Document(s) 7 of 14

Many Latin American cities draw on both surface and underground sources for their water supply. In some cases, for example Buenos Aires, surface water is used predominantly in areas near rivers, whereas groundwater is used in more distant neighbourhoods where bringing water from the river would be expensive or impractical. In other cases, such as San José in Costa Rica, the city originally depended on groundwater, but with the construction of a reservoir a significant area of the city began to use surface water. Cities such as Santa Marta, Lima, and, to a lesser degree, Recife are near small rivers with insufficient volumes to supply their populations and activities; groundwater is tapped to make up the deficit.

Greater Buenos Aires and La Plata

Environment and history

The city of Buenos Aires was founded in 1536 by the Spanish explorer, Pedro de Mendoza, near the confluence of the Paraná and Uruguay rivers on the southwest shore of the Río de la Plata estuary. The city is located on one of the largest grassland plains in the world: the pampas. These plains cover a vast, almost flat area of about I million km². The inclination of slopes in the region is less than one per thousand, drainage is poor, and lands are easily flooded.

Before the Spanish arrived, the pampas were the domain of a large number of herbivorous mammals (e.g., deer, capibaras, armadillos of several species, and nandus) and birds that sustained a sparse nomadic population of hunters and gatherers. The most important ethnic group among these early people was the Pampa nation. The new colony was destroyed by the indigenous population within a few years of its establishment; in 1580, it was rebuilt by Juan de Garay.

From a purely environmental point of view, the original site of Buenos Aires could not have been better chosen (Fig. 9). It enjoyed a moderate subhumid climate, excellent agricultural lands, easy maritime access, good land communications, and practically unlimited volumes of water. The city was also located at the mouth of one of the largest navigable waterways of the continent.

Fig. 9. Aerial view of the region surrounding Buenos Aires-La Plata.

As a result, the city developed quickly from a small village in the 16th century, to a medium-sized town in the 1800s, and to one of the largest metropolises of the world in the 20th century. In 1990, the population of greater Buenos Aires exceeded 12 million and, although its rate of growth has slowed somewhat, it is expected to reach almost 14 million by the year 2000 and 16 million in 2010.

The city is the capital of the Republic of Argentina and home to almost 40% of the country’s population (Pirez 1991). The area around Buenos Aires has also become densely populated, with intensive agricultural and industrial activities; it has become one of the most important grain- and cattle-producing areas of the world. Industrialization is related to agriculture (e.g., slaughterhouses, tanning and textile factories, mills, and food processing) and metallurgy (e.g., foundries and automotive industries). The province of Buenos Aires, which contains the almost 300 000 km² surrounding the federal capital, is the site for most of this activity.

In 1888, a new city was designed and built on a site not far from the city of Buenos Aires to house the provincial government. The population of the provincial capital, La Plata, rapidly grew to 600 000. Because of the rapid expansion of suburban neighbourhoods, La Plata has almost merged with the outer suburbs of Buenos Aires to form a single macrourban region.

Water supply

The phenomenal growth of Buenos Aires has begun to have overwhelming, deleterious effects on the environment. Originally, the city’s water came from small streams, such as El Riachuelo (also called the Matanzas River), and a number of shallow wells. With time, these water sources became insufficient and contaminated (El Riachuelo contains sewage and all the older wells have been abandoned) and a municipal water system was developed to use water from the Río de la Plata. In many cases, the outlying suburbs, such as the large municipality of Quilmes east of the federal capital and La Plata, preferred to use groundwater obtained from underlying alluvial aquifers.

Most of the groundwater used in Buenos Aires and surrounding areas is drawn from the Arenas Puelches (Puelches sands), a permeable, alluvial aquifer, 30–50 m thick, filling a paleovalley (the ancient wide, flat Paraná alluvial plain) and covered by a semipermeable, silty eolian formation (Pampeano) that is about 40 m thick (Fig. 10). Unfortunately, a narrow strip of Quaternary material (Querandinense-Platense) along the edge of the Río de la Plata, which is a remnant of the late Pleistocene and Holocene marine encroachments, contains highly saline groundwater and is hydraulically connected with the Puelches sands. In fact, along the coastal fringe, the whole Quaternary sequence (including the Arenas Puelches) contains salty water. The level of total dissolved solids in the Puelches sands is usually higher than in the Querandino or the Pampeano. Whether the original Querandino salty water contaminated the Puelches aquifer is not known (although it is likely). On the other hand, the Río de la Plata at Buenos Aires contains fresh water.

As a result of overpumping, saline groundwater has entered a large number of coastal wells and they have had to be closed. The unusual feature of this problem is that the saline intrusion is not related to the nearby estuary, but in all likelihood to a narrow saline remnant of a marine transgression (or ingression).

Fig. 10. Cross-sections of the alluvial plain in the Buenos Aires-La Plata region.

All of the water for the federal capital, and a considerable volume of the suburban water supply, is obtained through intakes located in the Río de la Plata. The intake system was originally situated a few kilometres upstream of the Buenos Aires’ port, not far from the coast, but a new one was built in the 1950s near Bernal, downstream from the federal capital.

Changes in quality of the water in Río de la Plata

Water quality and treatment problems are associated with the use of the Río de la Plata waters for urban supply. The Río de la Plata receives water from the Paraná and Uruguay rivers, which in turn drain a vast basin of nearly 2 million km². The composition of the water in the estuary is affected by the activities taking place throughout its large hydrographic basin. Most of the water comes from the humid highlands of the Brazilian shield, the planalto, and the subhumid Chaco-Mato Grosso regions.

The Río de la Plata originally contained almost sediment-free water; its volume was fairly constant throughout the year, except for short periods of flooding in the irregular tributaries of the western portion of the basin. A considerable volume of water flows into the Paraná during the rainy seasons in the semi-arid Chaco and the arid cordilleran foothills. One of the main rivers draining this western area of the basin is the Bermejo, which is heavily loaded with reddish suspended solids during wet periods. Smaller quantities of sediment enter the Paraná-Paraguay main valley from the right margin, e.g., in the Pilcomayo and Salado rivers. In spite of the relatively small volume of water contributed by the western tributaries, it is concentrated over a short time and, during these periods, the Río de la Plata receives a considerable volume of suspended sediments.

