Dardanelos

THE DARDANELOS HYDROELECTRICDEVELOPMENT ON THE ARIPUANÃ RIVER

This paper was written by Leonardo Borgatti, Pedro Diamante Miranda, José Piccolli Neto and Maíra Fonseca da Cunha.The figures were made by Pedro Diamante Miranda and Luciano Ouverney. The pictures were taken by Jeovane Alves Cordeiro.

Main Brazilian Dams III

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THE DARDANELOS HYDROELECTRICDEVELOPMENT ON THE ARIPUANÃ RIVER

1. INTRODUCTION

The construction of Dardanelos Dam started inSeptember 2007 and is scheduled to end in October 2010with the commissioning of the last generator unit.

Since this article was written in mid-2008 someaspects of this plant described herein may not as closelyrepresent the as built project.

The owner of the development is Energética Águasda Pedra S/A, Sociedade de Propósito Específico (SPE),which in turn is owned by the companies: Neoenergia,Centrais Elétricas do Norte do Brasil - Eletronorte andthe Companhia Hidro-Elétrica do São Francisco - Chesf.

The powerhouse is located on the left bank of theAripuanã river, by the city of the same name, in thenorthern part of the state of Mato Grosso. Access isthrough the city which is 950 km by land from the capitalof Cuiabá.

The Aripuanã river is part of the Amazon river basinand is 1,110 km long from its headwaters in the NorthMountain Range in the Northwest of the state, to theriver end at the confluence with the Madeira river. Theriver basin covers an area of 146,257 km² and embracesparts of the states of Mato Grosso, Rondônia and theAmazon. In this region the climate is equatorial andvegetation is dense, a characteristic of the Amazonrainforest.

The inventory of the river for hydroelectric developmentwas carried out in 2001 by ANEEL - Agência Nacionalde Energia Elétrica, and FUMEC - Fundação Mineira deEducação e Cultura. These studies covered a 140 kmlength of the Aripuanã river, from the confluence with theBranco river to the Lontra stream.

The inventory studies for Dardanelos' dam were revisedin August 2005, with the purpose of integrating it withthree other hydroelectric developments in the same area- Aripuanã, Faxinal l and Faxinal ll,

The interconnection of Dardanelos with the regionalpower line wasn't changed during the revision, and theconnection with Juína's substation was maintained as itwas the most economical alternative.

To carry out the design, construction and equipmenterection of the development, a turnkey contract forEngineering, Procurement and Construction was signedwith the Dardanelos Construction Consortium.

This consortium consists in the following companies:Odebrecht, IMPSA and PCE, which are responsiblerespectively for the civil works, equipment procurementand erection, and the final design of the project.

2. DESCRIPTION OF THEDEVELOPMENT

The hydroelectric development consists in theconstruction of a dam with a powerhouse to harness thehydraulic energy of the Aripuanã river. The main technicaldata of the development are listed in Table 1.

Ever since the feasibility studies certaincharacteristics of the site area influenced the definitionof the initial layout, of which the main ones were:• The topography of the site along the Aripuanã river,known as the Dardanelos and Andorinhas (Swallows)Falls, where there are falls and rapids with a 100 m drop;• Intense human occupation of the right river bank, whichis in the city of Aripuanã;• The main river leisure areas for the city's inhabitants onthe upstream and downstream side of the rapids andfalls and on the banks of the islands and sandstone riverslabs, where two water parks and infrastructure aresituated;• Strong components of landscape, ecology, scenery andtourist attraction, of rare beauty, characterised by thewaterfalls, rapids, forested islands and jagged rockoutcrops;• The dense vegetation of the Amazon rainforest whichcovers most of the left bank;• Three small operating hydroelectric powerplantscomplete the list and were factors that had to beconsidered with minimum negative impacts.

In all phases of the design, the project layout wasalways guided by these characteristics and conditions,which are the criteria that are being maintained sincethe feasibility studies.

Table 1 - Technical Data of the Development

The concentration of the head difference in the areaand the topography of the upstream part of the rapids ledto the site development in a diversion with a low heightdam that conveys water to the headrace channel and


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finally to the hydraulic circuit.This characteristic with the design of an ungated

overflow spillway allowed the upstream river flow to remainunaltered, in other words, after the construction ofDardanelos dam, the river flow and upstream water levelswill remain constant and equal to the natural river levels,which means there is no reservoir storage.

In relation to the leisure/recreational requirements,the layout allows the optimization of their use all yearround and not only for some months during the dry seasonas was the case before the project.

The layout of the feasibility studies was maintained,and each structure was optimized during the design andconstruction phases.

