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close this bookDiversity, Globalization, and the Ways of Nature (IDRC, 1995, 234 p.)
close this folder12. The urban environmental challenge
View the documentThe development of modern cities
View the documentLarge cities in the Third World
View the documentThe megacities of today

The megacities of today

Many cities of 10 or more million people concentrated in a relatively small area are trying to survive. Some, such as Tokyo and Los Angeles, are in the “old” industrial countries. However, the majority are found in the Third World. Some of the problems they are experiencing are representative of the challenges affecting all urban areas today.

Mexico: a thirsty city

There are few cases in the world in which the physical environment has been so completely transfigured by urban development as it was in Mexico City. The valley of Mexico is a 9 600 square kilometre closed basin that is more than 2 200 metres above sea level, in the heart of the Mexican neovolcanic belt. Before the arrival of Europeans in 1521, the valley was a depression in whose bottom several large lakes had developed because of volcanic obstruction of their outlets about 700 thousand years ago. The lakes covered a total area of about 2 thousand square kilometres and were partly connected, especially during periods of high water. Three of the lakes contained fresh water - Chalco, Mexico, and Xochimilco - and the other three, brackish water - Ecatepec, Texcoco, the largest at 800 square kilometres, and Zumpango.

The area was, and to a certain extent still is, subhumid. Rainfall was probably slightly more than the current amount, which ranges from 600 millimetres per year at the bottom of the valley to l 200 millimetres per year in the nearby mountains. The average temperature was relatively cool for the subtropic latitude at which the city is located, ranging from 8° to 15°C depending on the altitude. Soils were deep, highly fertile, and easy to work.

The land was completely covered by thick forests, particularly on the slopes of the mountains and highland areas. The plains in the valley, which were originally also covered by forests, were soon allocated for agriculture, and parts of the forest were cleared to make way for farms. In addition to the freshwater lakes, a large number of springs around the lakes and in the foothills of the nearby mountains provided considerable volumes of good-quality water.

Because of its abundant resources, the valley was occupied early by a number of indigenous peoples, who based their economy on locally domesticated crops and farm animals: corn, tomatoes, chili peppers, cacao, turkeys, dogs, honey bees, and fish. Because these people did not have draft animals or use the wheel, most trade was carried out by boat (or walking).

Several peoples successively inhabited and established political control over the lacustrine area during the few centuries before the arrival of the Europeans. The last group was the Aztecs, who arrived from the legendary land of Aztlan (probably in the northern arid territories) during the 14th century.

The Aztecs probably maintained a livelihood by fishing and trading with neighbouring groups. Gradually, they managed to build an island in the centre of the Lake of Mexico on which a town developed: Tenochtitlan. Through alliances and wars, the Aztecs built an empire, and Tenochtitlan became a thriving city of several hundred thousand people. A bridge was built to connect the island with the mainland, and large boats transported people and merchandise. The Aztecs also built earth dikes to control flooding and to separate the brackish lakes from the fresh water. Aqueducts carried fresh water from springs to the city through the lake and along the dikes.

It is difficult to comprehend the extent of the changes that took place in the few centuries after the Spanish conquest. Today, the proud Tenochtitlan has disappeared, and only scattered archaeological remnants can be found. In its place stands the highly urbanized downtown area of Mexico City.

The Lake of Mexico is gone. In its place are several hundred square kilometres of urban neighbourhoods built on what used to be the lake bottom. A few canals and small lakes are the only remnants of Chalco and Xochimilco lakes. Like the southern lakes, the three northern lakes were gradually drained (beginning in 1786), and the former Texcoco Lake has become a vast flat plain on which little vegetation grows because of the highly alkaline soil (pH is over 10). An intricate maze of wells and pipes pump brine from the lacustrine sediments for sodium carbonate and sodium chloride extraction.

