New concepts and trends in design and building of hydroelectric power plants in Brazilian Amazon Region

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1 New concepts and trends in design and building of hydroelectric power plants in Brazilian Amazon Region H. R. Gama, A. de Souza Pinto, C. Gonçalves & A. L. Albuquerque Eletrobras-Eletronorte, Project Manager and staff members D. V. Znamensky CBDB-GO/DF & University of Brasilia-Institute of Geosciences, Seismological Observatory ABSTRACT: Main advantages of concepts of platform type hydroelectric power plants, as named by the present Brazilian government, are (i) harmonic coexistence between natural biophysical and social/human environments assuring a sustainable development form, since the early construction phase, until exploitation and finally an unavoidable decommissioning stage; (ii) environmental impact reduction during construction and operation periods, with minimal interferences in rainforest domains at dams and reservoir areas. Recent projects are: Dardanelos plant executed at Aripuanã River, and the planned Tapajós/Jamanxim Rivers scheme composed by, São Luis of Tapajós and Jatobá plants (Tapajós), and Jamanxim, Cachoeira do Caí and Cachoeira dos Patos plants (Jamanxim) rivers. Projects as Belo Monte, Santo Antonio and Jirau, on Xingu and Madeira Rivers, follow the same trends. Environmental and socio-economic advantages are emphasized using increased control and preservation of forestall reserves at reservoirs and dams neighborhood compared with previous procedures of building power plants and appurtenants in the Brazilian tropics. 1 INTRODUCTION 1.1 General considerations The previously successful mobilization and development of natural hydraulic resources in Brazil enables their exploitation in the Northern and North-Western parts of its territory. The development of natural hydraulic resources in the Southern and Eastern-Central parts of the country, the obtained experience and skills, encourages their exploitation also in the reminiscent parts of the territory and specifically in the Amazon Region. The country s economic and industrial development with a fast population growth, attaining 190 million of inhabitants, asks for an increase and improvement of the standard of life. These factors oblige the Brazilian society and authorities to explore, between others forms of energy, the available hydraulic potential of the Brazilian Amazon Region. The adopted policy assures in this way a continuous sustainable economic and social development which results in general welfare of the society utilizing the country s natural resources in an intensive but also strictly rational mode. The main topics to be observed in this case are a maximal possible conservation of the rain forest vegetation, preservation of natural ecological reserves and sites of natural scenic beauty, while creating a minimal interference with the existent Indian communities and other minor factors. All exposed items pose a highly defiant challenge for Brazilian dam engineers and other professionals. The task of erecting dams, creating water storage conditions, constructing power plants, transmission lines and access roads in the equatorial or subequatorial environment of the country, conducts both designers and constructors in the search of rational and responsible equilibrium in engineering solutions concerning planning, design, construction and exploitation of hydroelectric power plants in Brazil s Amazon Region. 1.2 Main Brazilian hydrographic basins Brazil is a country with an abundant net of watercourses of large natural discharges and also extended and frequently navigable rivers. An expressive majority of such watercourses are lo- 1

2 cated in the Northern tropical/subtropical environment known as the Brazilian Legal Amazon Territory. The major part of the hydrographic basins in the Amazon territory are covered by dense humid tropical rainforest (Northern part), or alternatively by a strong developed typical savanna vegetation mantle with the denser vegetation only along the watercourses (Southern part). Figure 1. Main Brazilian Hydrographic Basins, their principal streams and main planned and constructed HEP in the country s Amazon Region. Figure 1 indictes the Amazon River basin (1) with tributaries located in both hemispheres, Tocantins-Araguaia (2), São Francisco (4), Paraná-Paraguai (6) and Uruguai (7) River basins, all of them with their numerous tributaries. Minor hydrographic basins (3, 5 and 8) are constituted by rivers discharging directly to the Atlantic Ocean. 2