The excavation works at the beginning of 2009 aredepicted in Photo 1 and in Photo 2.

Photo 2 - Aerial View of the Excavation Works seen from Upstream

Photo 1 - Aerial View of the Excavation Works seen fromDownstream

2.1. LayoutAlong the dam axis there are three residual flow outlet

structures that are to maintain a natural river flowdownstream in different places, independently of thepowerplant of Dardanelos.

The dam starts with the right bank dike of compactedearthfill along the right bank of the Aripuanã river, and curvesat the end towards the river, so that the existing buildingson the riverbank, can be preserved (See Figure 1).

The first river outlet is called the Andorinhas' FallsResidual Flow Structure and is located at a third of thedistance from the beginning of the dike, in a gallerystructure across the dike, with a tower intake and gates,controlling a steady 14 m3/s flow that feeds a channel toAripuanã's powerplant and Andorinhas' Falls. Thismaintains the conditions required by the environmentalstudies for operation of the mini powerplant and the sceniclandscape of the natural falls.

The second river outlet is called the Water ParkResidual Flow Structure and is located near the end ofthe dike in the riverbed, and across it, designed for a2 m3/s residual flow to the municipal water park. This willallow it to be used safely all year round, as now it canonly be used during dry seasons with low river flows ofthe Aripuanã river.

In the layout of the structures there was a concernthat they be visually integrated as much as possible inthe local scenery, minimizing the structures view fromanyplace in the city.

The location of the right bank dike was determinedso as to avoid interference with any urban areas of thecity, including the municipal water park.

This structure was conceived so as to optimize theuse of the area, and maintain an adequate river flow, thatallows the use of the river banks for leisure all year round,which would not be possible without the hydroelectricdevelopment.

At the end of the right dike, and just before the spillway,there is a wall at right angles to the dike, called the WaterPark side wall, and is designed to protect the park fromsharp variations of water levels due to load rejections ofthe powerhouse units.

The next structure is the ungated overflow spillwaywith an overall length of 944.50 m, which crosses theriver and curves downstream on the left bank along theapproach channel, and is part of it's right side. The ogeeelevation and crest length were determined to maintain,as much as possible, the natural river flow. It is designedfor a 10,000 year flood of 2,880 m3/s.

In the spillway section in the riverbed, lower weirs arebuilt into the structure to maintain a downstream flowacross the spillway during dry seasons, guaranteeing aresidual flow to the downstream sandstone slabs in theriverbed all year round, preserving in this way theenvironmental conditions.

Since the overflow sill is low, the sediments can bewashed downstream during high water river flows. In


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Figure 1 - General Layout

addition, the three continuously operating residual outflowstructures are strategically located in the layout to releaseany of the remaining sediments that may be retainedabove the spillway. These devices will insure that theriver flow and sediments along the falls and rapids will bethe same as the natural conditions before the development,preserving environmental, scenic, landscape and touristicconditions.

The approach channel, starts on the left bank at aboutthe middle of the spillway, and incorporates it on the rightside. It is built in a transition between the left bank of theriver and an area of dense vegetation. The channel hasan inflow capacity for power generation and for passingthe design flood. To limit the environmental impact in thearea, the channel width was limited to a minimum size.

The principle of minimizing the size of the structuresin the project area was adopted throughout thedevelopment to reduce unnecessary impacts in a regionwhere the tropical forest predominates.

The third outlet is called the Main Residual FlowStructure, and is located at the end of the approachchannel on the river side. It discharges a 12 m3/s flowstraight into the main riverbed of the Aripuanã river,upstream of the intake of the small hydroelectric station- PCH Faxinal II, which is responsible for the partition ofthe river flow between the falls of Dardanelos andAndorinhas. This maintains the environmental flowrequired by the related studies downstream to Dardanelo'sFalls, and also carries sediments deposited on the riverbeaches.

The bottom of the approach channel conveys the waterthrough a transition and creates hydraulic conditions tocarry sediments to the sand trap of the main residualflow structure. The design of the structure enables it tobe used for constructing a cofferdam for maintenance of

the downstream channel in case it is necessary.On its side the residual flow main structure discharges

the residual flow as established by the environmentalstudies. This flow is discharged straight into the mainriverbed of the Aripuanã river, upstream of the PCH FaxinalII intake structure, which divides the flows betweenDardanelos and Andorinhas Falls flushing the channel,carrying the fine sediment downstream and feeding thelocal beaches with this material.

At the end of the approach channel is the headracechannel that conveys the turbine flow to the forebay. Theleft side of this structure was dug straight into the leftbank and the right side is contained by the right side dike.

