RETIRO BAIXO HYDROPOWER PLANT ON THE PARAOPEBA … · The Retiro Baixo HPP is being built in the...

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RETIRO BAIXO HYDROPOWER PLANT ON THE PARAOPEBA RIVER Authors: Vicente de Paulo Soares Sobrinho and Newton Goulart Graça

Transcript of RETIRO BAIXO HYDROPOWER PLANT ON THE PARAOPEBA … · The Retiro Baixo HPP is being built in the...

Page 1: RETIRO BAIXO HYDROPOWER PLANT ON THE PARAOPEBA … · The Retiro Baixo HPP is being built in the Paraopeba River, located on the border between the municipalities of Curvelo and Pompéu,

RETIRO BAIXO HYDROPOWER PLANTON THE PARAOPEBA RIVER

Authors: Vicente de Paulo Soares Sobrinho and Newton Goulart Graça

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RETIRO BAIXO HYDROPOWER PLANTON THE PARAOPEBA RIVER

1. INTRODUCTION

1.1. BackgroundThe first studies carried out concerning the power

development potential of the stretch of interest in theParaopeba River were contained in the hydroelectricalinventory study of the São Francisco River basin, in MinasGerais, executed by CEMIG and CANAMBRA in 1966.Subsequently, in 1985/87, CEMIG contracted EngevixEngenharia to re-evaluate that inventory in view of thenew environmental conditioning factors and new technicalalterations introduced by ELETROBRAS for similarstudies.

The conclusion of this re-evaluation indicated aninstalled power of 110 MW and a flooded area of51.2 km², for the then-named Retiro HPP (integrating acascade of three other upstream developments).

In the course of 2001, Poente Engenharia carried outoptimization studies of this development, resulting in thedisplacement of the dam axis upstream with a reductionof the flooded area to 23.8 km², and a small reduction inthe drainage area from 11,900 to 11,160 km², having nowreceived the denomination of the Retiro Baixo HydropowerPlant.

The technical feasibility studies for this developmentwere concluded in November of 2002, by the Consortiumof Arcadis Logos Energia S.A., Orteng Equipamentosand Poente Energia, these studies being prepared bythe consulting firms of Poente Engenharia e ConsultoriaS/C Ltda. and Enerconsult S.A..

In December of 2005, the Consortium was awarded,through a new energy auction held by the ANEEL, theconcession for the construction and operation of thedevelopment for 30 years. The Poente Energia S/C Ltda.subsequently withdrew from this Consortium.

During the first semester of 2006, the new Consortiummade various contacts seeking the inclusion of a newpartner and met with success in reaching closeunderstandings with Furnas Centrais Elétricas S.A., whopresented some suggestions with reference to a studyof alternatives for the principal works.

The work commenced in March of 2007 and itsconclusion is scheduled for the year 2010. Since thisarticle was written in mid-2008, some aspects of the plantdescribed herein may not represent the as built projectas closely.

The owners of the enterprise and their suppliers ofgoods and services are listed below:

Owners:RBE - Retiro Baixo Energética S.A., constituted by thefollowing firms:• FURNAS Centrais Elétricas S.A., with 49%;• ORTENG Equipamentos e Sistemas Ltda, with 25.5%;• LOGOS Engenharia S.A., with 15.5%;• ARCADIS LOGOS Energia S.A., with 10%.Suppliers of goods and services:Owner's Engineering Services:• FURNAS Centrais Elétricas S.A.• MARTE Engenharia LTDA.Construction Consortium Retiro Baixo S.A.:• ORTENG Equipamentos e Sistemas Ltda.• LOGOS Engenharia S.A.Engineering, Structuring and Development of theEnterprise:• SPEC Engenharia• ENERCONSULT S.A.Civil Construction:• Concrete Works: Construtora Quebec Ltda.• Earth and Rock Works: Mecanorte Ltda.Supply, electromechanical equipment erection servicesand construction of transmission lines:• SADEFEM Equipamentos e Montagens S.A.

