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The Cutzamala water supply system serves the growing needs of Mexico City's metropolitan area
The Cutzamala Water Supply System Serves the Growing Needs of Mexico City's Metropolitan Area Elias Sahab Haddad
Abstract--Water supply to the metropolitan area of Mexico City has required the completion of an outstanding and expensive hydraulic engineering construction project, the Cutzamala System, which will permit the transfer of water resources from neighboring basins into the Valley of Mexico. The water supply system is necessary because local sources of supply have become insufficient to meet the growing demand and, consequently, have suffered from severe overexploitation. This overuse will diminish when new projects such us the Cutzamala System contribute the necessary flow demandedbythevarioussectorsofthepopulation~ Thisconstruction work posed a great challenge to Mexican engineering because all of the study, design, and construction aspects, as well as all of the equipment and material needed for its execution are products of national technology: only the motors, spheric valves and some electro-mechanical devices had to be imported. This important project is being executed by the Bureau of Agriculture and Water Resources through its Water Commission for the Valley of Mexico.
Background n the past few decades, accelerated urbanizat!on has affected several of Mexico s cities. Within this context, the metropolitan area of Mexico City has become the main receiving point of migratory movements in the country, caused by a high concentration of economic, political and cultural activities in the city. As a consequence of this urbanization, the city's nearly 19 million i n h a b i t a n t s - 23% of the nation's total population-have settled in the Valley of Mexico, located 2240 m above sea level This expansion of Mexico City's urban area has decreased the amount of land where the more important inR1trations of rainfall would naturally
I
Present address: Ing. Elias Sahab Haddad, Executive Chairman, Water Commission for the Valley of Mexico. This article is translated from a paper that was originally presented at the ~Coloquio Internacional sobre Tuneles y Obras Subterr~eas ", held October 3-4,1988, and jointly sponsored by the AsocacidnMexicana de Ingenieria de Tunneles y Obras Subterr~neas (AMITOS) and the International ~+nnelling Association.
occur, thus depriving the Valley of Mexico of natural reservoirs and adequate sitesfor erecting dams in which to store rain water. In the process of satisfying the population's needs, exploitation of local resources was first attempted and, gradually, neighboring regions were explored in order to meet the demands posed by the progressive expansion of the city. The demand for drlnldng water is particularly critical, considering t h a t current availability of water resources within the valley would only sufficc ~underground deposits were not exploited--to meet a bare 42% of the present demand, which amounts to 62 mS/sec. The problem brought about by the inability of local sources of supply to meet greater demands resulted in overexploitation of underground deposits, which currently amount to more than 100% of n a t u r a l aquifer recharge capacity. This overexploitation has caused land subsidence in urban areas, cracking and s~nl~ngproblems, collapse of structures, and degradation in water quality. This situation has forced the city to undertake the construction of works for intake, conveyance and purification of water, and transferring
Tunnelling and Under~'ou~ulSptu'e Technolol.,~, Vol. 6, No. 1. pp. 9 3 - 9 5 , 1991. Printed it+ Grt-at Britain.
l~sumA--L'approvisionnement en eau de la r4~gionmL,tropolitaine de la ville de Mexique a n~cessit~ l'acbhvement d'un projet hydraulique, remarquable et coflteu~ le syst~me de Cutzamala, qui achemine vers la valbJe de Mexiqus, l'eau provenant des bassins hydrologiques avoisinants. Le syst~me d' approuisionnement en eau eat ru~eessaire parce qua lea ressources locales sont devenuss insuffisuntes pour faire face &la demande croissante et ont d~s lots dtdsdv~rementsurexploit~es. Cettesurexploitationdesressourcesva d~cro~tre lorsque de nouveaux projets, tele que celui de Cutzamala, eontribueront suffisumment e~ la demande en eau des diff~rents secteurs de la population. Ce projet de gdnie civil a constitud un important ~ ~ l'industrie mexicaine, paree que tous lea aspects de l'dtude, de la conception, et de la construction, ainsi que lea dquipements et lea matdriaux ndcessaires d son exdcution sont des produits de la technologic nationale; seulement lea moteurs, lea soupapes h~mispt~riquss, et certains appareils ~lectro-m~caniquss ontduStreimportds. Cetimportantprojetadtdexdcut~parleBureau de l'Agriculture et des Ressources en Eau, par l'entremise de la Commission en Eau pour la Vall~e de Mexique.