The forebay starts at the end of the headrace channeland ends at the intake. The forebay consists in thewidening and deepening of the headrace channel as itapproaches the intake structure and penstocks, and isthe transition between both.

The emergency wheel gates control the flow of theintake, which is provided with stoplogs for maintenance,and trash racks at the entrance. The intake is connectedto the five penstocks, one for each unit.

The powerhouse has five generator units of which fourare rated at 58 MW and the fifth at 29 MW, and is locatedso that the penstocks could be shortened on thedownstream side.

Beside the powerhouse there is the erection andequipment unloading bay. These bays have access tothe site roadway system.

From the downstream wall of the powerhouse, theoutlet electric power lines connect to the substationinstalled on the left bank of the tailrace channel.

The tailrace channel leads back to the Aripuanãriverbed.


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3. GEOLOGY, GEOTECHNICS ANDFOUNDATIONS

3.1. Regional GeologyThe geology of the project area is composed of

cristalline rocks of the Xingu Complex, from the Archaeanera, which is about 2.6 billion years ago (UpperProterozoic) and is represented by volcanic rocks of theUatumã Group and sedimentary rocks of the CaiabisGroup.

The Aripuanã river flows in a south-north directionbefore arriving at the dam site. At this point the river curvessharply eastwards, in the area of the Dardanelos andAndorinhas Falls. After the hydroelectric development theriver returns to a N/NE direction. At this sharp bend ofthe river there is evidence of a NW alignment which isthe main direction of the fault system.

3.2. Geomorfological CharacteristicsThe Aripuanã river is the main drainage axis of the

region, and originates in the Parecis Plateau withelevations around 500 m high, and flows down to theInter-Plateau Depression, crossing the DardanelosPlateau and returning to the depression maintaining thesouth-north direction. Near the Sucurundi MountainRange, the river curves to NW and only then becomes alow plain river. In the rest of the river course it is containedwith rapids, in some places along the river.

The area sub-unit of the Aripuanã basin is called theDardanelos Plateau with an area of 55,300 km2. It is ablock of residual relief with a massive aspect, limited NEby fault scarps, that are part of the edge of a structuralledge with a low slope that can be clearly seen to be inthe SW direction.

3.3. Local Geological - Geotechnical CharacteristicsGeological and geotechnical characteristics were

obtained by site investigations, mainly mapping anddrilling.

The project site is located in a region of sandstonefrom the Dardanelos Formation of the Caiabis Group thatoutcrop or are covered by alluvium and, or colluvium. Thesandstone can be intensely silicified with high strength,which is found in the approach channel area, justupstream from the dam. Towards downstream thesandstone becomes coarser, with a weak cement andless resistant.

Except for the riverbed section and the rock slabs onthe left bank, along the overflow axis, the headrace channeland the hydraulic power circuit, a layer of altered soilsandstone was found that reached 3 m thick, was spongyon the surface and more compact in depth and had a lowto high permeability.

A geological feature that was given special attentionduring the design was the existence of subhorizontallayers of clay (pelites) with low shear strengths. These

layers were noticed in various places, at different depthsand thicknesses.

3.4. Construction MaterialsThe investigations to find construction materials near

the site were carried out considering the various materialsfound, the distances to the structures and the availablevolumes.

Rock materials for construction are obtained from theexcavations of the initial stretch of the approach channelrock foundation, which is composed of silicifiedsandstone. Results of laboratory tests of this materialshowed that it was adequate for construction purposesof the dam.

The investigations for earth materials was done onaltered soils of sandstone and dacite. For sands researchwas done on alluvium deposits, and hand augers wereused for laboratory sampling and determining thethicknesses of earth layers.

Four borrow areas were investigated of which onlyone was used. This area was located near the upstreamside of the approach channel and was the main sourcefor earth construction materials of the dam. The superficiallayer had an average thickness of 2 m and was composedof sandy silty clay colluvium, with medium plasticity andwas found to be adequate for earthfill construction. Thevolume of the material was estimated in 260,000 m3.Below the layer of colluvium there was altered sandstonesoil with similar grain size distribution and physicalcharacteristics, which was also adequate for constructionpurposes.

The sources for sand were located in the Aripuanãriverbed, downstream from the dam, but the volume wasinsufficient and other sources had to be found on theupstream side of the dam.

4. HYDROLOGY, HYDRAULICS ANDENERGY STUDIES

4.1. Physiographic and Hydro-meteorologicalStudies

The main basin characteristics of the Aripuanã river,considering both the whole basin and at the Dardanelos'dam site, are listed in Table 2.