Photo 1 shows an aerial view of the project site from theleft bank with the aggregate stockpiles, the excavation ofthe generation circuit (headrace, intake, powerhouse andtailrace) and of the approach channel and spillway, on thebackground the works underway for the earthfill dams.

Photo 1 - Aerial View of the Project Site during Construction

1.2. LocationThe Retiro Baixo HPP is being built in the Paraopeba

River, located on the border between the municipalitiesof Curvelo and Pompéu, in the State of Minas Gerais, ata distance of 62.3 km from its mouth into the SãoFrancisco River, and approximately 6 km upstream fromthe backwater of the Três Marias dam (see Figure 1).

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The main access is by highway BR-040 - Brasília /Belo Horizonte, at km 377. This stretch is 153 km fromBelo Horizonte.

2. DESCRIPTION OF THE ENTERPRISE

Figure 2 shows the general layout selected for theRetiro Baixo dam. The river diversion gallery is located inthe right bank, while the left bank contains the spillwayand the hydraulic circuit of the energy generation.

3. GEOLOGY, GEOTECHNOLOGY ANDFOUNDATIONS

The region of the project is predominantlycharacterised by the occurrence of neoproterozoic rocksof the Bambuí Group. This group commences with a basalconglomerate, continues with a thick clay-carbonatedsequence and finishes with siltstones and arkoses.

At present, the Bambuí Group is divided into fiveformations (from the bottom upwards) comprising:Sete Lagoas, Serra de Santa Helena, Lagoa do Jacaré,Serra da Saudade and Três Marias. Pedrosa-Soareset al. (1994) classified the first four formations under thedesignation of Paraopeba Subgroup, which constitutedthe predominant unit at the Retiro Baixo site.

The Paraopeba Subgroup is mainly covered by recentQuaternary sediments (Pleistocene and Holocene),constituted by calcipherous siltstones, slate siltstones,slates of grey-green to dark-grey colour, marls, beds ofFigure 1 - Location of the Development

Figure 2 - General Layout

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calcareous lenses and claystones tometaconglomerates. The pelitic terms are predominantin the unit showing, at times, a lateral and verticaltransition to the carbonaceous rocks which, in turn, arepredominantly represented by dark-grey limestone.

The Três Marias Formation occurs over a significantarea in the extreme north of the basin, in the region closeto the Três Marias dam, being constituted by arkoses,arkose sandstones, siltstones and claystones.

Covering the metasedimentary rocks (as a rule to alow extent attributed to the burial pressure) of the BambuíGroup, there are undifferentiated superficial coverings andrecent alluvial deposits, of ages estimated to beTertiary/Quaternary.

The superficial quaternary sediments, designated asundifferentiated coverings, occur widely in the lowercourse of the Paraopeba River, constituting unconsolidateddeposits of reduced thickness, on average from2 to 5 metres, formed by the disaggregation and erosionof a great variety of lithologies.

3.1. Local GeomorphologyThe relief of the region is constituted by elongated

hills with convex and flattened tops.The site of the development comprises an open valley,

with gentle slopes, of declivities below 10º, with relativelysymmetrical and convex forms. The local altimetry variesfrom El. 575 m in the region of the powerhouse, toEl.655 m at the top of the ridge of the left bank.

The Paraopeba River has an average width of80 to 100 m, with rocky riverbed and margins, or cappedby thin alluvial overburdens.

3.2. Local GeologyThe principal lithotype found at the Retiro Baixo site

is represented by a packet of metasiltstones of pale greyto greenish colouring, sometimes with blue tonesintercalated with metasandstones of grey-white colouringand metaclaystones (rarely) of brown colouring. Thelayers are of thicknesses measured in millimetres tocentimetres, and sometimes decimetres, presentingfrequent stratifications and laminations of small size(millimetres) of undulated and truncated forms. Theoutcroppings of the rocky packet present sets of moresandy strata of thicknesses from centimetres todecimetres alternating with millimetre to centimetrelayers of metasiltstones. At the top of the layers it ispossible to identify sedimentary structures of the ripplemark type, asymmetrical, with centimetre to decimetrewavelengths from centimetres to decimetres and waveheights close to 1 cm.

