Chiapas and the new hydroelectric projects. Threat to peoples and climate change

Chiapas and the new hydroelectric projects. Threat to peoples and climate change

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By Gustavo Castro Soto

In 4 Hydrological Systems of the Southeast Region, the new hydroelectric projects in Chiapas located in the Tonalá, Tacotalpa, Usumacinta and Grijalva basins are to be tendered soon. Therefore, the Mexican Movement of People Affected by Dams and in Defense of Rivers (MAPDER) is increasing its resistance struggles to achieve RIOS VIVOS!

On March 14, 2010 in Chiapas we remember the International Day Against Dams.

As an agreement of the VII Meeting of the Mexican Movement of People Affected by Dams and in Defense of Rivers (MAPDER) held in February 2010, the organization of the Civil Society Las Abejas y Otros Mundos AC painted blankets to remember the global protest against the dams but also to warn about what is coming again in Chiapas. Governments continue to fail to understand that these megaprojects are ecologically, socially, economically and politically unsustainable. However, now the government presents itself to a new generation of social movements against dams and in defense of the rivers that have managed to stop these dams.

In a document from the Federal Electricity Commission (CFE) of July 2008 entitled “Potential in the State of Chiapas”, it refers first to the National Hydroelectric Potential indicating 6 levels of study of dams. The first four correspond to the Planning Stage and the last two to the Design Stage. These levels of the hydroelectric project development process are: 1) Identification (“locate sites for possible hydroelectric uses at the national level”); 2) Great Vision ("propose comprehensive use schemes of a basin or hydrological system, ranking projects"); 3) pre-feasibility (“propose the best exploitation scheme and optimal dimensioning of the works in a selected site”); 4) Feasibility ("establish the technical, economic, social and environmental feasibility of the project, defining the works of use"); 5) Design consisting of Conceptual Engineering ("studies that allow defining the comprehensive scheme of exploitation") and Basic Engineering ("development of general plans of each of the works that make up the project with scope
enough to make the bidding conditions ”); and finally, 6) Construction. (See box)

In total, 505 projects with an installed capacity of 42,132 MW. But specifically the "Hydroelectric Potential in the State of Chiapas" the CFE distinguishes 90 projects in the Planning Stage with an installed capacity of 9,060 MW, with 79 projects identified, 4 of Great Vision, 2 of Pre-feasibility and 5 of Feasibility. (See box)

The CFE thus confirms that in 4 Hydrological Systems of the Southeast Region the new hydroelectric projects in Chiapas located in the Tonalá, Tacotalpa, Usumacinta and Grijalva basins are soon to be put out to tender. The 4 Great Vision Projects for Chiapas, all of them located in the Usumacinta Basin, are the dams:

1) Altamirano Dam on the Tzaconejá River with an installed power of 185 MW.
2) Livingstone Dam on the Tzaconejá River with an installed power of 285 MW.
3) Santo Domingo Rapids Dam (formerly Huixtán I Dams) on the Santo Domingo River with an installed capacity of 160 MW.
4) Santa Elena Dam (formerly Huixtán II Dams) on the Santo Domingo River with an installed capacity of 300 MW.

The two Pre-Feasibility Projects are the El Retiro Expansion Dams on the Cahua River and in the Cahuacán Basin and the Chinín Dam on the Tacotalpa River in the basin of the same name, with an installed potential of 7 and 170 MW respectively.

The five Feasibility Projects are:

1) Acala Dam on the Grijalva River in the basin of the same name with an installed potential of 135 MW.
2) Copainalá Dam on the Grijalva River in the basin of the same name with an installed potential of 225 MW. It will have 3 Kaplan turbines and its powerhouse will be 60 meters high by 124 meters long and 22 wide. With a gravity curtain 30 meters high, 10 wide and 135 meters long, its 9 kilometer reservoir will flood 189 hectares. It will be in the middle of four other dams (Peñitas, Malpaso, Chicoasén and La Angostura). This project is intended to be put out to tender in 2013, after the new presidential elections of 2012, and whose construction would take between 2014 and 2017. Its initial cost is expected to be almost 3 billion pesos, although the cost is generally of the dams exceeds the original budget.
3) Itzantún Compact Dam on the Tacotalpa River in the basin of the same name with an installed potential of 440 MW. This project was attempted to be built and was suspended due to a strong popular mobilization in the 1980s. (one)
4) Rehabilitation of Bombaná on the river Bombaná in the Grijalva basin.
5) Tenosique Dam on the Usumacinta River in the basin of the same name with an installed potential of 420 MW. This project was previously named as Hidroeléctrica Boca de Cerro and is part of a network of dams that the government intends to install along the Usumacinta River that divides Mexico with Guatemala through the state of Chiapas. The other projects for this river are the Yaxilán, Isla El Cayo, El Porvenir and La Línea dams that would add 690 MW of installable power, before flowing into the dam now called Tenosique, which alone this project would have an installed potential of 420 MW between states of Chiapas and Tabasco. With a flexible curtain 41 meters high and 305 meters long at its crown. With three Kaplan turbines the powerhouse would be 75 meters high by 172 long and 20 meters wide. Its initial budget is 545.67 million dollars. The tender is planned for 2013 and its construction between 2014 and 2017.