4.2. ClimateThe climate in the region of the Aripuanã river basin,

according to Köeppen's classfication, can be defined astype AW - hot and humid as monsoonic, with a rainysummer and dry winter, with a predomination of a sub-domain of humid climate with three months of no rain(NIMER 1979), based on Gaussen and Bagnouls'sformula(1953), that considers a dry month the one inwhich the total amount of precipitation in mm doesn'texceed twice the mean monthly temperature in degreescentigrade.


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Table 2 - Main Characteristics of the Aripuanã River Basin

4.3. PrecipitationTo characterize the regimen of precipitation, of the

Aripuanã river basin, there are some observations to bemade:• There is a great homogeneity in the region, with yearlyprecipitation values varying between 1,899 and 2,038 mm;• The rainy season is concentrated between Novemberand March, with a rainier three month period in the monthseither from December to February or January to March,depending on the latitude, according to the regionaltendency;• The dry season starts in April and goes on to October,with the driest months in the June to August trimester;• The yearly distribution of rainy days is very regular.On average, in the wettest three month period, there areabout 45% of rainy days. The other 55% of rainy daysare distributed in the other months, and in a lesser degreein the June to August trimester with only 4%.

4.4. TemperatureThe mean annual temperature in the region is 25,2°C,

with extreme values of 27,7°C and 24°C. The coldestthree month period is from May to July, and the hottestis between February and April.

4.5. Humidity• The extreme mean annual humidity values vary betweenmaximums of around 83% and minimums which are above61%.• The minimum values occur in the three month period ofJuly to September, and the maximums from January toMarch.• The mean humidity is 73%.

4.6. EvaporationThe mean yearly evaporation in the basin is about

1,214 mm, and the maximum monthly mean is 181 mmin August, and the minimum is 60 mm in February.

4.7. Fluvial RegimeThe Aripunã river is characterized by periods of floods

and droughts that are very well defined. On average the

river starts rising during the month of October reaching amaximum in February to April and falling until September.

Near the development, the three month period withthe greatest river flow is February to April. The mostfrequent monthly maximums are in March (65%), followedby April (23%) and February (12%). The least flow isfrom August to October, with September as the mostfrequent month.

The mean recorded river flow (1979 to 2004) was322 m³/s, with a mean specific flow of 21.5 l/s/km2. Themaximum daily discharge was 1,482 m³/s on April 7th1994 and the minimum was 9.08 m³/s on October6th 1998.

There is a large variation in the flow of the Aripuanãriver due to the geological and topographical features ofthe basin, which if on one hand allows a fast dischargeof precipitation surges, on the other, makes groundinfiltration become more difficult, and with less retentionreduces river flow during the dry seasons.

Hydrological studies for the 10,000 year flood reacheda river flow value of 2,880 m3/s, and a 10 year return of aminimum weekly average was 14.8 m3/s.

4.8. Hydraulic StudiesDardanelos is a run-of-river powerplant with only a

headpond and no reservoir, and the level is controlled byan ungated overflow spillway at El. 213.5 with adischarge capacity larger than the natural river flow. Asa result no studies were carried out for impoundingthe reservoir, routing of the design flood and freeboard.

Studies of the headpond were made to check theinfluence of the overflow spillway on the upstream waterlevels. The results showed that instead of lower upstreamlevels that are normally expected, the previous conditionsof the river would be maintained after the dam was inplace, and can be explained by the greater dischargecapacity of the overflow spillway than the natural riverflow.

Studies showed that no sediment deposits werenoticed upstream which shows the reduced transportcapacity of the Aripuanã river near the falls. Below thefalls, small sand deposits occurred. In the area wherethe discharge channel was to be implanted, there was acommercial sand exploration.

The overflow spillway is a little more efficient than thenatural flow and results in a small increase in thesediment transport capacity upstream. If in the previouscondition no sediment deposits were observed, with thedevelopment this tendency will increased, because ofthe hydraulic characteristics of the layout.

As mentioned before, the layout includes threehydraulic structures that are to maintain the waterpassages constantly open, to make sure the residualflow discharges downstream to Andorinhas' Falls, theWater Park and Dardanelos' Falls (main residualdischarge structure by the headrace channel sill). Thesestructures are located along the right bank dike axis/


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overflow spillway and together with the overflow spillwaywill wash retained sediments downstream.