The characteristics found in the description andcharacterization of drill core samples, as well as frommapping in the field, indicate the rocky materials asbelonging to the metasandstones and metasiltstones ofthe Paraopeba Formation, of the Bambuí Group.

3.3. Structural GeologyThe most striking structural feature at the power plant

site is undoubtedly the horizontal sedimentary layeringof the rocks of the Paraopeba Formation. As a rule theplanes of these structures of the sound rock mass aresealed. According to the data from the soundings, in themost relaxed zone of the rock mass these discontinuitiescan appear totally or partially open and oxidized, or evenfilled in with washable materials.

In second place, but no less important, there arefractures and subvertical joints, inclined andsubhorizontal. The principal orthogonal layout of the setof these structures is clearly defined, presenting spacingof around 1 m in the sound rock mass and spacing of20 cm in the weathered rock. The principal features ofthe planes are curved lines, sometimes undulated, wherethe surfaces appear wrinkled, with openings and partialoxidations, principally in the relaxed zone of the rockmass where, according to the surface investigations,these openings extend, on average, close to 5 metresinto the interior.

Three most important fracture families were identified;these being: family 1 parallel to the axis and transversalto the flow; family 2 forming a 90º angle with family 1,and family 3, similar to family 2 but with a greater dip.The subhorizontal family did not present risk for thestability of the slopes or walls, but demanded greatercare for the waterproofing treatment by means of the groutcurtain.

4. HYDROLOGY, HYDRAULICS ANDENERGY STUDIES

4.1. Stream GagingThe stations were inventoried based on the publication

"Inventory of Stream Gaging Stations (DNAEE, 1983)".Among them, the stations of Ponte da Taquara and PortoMesquita, both located in the main course of theParaopeba River, were considered to be the mostrepresentative to subsidize the consolidation of the basichydrological data, serving to support the characterizationof the fluviometric regime of the river referred to. Thecriterion for the choice of these stations was foundedupon their proximity to the hydroelectric development ofinterest, together with the availability and consistency oftheir data. Items also taken into account were the lengthof the period of observation (above 25 years), the stabilityof the rating curve, the number of dischargemeasurements and their distribution, among otheraspects.

4.2. The Drainage BasinThe Paraopeba River which, together with the Pará

River, constitutes the principal tributary of the upperstretch of the São Francisco River has its sources in themunicipality of Cristiano Otoni, approximately at

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El. 1,140 m. Its longitudinal development runs in the north-northwest direction, slightly more than 400 km, from itssource to its mouth in the Três Marias reservoir. Itswatershed covers a total surface of 13,160 km2,corresponding to 2.5% of the total area of the State ofMinas Gerais, draining densely populated areas, as themetropolitan region of Belo Horizonte. The ParaopebaRiver also serves as a water supply source for that region,whose economy is mainly based on mining, industry andagriculture in the high and middle reaches, and livestockbreeding in the lower course.

The Paraopeba River basin has as neighbours thebasins of the Pará and das Velhas Rivers. The Paraopebaand Pará Rivers constitute the principal sources for theTrês Marias reservoir, in the stretch being considered.

The physical aspects of the basin constitute elementsof great importance in the evaluation of the hydrologicaland sedimentological behaviour. The principal physicalcharacteristics of the Paraopeba River basin down to itsmouth in the Três Marias reservoir are described below:• Drainage area 13,160 km2

• Length of the main watercourse 401 km• Mean slope of the thalweg (Si) 0.75 m/km• Perimeter 650 km• Form factor (Kf) 0.08• Coefficient of compactness 1.59

The coefficient of compactness is a factor indicatingthe tendency to form large flood peaks, when it equalsunity corresponding to a circular basin, it would beexpected to have sharply peaked flood discharges. TheParaopeba basin presents a small tendency to large floodpeaks since the coefficient of compactness is greaterthan unity.