0886-7798/91 $3.1t{t + .00 l+e~ g a m o n Press pie
it from one basin to a n o t h e r - - a process
accompanied by the necessarily high investments and elevated operational costs associated with the massive e n e r g y c o n s u m p t i o n r e q u i r e d to perform the pumping process. In 1951, a project called Lerma System, the first to transfer water among basins, began operations yielding 4 mS/ sec. In the 1960s, this project extracted as m u c h as 14 mS/sec, eventually causing overexploitation of the Lerma Valley. This situation resulted in the need to perform new studies in several regions, culminating in the selection of the Cutzamala River Basin, which will yield 19 mVsec on average and up to 24 mS/sec as a maximum.
The Cutzamala System The works for this system comprise: 1. Six storage d~m~ and a diversion d a m located in the high part of the Cutzamala River Basin. 2. The construction of an hourly regulation reservoir. 3. A 127-km-long aqueduct that includes a 19-kin stretch of t~mnels and 7.5 k m of open channels. 4. The construction of a treatment plant with a 24 mVsec capacity.
93
5. Six pumping stations, to overcome a total height of more than 1100 m, requiring a total energy consumption of 1650 million KW/hr per year; 6. Two 12.5-km tunnels within Mexico City's metropolitan area, corresponding to the deep well batteries located to the north and south, to allow water distribution to the urban areas in the State of the Mexico and the Federal District. Works for the Cutzamala project began in 1976, in three construction stages yielding 4, 6 and 9 m3/sec, respectively. Previously, water in the system had been used for energy generation. A shii~ in utilization saved a flow of 3 m3/sec for energy generation during peak hours and an equal amount to meet both current and future local needs required for agricultural and industrial development in the region. The first stage, completely finished and in operation since May 1982, extracts 4 m3/sec from Villa Victoria Dam. The second stage, also completed and in operation since July 1985, handles the intake and conveyance of 6 mS/sec from Valle de Bravo Dam. The third stage, which is currently under construction, takes in and transports 9 m3/ sec from Chilesdo and Colorines Dams, located 1600 m above sea level. To convey water 127 kin, overcoming heights greater than 1100 m, the system relies on six pumping stations. In some cases, these stations are equipped with impelling devices totalling 22,000 hp in every motor-pumpspheric valve assembly in order to deal with flows of 4 m3/sec, and overcoming dynamic heads of up to 350 m. Each pumping site features an electric substation; the combined total installed power in the system is 450,000 hp. The energy to activate these impelhng devices and most of the electrical installations is provided by the Federal Commission of Electricity from its Infiernillo-Nopala system via a main reducing substation called Donato Guerra. The signalis lowered from 400 kv to 115 kv by means of two shifting benches. Energy fed from the benches to the pumping stations through transmission lines measuring 80 km to reach the electrical substations results in a new tension reduction, from 115 kv to 13.8 kv, which is adequate for equipment performance. To feed the motors in each pumping station, specialelectricalequipment was required. This equipment consists of panels with 13.8-kv intensity, low-tension panels for auxiliary serivces, and programmable electronic controllers. Each pumping station has a surge tank and a regulation shaft. The former provides the volume and dynamic head required for engine start-up; the latter counteracts the water-hammer effect on the pressure steel pipeline connect-
ing the pumping station to the regulation shaft, thereby eliminating said effect in the remaining stretch of the aqueduct. Both the surge and the regulation shaft.s are cylindrical structures of reinforced, single-pour concrete, with heights varying from 37 to 58 m - approximately equivalent to a 20-story building. These structures, which have inner diameters of 10 m and wall thicknesses up to 1.60 m, were built in 20 consecutive days at most. The shafts reach the pumping stations through both high- and low-pressure steel pipelines with diameters ranging from 1.85 to 3.27 m. In most pumping stations, a considerable reduction in plate thickness has been achieved by placing the pipelines in concrete-filled ditches. Overall conveyance is attained through two parallel prestressed concrete pipelines 2.5 m in diameter and having a carrying capacity of 12 mS/sec each. For a 7.5-kin stretch, the liquid is conveyed through an open channel that is trapezoidal in section and has a carrying capacity of 24 m3/sec. The t r e a t m e n t p l a n t c o m p r i s e s six potabilization modules of 4 m3/sec, wherein the following processes take place: 1. Dosified addition of chemical reactives. 2. Flocculation. 3. Sedimentation. 4. Filtering. The Agua Escondida and AnalcoSan Jose tunnels (see Fig. 1 and Fig. 2), 3.1 and 16 km long, respectively, were excavated, as well as the North and South Batteries (12.5 km each), for water distribution within Mexico City's metropolitan area.