The old springs that provided water to the riverine populations are also gone. Now over 5 thousand wells draw more than 50 cubic metres of water per second from an average depth of 100 metres, causing the level of water in the aquifers to subside by as much as 1 metre per year. As a result of this overpumping and the compaction of the upper layers of sediments, widespread subsidence is occurring. The surface has dropped 6 metres in several places and, because of differential rates of subsidence, many structures have been weakened. This phenomenon has been exacerbated by frequent seismic activity, of which the most recent destructive example was the earthquake of September 1985.

The forests that used to cover the adjacent hills have practically disappeared, and widespread soil erosion occurs. Most former agricultural land has been covered by pavement, houses, and other urban constructions. Quarries, which supplied construction materials, can be found throughout the legion. Some have become garbage dumps, into which some of the annual 10 million tonnes of garbage is thrown. A significant portion of the garbage is dumped on the “shores” of the former Texcoco Lake, particularly in the south. Ciudad Netzahuatcoyotl, in that area, is a neighbourhood of 3 million people. Although recently established, this urban area is extremely degraded; developed areas alternate with garbage dumps and slums.

Water, which used to flow into the lakes, is channeled out of the basin, together with urban wastewater, through a system of canals and tunnels into the Gulf of Mexico hydrographic system. A number of pumping wells used to supply the city are located next to the canal (the Chalco Canal). Risks of contamination are obvious and, in fact, some wells had to be closed because of the presence of nitrates in the water.

The atmosphere of the valley has also changed. Emissions from 4 million vehicles and 25 thousand industrial establishments in a poorly oxygenated environment (because of the altitude) have transformed the air in Mexico City into one of the most unhealthy urban environments for human life, particularly near the downtown core.

Mexico City contains 21 million people, making it the largest urban centre in the world. Every year, its population increases by 750 thousand people, including both births and migration from the rest of the country. By the year 2000, the city will hold 29 million people (surpassing the population of Canada) and, by 2010, 38 million. If corrective measures are not taken, the city’s problems will continue to grow, and the ancient paradise may become one of the worst environ’ mental nightmares of the 21st century.

The aquifer underlying the valley of Mexico is one of the key natural elements in Mexico’s environment. It provides the bulk of the water that makes the existence of the city possible. Although some water is brought in from the Lerma-Cutzamala basin, the volume is less than one-fifth of total requirements.

Any other option for bringing water from outside the valley is becoming impractical or too expensive. The Lerma-Cutzamala resources are almost exhausted, but using other basins (such as the Balsas basin or the Amacuzac subbasin) may mean pumping water 1 200 to 1 500 metres upward and constructing long pipelines, storage reservoirs, and other expensive engineering works. Bringing this water into Mexico City will also deprive a number of communities that now depend on it for irrigation and other uses.

Mexico’s aquifer is contained in a number of Tertiary and Quaternary units with a thickness ranging from a few hundred metres to nearly 2 thousand metres. These units comprise a wide range of sedimentary materials. Continued volcanic activity produced huge volumes of pyroclastic material, which has been more or less reworked by fluvial action, and intercalated lava flows. During periods of volcanic activity, tuffs, breccias, ashes, and lava formed; at other times, alluvial and lacustrine action was more important. The main water-bearing layers are the Tarango formation and associated alluvia and the Cenozoic sequence of fractured pyroclastic and lava flows. These are covered by younger lacustrine sediments, confining the main aquifer.

The whole sequence can be up to 2 000 metres thick, but the lower 1 500 metres are more consolidated and less porous. The upper few dozen metres of the aquifer are too close to the upper lacustrine clays and continued pumping might produce dewatering and consolidation of these clays, causing subsidence. Therefore, the usable portion of the aquifer is generally between 100 and 500 metres underground.

The aquifer is recharged mainly in the mountain region (Sierra Chichinautzin in the south, Sierra Las Cruces in the west, and Sierra Nevada to the east). The total available recharge volume has been estimated to be 25 to 50% of precipitation: 25% in Sierra Las Cruces, 35% in Sierra Nevada, and 50% in Sierra Chichinautzin. Of these volumes, about half flows toward the valley of Mexico and the rest outward to other basins. An accurate figure for inflow to the aquifer itself is difficult to estimate (probably 30 to 40 cubic metres per second). However, it is certainly below 50 cubic metres per second - the amount being pumped out - because the water level is sinking.