The form factor, apart from suggesting the approximateshape of the basin, is another further data indicating thetendency to have high flood peaks. A form factor below1, such as occurs with the basin in question,corresponds to an elongated basin and indicates smallpropensity for large floods.

4.3. MeteorologyDue to its geographical location, between latitudes

18º30' and 20º55' south and longitudes 43º50' and45º05' west, the Paraopeba River basin has a humidtropical climate typical of the continental interior. Theprincipal features of this climate are:• The occurrence of a hot and rainy season, normallybeginning at the end of September and extending untilMarch, affecting the entire basin. The months of transitionfor this period are September and October.• The occurrence of a dry season, predominantly betweenJune and August and characterised by tropical conditionsof a continental nature. The transition months for thisperiod are April and May.

The occurrence of two well defined periods (rainy anddry) permits stating that there is a certain climatologicalhomogeneity over the area of the study.

The basin is also characterised by the dominance ofa mass of continental equatorial air; humid and unstable.The annual mean relative humidity, transported by thewinds from the NE, varies from 75.5% in the upper and70.5% in the middle and lower reaches of the river.

According to the Köppen classification, the region isof the Aw type - humid tropical (megathermal) savannahclimate, with dry winter and rainy summer and, accordingto Nimer, the climate type of the region is sub-hot,sub-humid with 4 to 5 dry months. In this climate, thelower frequency of high summer temperatures and thepredominance of mild temperatures in winter are mainlydue to the influence of the altitude. However, the influenceof the latitude also becomes important due to the regionbeing situated along the trajectory of the disturbedcurrents of sub-polar origin. This region presents at leastone month with a mean temperature below 18ºC, withthe coldest month (June or July) recording temperaturesof around 15º to 18ºC. The mean annual temperature isalmost always lower than 22ºC, varying mainly between18º and 20ºC. The summer, despite not presenting veryhigh maximum daily temperatures is, nevertheless, hot.The hottest month has a mean surpassing 22ºC,throughout almost its entire domain.

Review of the Pluviometric Data• The total annual mean precipitation at the head of thebasin decreases from 1,400 mm, at the sources, to closeto 1,200 mm in the region close to the mouth, i.e., in theTrês Marias reservoir;• The rainy period extends from November to March;• April and May are the transition months for the dryperiod, with April being the rainiest of the two;• The months of September and October represent thetransition for the rainy period, with October having thehighest total monthly precipitation;• The rainiest quarter at the headwaters occurs in themonths of November, December and January, and overthe total extension of the basin varying a mean of 53% ofthe annual total at the headwaters and 56% in the middlestretch and about 58% close to the mouth. It can thereforebe concluded that the basin behaves in a similar mannerwith regard to the distributions of the precipitationthroughout the seasons of the year.• The driest quarter occurs in the months of June, Julyand August in the whole basin, when rainfall is 2% to 3%of the annual total;

For the majority of the stations presented, the greatestmonthly precipitations recorded in the Paraopeba Riverbasin occur in the month of January: 704.8 mm inPonte da Taquara (the closest to the dam site),767.0 mm in Fazenda Escola Florestal, 565.9 mmin Melo Franco, and 540.8 mm in Congonhas.

Hydrometeorological DataThe following table provides the hydrometeorological

data for the area of the project.

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4.4. Filling of the ReservoirThe study of the filling of the reservoir was based on

the series of mean monthly flows, referred to the periodfrom January 1931 to December 2000, and the data fromthe curve of elevation x area x volume of the reservoir.The mean monthly values of the precipitation andevaporation data considered were from the Ponte daTaquara and Pompéu station respectively, since they werethe stations closest to the dam site.