The excavation of 44 km of tunnels was possible thank.q to the ample experience that Mexican engineers have accumulated in this area. This experience, in combination with technical research activities conducted both locally and abroad, have been responsible in recent years for the attainment of safer designs, featuring more adequate supporting structures and lini n g - a n d , therefore, better economy for this type of construction work. The Agua Escondida tunnel, which traverses the mountainous region bearing the same name, is located before the treatment plant A1 Los Berros. The cross-section of the horseshoeshaped tunnel is 4.20 high. The 3.1kin-long t11nnel has a conveying capacity of 24 mS/sec. Activities were undertaken on both arcades using the traditional technique of boring, blasting and loading. The main problems encountered resulted from geological conditions, which presented varying degrees of alteration in the rock, as well as in clay layers. A significant collapse occurred along a 60-m stretch located in a juncture of two different formations. This collapse forced a long period of suspension of activities, as well as various other problems. Repairing the collapse took approximately three months because the supporting frames, which originally were placed 1 m apart, were deflected both vertically and sideways over a 200-m stretch. New frames were erected every 50 cm, endowing them with lateral support. The lining over this stretch received an additional steel reinforcement. Drainage in the area also improved after contact injection between the lining and the rock. The Analco-San Jose tunnel crosses the Sierra de Las Cruces, forming the
Figure 1. Portal entrance of the Agua Escondida Tunnel.
94 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
Volume 6, Number 1, 1991
Figure 2. Entrance to the Analco-San Jose tunnel.
watershed between the Valleys of Toluca and Mexico, and conveys the already purified water from the Cutzamala system (S~inchez Trejo 1988). In this t-nnel, because of the favorable conditions of the Mmost ubiquitous andesitic rock, infdtration control became the main problem. The 16-m-long t-nnel, which had a 4.6-mhigh portal cross-section, was excavated from four main working fronts-both entrances and two 210-m-deep shaRs--with the support of a 30-mdeep third shaft that housed the control devices. These fronts allowed water diversion toward the Ramal Norte and Ramal Sur tlmnels, and conveyed water to the State of Mexico and the Federal District, respectively. Because of the length of the t~mnel, itwas necessary to provide outletsevery 500 m and to provide a lining design especially suited to the geological conditions of the rock being traversed (see Fig. 3). The t~mnel was designed not only for the m a x i m u m capacity of the Cutzamala project (24 m3/sec), but also to provide a conveyance reserve margin of 10 m3/sec for future projects. A receiving reservoir for this flow was constructed so as to avoid interfering with the supply from Cutzamala to Mexico City's metropolitan area. The Ramal Norte tunnel, which has a m a x i m u m carrying capacity of 18.5 m3/sec, did not require shafts because it was excavated in five stretches. Excavation and lin~ngwere undertaken through two fronts. The 3.5-high section is horseshoe-shaped. Excavation oftheAnalco-San Jose and RamalNorte tunnels alone produced 870,000 m s of rocky m a t e r i a l - - a volume comparable to that of the Pyramid of the Sun in
Volume 6, N u m b e r I, 1991
Teetihuacan. Lining of the tunnel required the pouring of 225,000 m s of concrete cquivalent to the material needed for paving a 325-kin-long road. In view of the necessary synchronization among all pumping stations, operation of the system at full capacity required designing a S u p e r v i s o r y Control System that measures a large number of variables in all the elements of the system (e.g., motors, pumps, surge and regulation shafts, pipelines). These variables are then transmitted to a series of substations, as well as to a central station where they are processed to determine prevailing conditions in each element of the system. The system then accordingly performs an automated joint operation or a semiautomated operation, or sends this information to signalling panels and screens for manual operation. The Supervisory Control System is being installed in successive stages. Its installation