In the days when dense forest covered their catchment areas, the Paraná and Uruguay rivers, flowing from the north and northeast, had constant volume and clean water. Most of the planalto and shield highlands consisted of single-species Araucaria forests (Brazil pine) and other less-extensive forest systems; the Mato Grosso was covered by tropical rainforest and the Chaco by dense xerophytic forest vegetation.

During the last 20–50 years most of these forests have been destroyed. The Araucaria forest of the planalto has almost completely disappeared, astonishingly in less than 20 years. The trees were cut for lumber and land was cleared mainly to provide not only for grazing land for cattle, but for other agricultural activities as well. The forest survives only in isolated pockets and on the steepest slopes. The Mato Grosso forest is rapidly giving way to short-lived rice fields, which are finally used for raising cattle. A large tract in the Chaco hinterland has also been heavily damaged. As a result of these changes, fluvial regimes have been substantially modified and the percentage of suspended materials in the Río de la Plata has dramatically increased.

A second problem is the increase in the outflow from city sewers and storm-water systems, which is approaching 100 m³/second. This wastewater is heavily contaminated and is flushed, untreated, into the Río de la Plata.

Third, because the city has a large port, intensive shipping activity takes place in the waters surrounding the port — the same water that is used to supply the city. Ships are known to be sources of heavy pollution and their presence affects the quality of the city’s water at the intake point.

Because of these problems, treatment of the municipal water supply for Buenos Aires is costly and probably insufficient. The risk of contamination is increasing, to a point where

wastewater treatment must be implemented or alternative sources of uncontaminated water must be found.

The groundwater alternative

Groundwater is one alternative source. It is used at present to a considerable extent in some municipalities of greater Buenos Aires. Metropolitan Buenos Aires consumes 85 m³ of water per second: 65 m³/second is for domestic use and 20 m³/second for industry. Of the 65 m³/second used for domestic consumption, 24 m³/second (37%) is obtained from groundwater sources; the rest (63%) comes from the Río de la Plata. A considerable volume of the industrial water supply is also obtained from groundwater (probably as much as 40% or 8 m³/second). Therefore, over 30 m³/second of groundwater is already consumed in the Buenos Aires area; this appears to exceed the current recharge volume, at least locally.

The presence of a protecting aquitard over the Puelches aquifer does not seem to prevent some contaminants from entering the groundwater reservoir. Many wells are located close to industrial areas in which various hazardous wastes are disposed of without adequate control.

In addition, many zones supplied by groundwater have no sewers. Contamination from domestic septic tanks is affecting or might affect the water supply of as many as 3 million people in greater Buenos Aires, particularly at present when a cholera epidemic has extended throughout the Latin American region.

These factors may make the use of groundwater in Buenos Aires and surrounding areas an unsustainable proposition unless sound environmental controls and water management practices are introduced. Buenos Aires has placed itself in a difficult position because of irrational use of its abundant water resources. The solution to its water-supply problems will have to consider the growing degradation of the environment.

The Cochabamba valley

Environment and history

Cochabamba is one of the largest cities in Bolivia. With nearly 0.5 million inhabitants, it has become the “capital” of the sierra region, located in the dissected mountains of the intermediate zone between the altiplano to the west and the “llanos de Santa Cruz” to the east. The department of Cochabamba is one of the most densely populated of the country, including not only the city of Cochabamba, but also other cities and villages in the valley and on the neighbouring highlands.

The geographic character of Cochabamba is partly a result of its altitude (2 550 m above sea level), which is intermediate between La Paz (3 700 m above sea level in the downtown area) and Santa Cruz (415 m above sea level). The climate is also intermediate between the 100°C annual average temperature of La Paz and the 27°C of Santa Cruz. Average rainfall in the city itself is about 450 mm/year, concentrated mainly during the summer months of January and February. The valley can be classified as semi-arid, with a considerable water deficit during the winter and spring. Because of this climate, crops are subtropical and temperate; fruit is grown there as well as several kinds of grains and vegetables and dairy farming is common.

The Spanish city of Oropeza (later renamed Cochabamba) was founded in 1574 by Sebastian Barba de Padilla. During the few centuries before the arrival of the Europeans, the region around Cochabamba was part. of the mighty Tahuantisuyu, the Incan empire that extended from Ecuador to Argentina. The capital of the Tahuantisuyu was Cuzco (in Peru) and the whole altiplano and sierras of Bolivia were part of the Incan domain.

The dominant ethnic group of the Incan empire was the Quechuas, who gradually extended their cultural control over most of the empire. Some areas of Bolivia retained their ancient culture and language (e.g., the Aymaras of the altiplano and the La Paz region). However, by and large, Cochabamba was “Quechuanized” and now represents one the most important Quechua-speaking regions south of Cuzco.

During the centuries of Spanish and criollo domination, Spanish became the dominant language in the city. Quechua, however, has remained the main language used in rural areas, in urban shanty towns, and in folklore. As a result, Cochabamba is considered to be the “Quechua capital” of Bolivia.

Because of its climate, agricultural productivity, and commercial importance, Cochabamba has recently attracted a number of people displaced from the mining communities of Oruro and Potosi in the altiplano during the tin crisis. The newly arrived migrants are mainly Aymaras, adding a new element to the cultural diversity of the city.

In spite of its demographic growth, the valley of Cochabamba remains a predominantly agricultural region and is one of the most productive areas of Bolivia. Because precipitation is low, a significant number of crops must be irrigated, which adds to the water requirements of the valley. The high volumes of water needed for irrigation and for the dense local populations make management of water resources one of the key elements in the sustainable development of the valley and the urban region.

