saving labor and energy. A small computer can operate a number of these sprinkler systems, saving even more labor. These systems also can deliver chemicals (fertilizers, pesticides) in the water. The major disadvantage is that the technology is energy intensive. However, people use sprinkler systems throughout much of the world; people flying in an airplane at 10,000 meters can see the green circles made by a rotary sprinkler system.

The other form of pressurized system is drip irrigation. Developed mainly in Israel (where the need to conserve water is great), drip irrigation uses long hoses with holes in them that are buried in the root zone. Water is forced through the hoses and exits the hoses through the holes. People also can put fertilizer and pesticides into the water, thus delivering them directly to the root zone. These systems are even more efficient than sprinkler systems, approaching 0 percent water loss, and they save on the labor to apply fertilizer and pesticide. A major disadvantage, of course, is the cost in energy to run the system. Another disadvantage is that the holes in the pipes can clog. Clogging requires that the hoses be exposed, which means excavating them, with possible damage to the crops.

Water Management in History

People have used irrigation systems and drainage systems to manage water for thousands of years and have built and operated such systems without writing and without scientific laboratories. The relationship between water stress (too much, too little) and the health of a green plant is obvious to any intelligent observer. People can use simple tools, easily made, to loosen and move dirt to dig ditches. Ditches will not function if their layout is wrong because water will not flow uphill in an open ditch.Trial, error, and correction are part of the success. A modern scientific understanding of water, green plants, soil, solutions, the hydrological cycle, and photosynthesis began during the nineteenth century and is still generating knowledge. People needed instruments (microscope, thermometer, balance) and the disciplines of physics, chemistry, anatomy, and physiology to achieve the scientific knowledge that we now have.

The impact of irrigation and drainage on world history has been great. Irrigation and drainage permit people to grow crops where otherwise it would be difficult or impossible.The growing of crops in turn permits a larger, denser population. Some scholars have claimed that civilization itself could not have occurred without irrigation and drainage. If that is true, these technologies have been important in the birth of cities and have played a role in economic surplus, fulltime division of labor, metal tools, astronomy, and eventually other sciences. However, people built and operated water management systems for millennia in areas that did not acquire cities and writing (such as New Guinea in the Malay Archipelago and the Hohokam people in Arizona).

Irrigation and drainage change the water balance of the landscape, and along with agriculture they change the plants and animals there. In order to safely grow our domesticated plants and animals people have wanted to eliminate plants and especially animals that are dangerous. Lions, tigers and elephants have been hunted and killed. The entire landscape has been changed in ways that we could call domestication. At the same time, however, we have provided habitats for small dangerous life forms, such as malaria. The blessings are mixed.

The simple tools and knowledge needed to build and operate irrigation systems and drainage systems exist everywhere, and traditionally there was little variation in the forms of such systems. With the Industrial Revolution, however, the scenario changed. European colonial powers built large storage dams during the nineteenth and twentieth centuries, using industrial technology. Storage dams were not new, but the scale of them was. The practice of lifting water with heat engines diffused widely, and this practice, too, used an industrial technology. Today people everywhere use heat engines linked to pumps, replacing traditional systems. Significantly, the technology is also manufactured just about everywhere.

The Future

The future of water management is a cloudy one. World population is growing, and such growth will increase the demands for food and for space for buildings. A substantial portion of the world’s food is now grown with irrigation, and this portion will only increase in the near future. An easy way to gain space to build is to drain wetlands. With industrial technology and (cheap) energy we have the technical capacity to build and operate large water management systems.

However, the best places for storage dams have already been taken, and finding new sources of water will be increasingly difficult. The draining of wetlands damages the environment, and people are trying to limit how much can be drained. Industrial populations are voracious users of water (for toilets, manufacturing, irrigation, recreation, etc.), and thus pressure to limit the amount of water that farmers can use is growing. Multiple uses of sweet water (for navigation, recreation, biological diversity) grow in number and in intensity. No clear way exists to solve the water problems that occur in nearly every nation. One technical solution is to increase the efficiency of our water use, and science will be crucial in that solution. However, the problems are not just technical ones—the beliefs and expectations of the consumers of water are also relevant and far less understood than are the properties of dirt, plants, and water.

Robert C. Hunt

【Famous sayings】：

Aristotle may be regarded as the cultural barometer of Western history. Whenever his influence dominated the scene, it paved the way for one of history’s brilliant eras; whenever it fell, so did mankind. · Ayn Rand (1905-1982)

【Further Reading】：

Adams, R. M. (1966). The evolution of urban society: Early Mesopotamia and prehispanic Mexico. Chicago: Aldine.

Butzer, K. W. (1976). Early hydraulic civilization in Egypt: A study in cultural ecology. Chicago: University of Chicago Press.

Childe, V. G. (1951). Man makes himself. New York: New American Library.

Denham, T. P., Haberle, S. G., Lentfer, C., Fullagar, R., Field, J., Therin, M., Porch, N., & Winsborough, B. (2003). Origins of agriculture at Kuk swamp in the highlands of New Guinea. Science, 301, 189-193.

Doolittle, W. E., Jr. (1990). Canal irrigation in prehistoric Mexico: The sequence of technological change. Austin: University of Texas Press.

Gumerman, G. (Ed.). (1991). Exploring the Hohokam: Prehistoric desert peoples of the American Southwest. Albuquerque: University of New Mexico Press.

Hall, A. R., & Smith, N. (Eds.). (1976). History of technology:Vol. 1. From early times to fall of ancient empires. London: Mansell.

Helms, S. W. (1981). Jawa, lost city of the desert. Ithaca, NY: Cornell University Press.

Hills, R. L. (1994). Power from wind: A history of windmill technology. Cambridge, UK: Cambridge University Press.

Hunt, R. C. (2002). Irrigated farming. In J. Mokyr (Ed.), Oxford encyclopedia of economic history (Vol. 3, pp. 165-168). Oxford, UK: Oxford University Press.

Scarborough,V. L. (2003). The flow of power: Ancient water systems and landscapes. Santa Fe, NM: School of American Research.

Service, E. R. (1975). Origins of the state and civilization: The process of cultural evolution. New York: W. W. Norton.

Wikander, O. (Ed.). (2000). Handbook of ancient water technology. Leiden, the Netherlands: Brill.

Wilkinson, T. J. (2003). Archaeological landscapes of the Near East. Tucson: University of Arizona Press.

Wittfogel, K. (1957). Oriental despotism. New Haven, CT: Yale University Press.