is considered to be among the most important in Latin America, and special attention has been paid to its operation and maintenance. Completion of works to date has required the participation of 90 companies speciMi~ng in different construction activities such as roads, channels, aqueducts, tlmnels, struc~res, electromechanics, etc. Similarly, it has been necessary to draw up some 300 contracts with manufacturers to supply the necessary equipment and material. In accordance with federal government policies to effect investments favoring the development and improvement of the catchment areas, as well as the preservation of the quality of water in regions that form part of the Cutzamala system, numerous i m p o r t a n t
works to support rural communities have been undertaken, such as irrigationchAnnels, small dams, accessroads, schools and potable water and sewerage systems. Among the latter, the rehabilitation of the drinldng water systems serving the towns of Valle de Bravo and Colorines stand out, as well as the sanitation of the Valle de Bravo Dam through the construction of a system for the collection, diversion and disposal of sewage, which is conveyed to oxidation pools now under construction. The communities served by these systems have experienced a growth in tourism, and this trend is expected to increase. The system for the development of agriculture and cattle ranching in Santa Magdalena Tilostoc, in the vicinity of pumping station 2, is also an outstanding project and one that has become a source of income for local farmers and peasants.
Conclusion The experience acquired in completing all of these works, particularly the tunnels, represents a valuable and useful legacy since, in the foreseeable future, systems similar to the one described h e r e i n - - a n d p e r h a p s even larger--will be needed to face population growth in the large cities of our
country.
[]
References S{mchez Trejo,R. 1988. InRltracionesde agua en un ttmelduraute su construccion y sistemas de captacion durante su explotacion. In Tunnels and Water, Vol. 2 (J. Manuel Serrano, ed.),1115-1126. Rotterdam: A. A. Balkema.
Figure 3. Lining used for the Analco-San Jose tunnel. ~N~LLmG
AND UNDERGROUND SPACE TECHNOLOGY 95
Abstract--Water supply to the metropolitan area of Mexico City has required the completion of an outstanding and expensive hydraulic engineering construction project, the Cutzamala System, which will permit the transfer of water resources from neighboring basins into the Valley of Mexico. The water supply system is necessary because local sources of supply have become insufficient to meet the growing demand and, consequently, have suffered from severe overexploitation. This overuse will diminish when new projects such us the Cutzamala System contribute the necessary flow demandedbythevarioussectorsofthepopulation~ Thisconstruction work posed a great challenge to Mexican engineering because all of the study, design, and construction aspects, as well as all of the equipment and material needed for its execution are products of national technology: only the motors, spheric valves and some electro-mechanical devices had to be imported. This important project is being executed by the Bureau of Agriculture and Water Resources through its Water Commission for the Valley of Mexico.
Background n the past few decades, accelerated urbanizat!on has affected several of Mexico s cities. Within this context, the metropolitan area of Mexico City has become the main receiving point of migratory movements in the country, caused by a high concentration of economic, political and cultural activities in the city. As a consequence of this urbanization, the city's nearly 19 million i n h a b i t a n t s - 23% of the nation's total population-have settled in the Valley of Mexico, located 2240 m above sea level This expansion of Mexico City's urban area has decreased the amount of land where the more important inR1trations of rainfall would naturally
I
Present address: Ing. Elias Sahab Haddad, Executive Chairman, Water Commission for the Valley of Mexico. This article is translated from a paper that was originally presented at the ~Coloquio Internacional sobre Tuneles y Obras Subterr~eas ", held October 3-4,1988, and jointly sponsored by the AsocacidnMexicana de Ingenieria de Tunneles y Obras Subterr~neas (AMITOS) and the International ~+nnelling Association.