Another factor that cannot be overlooked is the transformation of Cochabamba into one of the main regional centres for the processing and sale of cocaine. Coca leaves are produced in the hot, humid areas of El Chaparé, Chungas, and other isolated sites on the lower slopes of the sierras. Traditionally, coca leaves have been used by the Andean peoples as a stimulant and a medicine; their legal use is still widespread. The processing of coca leaves to extract cocaine is a relatively new activity.

Cocaine is believed to be produced in the Cochabamba valley using the recently arrived migrants as a source of cheap labour. Because processing requires kerosene, sulfuric acid, and other environmentally harmful substances, there is some concern not only about the social impact of drug production, but also about its environmental effects, particularly on water resources.

Geology and geomorphology

The Cochabamba valley is narrow (5–10 km wide), apparently at least partly of tectonic origin, and overlies a Paleozoic and Mesozoic basement (Ordovician, Silurian, and Cretaceous periods) (Fig. 11). The Ordovician formation is composed of a lower sequence of siltstones, claystones, and sandstones (Cuchu-Punata formation) and an upper sequence of quartzitic sandstones (San Benito formation). The Silurian section contains a lower formation of quartzites and clay grits (Cancaniri formation) covered by claystones (Uncia formation).

Fig. 11. Cross-section of the Cochabamba aquifer. Note: arrows show groundwater flow.

Mesozoic sedimentary rocks of the Cretaceous period are also found overlying the Paleozoic rocks. They are mainly limestones and marls at the bottom (El Molino formation), underlying a flysch-type sequence of calcareous sandstones, marls, and clays (Santa Lucía formation). During the Paleocene epoch of the Tertiary period, the molassic deposits of the Morochata formation were laid down; they consist of conglomerates covering a limited area.

The bottom of the valley is filled with a thick sequence of Quaternary deposits beginning with Pleistocene lacustrine deposits (clays, sandy and silty clays, etc.) in the lower areas that develop into fluvio-lacustrine and fluvial sediments toward the top. In the foothills on the lateral slopes, coarse deposits have accumulated (agglomerates, gravels, and coarse sands) related to the alluvial fans of a number of torrential streams descending from the neighbouring highlands.

Only the fluvio-lacustrine, fluvial, and fan deposits have demonstrated potential for groundwater extraction. Yields in the lower fluvio-lacustrine deposits vary from about 1800 L/minute at the edges of the basin to less than 100 L/minute in the centre. Fluvial and fan sediments have a much higher permeability with yields of fluvial deposits reaching 3 600–4 800 L/minute and those of fan sediments even higher. The quality of water in the fluvial and fan aquifers is good (Von Borries 1988).

Hydrology

The Cochabamba basin covers about 1150 km². The main river is the Rocha, which has a low flow volume during dry spells, but can cause destructive floods during intense rainy periods. The Rocha receives water from the Cuchu-Punata basin, via the Tamborada River, whose flow is controlled by the Mexico dam forming Lake Angostura.

A number of lakes (some natural, some artificial) are found throughout the basin. The natural lakes are presumably of glacial origin and, together with the artificial reservoirs, they constitute one of the main sources of water supply for the city.

Water supply

Water for the Cochabamba region is derived partly from surface water, brought by open aqueducts from lakes Warawara, Escalerani, and Saytokocha in the neighbouring highlands (about 4 000 m elevation). The rest is extracted from the alluvial aquifers of the valley. Under the direction of the Servicio Municipal de Agua Potable y Alcantarillado, several batteries of wells are in operation: 14 in Muyurina, 10 in Vinto, 9 in Cona Cona, and 3 in El Paso. In addition, there are many private wells.

At the edge of the valley, wells are phreatic; in the centre of the valley, they are usually artesian. Currently, intense extraction has significantly lowered water levels and, therefore, many wells are no longer free flowing and pumping is required.

Water consumption in the urban region is 0.65–0.75 m³/second (60 000-70 000 m³/day). About 60% comes from surface sources and 40% from the aquifers, perhaps as much as 25 000 m³/day. In addition, a significant amount of groundwater is used for irrigation and other farming activities; this volume is probably as much as that drawn for the city.

Environmental problems

Both surface and groundwater in the Cochabamba valley are vulnerable to damage from overuse. Drilling of wells continues at an unabated pace with no legal constraints. As a result, overextraction may lower the level of groundwater, thus increasing pumping costs and risking complete loss of water from higher areas of the aquifers.

Recharge areas are not protected and waste disposal is relatively unrestricted. Currently, the alluvial fans constitute the main recharge area, and they have not been strongly affected by urban encroachment, but the threat is increasing as the cities grow. In the central part of the valley, the aquifers are semiconfined and the risk of contamination is lower, although, if water levels continue to drop, contaminants are more likely to make their way into groundwater reservoirs.’

Surface waters are also threatened. The Rocha River is heavily polluted and, therefore, cannot be used for water supply or irrigation. The lakes are less threatened because of the relatively low population density around them, but they must be protected.

There are other environmental risks in the city, mainly relating to the irregular flow of the Rocha River and its flood-control systems. To prevent destruction during periods of high-volume flow of the river, a diversion scheme was established. An artificial lake (the Laguna Alalay) stores excess water during floods; water is diverted through a tunnel excavated through hills arising in the centre of the valley near the city’s core. Settlement on the shores of this lake, however, has caused it to become a dumping ground for various types of wastes and local sewage. Lake Alalay has become a primary

environmental concern in the Cochabamba urban area. In addition, Cochabamba periodically suffers acute droughts. Surface water cannot be used at these times, putting greater demand on limited groundwater sources.

In spite of its moderate size, Cochabamba has many actual and potential problems that must be solved if the city is going to continue growing in a sustainable manner. More studies, investment, and action are required to prevent further degradation of the beautiful Cochabamba valley.