Additional lowering of water levels will increase inflow from the Sierras because of an increase in gradient. This will not compensate for the deficit, however, particularly if pumping is increased. Precise forecasting of the aquifer’s reaction to prolonged extraction requires accurate modeling. Only recently has adequate information on the geometry and hydraulic properties of the reservoir been available. Modeling of the aquifer has been carried out at the Instituto de Geofisica, and it is expected to allow prediction of the actual potential of the groundwater resources of the valley.

It has recently become clear that the groundwater resources of the valley of Mexico are limited and that additional water will have to come from external sources. Such external sources are all found at elevations lower that that of the city. Therefore, tapping this water will not only require enormous energy consumption but will also deprive downstream communities of this vital resource. The bottom line is that the urban model of Mexico City is unsustainable. It has become too large for its territorial base. The city has not only run out of water, but also its air is heavily polluted, the local ecosystems have been destroyed or critically damaged, and the surrounding soils are under severe strain as a result of heavy urbanization. To check this continuous destruction of resources, radical policy shifts are essential. The window of opportunity to save Mexico City is rapidly closing.

Los Angeles: setting priorities

Los Angeles, which was founded by the Spaniards in the 18th century, contained only 1 600 people in 1848. The population was half Spanish and half indigenous peoples and it was twice the size of San Francisco’s. In the 1850s, when San Francisco became one of the largest cities of the United States, with more than 50 thousand people and one of the busiest ports in the world, Los Angeles remained a torpid little town. Too far from the gold fields, sitting on an arid plain, and lacking a port and a railroad, it did not possess the conditions for rapid growth.

In the 1860s, Mormons started growing fruits and other vegetables in the area. Later, agriculture was firmly established by Quakers and German farmers. Groundwater was easily accessible and abundant; artesian pressure threw it 2 to 3 metres into the air. In 1867, when a rail’ road line was established, the city began to grow.

California’s Sierra Nevada mountain range blocks moist air coming from the ocean and annual precipitation may vary from 2 400 millimetres on the western slopes to 300 millimetres or less on the east. Rivers flowing west are substantial; those on the east are small, except for the Owens River. The Owens River arises southeast of Yosemite, flows west and south into the Owens Valley, then into highly saline Owens Lake. The region contained a rich ecosystem; shrimp and flies provided food for millions of waterfowl. In the 1860s, the Paiute Indians were practicing irrigation learned from the Spaniards. By the 1870s, settlers had displaced them, taking over the farms and irrigation systems. By the end of the century, 15 to 20 thousand hectares was under cultivation.

When the water supply in Los Angeles became insufficient, one of the first alternative sources to be considered was the Owens River. It was almost 400 kilometres away, but it could provide water for I million people - at least that was what the founders of the Los Angeles City Water Company thought at the time. In 1880, however, an expensive engineering project of this type was not possible, and the idea was not acted upon. By 1900, the population had reached 100 thousand, and the artesian pressure of the aquifer supplying their water continued to drop. In 1904, the municipal government took over the city’s water company and the LA Department of Water and Power (LADWP) was created. One of its first tasks was to try to secure water rights in the Owens Valley and construct an aqueduct to the city.

City officials also wanted to use excess water from the Owens Valley to irrigate land in the San Fernando Valley. The words of Theodore Roosevelt give us an idea of the ideology of the times: “It is a hundred, or a thousandfold more important to state that this water is more valuable to the people of Los Angeles than to the Owens Valley.”

The aqueduct took 6 years to build, up to 6 thousand workers were involved in the enterprise, and it was 360 kilometres long, of which 80 kilometres was in tunnels. More than 190 kilometres of railroad track and 800 kilometres of roads and trails had to be constructed. Up to 380 kilometres of telephone lines and 210 kilometres of power transmission lines were installed. It was a huge undertaking for the time.