3 The main watercourses of the mentioned basins (except the minors) and their most important hydrologic characteristics are listed in Table 1 (Fiorini 2002). Table 1. Major Brazilian hydrographic basins. Basin Principal River Mean Rainfall (mm/year) Mean Discharge (m 3 /s) Mean Specific Discharge (l/s/km 2 ) 1 Amazon* 2, , Tocantins-Araguaia 1,660 11, São Francisco** 916 2, Paraná-Paraguai** 1,385 11, Uruguai** 1,567 4, *Basin area located only in territory of Brazil. **Portuguese designation of the streams as used in the text. 2 HYDROELECTRIC POTENTIAL OF THE BRAZILIAN AMAZON REGION BASINS 2.1 Main Amazon Region hydrographic basins The Amazon Basin Rivers are potentially responsible for an amount of 72% of the country s hydraulic resources. The twelve major rivers of the Amazon basin are listed in Table 2, indicating their respective mean annual discharge utilizable for hydraulic energy generation. Table 2. Amazon streams and their mean annual discharge utilizable for energy generation purposes. Stream Discharge (m 3 /s) Stream Discharge (m 3 /s) 1 Amazonas 209,000 7 Tocantins-Araguaia Solimões 103,000 8 Purus 11,000 3 Madeira 31,200 9 Xingú Negro 28, Içá Japurá 18, Juruá Tapajós 13, Araguaia* * Tocantins-Araguaia basin (2) including Araguaia River. 2.2 Existing and operating large and medium HEP Several large and medium size hydroelectric power plants (HEP) were built in the Brazilian Amazon Region in the past. Among them is the largest exclusively Brazilian plant of Tucuruí, located on Tocantins River with an installed capacity of 8,370 MW. The dam includes one of the largest spillways in the world (Figure 2) with a discharge capacity superior to 110,000 m 3 /s. Several other smaller and local schemes, Balbina, on Uatumã, Curuá-Una, on Curuá-Una, Coaracy Nunes on Araguari, and Samuel on Jamarí Rivers, were built in the Brazilian Amazon Region supplying cities as Manaus (AM), Porto Velho (RO), and specific mining and industrial plants demand of the region. At the mentioned sites new engineering experience of building dams in tropical rainy environment was obtained such as: a) foundations treatment of dams erected on sedimentary and metamorphic rocks, and b) construction of embankments using weathered and humid material (tropical soils). Some previous experience at hydroelectric plants built in the Amazon Region inside and outside of Brazil was also obtained with regard to reservoir performance. In the past the Brokopondo, in The Netherland s Guiana, Curuá-Una, Balbina, Tucuruí and Samuel dams in Brazil, and their respective reservoirs created a concern in face of the large amount of submerged area with a great quantity of drowned vegetation (biomass) if compared to the amount of generated energy. Several values of obtained ratios between the energy produc- 3

4 tion and submerged areas were observed on Brazilian reservoirs and are presented in Table 3 (Taioli 2001). Recent researches performed by Eletrobras-Eletronorte indicate several benefits in maintaining a submerged biomass reserve with the purpose of fish protection and also aiming at an increase in fish reproduction. Figure 2. Tucuruí hydroelectric power plant, the 1 st large plant built in the Brazilian Amazon Region. Table 3. Specific energy production vs reservoir submerged area of several Brazilian Power plants. Power plant Energy Production (MW/km 2 ) Power plant Energy Production (MW/km 2 ) Balbina (AM)* Belo Monte (PA)* 0,11 21,79 Jirau (RO)* Santo Antonio (RO)* 11,40 11,62 Dardanelos (MT)* 1087,50 Serra da Mesa (GO)* 0,67 Itaipú (Brazil/Paraguai) 9,40 Tapajós (MT/AM)* 5,55 Itaparica (PE)* 1,80 Tucuruí (PA)* 1,40 Porto Primavera (SP/MS) 0,8 Xingó (SE/AL) 58,80 *Power plants constructed/planned in the Amazon Region. The high value of the Dardanelos HEP is due to the run-of-river scheme diverting the natural discharge without storage or pondage preserving the original ecosystem and natural waterfalls scenery. Recently several controversial questions were raised involving undesirable gas (CO2 and CH4) emissions by large reservoirs observed and measured at some of the above mentioned Brazilian reservoirs. Punctual, isolated and reduced data point in this direction, but there are still no conclusive reports supported by a long term and generalized observations, neither in Brazil nor abroad, that validate the collected data. In every case runoff river schemes produce very small values of such emissions. 