occur, thus depriving the Valley of Mexico of natural reservoirs and adequate sitesfor erecting dams in which to store rain water. In the process of satisfying the population's needs, exploitation of local resources was first attempted and, gradually, neighboring regions were explored in order to meet the demands posed by the progressive expansion of the city. The demand for drlnldng water is particularly critical, considering t h a t current availability of water resources within the valley would only sufficc ~underground deposits were not exploited--to meet a bare 42% of the present demand, which amounts to 62 mS/sec. The problem brought about by the inability of local sources of supply to meet greater demands resulted in overexploitation of underground deposits, which currently amount to more than 100% of n a t u r a l aquifer recharge capacity. This overexploitation has caused land subsidence in urban areas, cracking and s~nl~ngproblems, collapse of structures, and degradation in water quality. This situation has forced the city to undertake the construction of works for intake, conveyance and purification of water, and transferring
Tunnelling and Under~'ou~ulSptu'e Technolol.,~, Vol. 6, No. 1. pp. 9 3 - 9 5 , 1991. Printed it+ Grt-at Britain.
l~sumA--L'approvisionnement en eau de la r4~gionmL,tropolitaine de la ville de Mexique a n~cessit~ l'acbhvement d'un projet hydraulique, remarquable et coflteu~ le syst~me de Cutzamala, qui achemine vers la valbJe de Mexiqus, l'eau provenant des bassins hydrologiques avoisinants. Le syst~me d' approuisionnement en eau eat ru~eessaire parce qua lea ressources locales sont devenuss insuffisuntes pour faire face &la demande croissante et ont d~s lots dtdsdv~rementsurexploit~es. Cettesurexploitationdesressourcesva d~cro~tre lorsque de nouveaux projets, tele que celui de Cutzamala, eontribueront suffisumment e~ la demande en eau des diff~rents secteurs de la population. Ce projet de gdnie civil a constitud un important ~ ~ l'industrie mexicaine, paree que tous lea aspects de l'dtude, de la conception, et de la construction, ainsi que lea dquipements et lea matdriaux ndcessaires d son exdcution sont des produits de la technologic nationale; seulement lea moteurs, lea soupapes h~mispt~riquss, et certains appareils ~lectro-m~caniquss ontduStreimportds. Cetimportantprojetadtdexdcut~parleBureau de l'Agriculture et des Ressources en Eau, par l'entremise de la Commission en Eau pour la Vall~e de Mexique.
0886-7798/91 $3.1t{t + .00 l+e~ g a m o n Press pie
it from one basin to a n o t h e r - - a process
accompanied by the necessarily high investments and elevated operational costs associated with the massive e n e r g y c o n s u m p t i o n r e q u i r e d to perform the pumping process. In 1951, a project called Lerma System, the first to transfer water among basins, began operations yielding 4 mS/ sec. In the 1960s, this project extracted as m u c h as 14 mS/sec, eventually causing overexploitation of the Lerma Valley. This situation resulted in the need to perform new studies in several regions, culminating in the selection of the Cutzamala River Basin, which will yield 19 mVsec on average and up to 24 mS/sec as a maximum.
The Cutzamala System The works for this system comprise: 1. Six storage d~m~ and a diversion d a m located in the high part of the Cutzamala River Basin. 2. The construction of an hourly regulation reservoir. 3. A 127-km-long aqueduct that includes a 19-kin stretch of t~mnels and 7.5 k m of open channels. 4. The construction of a treatment plant with a 24 mVsec capacity.
