Where have all the rivers gone?

• Author: Postel, Sandra
• Position: Cover Story

SOME OF THE EARTH'S MAJOR ARTERIES ARE NOW SO CONSTRICTED THAT THEIR LIFEBLOOD NO LONGER REACHES ITS NATURAL DESTINATION. THE RESULT IS A MASSIVE FAILURE OF ECOSYSTEMS AND ECONOMIES.

In 1922, American naturalist Aldo Leopold journeyed by canoe through the great delta of the Colorado River. What he reported seeing there was a verdant waterscape, where for millennia the river had been depositing its rich silt and building up a diverse ecosystem before entering the Sea of Cortez - known north of the border as the Gulf of California. He saw deer, quail, raccoon, bobcat, vast fleets of waterfowl, and even the great jaguar, el tigre - "the despot of the Delta." The meandering river, slowing as it spread out through countless green lagoons, led Leopold to muse, "for the last word in procrastination, go travel with a river reluctant to lose his freedom in the sea."

Leopold never returned to the Delta for fear of finding this "milk-and-honey wilderness" badly altered. His fears were justified; today, the Colorado's freedom has been lost to a degree even the prescient Leopold could scarcely have imagined. Except in years of unusually high precipitation, the Colorado River no longer reaches the sea at all - it literally disappears into the surrounding desert. Much of the abundant wildlife is gone. Off the coast to the south, the once-productive fisheries in the Sea of Cortez have declined dramatically. In striking contrast to Leopold's experience, author Philip Fradkin more recently characterized what is now a dessicated place of mud-cracked earth, salt flats, and murky pools as "the most inhospitable terrain on the North American continent."

What has happened to the Colorado is but an extreme example of a disturbing worldwide trend: more and more rivers are running dry as dams and diversions siphon water off for burgeoning cities and thirsty farms. In Arizona, the Salt and Gila rivers used to converge west of Phoenix; but now they dry up east of the city because of extensive diversions for irrigated farms in the region. In California, some 35 kilometers of the San Joaquin River have been so permanently dewatered that thickets of trees have sprung up in the dry riverbed, sand and gravel are mined from it, and developers have even proposed building houses in it. In China, about 50 kilometers south of Beijing, villagers say the Heaven River dried up 20 years ago. And in the water-deprived Middle East, where surface streams are extensively overtapped, the lower stretches of the Jordan River have dwindled to a salty trickle.

It is the arresting decline of the world's larger rivers, however, that most graphically conveys the magnitude of the problem. The Nile, the Ganges, the Amu Dar'ya and Syr Dar'ya, the Huang He (or Yellow River), and the Colorado are each now so dammed, diverted, or overtapped that for parts of the year, little or none of their fresh water reaches the sea. Their collective diminution portends not only worsening water shortages and potential conflicts over scarce supplies, but mounting ecological damage. That damage, in turn - from degraded river deltas and species on the brink of extinction to shrinking inland lakes and disappearing wetlands - places the economies and people who depend on them at growing risk.

Many regions have now fallen into a zero-sum game - in which increasing the water supply to one user means taking it away from another. More water devoted to human activities means serious and potentially irreversible harm to natural support systems. With population and consumption levels rising at record rates in many parts of the world, it is a dilemma with far-reaching consequences - one that calls for a wholly new approach to valuing and managing rivers.

RIVERS AT RISK

Human efforts to control rivers date back thousands of years. The Assyrian Queen Sammu-Ramat, who ruled during the late 9th century B.C. in what is now northern Iraq, is reputed to have had inscribed on her tomb: "I constrained the mighty river to flow according to my will and led its water to fertilize lands that had before been barren and without inhabitants." In Zhengzhou, China, about 700 kilometers southwest of Beijing, stands a statue of the emperor Yu, under whose reign the Chinese people were said to have prospered from the building of dikes and irrigation canals to control the mighty Yellow River.