During the next 20 years, however, no water from Owens Valley went to Los Angeles. It was all used for irrigation in the San Fernando Valley. From fewer than 1 400 hectares in 1913, the area of irrigated land increased to 35 thousand hectares in 1918. In the 1920s, a drought necessitated the construction of several complementary reservoirs.

In the early 1920s, Los Angeles began to use water from Owens Valley. It was then that the problems began. The city managed to buy most of the remaining water rights, depriving local farmers of the vital resource. At the same time, the drought was becoming serious. In 1923, total rainfall was 250 millimetres; in 1924, 150 millimetres; in 1925, 175 millimetres. In addition, the city’s population had grown beyond all expectations over the last decade to 1.2 million. The increased need for water forced Los Angeles authorities to continue buying water rights. The conflict between the city and the farmers became nasty and violent. In 1924, at the height of the drought, the farmers remaining in the Owens Valley flooded their land to stop water from entering the aqueduct. By 1927, terrorist actions had started; large pipes and sections of the aqueduct were dynamited. Roadblocks, car searches, and floodlights transformed the valley into a giant penitentiary.

When the crisis continued, the head of the LADWP, William Mulholland, decided to enlarge an existing dam in the nearby San Francisquito Canyon. In 1928, the storage capacity of the San Francis dam was increased to 4 million cubic metres. The work was no sooner finished than the dam started to leak. Soon after, it collapsed. A wave, 60 to 70 metres high, hit 160 men sleeping downstream in a construction camp and 75 families were killed in San Francisquito Canyon. Where the canyon opens onto the plain, the wave was still 25 metres high and engulfed the village of Castaic Junction. The death toll was about 450.

Finally, a new dam in Long Valley, on the Owens River, was built. By the 1930s, the farming and ranching community of Owens Valley ceased to exist. The last rancher left in the 1950s. Later, several other megaprojects were built, the Colorado was “tamed,” and two giant aqueducts were constructed to transfer water from the Colorado Valley to the California valleys and Los Angeles.

In the 1950s and 1960s, large hydroprojects continued to be constructed. The largest one, in the Central Valley, was proposed to supply Los Angeles. However, the real purpose was to increase the value of desert land and the wealth of a few speculators. The Central Valley project is depicted in the film Chinatown. As soon as the project was approved, the value of the land increased severalfold. Not a single drop of the water from the Central Valley aqueduct reached Los Angeles. It was used to supply inexpensive irrigation water to farmers. However, despite the dams and aqueducts, overpumping of the valley’s aquifers did not stop. Groundwater levels continued to drop and soon new megaprojects were being discussed.

A similar situation had developed on the coastal plains next to the metropolitan area of Los Angeles. In this area, more imaginative approaches were being considered to increase water availability. Instead of investing huge sums of money in distant projects, Los Angeles and Orange counties preferred better management of nearby water resources, especially by increasing recharge into the aquifer by artificial means. Today, in Orange County, groundwater recharge through the bed of the Santa Ana River satisfies 70% of the needs of its 3 million inhabitants. In Los Angeles, a similar solution has been implemented in the Los Angeles River. Neighbouring cities of southern California, such as San Diego, do not have available groundwater and depend almost exclusively on imported water.

Water has been, and still is, a key issue in the urbanization of southern California. However, as difficult as it seems, it is only one aspect of a much larger issue: the development model that has been applied in that region. Water scarcity, poor air quality (see also Chapter 8), soil degradation, and ecosystem destruction have made southern California a veritable urban nightmare. Drastic measures will be needed to begin the healing process. If Los Angeles is to survive, a sustainable and long-term development strategy is needed; and this will require a profound rethinking of southern California’s future.