93
5. Six pumping stations, to overcome a total height of more than 1100 m, requiring a total energy consumption of 1650 million KW/hr per year; 6. Two 12.5-km tunnels within Mexico City's metropolitan area, corresponding to the deep well batteries located to the north and south, to allow water distribution to the urban areas in the State of the Mexico and the Federal District. Works for the Cutzamala project began in 1976, in three construction stages yielding 4, 6 and 9 m3/sec, respectively. Previously, water in the system had been used for energy generation. A shii~ in utilization saved a flow of 3 m3/sec for energy generation during peak hours and an equal amount to meet both current and future local needs required for agricultural and industrial development in the region. The first stage, completely finished and in operation since May 1982, extracts 4 m3/sec from Villa Victoria Dam. The second stage, also completed and in operation since July 1985, handles the intake and conveyance of 6 mS/sec from Valle de Bravo Dam. The third stage, which is currently under construction, takes in and transports 9 m3/ sec from Chilesdo and Colorines Dams, located 1600 m above sea level. To convey water 127 kin, overcoming heights greater than 1100 m, the system relies on six pumping stations. In some cases, these stations are equipped with impelling devices totalling 22,000 hp in every motor-pumpspheric valve assembly in order to deal with flows of 4 m3/sec, and overcoming dynamic heads of up to 350 m. Each pumping site features an electric substation; the combined total installed power in the system is 450,000 hp. The energy to activate these impelhng devices and most of the electrical installations is provided by the Federal Commission of Electricity from its Infiernillo-Nopala system via a main reducing substation called Donato Guerra. The signalis lowered from 400 kv to 115 kv by means of two shifting benches. Energy fed from the benches to the pumping stations through transmission lines measuring 80 km to reach the electrical substations results in a new tension reduction, from 115 kv to 13.8 kv, which is adequate for equipment performance. To feed the motors in each pumping station, specialelectricalequipment was required. This equipment consists of panels with 13.8-kv intensity, low-tension panels for auxiliary serivces, and programmable electronic controllers. Each pumping station has a surge tank and a regulation shaft. The former provides the volume and dynamic head required for engine start-up; the latter counteracts the water-hammer effect on the pressure steel pipeline connect-
ing the pumping station to the regulation shaft, thereby eliminating said effect in the remaining stretch of the aqueduct. Both the surge and the regulation shaft.s are cylindrical structures of reinforced, single-pour concrete, with heights varying from 37 to 58 m - approximately equivalent to a 20-story building. These structures, which have inner diameters of 10 m and wall thicknesses up to 1.60 m, were built in 20 consecutive days at most. The shafts reach the pumping stations through both high- and low-pressure steel pipelines with diameters ranging from 1.85 to 3.27 m. In most pumping stations, a considerable reduction in plate thickness has been achieved by placing the pipelines in concrete-filled ditches. Overall conveyance is attained through two parallel prestressed concrete pipelines 2.5 m in diameter and having a carrying capacity of 12 mS/sec each. For a 7.5-kin stretch, the liquid is conveyed through an open channel that is trapezoidal in section and has a carrying capacity of 24 m3/sec. The t r e a t m e n t p l a n t c o m p r i s e s six potabilization modules of 4 m3/sec, wherein the following processes take place: 1. Dosified addition of chemical reactives. 2. Flocculation. 3. Sedimentation. 4. Filtering. The Agua Escondida and AnalcoSan Jose tunnels (see Fig. 1 and Fig. 2), 3.1 and 16 km long, respectively, were excavated, as well as the North and South Batteries (12.5 km each), for water distribution within Mexico City's metropolitan area.
The excavation of 44 km of tunnels was possible thank.q to the ample experience that Mexican engineers have accumulated in this area. This experience, in combination with technical research activities conducted both locally and abroad, have been responsible in recent years for the attainment of safer designs, featuring more adequate supporting structures and lini n g - a n d , therefore, better economy for this type of construction work. The Agua Escondida tunnel, which traverses the mountainous region bearing the same name, is located before the treatment plant A1 Los Berros. The cross-section of the horseshoeshaped tunnel is 4.20 high. The 3.1kin-long t11nnel has a conveying capacity of 24 mS/sec. Activities were undertaken on both arcades using the traditional technique of boring, blasting and loading. The main problems encountered resulted from geological conditions, which presented varying degrees of alteration in the rock, as well as in clay layers. A significant collapse occurred along a 60-m stretch located in a juncture of two different formations. This collapse forced a long period of suspension of activities, as well as various other problems. Repairing the collapse took approximately three months because the supporting frames, which originally were placed 1 m apart, were deflected both vertically and sideways over a 200-m stretch. New frames were erected every 50 cm, endowing them with lateral support. The lining over this stretch received an additional steel reinforcement. Drainage in the area also improved after contact injection between the lining and the rock. The Analco-San Jose tunnel crosses the Sierra de Las Cruces, forming the
Figure 1. Portal entrance of the Agua Escondida Tunnel.