To ensure the viability of the project in its social, environmental, technical and economic aspects, the CFE proposes 4 Phases: Organization, Diagnosis, Forecast and Induction.

The projects are not feasible.

For 20 years, studies have warned that these projects are not feasible. (2) According to these studies, the so-called “Cancuc Transfer System” that would be located 50 kilometers northeast of the city of San Cristóbal de las Casas, intended to transfer between 34 o 22 m³ / sec of water from the Alto Usumacinta basin (Jataté and Tzaconejá rivers) to the Tacotalpa river basin, in order to increase from 1,687 or 1,209 GWh per year in the dams of the Tacotalpa, Chacté, Itzantún and Chinín System. On the other hand, the Cancuc Powerhouse would generate between 886 and 532 GWh per year.

For this purpose, it was intended to build two diversion dams called San Agustín and Altamirano or, where appropriate, the Tzaconejá dam on the Jataté and Tzaconejá rivers, respectively. Two canal tunnels would also be built, one would transfer water from the Altamirano or Tzaconejá dam to the San Agustín dam, and the other from the San Agustín dam to the Cancuc Powerhouse.

However, the study concluded that “Geologically, the region that would comprise the Transfer System is deeply affected by a fault system with an East-West orientation, of a passing type, which has earned the area the tectonic name of Province of Transcurrence Failures. " The rocks of the region are limestone-dolomitic, of marine origin and of Cretaceous to Early Tertiary age, and clayey conglomerate of Continental origin, deposited during the Middle and Upper Tertiary.

The Altamirano dam that would transfer 24 m³ / second of water from the Yalchiptíc and Tzaconejá rivers to the San Agustín dam through a 4 km long tunnel-channel. The Altamirano dam would have its Extraordinary Maximum Water Level (NAME) at an elevation of 1,242 meters above sea level (m.s.n.m.). The study observed that “it would displace on the right bank on hard and competent limestones, while the left bank on conglomerate-clayey sediments, highly plastic and permeable, with intercalations of evaporites that can, at a given moment, induce dissolution in the strata of the curtain. " In other words, the study concluded that "the site is not feasible from a geological point of view."

The study is very clear about the non-feasibility of the project: “The distribution in the Altamirano Project area of ​​the sediments called Ti made up of gravel, sand and fragments of loose limestone without cementing, which showed a very permeable material according to the results of the "Matzuo Akai" tests carried out for this purpose are one of the reasons why the site is not considered geologically feasible. On the other hand, during the execution of hole number 1 drilled in the area of ​​the nozzle, it was found that the first 38 m are occupied by Ti and the following 42 m are underlain by plaster and plastic clays. If we consider that when damming we will have a water load of 100 m, according to the preliminary project, this will cause water flows between the plasters, which will cause dissolution in them and will surely cause problems of settlements in the curtain that finally translate into rearrangements in the structure."