The aquifer at Lima

Environment and history

Lima, the capital of Peru, is located in the foggy coastal desert of the Pacific facade of South America at a latitude of 11°S. This desert is characterized by a quasipermanent layer of stratocumulus clouds, formed when the lower layers of the atmosphere cool as they come into contact with the cold waters of the Pacific Ocean. The ocean temperature along the coast from Chile to Peru is strongly affected by the cold Humboldt current and the upwelling of deeper, cooler waters from the bottom.

As a result of these phenomena, Lima’s climate is cooler than cities of the same latitude and altitude in other parts of the world. Its precipitation is also one of the lowest on the continent (about 10 mm annually). However, the city’s air is relatively humid, because of frequent fogs and heavy dew.

The city has developed near the foothills of the Andes, on the ancient alluvial fans of the short, torrential Rímac River descending from the neighbouring mountains (Fig. 12). Recently, the northern suburbs have extended onto the alluvial fans of another river with similar characteristics, the Chillón.

The city was founded by the Spanish as a port, mainly for export of precious metals from upper Peru, e.g., Cuzco and Potosi. The actual port city was Callao; the colonial city of Lima was founded at a prudent distance of 10 km from the coast. When Peru declared its independence in the early 19th century, Lima became the country’s capital.

The city grew slowly until the 1940s, when the population reached 300000. Since then, its growth has accelerated and, today, the population of metropolitan Lima is close to 7 million people. According to Olivera (1991), the city of Lima now contains 28% of the national population of Peru, 45% of the urban population, 69% of the industrial internal product, 70% of industrial enterprises, 87% of the fiscal income, 83% of the bank deposits, and 98% of the private investments.

Water supply

Almost all of the water for Lima and its suburbs comes from two sources (Binnie and Partners 1987):

• The Rímac River, via a treatment plant at La Atarjea and its distribution system, and
• Wells drilled in Lima’s coastal alluvial aquifer.

Total water consumption in the Lima metropolitan area in 1986 was estimated at about 21 m³/second: 11.35 m³/second from the Rímac River and 9.45 m³/second from groundwater

Fig. 12. Aerial view of the Lima-Callao region, showing inputs to the underlying aquifer from various sources.

sources. In 1990, demand had increased to about 25 m³/second and will continue growing at a rate of about 4% per year to reach 33 m³/second in the year 2000 and 45 m³/second in 2010.

The La Atarjea distribution network serves about 60% of the population with water from the river and 106 (42%) of the 253 producing wells. In 1985, it was estimated that about 70% of the population was legally connected to the main municipal water system. An additional 16% obtained their water illegally from the system, and the remaining 14% had to get water from public faucets or water tanks. With the recent growth, it is likely that the actual number of people not connected or illegally connected with the main network may be closer to 40%, i.e., 2.8 million people.

The remaining 147 wells are connected to local distribution networks. Industries, commercial businesses, and irrigated farms receive most of their water from these.

The aquifer

The area of the Lima aquifer is 390 km², including the lower Rímac and Chillón alluvial basins and associated coastal deposits. Water is contained in a coarse-grained formation of sands and agglomerates with thickness ranging from zero in places to probably about 500 m, although accurate figures are not available (Fig. 13).

The upper 100 m consists of highly permeable, relatively clean sands and gravels with few finer elements. From about 100 to 200 m to the bottom of the aquifer, the general permeability of the formation decreases, although little information is available about the structure below 200 m.

Fig. 13. Longitudinal section of the Rímac River basin.

Overpumping has caused water levels in most wells to drop by 1–2 m/year. A number of wells near the coast had to be closed due to high salinity; others further inland stopped producing. To compensate for the decrease in available water, new wells had to be constructed and pumping rates were increased in a number of existing wells.

Between 1969 and 1985, groundwater levels in the coastal zone dropped at least 10 m and up to 30 or 40 m in the higher plain near the foothills (Fig. 14).

Operational problems encountered in using water from the Lima aquifer (Binnie and Partners 1987) include:

• Pumping costs have increased because of lower well yields;
• Wells have become and are becoming dry, even when they are drilled into the bedrock;
• Salinization of groundwater has occurred near the coast because of lowering water levels;
• Pumps are (or have become) too large for the current yields, i.e., cost of running them is higher than necessary; and
• Dynamic water levels have fallen below the upper limit of well screens, producing encrustations on the screens and reducing well yields.

The rate of renewal of the aquifer is considerably lower than the rate at which water is being extracted. Recharge of the groundwater from the surface, which is the main route for water renewal, comes from several sources:

• River beds, mainly the Rímac River, but some also comes from the Chillón ; Swamps and other naturally vegetated areas north of the city;
• Agricultural irrigation in the nonurban areas of the coastal plain;
• Garden irrigation in urban areas;
• Losses from the water-distribution system; and
• Losses from the sewage system and disposal of untreated domestic wastewater.

Almost no direct recharge takes place, through rainfall or local run-off, because of the low level of precipitation in the Lima area (10 mm/year) and the type of precipitation (drizzle and dew). Run-off on the slopes surrounding the city and infiltration in the foothills and local fans are extremely rare.

Of the sources of recharge water listed above, the most important are the first four. Current rate of recharge from these sources is about 11 m³/second: about 4 m³/second from river beds; 3 m³/second from farms, parks, and gardens; and 4 m³/second from losses from the water-distribution system (Fig. 12). If underground water flow from upstream alluvial areas is included, the total input to the aquifer is about 13 m³/second.

Several of these sources of recharge are being threatened by urban growth. Many irrigated farms and parks surrounding the city have been displaced. If the current trend continues, recharge from these sources could be reduced by half in the next 20 years. The city is also encroaching on the river channels where a significant amount of infiltration takes place. For example, a new highway is being built along the Rímac River, which will make several dozen hectares of the valley surface impermeable.

Fig. 14. Decrease in groundwater levels (m) in the area around Lima between 1969 and 1985. Source: Binnie and Partners (1987).