2.3 Planned hydroelectric power plants. A large amount of 227 potential sites was identified by the governmental agencies for the planning, construction and operation of hydroelectric plants in the Amazon Region, representing an increase of 46,120 MW to the installed hydroelectric capacity of the country (Sipot 2010). 4

5 The 32 sites, principally identified and available, are located on large tributaries of the Amazon River, such as Xingu, Tapajós, Madeira, Purus, and at the Tocantins-Araguaia Rivers basin. During preliminary studies a set of 24 locals, with capacities ranging from 6,133 to 208 MW, were identified as the more attractive sites with a total capacity of 42,400 MW; 7 sites among them, were considered priority, including the Dardanelos pioneer plant (Table 4). Table 4. Planned Power plant sites at different project stages. Power plant River Stage Capacity (MW) Head (m) Discharge (m 3 /s) Belo Monte Xingu Feasibility 11, ,224 Cachoeira Porteira 2 Trombetas Feasibility ,458 Jirau Madeira Bidding 3, ,926 Cachoeira Porteira 1 Trombetas Bidding ,808 Santo Antonio do Jarí Jarí Bidding ,020 Santo Antonio Madeira Construction 3, ,224 Dardanelos Aripuanã Constructed AMAZON ECOSYSTEMS ENVIRONMENTAL RESTRICTIVE CONDITIONS Hydraulic power plants inserted in a humid rainforest environment are planned, designed and constructed in an optimized way, produce minimal interferences in the existent natural ecosystems while maximizing social and economic benefits for the native or more recently settled local population. Some statements are accepted as necessary premises for planning, design and construction of power plants in the Amazon Region, and they are: a) Maximal use of rivers natural discharge (run-of-river schemes) with reservoirs of reduced storage or with pondage capacities minimizing this way permanently submerged areas. b) Maximal removing of the natural vegetative cover (trees, bushes, grass) that forms the biomass when permanently submerged by water, therefore reducing the gas emissions. c) Soil borrows and stone quarries areas location in preferable permanently submerged places of the river channel or reservoir. d) Wildlife preservation in restricted areas and fish preservation, allowing migration and transposition of natural or of man-made water level differences. e) Reforestation of all scars and areas attained by roads, accesses, and provisory installation of construction equipment and/or logistic support that are decommissioned after end of construction. f) Implemented conservation and inspection of the forestall reserves close to the reservoirs compatible with their size. g) Preservation of tourist and recreational facilities, if existing, avoiding their submergence, as e.g. at Sete Quedas (Paraná River) and Canal of São Simão (Paranaiba River) waterfalls. h) Avoidance of building large and extended urban settlements close to the dams, for personal involved in the overall construction activities, but offering reasonable comfortable permanence and rest conditions during the turn-over periods (so-called platform type power plants). i) Indian Communities Territory integrity and Natural Reserve Parks preservation in strict accordance with the country laws. j) Fluvial transport facilities, such as locks, and other auxiliary structures. 4 HYDROELECTRIC PLANT TYPES ADAPTED TO LOCAL CHARACTERISTICS In compliance with the statements exposed above the power plant design results in exploitation of the rivers natural discharges without pluriannual flow regulating procedures exerted by dams, spillways, gates and reservoirs for storage purposes. Preferences are given to simple wa- 5