4.9. Energy and Economical StudiesThe conclusions of the feasibility studies are the

following:• Due to environmental limitations, the Maximum NormalUpstream Water Level was defined as El. 213.5.• Due to the low water depth upstream and small volume,the powerplant was considered operating as run of river.• It was recommended The installation of four generatorunits of 58 MW and one of 29 MW, with a total installedcapacity of 261 MW.• With the its final configuration Dardanelos HydroelectricPowerplant will add 138.61 MW mean (gross) of firmenergy.• The studies recommended the values of 95.6 and97.6 m as the reference and design head.• Based on the results of these studies, the energyproduced by the powerplants of MCH Aripuanã (MiniCentral Hidrelétrica i.e. Mini HPP), PCH Faxinal l andPCH Faxinal Il (Pequena Central Hidrelétrica i.e. SmallHPP), before the operation of Dardanelos HPP, wasapproximately equal to their maximum availability. Withthe construction of Dardanelos (261 MW) and consideringthe priority of this powerplant, power generation by thethree older plants will be reduced. But so as not topenalize them, these plants will be compensated by thenew development, maintaining their original contracts forconcessions of power generation.

The priority to generate power at Dardanelos HPP ismore favorable for the National Power System, as it usesthe hydraulic power of the river in a more efficient wayand is more productive than these small plants. If prioritywere given to the three other plants, MCH Aripuanã, PCHFaxinal ll and PCH Faxinal l, as specified in theircontracts, it would mean a loss of power generation.

5. MAIN STRUCTURES

5.1. River Diversion and CofferdamsThe diversion of the Aripuanã river was made in two

stages, due to the layout of various groups of structures,as can be seen in Figure 2.

The first group, includes the approach channel, mostof the overflow spillway, the sill of the headrace channeland the main residual flow structure and its channel, andare all being built after the construction of the 1st stagecofferdam.

The second group includes the rest of the overflowspillway, the water park residual flow structure, the waterpark side walls and the Andorinhas Falls residual flowstructure and will all be built after construction of the2nd stage cofferdam.

A third group of structures were built on dry land, anddid not depend on the construction of the cofferdams.They were: the right bank dike, the intake channel, theside dike, the forebay, the penstock support blocks andthe powerhouse hydraulic circuit, erection bay area,tailrace channel and substation.

Figure 2 - Diversion Works


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5.2. Approach ChannelThe approach channel, that can be seen in Figure 3,

was designed to convey the flow to the turbines for powergeneration and through the spillway overflow structureon the right side.

The channel conveys the power flow straight to thesill of the intake channel, and is about 850 m long and70 m wide at the bottom in most of its length, but starts175 m wide at the channel entrance. The design of thechannel considered various operating conditions of thedam and minimized head loss along the structure.

Due to the geological - geotechnical characteristicsof the approach channel area, the wall excavations onboth sides have slopes conformed to the rock qualities.

The bottom of the approach channel is excavated inhard sandstone rock. The right side of the channel at thelower part is excavated and the upper part is the concreteoverflow spillway, with its foundation on hard sandstone.The left side of the channel is partly excavated in naturalterrain: arcose sandstone at the lower level and soil higherup (alluvium at the upstream section and colluvium/alteredsoil in the middle and downstream section).

The surface of the approach channel bottom is treatedwith a 15 cm slush grouting layer.

The left wall section excavated in rock is treated withgunite where necessary.

Pelite and friable sandstone surface areas are treatedwith slush grouting, gunite, anchor bolts and drains,wherever required.

Close to the overflow spillway, decomposed areas orcavities on the downstream steps associated to lowresistance layers, are being treated in a selective andadequate way to avoid regressive erosions that couldaffect the stability of the concrete structure.

5.3. Headrace Channel and Side DikeThe headrace channel starts after the approach

channel and ends at the forebay, as seen in Figure 4.The channel bottom sill is at El. 209.5 with a sharp

transition to El. 206 and reaches El. 204 at the forebay.It is 724 m long with a trapezoidal cross section with abase of 21.2 m and side slopes of 1.0V:1.5H in soil and1.0V:1.0H in rock.

The right side of the channel is confined by the sidedike. This dike with a length of 890 m starts at theabutment wall by the intake sill, and ends at the forebay.It is built with compacted materials, is 6.0 m wide at thecrest, at El. 218 and external slopes of 1.0V:1.5H. Thedike material is compacted random, excavated for thestructures.

5.4. ForebayThe main purpose of the forebay is to maintain the

water level above the intake entrance under normaloperating conditions and during hydraulic transients, dueto rapid load changes or load rejection and inception onall the full rate opening and closing of the turbine wicketgates. The design studies led to a reduction of the

Figure 3 - Approach Channel

Figure 4 - Headrace Channel, Approach Channel and Forebay


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penstocks length, and an alternative without a surgechamber.