The current hydrological balance of the aquifer is negative; at least 1 m³/second more is extracted or lost to the sea through underground flow than is recharged from the various sources. Rate of extraction has not been reduced in spite of the decrease in recharge volume. As water levels become lower and saline intrusion continues, pumping costs are going to increase and many old wells will become dry or saline. On the positive side, a project is under way to artificially inject water into the aquifer to restore the balance.

Surface water sources

Surface water provides 55% of the urban supply in the Lima area. The present average rate of flow of the Rímac River is 32.3 m³/second in Chosica, upstream from Lima; that of the Chillón River is 7.5 m³/second in Larancocha close to the exit to the coastal plain. About 10 m³/second is lost to the sea during flooding of the Rímac River; during these high-flow periods, too much water, loaded with sediments, finds its way into the sea. In the Chillón, such losses amount to about 2 m³/second. About 12 m³ of water per second from the Rímac River is used by the city and 4 m³/second is used for irrigation. About 5 m³/second infiltrates the aquifer. The Chillón is used almost exclusively for agricultural irrigation (4.4 m³/second).

Lima is using most of the water available in the two rivers; only a relatively small volume (12 m³/second) is lost during the most intense floods. Although this flood water is difficult to use because of the large amount of material in suspension and its rapid flow, it could contribute an additional volume to the urban supply.

An increasing problem is the risk of contamination of both surface and groundwater. Activity in the middle and upper Rímac basin is affecting the quality of water in this river. All wastewaters from the communities and cities located upstream of Lima enter the stream. Second, mining and industrial wastes are also disposed of in the river. In Lima itself, the river is further polluted by uncontrolled garbage disposal. As a result, the concentration of heavy metals and other toxic substances already constitutes a potential hazard to the city’s water supply. The Lima aquifer is also at risk. The alluvia are permeable throughout their depth, and hazardous wastes may find their way into the groundwater.

Conclusions

The continuing growth of the city of Lima and the lack of financial resources to implement environmental control measures are contributing to degradation of water quality. The city is growing at an accelerated rate, and water resources are fragile and limited. If the present growth continues, Lima will have a population of more than 10 million people by the year 2000 and close to 15 million by 2010. By then, the Rímac and Chillón rivers and the aquifer will be unable to satisfy the domestic, industrial, and environmental requirements of the urban region.

Alternative sources of water are difficult to find. The best options are probably in the mountain region, especially beyond the continental divide, in the headwaters of the Amazon’s tributaries. However, any project attempting to bring water from such distant and inaccessible sites will be extremely expensive — almost certainly in the order of several hundred million dollars.

Peru’s national debt is large and its credit rating in the international financial system is low. The level of investment required to tap new sources of water is unlikely to be attainable in the foreseeable future. Therefore, for the time being, the solution to the

problem must include better management and protection of the Rímac and Chillón basins and the Lima aquifer, reuse of wastewaters (at least for irrigation and industrial purposes), and better control of losses in the water-distribution system.

The final solution will be to reassess the environmental potential for growth of the city of Lima. The environment is fragile, and there is a limit to the degree of urbanization that can be sustained. This limit was certainly exceeded a long time ago. The coastal plain cannot sustain a population of 7 million people (much less one of more than 10 million as is projected for the next decade) without suffering irreparable damage.

Santa Marta on the Caribbean coast

Environment and history

Santa Marta, the oldest city in Colombia, was founded in 1525 and became one of the main centres of the Caribbean in colonial times. The city is located near the Sierra Nevada de Santa Marta, a large mountain massif close to the coast. Several short rivers descend the steep slopes of the Sierra toward the sea. Santa Marta is at the outlet of one of these rivers: the Manzanares. Since the Spanish colonial era, the city has developed slowly and was outstripped by the other two coastal metropolises of the Colombian Caribbean: Cartagena and Barranquilla. Its role has been mainly as a centre for tourism, although it remains a principal market for products of the Sierra Nevada and its port is still active.

The urban area of Santa Marta has a population of over 300 000 and is growing at the rate of 2–3% per year. The area is facing serious water-supply problems because surface-water sources are insufficient and its groundwater is becoming salinized. These problems have become critical, as demand is increasing and there is less potable water to go around.

Most neighbourhoods of the city are well established and living conditions are stable. However, about 15% of the population (40 000–50 000 people) live in slums (barrios de invasiones). These marginal communities usually house recent migrants from the countryside. Although no major health problems have been identified, water is scarce and there is concern over the possibility of waterborne diseases.

Santa Marta’s communities are organized under Juntas de Acción Comunal. These grassroots organizations provide lines of communication for community input and support for water and sanitation plans and activities. Research into the water-supply problem is being supervised by a committee that includes representatives of selected Juntas de Acción Comunal that are directly affected. The committee also includes a representative of the Corporación Nacional de Turismo; this body is concerned about safe water, because of the importance of the tourist industry in Santa Marta.

The Caribbean coast of Colombia: tourism depends on a reliable supply of clean water.

Water supply

Traditionally, the city depends on two main sources of water: surface water from the Manzanares River and groundwater from the narrow alluvial aquifers along the coast. Present water demand in Santa Marta is over 1.2 m³/second, but less than 0.8 m³/second is actually available. The current deficit (0.4 m³/second) is expected to double or triple by the year 2000. Studies to formulate a master plan for the city’s water-supply system (IFM 1979) have indicated that the integrated exploitation of surface and groundwater sources (Manzanares River and adjacent aquifers) is the most feasible solution to meet the increasing need for water, both technically and economically.

Surface water is treated at the Mamatoco plant, located 3 km upstream of the city; its intake area is at Paso del Mango about 3 km further upstream. The treatment plant’s output ranges from 160 to 340 L/second depending on river flow. When the river is low, additional water is drawn through an intake next to the plant (at La Solución). Surface water is treated using standard techniques (flocculation, filtration, and chlorination) with daily physical, chemical, and bacteriological analysis.