94 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY
Volume 6, Number 1, 1991
Figure 2. Entrance to the Analco-San Jose tunnel.
watershed between the Valleys of Toluca and Mexico, and conveys the already purified water from the Cutzamala system (S~inchez Trejo 1988). In this t-nnel, because of the favorable conditions of the Mmost ubiquitous andesitic rock, infdtration control became the main problem. The 16-m-long t-nnel, which had a 4.6-mhigh portal cross-section, was excavated from four main working fronts-both entrances and two 210-m-deep shaRs--with the support of a 30-mdeep third shaft that housed the control devices. These fronts allowed water diversion toward the Ramal Norte and Ramal Sur tlmnels, and conveyed water to the State of Mexico and the Federal District, respectively. Because of the length of the t~mnel, itwas necessary to provide outletsevery 500 m and to provide a lining design especially suited to the geological conditions of the rock being traversed (see Fig. 3). The t~mnel was designed not only for the m a x i m u m capacity of the Cutzamala project (24 m3/sec), but also to provide a conveyance reserve margin of 10 m3/sec for future projects. A receiving reservoir for this flow was constructed so as to avoid interfering with the supply from Cutzamala to Mexico City's metropolitan area. The Ramal Norte tunnel, which has a m a x i m u m carrying capacity of 18.5 m3/sec, did not require shafts because it was excavated in five stretches. Excavation and lin~ngwere undertaken through two fronts. The 3.5-high section is horseshoe-shaped. Excavation oftheAnalco-San Jose and RamalNorte tunnels alone produced 870,000 m s of rocky m a t e r i a l - - a volume comparable to that of the Pyramid of the Sun in
Volume 6, N u m b e r I, 1991
Teetihuacan. Lining of the tunnel required the pouring of 225,000 m s of concrete cquivalent to the material needed for paving a 325-kin-long road. In view of the necessary synchronization among all pumping stations, operation of the system at full capacity required designing a S u p e r v i s o r y Control System that measures a large number of variables in all the elements of the system (e.g., motors, pumps, surge and regulation shafts, pipelines). These variables are then transmitted to a series of substations, as well as to a central station where they are processed to determine prevailing conditions in each element of the system. The system then accordingly performs an automated joint operation or a semiautomated operation, or sends this information to signalling panels and screens for manual operation. The Supervisory Control System is being installed in successive stages. Its installation is considered to be among the most important in Latin America, and special attention has been paid to its operation and maintenance. Completion of works to date has required the participation of 90 companies speciMi~ng in different construction activities such as roads, channels, aqueducts, tlmnels, struc~res, electromechanics, etc. Similarly, it has been necessary to draw up some 300 contracts with manufacturers to supply the necessary equipment and material. In accordance with federal government policies to effect investments favoring the development and improvement of the catchment areas, as well as the preservation of the quality of water in regions that form part of the Cutzamala system, numerous i m p o r t a n t
works to support rural communities have been undertaken, such as irrigationchAnnels, small dams, accessroads, schools and potable water and sewerage systems. Among the latter, the rehabilitation of the drinldng water systems serving the towns of Valle de Bravo and Colorines stand out, as well as the sanitation of the Valle de Bravo Dam through the construction of a system for the collection, diversion and disposal of sewage, which is conveyed to oxidation pools now under construction. The communities served by these systems have experienced a growth in tourism, and this trend is expected to increase. The system for the development of agriculture and cattle ranching in Santa Magdalena Tilostoc, in the vicinity of pumping station 2, is also an outstanding project and one that has become a source of income for local farmers and peasants.
Conclusion The experience acquired in completing all of these works, particularly the tunnels, represents a valuable and useful legacy since, in the foreseeable future, systems similar to the one described h e r e i n - - a n d p e r h a p s even larger--will be needed to face population growth in the large cities of our
country.
[]
References S{mchez Trejo,R. 1988. InRltracionesde agua en un ttmelduraute su construccion y sistemas de captacion durante su explotacion. In Tunnels and Water, Vol. 2 (J. Manuel Serrano, ed.),1115-1126. Rotterdam: A. A. Balkema.
Figure 3. Lining used for the Analco-San Jose tunnel. ~N~LLmG
AND UNDERGROUND SPACE TECHNOLOGY 95