Calcutta: a matter of survival

Calcutta, on one of the branches of the Ganga delta, the Hooghly River, is strategically located 130 kilometres from the mouth of this river in the Bay of Bengal in an area of commercial transshipment from sea to river and land. Although a village named Calcutta existed in the area in the 16th century, it was not until the end of the 17th century that the English East India Company established the trading post that was going to become the current megalopolis. This post was in direct competition with the upstream river port of Hooghly, controlled by the Mughals. The site of Calcutta was also selected because it was downstream of the Dutch and French settlements and protected by the Hooghly River to the west and three brackish lakes on the east. However, the site was far from ideal from a physical point of view. It is on a low, hot, humid floodplain no more than 10 metres above sea level. Calcutta’s environment is subtropical, with average temperatures of about 22°C and rainfall in excess of 1 500 millimetres per year, concentrated in a relatively short period of 4 months (June to September).

The trading post grew relatively quickly, as merchants arrived from nearby Satgaon and the Mughal emperor decreed freedom of trade in 1717, which encouraged many tradesmen to move to the city. By 1706, the population was already over 10 thousand; in 1752, it reached 115 thousand; and in 1822, it was 300 thousand, becoming one of the largest cities in India. By the beginning of the 20th century, the city contained 1 million people and 10 million in 1975. In 1991, its population was estimated to be 15 million, and it is expected to exceed 20 million before the end of this decade.

The metropolitan area is principally confined to two strips, 5 to 8 kilometres wide, on both sides of the river. The Salt Lake project, which reclaimed the lowlands on the northeast fringe of the city, was followed by other local projects allowing lateral expansion of the urban conglomerate.

Throughout most of its history, the city obtained water from wells and the Hooghly River, which in 1947 was supplying 75% of the required water. This stream provided fresh water during the rainy season and brackish water during the dry period. However, contamination of the river from urban sources has become so acute that, today, the water is unusable for most purposes. However, many riverine neighbourhoods still use it directly. Since construction of the Farakka barrage in the Ganges, a substantial volume of water is obtained from this surface source. The rest comes from about 200 large wells, some of which were drilled during colonial times.

Although the city needs an estimated 3 million cubic metres of water per day (assuming a low per-capita consumption of 200 litres per day), the actual supply is about half that amount. This deficit has pushed many citizens to drill or excavate their own wells, adding to the strain on groundwater resources.

Unfortunately, no attempts have been made to develop a comprehensive plan to manage the groundwater resources of the city. In fact, even the detailed underground structure of the aquifers is unclear. The major water-bearing horizons are sandy (coarse and medium) with occasional gravel. In the north of the city, these layers are found at a depth of between 46 and 137 metres, dipping toward the south, where they lie between 187 and 274 metres below the surface. In the Calcutta region, these layers are covered by a confining clay layer, which disappears about 50 kilometres north of the city.

The quality of the groundwater is medium to poor. It has a relatively high lime content and total dissolved solids (TDS) values between 500 and 2 000 ppm (hard water). The salinity increases toward the south and east because of the proximity of the Bay of Bengal, and it may become too hard for drinking. In the north and west, the problem is less noticeable. It also has a relatively high iron content, which together with the lime causes corrosion in well tubing and screens and in industrial equipment.

Recharge to the aquifer does not seem to occur under the urban area, fortunately, because of the presence of the impenetrable clay layer. It is believed that it takes place by infiltration in the sandy deposits located near the surface toward the north and west of the city. It is essential to identify and protect these areas to prevent contamination that could irreversibly harm the underground reservoir.

The city contains about 700 kilometres of sewers and about the same length of surface drains. Domestic and human wastes are improperly disposed of in all areas where there are no sewers, contaminating the river. As mentioned, contamination of the groundwater is less likely. However, there are indications that the Farakka barrage is receiving an excessive volume of wastes (urban and agricultural). The Ganga River basin receives practically untreated wastes from a population of 300 million and nearly 1 million square kilometres of active agricultural land. This will affect the quality of the water and increase treatment costs.

For some time, Calcutta has been one of the least healthy cities in the world because of the mismatch between population growth and investment in infrastructure. Calcutta is probably one the first urban nightmares of the Third World, one of the largest cities without the resources it needs to maintain the influx of people. Although degradation of Calcutta’s environment has been somewhat slowed recently, the situation remains precarious. Considerable investment and intelligent and imaginative planning will be necessary to transform the city into a liveable place for the majority of its population.