The other option would be the construction of the Tzaconejá dam, as an alternative to the Altamirano dam, which would transfer half the water compared to the Altamirano dam from the Tzaconejá river to the San Agustín dam. However, the study clarifies the weakness of the dam since “the fracturing in the bed of the Zaconejá river, caused by the Huixtán Fault, forces us to think about a suitable waterproofing treatment, to avoid water leaks in the same area of ​​displacement . "

The San Agustín dam, the center of the Cancuc System, would bring together the waters of the Jataté River with the water that would be transferred from the Altamirano dam by means of a glass at an elevation of 1,232 m.s.n.m. made up of impervious sediments from the El Bosque Formation, with a 50 m high curtain over permeable and fractured limestone from the Upper Cretaceous. The CFE study concluded 20 years ago that this is not feasible: “(…) the main problem observed in the area (this includes the three sites studied) is the lack of closure and the high permeability in the area of ​​the shaft that would put in doubt the damming of the dam. In addition to the high degree of fracturing observed in limestone and dolomites. "

But this dam that would be the center of the system presents important risks that make it impossible for it to function well. In the San Agustín canyon where the curtain would be, there is a “tectonic knot, so it was glimpsed that within the canyon itself there is no possibility of finding a site neither with acceptable mechanical characteristics in the rock, nor with permeability conditions that assure us the tightness of the reservoir ”. When conducting the studies with the drilled holes to see how much it is permeable and if the quality of the rock is good, the conclusion was negative. “With the above, it was confirmed that the bad mechanical conditions in the rock found along the San Agustín canyon are not due to circumstantial effects and a well-restricted location, but on the contrary, those conditions are generally due to horse riding. that the limestone massif has suffered and with it, compressive and shear effects that have inflicted on the rocks, the degree of advanced fracturing characteristic of a tectonic node. " Simply put, preying is suicide.

Well, even worse. The tunnel that would bring the water from the San Agustín dam to the Powerhouse in Cancuc would have to cross the mountain that divides the Usumacinta basin from the Grijalva, crossing sandstones, shales, siltstones and conglomerates of the El Bosque Formation, with the water table ( possibly hanging) above the Cancuc Transfer Tunnel. The geophysical studies through which this tunnel would pass to channel the water, concluded that “70% of the excavation would be below the water table or hanging water. There is the possibility that falls will occur due to the inclinations of the rock on the left wall of the excavation, and the mechanical conditions of the same, which in certain areas are fair to poor. A similar situation is forecast on both portals. " In other words, it is not advisable to do the tunnel because it collapses.

The objective is that the water that comes from the previous dams goes to the Cancuc Powerhouse to generate energy by turbineing the 34 m³ / sec of the transfer of the dams and generating 886 GWh per year. This powerhouse and the regulating tank would be located south of the Tenango Syncline, made up of somewhat karst fossiliferous limestone.

After the Power House, this one would throw the water to the Chacté dam that would be to one side. It is estimated that the reservoir would have a NAME at elevation 865 and “on fossiliferous limestones, somewhat karst from the Paleocene age”, and the area for the nozzle “would be housed in the Chacté Canyon, made up of compact limestone and dolomite. Given this, the report concludes that "its main problems will be the thickness of decompressed rock, the presence of some unstable blocks and possible karst development." In other words, the Chacté dam is not viable.

Around 27 billion tons of Carbon Dioxide (CO2) are emitted worldwide, the most harmful Greenhouse Gas in Climate Change. Mexico emits less than 2% of the world's CO2 and is in the first 14 places of the most polluting countries in the world. Mexico is the 4th emitter of CO2 in Latin America. Mexico City emits 4 tons of CO2 per person per year. On the other hand, 59 percent of the GHG in Mexico comes from energy generation and its use3. However, the percentage is higher since GHGs such as methane generated by dams in the country and the amount of CO2 that the flooded biodiversity stops absorbing from the environment is not taken into account when the reservoirs leave thousands and thousands under water. thousands of hectares of jungles, forests and other ecosystems. Not only the removal of the forest layer and its flooding, but also the displacement of indigenous and peasant communities accelerate deforestation. Large dams are no longer an alternative. The Mexican government ignores the recommendations of the World Commission on Dams. For this reason, the Mexican Movement of People Affected by Dams and in Defense of Rivers (MAPDER) is increasing its resistance struggles to achieve RIOS VIVOS!

Gustavo Castro Soto placeholder image - Other Worlds AC /
San Cristóbal de las Casas, Chiapas, Mexico; March 25, 2010


(1) This history and process can be consulted at in the chapter on “dams”.

(2) CFE. Construction Subdirectorate. Civil Engineering Studies Unit. “Geological exploration works developed in the Cancuc System, upper transfer Usumacinta-Tacotalpa, Chiapas, 1987 by Gustavo Arvizu Lara and Moisés Dávila S. Reviewed: Jorge I. Navarro.

(3) CFE, Informative Synthesis, July 8, 2009.

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