A statistical study was made considering thecommencement date of the filling as being the first dayof each one of the twelve months of the year. In thismanner, the basic data for the study was collected, asfollows:• Initial date of filling: First day of each month;• Reservoir volume corresponding to the maximum normaloperating elevation (El. 616.0 m) of 241.6 x 106 m³;• Long Term Mean Flow: 159.62 m³/s;• Residual flow in the period: 18.54 m³/s (80% of theminimum mean monthly flow).

Simulations of the filling of the reservoir were madethroughout the entire period of the series of mean monthlyflows (70 years of data). The results obtained indicatethat the filling of the reservoir, up to the El. 616.0 m, isconcluded in a maximum mean time of 70 days,independently of the month of the final closure operationof the reservoir, adopting the previously mentionedresidual flow.

4.5. Freeboard StudiesThe basic data of Retiro Baixo reservoir is as follows:

• Fetch of 6.8 km• Wind velocity of 120 km/h

By applying the method proposed by the publication"Design of Small Dams" issued by the United StatesDepartment of Interior - Bureau of Reclamation, a waveof 1.25 m was obtained and a minimum freeboard of1.80 m.

Therefore, a freeboard of 2.00 m above the maximumflood level was adopted.

4.6. HydrosedimentologyBased on the "Diagnosis of the Sedimentological

Conditions of the Principal Brazilian Rivers" byELETROBRÁS, 1987, which presents a study on somestations located in the course of the Paraopeba, an

It should be emphasized here that the objective ofthe above results is only to indicate the tendency towardssilting-up of the reservoir being studied, and should notbe taken as absolute values to be employed for the region.Thus, for the results to be more coherent with the realityat the site, it is necessary to execute frequent campaignsof sediment load measurements in the region of the dam,during and after the construction.

5. PRINCIPAL STRUCTURES

5.1. Diversion WorksThe diversion of the river to permit construction of the

works of the Retiro Baixo development is made in theleft bank through a gallery constructed in reinforcedconcrete in the intermediate stretch of a channelexcavated in earth and rock over an extension of 600 m.

The dimension of the gallery was established toconduct the incoming flood, with reference to the dailypeak flow of the dry period equal to 552.00 m3/s,corresponding to a recurrence interval of 50 years and amaximum velocity of 10.00 m/s.

This gallery has a length of 182 m, corresponding tothe width at the base of the cross section on the axis ofthe dam. It is composed by two bays of 22.00 m2 each.It possesses eight elements of 19.70 m each, whosejoints are provided with double waterstops of the type0-35.

A concrete control structure at the inlet of the galleryis provided with fixed-wheel gates for its closure. Inelement 5, after closure of the gates, a concrete plug isto be built with a length of 10 m.

The approach channel, excavated in earth and rock,has a trapezoidal section with a length of 477.00 m and21.80 m width at the base. Its slopes are 1.0 (H): 1.0 (V)and 10 (H): 0.5 (V), in earth and rock respectively.

Photos 2, 3 and 4 depict the excavation works for thediversion channel and the construction of theembankment dams.

estimate of the sediment load carried by the water courseof the sub-basin of the Paraopeba River was preparedand the information referenced to the Porto MesquitaStation, since a series of mean monthly liquid dischargerating curves of the Retiro Baixo HPP were obtained bymeans of the data from this station.

The service life of the reservoir can be evaluated bymeans of the time for silting-up which, together with thedata collected and the minimum operational level, ispresented in the following table.

Table of the Time for Silting-Up the Minimum Operational Volume

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Photo 2 - Excavation of the Diversion Channel and Construction of the Earthfill Dam ( seen from downstream)

Photo 3 - Excavation of the Diversion Channel

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Photo 4 - Construction of the Embakment Dams on both Banks and Excavation of the Diversion Channel ( seen from upstream)

5.2. Generation CircuitThe generation circuit is located at the left end of the

dam, being constituted by a headrace channel, forebay,intake, penstocks, powerhouse, erection area andtailrace.