6 ter pondage in detriment of storage (run-of-river schemes), resulting in small dams and in free overflow weirs of reduced height avoiding excessive bank inundation. Optimized use of natural head and/or water level differences at rapids and waterfalls (Paulo Afonso on São Francisco, and Cachoeira Dourada on Paranaiba Rivers) is already an old practice in Brazil (Znamensky 2008). Recently, the creation of shunt flow conditions was contemplated by introducing by-pass channels in large natural bends of plain river courses with a small topographic gradient. Low-head schemes are favored by the use of horizontal shafts and axis machinery such as existing coaxial generators and turbines or bulb units. Such machinery allows minimizing the submergence of river banks and their surroundings and reduced interference on natural vegetation. Fish migration structures such as stepped channels and elevators (locks) for spawning and reproduction is already an obligatory facility at Brazilian dams (example: Itaipu dam). Also, fluvial navigation and transportation practice such as locks, berth and terminal structures are inserted in dam lay-outs, where the condition of such activity exist as e.g. at Sobradinho dam on the São Francisco River. An example of such diversified water resources exploitation occurs at Tucuruí Dam and Reservoir, with an upstream-downstream level difference transposition system that was recently built. A pair of locks chambers of very large size (jumbo), 210 m in length and 33 m in width, placed at a distance of 6 km between them, were designed and inserted in the dam. The constructed locks allow performing a low cost and energy saving mode of transportation, a practice exerted by the riverain population of the Tocantins River since immemorial times (Costa Neto & Zolcsak 2010). 5 NEW CONCEPTS AND TRENDS ADOPTED FOR HYDROELETRIC PLANT PROJECTS New power plants to be built in the Amazon Region favor the run-of-river type layout close to the rapids and waterfalls in the upstream reaches, or the low-head dams and plants powered by bulb units in the downstream reaches of the rivers. In this way the use of the natural available head and discharge is obtained at a low cost investment allied to minimal interferences in the ecosystems. The first and positive example of what is called by Brazilian authorities a platform power plant, i.e. the Dardanelos project, is at the final stage of construction and performing the initial operational tests. Since the feasibility study stage certain characteristics of the selected site influenced the plants initial layout, namely: 1) The topography along the Aripuanã River with 100 m high waterfalls and rapids. 2) The sedimentary rock foundation (sandstone) at overflow weir and powerhouse locations. 3) The human settlement with river right bank occupation by the town of Aripuanã (MT). 4) The conservation of recreational and leisure areas close to the waterfalls. 5) Conservation and stand-by of three small operating power plants at the selected site. 5.1 Dardanelos hydroelectric power plant The characteristics of the mentioned hydroelectric power plant built downstream of the Dardanelos and Andorinhas waterfalls on the Aripuanã River, a tributary of Madeira River, Mato Grosso State (MT), are given in following Table 5 (CBDB 2009). Table 5. Technical Characteristics of Dardanelos hydroelectric scheme power plant Power plant capacity 261 MW Firm capacity Generators units Rated head 154 MW 4x 58 MW and 1x 29 MW 95.6 m 6

7 Figure 3Preserved Dardanelos waterfalls and the constructed hydroelectric power plant as upstream view. Figure 4. Dardanelos power plant as a downstream view with restoration measures of adjacent forest area. Certain characteristics of the selected site influenced the definition of the layout already during the feasibility study jointly with the local physical conditions, all accepted as design criteria. The topography of the site known as Dardanelos and Andorinhas (Swallows) Falls at the Aripuanã River presents a 100 m high drop (Fig. 3). The hydroelectric development basically consists of an upstream low-head dam with an overflow weir, an approaching channel, an intake structure, and penstocks conducting the water to the powerhouse with restitution channel, where the hydraulic energy of the Aripuanã River is harnessed (Fig. 4). The strong components of landscape, ecology, scenery and tourist attraction of rare beauty are characterized by the waterfalls, rapids, forested islands and jagged rock outcrops. The main preserved leisure areas for the inhabitants of Aripuanã city are located on the upstream and downstream side of the rapids and falls on the banks of the river s islands and sandstone slabs consisting of two water parks and their pertinent infrastructure. A dense natural and preserved rainforest mantle covers most of the river left bank. In the channel area three small operating hydroelectric power plants are conserved as small stand-by plants representing a historic value memorial of the initial development stage of the region. 5.2 Other power plants projects planned to be built. 7