Cairo: the desert megacity

Cairo developed in a fragile environment. With an average annual rainfall of barely 20 millimetres, it depends almost exclusively on water from the Nile River, which crosses the city in an approximate south-north direction. The Nile valley is relatively narrow, seldom more than 20 kilometres wide, and frequently less than 5 kilometres. The valley has developed as the floodplain of the river, and these flatlands have been the site of development of an ancient agricultural civilization that has occupied the region continuously from the time of the Pharaohs (2 to 3 thousand years BC).

The region’s economy was (and still is, to a large extent) based on the use of the river waters and sediments for irrigation and fertilization. Since the construction of the Aswan High Dam in 1960, the level of the river has been stable, and flooding no longer occurs. Although the Nile still provides water, the supply of nutrients and sediments has been significantly reduced, and Egyptian farmers are increasingly dependent on (imported) fertilizers.

The Nile widens significantly about 100 kilometres from the Mediterranean Sea. In this area, the riverbed separates into two main canals (the Rosetta and Damietta canals) and many more smaller canals forming a delta-shaped alluvial region. The city of Cairo was established a few kilometres upstream from the widening portion of the valley. This site was repeatedly selected as an urban centre: the Giza pyramids were built (2500-2700 BC) to the west of the river; later, the city of On was founded as a commercial and religious centre for the worship of Ra to the east, where Masr Gadid or New Cairo now stands. Although there were Persian and Roman forts (Babylon) on the site of Old Cairo, the city did not gain importance until the arrival of the Arabs in the 7th century, when the town of Fustat was founded, gradually extending to Askar and Katai. Almost three centuries later, the town of al Qahira was founded in a neighbouring site and, under Saladin, the four locales were united into a larger city.

The city has grown considerably since then. In 1991, there were nearly 14 million people living permanently in the metropolitan area, which extends 80 kilometres, north-south, from al-Matariyah to al-Ma’adi, and more than 15 kilometres on each side of the river, particularly toward the northeast.

Cairo has been built on a plain that lies over alluvial silt-clay deposits about 10 metres thick. Under these deposits is a 60-metre thick, water-bearing sandy formation, which, in turn, covers Mesozoic limestones outcropping toward the south of the urban region.

For centuries, the Nile has been (and continues to be) the main source of water for the people of Egypt and upstream nations. Its waters are abundant and, since construction of the Aswan Dam, shortages do not occur. Wells are used by more distant and isolated communities. Currently, water from the river is treated in three plants, which supply only a portion of the 3 million cubic metres per day needed by the large metropolitan population. More than 3 million people in Cairo have no access to the urban water-supply system, and must buy their water from the carriers (or obtain it directly from the river or shallow wells). The number of households not connected to the system is likely to increase as the population increases. By the end of the century, as many as 5 million people will not be served by the city’s water-distribution network.

Before 1980, wastewater and sewage flowed regularly in the lowlying streets of the city. In the early 1980s, the system was gradually reconstructed, but at the end of the decade more than I million cubic metres of untreated raw sewage was still entering the river; slightly less than half of the total 2 million cubic metres of wastewater per day was treated. The disposal of untreated sewage into natural systems is causing the spread of waterborne diseases, especially diarrhea, and increasing the risk of cholera and typhoid. Filtration plants are inadequate to process the increasingly polluted Nile waters.

The gravity of the issue has pushed national authorities and international agencies into solving some of the most pressing problems. In 1980, an overhaul of the old system was started (Bedding 1989). The sewers were clogged with dust, dirt, and garbage. As much as 43 thousand tonnes of muck, untreated industrial wastes, and other substances and residues were removed from 57 kilometres of sewers over a 6-year period.