Headrace ChannelThe principal characteristics of the headrace channel

are the following:

IntakeThe intake (Figure 3) is constructed in structural

concrete and possesses the hydromechanical equipmentrequired to control the supply to the penstocks, i.e., thetrashracks, the gates and the emergency gates of thefixed-wheel type. The trashracks are cleaned by a rakeinstalled in a gantry crane, which is also used formaintenance of the gates.

Photo 5 depicts the water intake structure duringconstruction.

PenstockThe layout foresees the construction of two penstocks

with a per-unit diameter of 6,200 mm for a flowcorresponding to 130.0 m³/s.

The penstock will be supported upon concrete blocksspaced at regular intervals. The length in plan-view is104.67 m, and its anchorage is to be only obtained bymeans of a block constructed between the structures ofthe intake and the powerhouse. Each penstock will havean expansion joint installed directly after its outlet fromthe intake.

Photo 6 depicts the penstock erection works.

Figure 3 - Water Intake - Cross Section

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Photo 5 - Water Intake Structure during Construction

PowerhouseFigure 4 shows a cross section of the powerhouse,

which is of the indoor type.The energy studies led to the selection of two Kaplan

type turbines with vertical shaft. They should supply, undera net head of 36.84 m, a power of 41 MW with a ratedflow corresponding to 128.18 m³/s.

The overhead traveling crane of the powerhouse, tobe used for the erection, operation and maintenance ofthe generator units, has a span of 14,500 mm, main hookcapacity of 1,300 kN and 150 kN for the auxiliary hook.

The fixed-wheel type gate serves to close the drafttube of the turbines in the powerhouse for maintenance.The gate is formed by panels erected at the jobsite, builtof welded structural steel, with upstream facing andsealing. It is of the sliding type for operation in still waters,with a by-pass valve for filling.

Photos 7 to 10 show the powerhouse in differentstages during construction.

5.3. SpillwayThe spillway, located in the left abutment, has an

approach channel excavated in earth and rock, controlstructure, chute terminating in a ski jump, dissipation

Photo 6 - Penstock Erection Works

Figure 4 - Powerhouse - Cross Section

Photo 7 - Powerhouse - Construction of the Draft Tube (Dec. 2007)

Photo 8 - Powerhouse Construction (Dec. 2007)

basin and discharge channel. Figure 5 shows the profileof the spillway.

The approach channel has a length of 220.00 m, withthe width of the bottom sill being 55.00 m, at the constantelevation of 598.00 m.

The spillway is of the ogee type, equipped with threeradial gates, with a width of 13.30 m and a height of

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Photo 9 - Powerhouse - Erection Works (Dec. 2008)

Photo 10 - Powerhouse - Erection Works (Dec. 2008)

Figure 5 - Spillway - Profile

13.50 m, and has the capacity to discharge a maximumoutflow of 3,945 m3/s, equivalent to a recurrence intervalof 10,000 years.

The spillway has four contiguous blocks, separatedby contraction joints, forming a set of three bays,separated by two pillars 4.00 m thick. The total width ofthe spillway is 52.00 m.

In the upper part of this structure there is a bridge,constituted by precast concrete beams, upon which runsa gantry crane on rails to manoeuvre the stoplogs duringthe maintenance periods of the radial gates.

Photo 11 - Spillway Excavation Works

Photo 11 depicts the excavation works for the spillwayand Photo 12 the construction of the concrete structure.

5.4. Earthfill and Rockfill DamThe definition of the typical section of the dam was

made taking into consideration the materials available atthe jobsite, principally those provided by the obligatoryexcavations, and from the conditions of the bedrockfoundation.

The right bank dam presents a typical homogeneousearthfill section, with a vertical sand filter coupled to adrainage blanket and seated upon a foundationconstituted by residual soil of medium permeability(average k = 6,0 x 10-5 cm/s). The maximum height ofthe dam is 29.00 m.

The dam in the riverbed (Figure 6) presents a typicalsection similar to that previously described, seated upona rock foundation, and has a maximum height of 44.0 m.