8 The positive pioneer experience obtained at the Dardanelos Project is applied to several other power plants to be built on the tributaries of the Amazon River. The next hydroelectric power plants to be constructed are situated at the following rivers and sites: 1) Xingu River complex, presently known as Belo Monte complex (11,233MW) completely redesigned substituting the former Babaquara-Cararaó project. 2) Tapajós/Jamanxim Rivers complex composed of São Luis de Tapajós (6,133 MW) and Jatobá (2,338 MW) plants on Tapajós River, and Cachoeira do Caí (802 MW), Jamanxim (881 MW) and Cachoeira dos Patos (528 MW) on Jamanxim River. 3) Madeira River complex, involving Santo Antonio (3,150MW) and Jirau (3,350MW) schemes being already in the initial construction phases. 6 CONCLUSIONS Platform type power plants are an adequate solution for development of hydropower on Brazilian Amazon Rivers. The dams and plants respect the natural environment, offer social and economic advantages and represent a sustainable development processes. Rivers are largely preserved at their original state. Plants construction excludes large urban settlements inserted in the neighborhood of the dams or reservoirs. Auxiliary access and roads are reduced to strictly necessary ways of communication. Forested areas if attained by vegetal mantle removing, are recovered by original specimen s plantations. All scars produced in forested area during construction are eliminated. Construction is conducted by turn-over labor periods justifying the designation platform plants by analogy with petroleum drilling and pumping structures employed offshore. 7 ACKNOWLEDGMENTS Special thanks for permission of publishing the present data are presented to several governmental and private entities, identified by their following Portuguese designations, as: 1. Agencia Nacional de Águas, Eletrobrás, Eletrobras-Eletronorte, Eletrobras-Chesf; Empresa de Pesquisa Energética (EPE). 2. Energética Águas da Pedra SA, Neoenergia SA, Consórcio CCD (ODEBRECHT, IMPSA, PCE), Comitê Brasileiro de Barragens (CBDB), Universidade de Brasília - Instituto de Geociências (UnB). Permission for use and reproduction of photographs is thankfully recognized and due to their respective authors. Special thanks are directed to R. Boes for his highly appreciated contribution in improving the English text the papers format. REFERENCES Brazilian Committee on Dams (CBDB) (2009a). The Dardanelos Hydroelectric Development on the Aripuanã River, in Main Brazilian Dams III (2009), Brazilian Committee on Dams (CBDB) (2009b). Main Brazilian Dams III, Design, Construction and Performance. Organized by E. Carvalho. Edited by CBDB, 436. Costa Neto W. F. & Zolcsak, W. (2010). Transposition System of upstream-downstream water level difference created by the dam and Tucurui Hydroelectric Power plant constructed at the Tocantins River. Proc. 78 th ICOLD Annual Meeting-Internat. Symposium (2010). Hanoi, Vietnam, 8. Fiorini, A. S. (2002). Large Brazilian Spillways-An Overview of Brazilian Practice and Experience, in Designing and Building Spillways for Large Dams. Coordinators: Machado, B.P. and Fiorini, A. S. 70th ICOLD Annual Meeting, CBDB Special Edition (2002), 205 p. Sistema de Informação do Potencial Nacional Hídrico Brasileiro (Sipot) (2010). Eletrobras Special Task Group Internal Report (in Portugues). Taioli, F. (2001). Energetic Resources -Deciphering the Earth Chap. 22, Ed. USP & Oficina, 488. Znamensky, D.V. (2008). Dam heightening or power plant construction by stages as a solution for larger power output. Proc. 76 th ICOLD Annual Meeting-Internat. Symposium (2008). Sofia-Bulgaria, 11. 8