About 45% of the municipal water comes from 11 wells with yields ranging from 10 to 60 L/second. The main wells are: La Carcel 1 and 2 (60 L/second each); La Federación (35L/second); Tanaca (35L/second); EI Estadio (18L/second); Universidad (17L/second); Bavaria (17L/second); Santa Catalina (14L/second); Los Trujillos (10 L/second); and Bastidas 1 and 2 (10 and 40 L/second, respectively). Total output from the wells amounts to 0.33 m³/second. During the dry season (November-May), which is also the tourist season, demand increases considerably and groundwater contributes 60% of total consumption. Groundwater quality is good, except in some areas near the seashore, where saline intrusion. may occur.

The aquifer at Santa Marta is an alluvial coastal aquifer. Water is drawn from it through a number of municipal and private wells, 50–100 m deep. Because of the coarse-grained texture of the sediments, the aquifer’s conductivity and capacity are high. However, overuse has caused several of the wells near the coast to become brackish.

The aquifer is hydraulically connected with the Manzanares River, which is its main source of recharge water. However, because of the steep longitudinal slope of the river bed and to its torrential flow, a considerable volume of water flows into the sea, especially during the rainy season. Probably less than one-quarter of the flow volume of the Manzanares River enters the aquifer through the river bed and the permeable Quaternary filling.

The aquifer is currently under considerable stress as a result of continuing extraction and the limited volume of recharge water available. Preliminary studies carried out by Cesar Rodríguez of the Universidad Nacional at Bogotá have shown that recharge water must be augmented; research is being done on this project. In addition, the city’s water supply and sanitation company, Metroaguas, is planning to pipe water from the nearby Piedras River with a hydrological regime similar to the Manzanares, i.e., high rate of flow over short periods and considerable losses to the sea. Some of the excess water entering the Piedras River during flooding episodes could also be stored underground through artificial recharge of the aquifers.

Water supply and sanitation were originally under the direction of the municipal government. Two years ago, a private company was formed to take over this responsibility, but the plan was unsuccessful and the municipality has recently taken over the company. Both the municipality and Metroaguas are responsible for water quality and environmental control in the city and will decide whether artificial recharge will be attempted to augment to the water-supply system.

Deficiencies in quantity and quality

Some pollution of surface water occurs in the upper parts of the river. However, the main sources of contamination are in the city itself below the intake area for the treatment plant. Some contamination is caused by a slaughterhouse just upstream from the lower intake (La Solucion), especially during periods of low flow. According to Metroaguas, the treatment plant reduces the pollution to acceptable levels.

The slum areas get water from public faucets or water trucks. Typically, trucks deliver water once a day to strategic locations in these neighbourhoods, not more than 500 m from most homes. Another 25% of the population, although connected to the system, does not receive a regular supply and must also get water from the trucks. Wells are connected to the municipal system and in continuous operation. They are the main source of water during the dry season.

Water received through the municipal system is metered at one of six rates depending on consumption and social status. Families pay from 400 to 8000 COP/month (400 Colombian pesos (COP) = US$1), which is less than 2–3% of the average family income.

Solutions

Water shortage in Santa Marta is mainly, but not exclusively, a hydrogeological engineering problem; the situation can be significantly improved by tapping new sources. Additional water will increase pressure in the pipes and allow water to reach the poorer neighbourhoods located in higher areas of the city.

However, water resources must be properly managed. Leakage from the municipal system is high (up to 40%). Metroaguas may be able to reduce these losses marginally through better monitoring and maintenance. However, to reduce leakage significantly (20–40%), it may be necessary to make investments that are clearly beyond the scope of the water company.

Reducing demand through pricing policies could be a temporary solution. According to Metroaguas’ estimates, increasing prices in high-consumption areas would not improve the situation, because there is already a forced reduction over long periods because of insufficient water or pressure. (Some neighbourhoods that depend on surface water may be without water for weeks.)

Excessive consumption by industries could also be controlled. The main industries in the area (a beer factory, a soft -drink company, and a dairy) have wells of their own and are only partly dependent on the municipal water system. It would also be difficult to penalize these industries, whose products compensate for the frequent lack of water in the city.

Sewerage exists in only one sector of the city, serving about one-third of the population. Any increase in the amount of water used in the city should be complemented by an improvement in the sewage and storm-water systems. However, the current belief in Santa Marta is that it is better to have water without sewerage than no water at all. Increasing consumption may put more pressure on the municipality to provide the needed infrastructure for disposal of wastewater.

A preliminary evaluation shows that the current deficit of 0.4 m³/second can be reduced through increased pumping if more water from the Manzanares River (and the nearby Gaires River) can be retained. The additional water might amount to as much as 1 m³/second, meeting the needs of the city for another 15–20 years, depending on its rate of growth. At the same time, transfer of water from the Piedras River basin, part of which could be stored underground through artificial recharge of the aquifers, would provide another 1–2 m³/second to satisfy further expansion for the next 20–30 years.

Recife and the Pernambucan lowlands

Environment and history

The city of Recife, capital of Pernambuco state in Brazil, was founded in the,16th century. It is situated on a flat coastal flood plain near the confluence of the Capibaribe and Beberibe rivers. A line of coral reefs protects this area of the coast from the strong wave action and currents.

The city was originally founded as a port for Olinda, the main city in the Portuguese colony of Pernambuco. Although it was attacked by French and English pirates in 1561 and 1595, it remained in Portuguese hands until 1630 when it was captured by the Dutch who remained in control of the city for 24 years. By 1710, the inhabitants revolted against Olinda in the “War of the Mascates” and established an autonomous municipality. The city grew to prominence and, in 1823, became capital of Pernambuco.

Recife is now the centre of the largest metropolitan area of the Brazilian northeast. Its population is about 2.8 million, which according to the 1991 census represented 40% of the total population of Pernambuco. The city’s annual growth rate has decreased from

2.7% in 1970–1980 to 1.8% in 1980–1991. However, the city is still gaining 50 000 new inhabitants per year.

The stagnation in growth is probably related to the decrease in birth rate, which was 51.4 per thousand in the 1960s, 35.1 per thousand in the 1970s, and less than 30 per thousand in the 1980s. The fertility rate also decreased during this period, and there has been a simultaneous increase in life expectancy from 43.2 years in the 1960s to 52.2 in the 1970s.