The left bank dam, with a typical section similar tothose described, is seated upon residual soil, of lowpermeability ( average k = 1,7 x 10-6 cm/s) and has amaximum height of 22.0 m. In the region of the abutmentwith the structures, the dam will have a typical section ofenfolding connections, comprising rockfill with a claycore.

The cofferdam protecting the execution of the left bank

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Photo 12 - Spillway - Construction of the Concrete Structure

Figure 6 - Earthfill Dam - Cross Section

dam is 580 m in length and has a maximum width at thebase of 54 m, including the rockfill, with an upstreamelevation of 593.00 m and downstream elevation of584.00 m.

Photo 13 depicts the equipment working on the earthfillembankment.

5.5. Transmission LinesThe Retiro Baixo power plant will be linked to the

National Interconnected System (SIN) by a three-phasetransmission line to be constructed with a length ofapproximately 43 km, operating at a voltage of 138 kVand interconnecting the substation of the power plant

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Photo 13 - Equipment Working on the Earthfill Embankment

with the Curvelo II substation, belonging to CEMIG, andlocated in the municipality of Curvelo/MG.

6. CONSTRUCTION

The construction plan, comprising the powerhouse,spillway, earthfill dam (subdivided into left bank, right bankand riverbed), diversion gallery, intake, headrace channel,substation and transmission system, is executed in fourstages, presented as follows.

6.1. Beginning of the WorksExcavations

Excavations are commenced for the powerhouse,spillway, left bank earthfill dam, diversion gallery, intakeand penstocks and of the right bank earthfill dam.

ConcreteWork commences successively with the concrete

placement of the powerhouse, the diversion gallery, theintake and the penstocks.

ErectionAt the end of this stage, erection commences in the

diversion gallery and in the powerhouse.

Earth EmbankmentThe earth embankment jobs commence with the

placement of earth into the embankments of the left bankearthfill dam and the right bank earthfill dam.

6.2. First Stage - Beginning of the secondary jobsfor the river diversion

Figure 7 depicts the original situation of the dam siteand at the end of stage 1.

ExcavationAt the end of this stage the excavations already reach

57% of the powerhouse, 59% of the spillway, 55% of thediversion gallery, and have been concluded in the leftbank earthfill dam, in the intake, the penstocks and inthe right bank earthfill dam.

ConcreteConcrete placement is concluded in the diversion

gallery, and reached 55% in powerhouse, 60% in theintake, 36% in the spillway and 25% in the penstocks.

ErectionThe erection is concluded in the diversion gallery,

advanced to 35% in the penstocks and 25% in thepowerhouse.

Earth EmbankmentThe earth embankment has reached 90% of the left

bank earthfill dam, and 18% of the right bank earthfilldam.

Photos 14, 15 and 16 depict the works of Retiro Baixodam during the first stage. Photo 17 depicts theconstruction site in April 2008.

Figure 7 - Construction Stages - Original Situation and Stage 1

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Photo 17 - Construction Site in April 2008

Photo 16 - Construction of the Intake & Powerhouse(seen from upstream) - April 2008

Photo 14 - Construction of the Powerhouse(seen from downstream) - April 2008

Photo 15 - Excavation of the Spillway (left) and Constructionof the Powerhouse (right) - April 2008

6.3. Second Stage - 1st Phase of the river diversionExcavation

In this stage the excavations are concluded in thediversion gallery, and already reach 60% of thepowerhouse and 62% of the spillway.

ConcreteConcrete placement in the powerhouse reached 59%,

in the intake 66%, in the spillway 41% and in thepenstocks 35%.

ErectionThe erection reached 42% of the penstocks and 30%

of the powerhouse.

Earth EmbankmentThe earth embankment reached 90% in the left bank

earthfill dam, and 24% in the right bank earthfill dam.

6.4. Third Stage - Beginning filling the reservoirFigure 8 depicts the situation of the works at the end

of construction stages 2 and 3.