For the construction of the forebay, the excavationsremoved surface soil, colluvium and weatheredsandstone, soft arcose sandstone and, at lower depthshard sandstone rock.

The structures on the sides of the forebay have theircrests at El. 218.00 m.

5.5. Right Bank DikeThis dike starts on the right bank of the Aripuanã river,

and ends at the water park, as can be seen in Figure 1.Along the dike there are two residual flow gallery

structures, Andorinhas Falls and the water park whichare shown in Figure 5 and 6.

The dike cross section is of homogeneous compactedsoil. The upstream slope is protected with layers oftransition and rip-rap of sound rock. For the dikeconstruction all alluvium soil on the foundation is beingexcavated, which is about 1 to 2 m thick.

The site construction materials - soils and sand - forthe dike construction come from the borrow areas and

Figure 5 - Andorinhas Falls Residual Flow Structure

Figure 6 - Oasis Water Park Residual Flow Structure

natural deposits. The rock materials - transitions androckfill - are obtained from the excavations of thestructures.

5.6. Concrete Structures5.6.1. Andorinhas' Falls Residual Flow Structure

This residual flow structure is made of reinforcedconcrete with a tower intake and a gallery that connectsthe headpond upstream to Andorinhas Falls,downstream. There are two gates to control the flow.See Figure 5.

The purpose of the structure is to maintain a continuousflow at Andorinhas Falls, as a scenic attraction.

The gallery has a length of 23 m with a rectangularhydraulic section 3.4 m wide and 2.0 m high and is locatedacross the right bank dike. The tower structure is 7.1 mlong, 2.65 m wide and 6.8 m high from the gate sill.

The structure's foundation is at El. 210.4, on hardsilicified arcose sandstone, and for surface treatment,only cleaning of the foundation is necessary.

The crest is wide enough for the gate installation andoperation, and the access for operation and maintenanceis through the crest of the side dike of the intake channel.

The design flow of the structure is 12.0 m³/s.

5.6.2. Water Park Residual Flow StructureThis residual flow structure is the same as at

Andorinhas' Falls, and is located across the right bankdike to ease the construction, as can be seen inFigure 6. The purpose of the structure is to maintain acontinuous flow of 2,0 m³/s to the water park.

The structure is founded on arcose sandstone atEl. 210.9.

5.6.3. Ungated Overflow SpillwayThe spillway is an ungated overflow gravity structure,

built of mass concrete, and lies across the river in theinitial section, then curves downstream parallel to theriverbed on the left bank up to the headrace channel sill,as can be seen in Figure 1.

In the section parallel to the river, the structure is partof the right side of the approach channel.

The basic characteristics of the overflow spillway are(see Figure 3):• Crest elevation: 213.50• Maximum height: 2.0 m• Total length: 944.50 m• Energy dissipation: In the riverbed• Design flood: 2,880 m³/s (10,000 year flood)

The maximum headpond elevation for the design floodis El. 215.3, in the area near the headrace channel sill.

The hydraulic design of the spillway, resulted in acrest elevation and overflow length which restricts theriver flow, in a very similar way as the natural river flowconditions existing before the construction of Dardaneloshydroelectric development.

The design of the crest considered a layout favorable


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for construction, without reducing hydraulic efficiency.As the foundation rock is of good quality, no special

treatment is necessary for the rock surface.

5.6.4. Headrace Channel SillThe headrace channel sill is a structure located at

the end of the approach channel. The main purpose is toallow the channel to be dewatered for eventualmaintenance, by being able to support a cofferdamdumped across it, in the channel.

It is a reinforced concrete structure, 39 m long andabout 12 m wide.

The structure also has the purpose of allowingsediments, carried through the approach channel, to beeasily cleared away by the sand trap of the main residualflow structure.

5.6.5. Main Residual Flow StructureThe main residual flow structure, located by the

headrace channel sill, is a gravity structure (seeFigure 7), with a purpose to maintain a constantenvironmental flow downstream, in addition to the flow

Figure 7 - Main Residual Flow Structure

that is necessary for power generation of PCH Faxinal II.The gates to control the flow and stoplogs for

maintenance are operated from the crest of the structure.The design allows a continuous flow of 8.0 m³ /s.

The main residual flow structure is 9.0 m long,6.35 m wide at the base and a maximum height of 9.5.The intake has four square sluiceways 1.0 x 1.0 m eachwith slots for stoplogs.

For construction of the concrete structure the surfacecolluvium and altered sandstone will be removed abovethe rock surface. In general the foundation sandstonerock is very hard.