The population of greater Recife has one of the lowest per capita incomes of all the cities in the Brazilian coastal region. In 1988, according to the Fundaçao Instituto Brasileiro de Geografia e Estadistica (FIBGE, Brazilian Institute of Geography and Statistics), 70.2% of the economically active population earned less than US$50 per month.

Water supply

Over the last 14 years, efforts have been made to reduce the number of homes without water service: in 1978, 38% of homes were in this category; in 1992, only 11% remained in this situation. The rapid growth of the slums and their concentration in inaccessible areas makes their linkage to the main water network more complicated.

Between 1975 and 1990, the favelas have grown by 50%; a third of them are in the hills and two-thirds on the flood plains.

The increase in service was not accompanied by an increase in the supply of available water. Thus, strict rationing has been imposed. Sanitation facilities are lacking in 72% of residences and almost all homes without a reserve tank receive water for only 12 hours/day; in low-income neighbourhoods, the level of service is even lower. The lack of sanitation in such a large portion of the urban area is One of the causes for degradation of the streams, canals, and coastal waters of the city. The polluted water provides a potential breeding ground for mosquitoes, rats, and disease and is a threat to human health.

The price of water has increased considerably because of the large proportion that is not accounted for (estimated at 45%), the elimination of subsidies, the increased cost of treatment because of contamination of surface waters, and the heavy administrative costs incurred by the Companhia Pernambucana de Saneamento (COMPESA). The high price still does not cover the capital costs of new infrastructure.

Rationing has increased the risk of contamination when the pipes are empty, forcing COMPESA to add large amounts of chlorine to the water daily when the pipes are refilled. The turning off and on of the water every day also creates unusual pressures in the system and surrounding surface waters.

The quantity of available water in the area is estimated to be 9.25 m³/second, but demand is 14.79 m³/second. COMPESA forecasts a reduction in this deficit by decreasing the high losses from the system. This plan does not seem to be realistic, considering the level of expenditure on maintenance and new equipment it would require. Although leakage from the Recife system is significant, other Brazilian cities show similar losses of nearly half the water pumped into their systems, e.g., Rio de Janeiro loses about 50% of the systems water, although it has spent more money than Recife on repairs.

Only 49% of connections to the system are metered. Consumption by other homes is estimated at 10 m³/month. However, this figure is probably too low (there are 4.2 people per connection and per capita consumption is 200 L/day). The actual amount of water

used is probably closer to 25 m³/month. The number of illegal connections and bypasses is probably high.

It is increasingly clear that the solution to Recife’s water problems must include, not only an increase in supply, but also better management including: reduction of leakage, bypasses, and illegal connections; installation of hydrometers; and policies to reduce wastage.

Problems in the use of surface water

A large portion of Recife’s water is drawn from one large surface reservoir, the Tapacura dam, from which 2.8 m³/s, on average, enters the Presidente Castelo treatment plant. Other smaller reservoirs are Botafogo, Monjope, Gurjau, and Duas Unhas. A new reservoir, Pirapama, is under construction. It will provide 6.8 m³/second, but by the time it opens, in 1994, the city will have outgrown its capacity.

Because surface sources depend on rainfall, they are limited and unreliable in times of drought. Alternative surface sources are too far away to be used economically.

Some reservoirs are showing signs of contamination. The Tapacura dam is located downstream from a sugar-producing area and a city of 50 000 people (Vitoria de Santo Anilio), which flushes untreated wastewater into the river. In summer, eutrophication occurs in the Tapacura reservoir and water quality is poor.

In late 1991 and early 1992, a cholera epidemic, which began in Peru, reached the state of Pernambuco. Because of poor sanitation and lack of safe water-supply systems, the disease spread through most of the state’s municipalities. In April 1992, over 600 cases of cholera were confirmed (the actual number was probably three or four times higher). A large proportion of the reported cases (about 100) occurred in the greater Recife region and other municipalities sharing its hydrographic basins. Vitória de Santo Antão, immediately upstream of the Tapacura dam, had the fifth highest number of confirmed cholera cases in the state; this city does not treat its sewage. The largest concentration of cholera cases (322) occurred in Bezerros, a small town located about 90 km from Recife. The epidemic caused a huge reduction in the number of tourists visiting Recife. In the first quarter of 1992, hotel accommodations were 30–40% below average. This affected the livelihood of several thousand people employed in the tourist industry, including a large number working in informal, tourism-dependent activities.

Additionally, there is growing feeling in the population that large infrastructural waterworks, such as dams, may entail an unacceptable natural and social impact. Construction of the Pirapama dam has forced the evacuation of 1 170 peasants; 836 received no compensation because they did not have a valid land title. According to local residents, before 1988, water from the Pirapama River was not considered acceptable for human consumption, even after treatment. Suspiciously, the water was declared potable in 1988 (data presented at a meeting organized by the Companhia Pernambucana da Poluição Ambiental e de Administração dos Recursos Hídricos, 23 March 1992). The dam will also reduce the volume of the river downstream, increasing contamination and promoting saline encroachment in the lower reaches of the river valley that will damage the fluvial and mangrove ecosystems.

Exploiting groundwater

In 1968, estimates had already shown that the cost of constructing and operating groundwater-extraction systems for urban supply was considerably lower than the cost of structures necessary for using surface water. This assessment was widely accepted and several hundred private wells were drilled. (At present, more than 1 400 private wells are used by industries, including soft-drink companies, hotels, and commercial buildings.) However, lack of government intervention has resulted in risk to the main aquifer (Beberibe) from overexploitation and saline intrusion.

The absence of an adequate legal framework for groundwater use certainly contributes to the current water problems. Only after the constitution of 1988 was enacted were underground waters considered to be public property. Since then, the government can, in theory, authorize their use and impose and enforce rules governing it. The actual application of this constitutional right requires a federal law (now, 1992, under study in the Congress) to transfer power to the jurisdiction of the individual states.

