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 located 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.
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 (m3/s)
|
Mean Specific Discharge (l/s/km2)
|
|
1
|
Amazon*
|
2,460
|
209,000
|
34.2
|
|
2
|
Tocantins-Araguaia
|
1,660
|
11,800
|
15.6
|
|
3
|
São Francisco**
|
916
|
2,850
|
4.5
|
|
4
|
Paraná-Paraguai**
|
1,385
|
11,000
|
12.5
|
|
5
|
Uruguai**
|
1,567
|
4,150
|
23.3
|
*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
(m3/s)
|
|
Stream
|
Discharge
(m3/s)
|
|
1
|
Amazonas
|
209,000
|
7
|
Tocantins-Araguaia
|
11.800
|
|
2
|
Solimões
|
103,000
|
8
|
Purus
|
11,000
|
|
3
|
Madeira
|
31,200
|
9
|
Xingú
|
9.700
|
|
4
|
Negro
|
28,400
|
10
|
Içá
|
8.800
|
|
5
|
Japurá
|
18,620
|
11
|
Juruá
|
8.440
|
|
6
|
Tapajós
|
13,500
|
12
|
Araguaia*
|
5.500
|
* Tocantins-Araguaia
basin (2) including Araguaia River.
2.1
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 m3/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 production 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 1st
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/km2)
|
Power plant
|
Energy Production
(MW/km2)
|
|
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.
2.1
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).
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 (m3/s)
|
|
Belo
Monte
|
Xingu
|
Feasibility
|
11,223
|
87.00
|
18,224
|
|
Cachoeira
Porteira 2
|
Trombetas
|
Feasibility
|
350
|
61.00
|
2,458
|
|
Jirau
|
Madeira
|
Bidding
|
3,350
|
15.10
|
17,926
|
|
Cachoeira
Porteira 1
|
Trombetas
|
Bidding
|
700
|
61.00
|
1,808
|
|
Santo
Antonio do Jarí
|
Jarí
|
Bidding
|
300
|
25.60
|
1,020
|
|
Santo
Antonio
|
Madeira
|
Construction
|
3,150
|
13.19
|
18,224
|
|
Dardanelos
|
Aripuanã
|
Constructed
|
261
|
95.62
|
318
|
2
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.
3
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 water 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
|
154 MW
|
|
Generators units
|
4x 58 MW and 1x 29
MW
|
|
Rated head
|
95.6 m
|
Figure 3 Preserved 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.
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 Prof.Dr. R. Boes for his highly appreciated contribution
in improving the English text and papers
format.
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Brazilian Committee on Dams (CBDB) (2009a). The Dardanelos Hydroelectric Development on the Aripuanã River,
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Costa Neto W. F.
& Zolcsak, W. (2010). Transposition System of upstream-downstream water
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River. Proc. 78th ICOLD Annual
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Fiorini, A. S. (2002). Large Brazilian Spillways-An
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Edition (2002), 205 p.
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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
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Znamensky, D.V. (2008). Dam heightening or power plant construction by
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