A new system is currently under construction, but will not be finished until well into the next decade (perhaps 2005). Digging in Cairo is an archaeological endeavour. No one knows exactly what is buried under the streets and buildings of the city. Old pipes, graves, ancient buildings, buried tunnels, and walls require careful excavation, which has to be carried out laterally at a depth of more than 25 metres below ground level. This work is partly completed, and when the system is finished, 25 cubic metres per second will be moved toward a treatment plant that will be built 15 kilometres from the city. The plan also includes a large 5 metre diameter tunnel to collect the sewage for later treatment, a pumping station, and effluent canals.

Another problem affecting the city is the rise in the water level in its aquifer, which creates problems during all tunneling operations and for some city basements, and is threatening to cause flooding in low-lying areas. Only a small proportion of the water recharging the aquifer is believed to come from surface rainfall. Because groundwater levels are higher than the Nile River, it is not a source for the aquifer. The most likely sources of recharge seem to be the following:

· Leakage from the water-distribution system;
· Leakage from the sewage system;
· Uncontrolled disposal of wastewater; and
· The return flow of irrigation water.

The partial solution to the problem has been to pump water out of the aquifer into the river. In 1979, nearly 300 thousand cubic metres per day was transferred, but that was insufficient at that time. Additional pumping may be necessary to bring groundwater down to manageable levels.

Cairo is drowning in its own population and wastes. The fragile environment, the lack of precipitation, its dependence on a single water source (which is also the disposal site), and the continuing growth of the city will force the investment of large sums of money to keep the situation even partly under control. The only final solution would be to put a halt to Cairo’s growing population, something that would require a drastic review of the current Egyptian development model.

Sao Paulo: giant of the Third World

Despite its relatively small area by Brazilian standards (245 thousand square kilometres), the State of Sao Paulo, with 33 million inhabitants, contains about 23% of the country’s population at a density that is among the highest in Latin America - almost 140 people per square kilometre. The state also produces over 65% of the industrial output of the country and is the largest agricultural producer; its sugarcane, coffee, and citrus fruit plantations are the largest in Brazil and among the largest in the world. Its cattle stock number nearly 12 million, and it is the biggest producer of milk and dairy products.

The population is mainly urban (over 80%); 29 cities have populations exceeding 100 thousand. The largest, the capital of the state, is the city of Sao Paulo, with 17.5 million inhabitants in early 1990. The 37 municipalities forming the greater Sao Paulo metropolitan area hold 55% of the population of the state and 15% of the total population of Brazil. The Sao Paulo urban area alone produces more industrial goods than the rest of the country. More jobs, by far, are created in Sao Paulo than in any other major city in Brazil. It is not surprising, then, that the city’s population has increased through constant immigration from other areas of the country. If current trends continue, greater Sao Paulo will hold 20 to 22 million people by the year 2000 and 25 to 30 million by 2010.

Portuguese settlement in the Sao Paulo region began in 1532, when Martin Alfonso de Souza founded the city of Sao Vicente on the Atlantic coast about 400 kilometres south of the bay of Rio de Janeiro. In that part of the country, the coastal area is a narrow plain at the foot of the Serra do Mar escarpment, with little room for agricultural expansion. Therefore, a settlement was needed in the interior, beyond the coastal mountains. The city of Sao Paulo de Piratininga or Sao Paulo dos Campos (which was to become simply Sao Paulo) was founded in 1554 on a hill between the Anhangabau and Tamanduatei rivers, tributaries of the Tiete.

During the 17th and 18th centuries, the growth of Sao Paulo was linked with its role as a centre for native workers for the sugarcane plantations of the northeast and for mineral exploration in the hinterland. In the 19th century, the city became a centre for coffee production, which would be the main export of the region and the country for many decades. During the 20th century, particularly during the last few decades, the city’s industries grew, producing both for national consumption and for export. Some of the most important industrial activities include metallurgy, automobile manufacturing, chemicals, textiles, and food.

The area’s climate is humid subtropical; the average annual temperature is 20°C, varying from an average low of 14°C in winter (July) to an average high of 26°C in the summer (January). Sao Paulo is among the most humid areas of Brazil. Average annual rainfall ranges from 1500 to 2000 millimetres, and can reach 3 000 millimetres in some neighbouring hilly areas.