But it was not until this century that engineering schemes began to alter natural water courses on a massive scale. The construction of dams to store water and diversion canals to transport it to cities and farms has been central to the economic growth of regions wet and dry alike. A controlled supply of water for irrigation became critical to boosting food production as population and consumption grew. Large-scale hydroelectric power fueled urban and industrial expansion. And the taming of flood waters allowed farms and towns to situate on fertile soils and near shipping channels.

Indeed, for a time, river basin "development" became the sine qua non of economic advancement. Winston Churchill, noting the Nile's importance to the entire northeast Africa region, after a military campaign on that river in 1908, prophesied that "One day, every last drop of water which drains into the whole valley of the Nile...shall be equally and amicably divided among the river people, and the Nile itself...shall perish gloriously and never reach the sea." He was not speaking sardonically. Four years later, a California engineer, Joseph Lippincott, foresaw a similar fate for the Colorado River. "We have in the Colorado an American Nile awaiting regulation, and it should be treated in an intelliggent and vigorous a manner as the British government has treated its great Egyptian prototype."

The construction of the great Hooever Dam on the lower Colorado in the 1930s broke all engineering records up to that time. Some 220 meters high and able to store 1.7 years' worth of the river's average flow, Hoover Dam presage, an engineering frenzy that was to tame many of the world's rivers over the ensuing decades. Around the world, the number of "large" dams (those more than 15 meters high, and backing up months' or years' worth of their rivers' flows) climbed from just over 5,000 in 1950 to about 38,000 today. More than 85 percent of large dams have been built during the last 35 years.

Hoover Dam was also the first of a generation of structures that became known as "superdims" - those more than 150 meters high. Today, there are more than 100 of these megaliths, most of them built during the past four decades. Besides Hoover, they include such giants as the Bhakra Dam in India and the Itaipu in Paraguay, as well as such familiar U.S. dams as Glen Canyon on the Colorado and Grand Coulee on the Columbia.

Worldwide, dams collectively store on the order of 6,000 cubic kilometers of water - equal to 15 percent of the earth's annual renewable water supply. Thousands of kilometers of diversion canals siphon water out of rivers and reservoirs and deliver it where and when needed to expanding cities and farming regions. Globally, Water demand has more than tripled since mid-century, and the rising demand has been met by building ever more and larger water supply projects. Many rivers now resemble elaborate plumbing works,w ith the timing and amount of flow completely controlled by planners and engineers so as to maximize the rivers' benefits to human activity.

But if the intended triumph of such plumbing was to bring rivers as neatly into the service of human convenience as a bathroom faucet, it hasn't worked out that way. Rivers are central to the planet's ecology; turning them on and off at will damages other parts of the system. And because aquatic organisms cannot live long without water, large reductions in streamflow - even for short periods of time - can be damaging or deadly to them. In addition, most water-based animals are well-adapted for living either in the flowing waters of rivers and streams or in the standing waters of lakes and ponds; relatively few thrive in both. When rivers are dammed, and flowing water is replaced by a permanent reservoir, many river species are placed at risk.

In short, the manipulation of river systemms is wreaking havoc on the aquatic environment and its biological diversity. Fresh waters contain extraordinary concentrations of animal life - including, for example, about 40 percent of the 20,000 recognized fish species. According to some estimates, the total diversity of animal life per unit area of rivers is 65 times greater than that of the seas.

In North America, the American Fisheries Society lists 364 species or subspecies of fish as threatened, endangered, or of special concern - the vast majority of them at risk because of habitat destruction. Many are found in arid regions where intensive water demands and rising salinity are destroying vital habitat. More than a third of the desert fish species of the American Southwest, for instance, are now listed as threatened or endangered. As Professor Alan Covich of Colorado State University puts it: "We have often ignored the high species richness associated with inland waters and have allowed many fresh water habitats to be dammed, channelized, drained, eroded, and polluted with nutrients, salts, silt, and chemicals. Biodiversity and ecosystem integrity are declining in a wide range of locations throughout the world...."

AND THEN THERE WAS NONE

The Colorado River ranks among the most heavily plumbed water courses in the world. Controlled by 10 major dams, it now irrigates some 800,000 hectares (about 2 million acres) of farmland, serves the household needs of more than 21 million...