The structure also has a sand trap.

5.6.6. IntakeThe intake, shown in Figure 8, is a structure that

conveys the flow from the forebay to the penstocks. Thestructure has trash racks and emergency gates, and is34 m long, 34 m wide and a maximum height of 17.2 mup to the gate sills.

The crest is at El. 218 where there is a gantry cranefor stoplog operation and maintenance of the trash racks.

The intake has five separate channels separated byconcrete walls. The top transition is an ellipse arc,between the entrance near the trash racks up to the gateslots.

Figure 8 - Intake


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The structure is made of two independent concreteblocks founded on hard sandstone reached after removingsoil, colluvium and weathered sandstone. The foundationtreatment involves conventional surface treatment andgrouting: consolidation and grout curtain.

5.6.7. Penstocks - Support Saddles and AnchorBlocks

The five penstocks are located downstream from theintake, as shown in Figure 9. They are made ofSAR-50A steel, and four are 4.2 m in diameter and one3.2 m.

Each penstock is connected to one turbine generatorunit. The diameters were determined consideringeconomical and mainly operating conditions of the powerunits, i.e. the turbine regulation and efficiency.

With the rated design flows, the velocity in thepenstocks is 4.85 m/s in the 4.2 m diameters and4.22 m/s in the 3.2 m diameter.

Figure 9 - Penstocks, Support Saddles and Anchor Blocks

For installing the penstocks, excavations are to becarried out in soil and medium rock. The saddle supportblocks may be founded on medium sandstone rock, andthe upper soils removed (colluvium with some rock blocks,altered and friable sandstone) with an overall thicknessbetween 3 and 5 m. The anchor blocks are to be foundedon hard sandstone with the removal of the top soils andmedium sandstone that are 6 to 10 m thick.

Photo 4 shows the erection of the penstocks.

5.6.8. Powerhouse and Tailrace ChannelThe powerhouse and tailrace channel can be seen in

Figure 10 and 11.Due to hydraulic transient conditions, in case of load

rejection, and to avoid the necessity of constructing asurge chamber, No subsurface treatment is necessaryfor the foundation, only conventional treatment for therock surface.

Excavations in sandstone require some rockstabilization treatment with anchoring of blocks. For

Photo 4 - Erection of the Penstocks

Photo 3 - The Intake Structure during Construction


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Figure 10 - Powerhouse Plan

Figure 11 - Powerhouse Section

exposed slope surfaces in soil, final protection is withvegetation and plants, and gunite for rock surfaces withsurface drains. The permanently exposed excavatedsurfaces will have a superficial drainage system.

For the upstream section (about 60 m) of the tailrace

channel, the same materials as the powerhouse are tobe excavated. From there on and up to the Aripuanã river,excavations are in 1 to 4 m thick alluvium soil on theupper part, followed by mainly medium sandstonebetween 5 to 10 m thick. Near the bottom of the channelthere is some hard sandstone and altered to hard riolite.

The geometry of the channel slopes are 1V:0.1H inrock and 1V:2H in colluvium and alluvium soil.

For excavations of the tailrace channel dewatering isnecessary. The end section excavation by the river isbeing carried out under water.

On the right side of the tailrace channel a protectiondike is located with the purpose of preventing the Aripuanãriver from (during floods) spilling over the right channelslope, and also to assure that the downstream waterdesign levels are maintained for power operation.

For stability, the design considers the maximumdownstream water level acting on the entire structure.And the cases analyzed were floating with total uplift,overturning and sliding, with water and lateral soilpressure loads.

There are five independent reinforced concrete blocksin the powerhouse structure separated by contractionjoints. The blocks are 14.0 m wide for units 1 to 4 (axis 2to 6) and 15.5 m wide for unit 5 (axis 1 to 2) and weredetermined by the size of the scroll cases, the draft tubes,the outside diameter of the generators and therequirement of sufficient space between units for accessof equipment to the galleries.


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The electro-mechanical equipment galleries arelocated on the downstream side. Above the galleries atEl. 125.35 is the transformer deck where the high voltagepower lines lead to the portal beam, downstream fromthe powerhouse.

The monorail winch is also located on the transformerdeck, and is used for operating the draft tube stoplogs.

There is an overhead traveling crane in the powerhouserated for the heaviest piece of equipment which is thegenerator rotor. The erection and loading bays are atEl. 125.35, and can be reached by the powerhouse crane.

The powerhouse is a reinforced concrete structure.The second stage concrete is used to anchor theembedded parts such as the spiral case and the steelliner of the draft tube.