ExcavationIn this stage the excavations are concluded in the

headrace channel, in the substation and in the earthfill

Figure 8 - Construction Stage 2 and 3

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dam in the riverbed, and have reached 95% in thepowerhouse and the spillway.

ConcreteThe concrete placement is concluded in the

powerhouse, the intake, in the penstocks and in the wingwalls of the headrace channel, and reached 98% of thespillway. The civil works of the substation and of thetransmission system are also concluded.

ErectionThe erection is concluded in the penstocks, the

spillway, in the intake and in the substation, and hasreached 86% in the powerhouse.

The Earth EmbankmentThe earth embankment is concluded along the entire

length of the earthfill dam.

6.5. Fourth Stage - Beginning of the Generation

Figure 9 - Construction Stage 4 - End of Construction

ExcavationIn this stage, the excavations are concluded of the

two restitution channels of the powerhouse and spillway.

ConcreteConcrete placement of the spillway is concluded and

of the plugging of the diversion gallery.

ErectionThe erection in the powerhouse has been concluded.This stage ends with the filling of the reservoir and

the commercial generation in the power plant. Figure 9shows the development finished with the power plant inoperation.

7. INSTRUMENTATION FOR MONITORINGTHE DAM

With the objective of observing the behaviour of the

dam and of its foundation during and after theconstruction, nine sections were chosen for theinstallation of monitoring instruments, of which: four werein the right bank in the earth foundation, one in theriverbed in the rock foundation, and four in the left bankwith its foundation in earth.

The instruments to be installed are basically:• Casagrande Type Piezometer• Magnetic Settlement Meter• Topographical Benchmarks

8. TECHNICAL FEATURES

BasinDrainage Area 11,160 km2

Mean Annual Precipitation 1,380 mmMean Annual Evaporation 1,155 mmLong Term Mean Flow 159.62 m3/s

ReservoirStorage Volume atMaximum Water Level 200.72 x106 m3

Flooded Area at Maximum Water Level 22.58 km2

Length 34 kmAverage Width 0.71 kmMaximum Normal Water Level 616.0 mMaximum Flood Water Level 617.0 m

DamCrest Elevation of the Dam 619.0 mLength of the Earthfill Dam (with clay core) 1,075.9 mMaximum Height of the Dam 44.00 m

DiversionDiversion Gallery inthe Right Bank 2 sections of 6.5 x 3.5 m

TurbineInstalled Power: two turbines of 41 MW 82 MWRated Power Factor 90 %Vertical Shaft Hydraulic Turbines 2 Kaplan TypeRated Flow (per unit) 128.18 m³/sNet Design Head 38.62 mMinimum Operational Head 36.06 m

VolumesCommon Excavation 1,409,400 m3

Rock Excavation 573,912 m3

Spillway Concrete 27,585 m3

Concrete for Intake and Powerhouse/Substation 38,155 m3

Concrete for the Diversion Structures 11,000 m3

Total Volume of Conventional Concrete 64,013 m3

Total Volume of the Earthfill andRockfill Dam (estimated) 2,226,638.00 m3

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9. BIBLIOGRAPHY

[1] Projeto Básico Consolidado - Relatório Final -Volume 1 - Texto - N.º: 1.3.034-AC-1100-RL-1001

[Basic Consolidated Design - Final Report - Volume1 - Text - No. 1.3.034-AC-1100-RL-1001]

[2] Manual de Montagem das Partes Embutidas daTurbina - Nº GEHI TNA060068-Ver. 2.

[Erection Manual of the Turbine Embedded Parts -No. GEHI TNA060068-Ver. 2.]

[3] Aproveitamento Hidroelétrico Retiro Baixo -Relatório Mensal de Progresso - Janeiro 2008 -DCT.C.EP.001.2008

[Retiro Baixo Hydroelectric Development - MonthlyProgress Report - January 2008 - DCT.C.EP.001.2008]

[4] Planejamento Construtivo - RBE - Retiro BaixoEnergética.

[Construction Planning - RBE - Retiro BaixoEnergética].

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