Although the city of Sao Paulo is in a high rainfall area, the volume of available water is limited because of the proximity of the Serra do Mar divide. All rivers are small, with small catchment basins, and many dams had to be built to store the water required by this megacity. Unfortunately, groundwater resources are not very abundant either. Sao Paulo is located on the crystalline Brazilian shield with few hydro-geologically productive areas. The main aquifers in the region are in the coarser sandy lenses of the Sao Paulo formation and the thick mantle of weathered crystalline rocks. The wells in the city are normally screened at a depth of 100 to 200 metres and can deliver 50 to 1 700 litres per minute.

In its early days, the city’s water supply was brought from several surface sources and springs by water carts of doubtful sanitary condition (Avelima 1990). In 1877, when the city’s population was about 50 thousand, the private Companhia Cantareira de Esgotos was created to manage the water supply and sanitation. Ten years later, as a result of popular dissatisfaction with this company, the government took it over, forming the Reparticao de Agua e Esgotos (RAE). In 1897, the water from the Tiete River already showed signs of contamination and, in 1914, a typhoid epidemic broke out in the poor neighbourhoods of the city.

Originally, all of Sao Paulo’s water drained toward the Parana basin. In 1920, however, a reservoir was built in the upper Pinheiro basin (the Billings reservoir) to take advantage of the elevation of the Serra do Mar to produce hydroelectric power and water was pumped into it from the Pinheiro River. At that time, this river was not contaminated, because the expanding city had not yet reached its banks. Since then, however, it has become an “open sewer,” containing highly contaminated urban wastewaters and storm runoff, which are being pumped into the Billings reservoir.

Instead of discontinuing use of the reservoir for the city’s water supply, it has been divided in two parts one that receives water from the Pinheiro and a smaller section from which water is taken to supply the large suburb of San Andre (with over 1 million inhabitants) and other urban and suburban neighbourhoods. The two sections are separated by a relatively permeable earth dam; however, the “water supply” is kept at a higher level than the contaminated water to restrict flow into it. Unfortunately, the Billings reservoir also probably receives polluted water from urban areas encroaching on its basin. Close monitoring of the situation is necessary to prevent the obvious hazards.

The upper course of the Tiete River, near and downstream from Sao Paulo, has also become highly contaminated. Its waters are used to irrigate vegetable farms, which supply Sao Paulo, then continue downstream through the “Paulista” hinterland, where they supply several communities of the interior. Several attempts to improve this situation have failed, and to correct it now would require a huge capital investment that is not readily available.

In 1973, water management in the area was consolidated under a new body, the Companhia de Saneamento Basico do Estado de Sao Paulo (SABESP). SABESP has made improvements from an organizational point of view. However, the growth of the metropolitan area has been faster than the expansion of water and sanitation services and, as a result, such services in many urban and suburban areas are inadequate. In a number of communities and in many industrial plants, groundwater is used; as many as 30% of the homes in greater Sao Paulo obtain their water from wells.

The main water supply for the city and neighbouring municipalities is delivered from a complex network of reservoirs in many small tributaries in the upper basin of the Tiete River, including the Billings reservoir in the upper Pinheiro basin. A complex system of pipes, tunnels, and storage tanks has been constructed to bring water into Sao Paulo. In 1990, total water consumption in the greater Sao Paulo area was 50 to 55 cubic metres per second. By the year 2000, it is expected to reach 65 to 70 cubic metres per second; by 2010, 80 to 85 cubic metres per second - exceeding the ultimate capacity of the city’s systems.

These estimates are for water obtained from surface sources and do not include private wells. Some groundwater is obtained for municipal use from aquifers contained in the Sao Paulo formation and in the weathered mantle of a crystalline complex. By far, the main users of groundwater (slightly more than one-third) are industries, which consume 20 to 25 cubic metres per second.

Sao Paulo will face a difficult future unless plans are made to manage its water resources more carefully. Although its environment was suitable to satisfy the needs of a small or medium-sized city, it is inadequate to provide water to a megalopolis of nearly 20 million people.