Surface-water pollution will not be reversed easily. Meanwhile, several aquifers, close to the city, can provide good-quality water that, if well managed, would satisfy the growing needs of the metropolitan region of Recife. Even if present trends continue, by 1995, about 0.5 million people in greater Recife will depend on groundwater. At the same time, the number of people not connected to the municipal water system could reach 0.5 million.

Groundwater has received little attention from the federal government, which has favoured reservoirs and surface-water systems. However, in Recife, as in other densely populated areas of Brazil, groundwater reservoirs contain much more water (probably as much as 100 times more) and are less vulnerable to contamination and leakage from the distribution networks (because conduction distances are shorter). Groundwater requires less treatment than surface water and a much smaller financial investment is needed to install and operate equipment to tap it.

At Recife, an important reservoir containing good-quality water lies under the city. However, this aquifer is thin just under central Recife, and larger volumes of groundwater can be obtained toward the north. In the past, the city used the thin reservoir, but because no management strategies were developed, water levels dropped and saline encroachment forced the closure of many wells. Today, only 98 wells remain in use. They are all located in the northern part of the city and are not always in operation.

The main reservoir on the coastal plain is the Beberibe aquifer, which is contained in Cretaceous sandstone. It is up to 100 m thick and overlies the crystalline rocks of the Brazilian shield along the coast. In Recife, the Beberibe sandstone is covered by Quaternary deposits (sands and clays) and by Upper Cretaceous and Paleocene limestones toward the north (Gramame and Maria Farinha formations). In addition to this productive aquifer, groundwater is found in the weathered mantle of the crystalline bedrock. Yields from these rocks are much lower, but they may be suitable for local use, particularly by favelas located on crystalline hills.

In many ways, Recife has outgrown its environment, partly because of inadequate and insufficient investment in its water supply and sanitation systems. Water-supply problems are especially critical for a city that depends to a large extent on tourism. One of Recife’s main advantages is its location, in a warm, coastal environment with pleasant beaches and a strategic position on the northeastern edge of the continent. Protecting its urban environment may, therefore, be the difference between prosperity and poverty in the city’s future.

San José in the central valley of Costa Rica

Environment and history

San José, the capital of Costa Rica, is located in a valley in the Central American volcanic range at an altitude of 1 150 m above sea level. The valley contains several other urban centres, including three major cities: Alajuela, Cartago, and Heredia. The proximity of these cities (Alajuela and Cartago, at the extremes, are only 40 km apart), coupled with the recent accelerated population growth of the country’s urban areas, has resulted in a gradual merging of these four cities around the metropolitan area of San José (Lungo Uclés and Pérez 1991).

The oldest city of the central valley is Cartago, which was founded in 1563 and remained the main city and political centre of the Costa Rican territory until the 19th century. The city was destroyed by volcanic eruptions and earthquakes several times. The worst catastrophe was probably the eruption of the Irazu volcano in 1723, when the city was completely demolished. Cartago was also strongly affected by the earthquakes of 1841 and 1910.

San José was established in 1736 as a centre for tobacco trade, but did not become the main political city until 1823 when the capital was transferred there from Cartago. During the 19th century, San José was a relatively small town, depending on coffee production, only exceeding 25 000 inhabitants at the end of the century. The later growth of San José, Alajuela, Cartago, and Heredia produced a large urban conglomerate that is frequently called the Gran Area Metropolitana. The valley now contains almost 1 million people (of whom 0.6 million are in the San José metropolitan area), which represents nearly 35% of the population of the country. The population of the San José region and neighbouring cities is expected to reach 1.5 million by the end of this century.

Water supply

Surrounded by volcanoes and other geomorphological features of volcanic nature, the cities of the valley have traditionally obtained their water supply from a number of springs flowing out of the lateral slopes and from drilled or excavated wells in the Quaternary volcanic aquifers.

The groundwater sources in use are mainly fractured lavas corresponding to the Colima (upper and lower levels) and Barba formations. Some water is obtained from the El Llano dam, which was built in the 1960s to generate electricity. This dam mainly supplies Cartago and parts of San José; its water is treated in a plant located at San Ramon de Tres Ríos.

The city of Alajuela (population 50 000) is self-sufficient, depending on three main springs for its water supply (La Chayotera, Sabana Redonda, and Ojo de Agua) and its system is municipally controlled. The other three cities are served by the national system (Servicio Nacional de Acueductos y Alcantarillados) and share their main (present and future) sources of water: the well field of La Valencia, the El Llano supply system, and the proposed Orosí project.

Over 90% of the population in the metropolitan area has access to water. Groundwater constitutes about 40% of this, not including the springs, which are actually groundwater discharges. Current average consumption in the region is 6.8 m³/second; this is expected to increase to 7.85 m³/second for the year 2000 and 10.5 m³/second for 2015. About 50% of the water supply is unaccounted for. Probably as much as two-thirds of this is loss to leakage from the conduction and distribution system. Future water needs of San José, Heredia, and Cartago, will be satisfied by two new well fields, now being planning: del Norte and Potrerillos.

San José and its sister cities are located in a high-risk seismic area, raising concerns about the reliability of the aqueduct bringing water from El Llano to the valley. From that point of view, the groundwater sources are more reliable, because they are connected with their users through several distribution lines and seismic damage would normally not jeopardize the overall supply, which might be interrupted if only a single pipeline was in place (as proposed for the Orosí project).

Pollution is an ever-present problem, because more than 60% of the metropolitan area is not served by the sanitation system. These residences have septic tanks and frequent overflow from them may reach the upper aquifer. Wastewaters are discharged, untreated, through a main collector pipe into the Rio Grande de Tarcoles, which flows into the Pacific Ocean. This river has lately become almost “dead.” Sanitation companies that empty the septic tanks usually dispose of the used liquid into the sewerage system, substantially increasing contamination of the system.

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