The following areas are located on the upstream sideof El. 125.35: offices, communication room, canteen,dress room, battery room, emergency generator room.The control room is located in the powerhouse atEl. 118.87.

Photo 5 depicts the powerhouse during construction.

6. CONSTRUCTION

6.1. Construction Site and Industrial InstallationsThe existing road accesses to the job site from the

city of Aripuanã were improved to be able to withstandthe increased traffic and load conditions duringconstruction. Additionally new accesses were built insidethe site to every work front, such as one along theheadrace channel and an interconnection between theintake and powerhouse.

As the construction site has a number of differentfronts and engineering works, two main jobsites wereorganized as site 1 upstream, and 2 downstream.

Site 1 is located on the left bank of the Aripuanã river,in an area that used to belong to a farm named FazendaDardanelos, and already had an access road to the city.Two types of buildings/installations are at this site.

The first group of buildings at site 1 is the living quartersand administrative buildings of the constructionconsortium.

The second group of buildings at site 1, which is alsoin Fazenda Dardanelos, near the main accesses, havethe following installations: machine shop and storehouse,tire mender/lubricating station/vehicle wash, vehicle loadbalance, fuel station, soil and concrete laboratories, rockcrusher plant, concrete plant, cement deposit and asubstation.

Site 2 which is located downstream from the tailracechannel, near the project substation, has a group ofbuildings that are used as support for the civil constructionand erection equipment of the intake, penstocks,powerhouse, substation and tailrace channel.

Site 2's main installation components are: rebar shop,carpentry shop, site offices, electro-mechanical deposit,electro-mechanical storage yard.

Photo 5 - Powerhouse during Construction

A warehouse for blasting explosives and accessoriesis located in an area near the side access of the intakechannel. The building conforms to all rules and regulationsfor explosives in civil construction works.

6.2. Water and Wastewater Infrastructure at theJobsite

To determine the source of water for use andconsumption, and the size of water treatment plants,various tests were carried out from different places to


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establish patterns of potability. For each case appropriatetreatments were adopted. According to federal healthregulations, all potable water is regularly monitored.

Domestic wastewater is treated in stabilization ponds,that have racks, sand boxes, a facultative pond and anaeration pond. Industrial effluents from the machine shop,car wash and fuel station are treated in tanks with sandboxes and oil separation compartments. Effluents fromconcrete and crusher plants, truck washers and concretemixers are treated in sedimentation ponds. The effluentsare periodically monitored to check emission standards.

6.3. Power Supply to the Construction SiteElectric power for the jobsite, living quarters and all

construction work fronts is furnished by CEMAT (CentraisElétricas do Mato Grosso - Mato Grosso State PowerAuthority) through a branch of the 34.5 kV electricaldistribution network, that starts at the PCH Faxinalsubstation and ends at the construction site substation.There the voltage is reduced to 13.8 kV and distributedto strategic points for use at the site. At the site there isalso an automatic emergency generator powerplant incase of power failure, rated at 2500 kVA.

6.4. Planning and ConstructionThe site works are all spread in groups, from the

approach channel to the tailrace channel, which is at adistance of about 3 km further downstream.

Construction is planned to last 38 months.Commercial operation of the 1st unit is to start after30 months of initial construction.

Construction was preceded by the site mobilizationand support works, such as delimiting the sites, buildingliving quarters and industrial installations. This periodlasted seven months.

Considering the diversity of the type of works to becarried out and the distances involved, the civil workswere divided in main work fronts, determined by access,type of work, planning, use of resources, and accordingto the following list:

First Front: In this front work is to be carried out inthe intake channel, side dike and forebay, including soiland rock excavations, foundation treatment, rockfill andfinal treatments as needed.

In this front, and after excavations for the forebay andfirst stage for the penstocks, on the higher section,construction and erection of the intake and side wallswill take place.

Second Front: This front includes work on the residualflow structure of Andorinhas' Falls and the right bank dike.

Third Front: This front will excavate and pour concretefor the approach channel, the overflow spillway, the mainresidual discharge structure and abutment wall, which ispart of the 1st stage river diversion.

Fourth Front: This front includes work on thepenstocks, the powerhouse and tailrace channel, andincludes excavations in soil and rock, foundation

treatment, pouring of concrete and erection, slopetreatments, construction of the protection dike of thetailrace channel and construction and erection of thepowerhouse substation.

Fifth Front: This front will start after the 2nd stage riverdiversion, and includes the remaining work of the spillwayand the finishing of the remaining residual flow structureand the side wall of Oásis water park.

These main work fronts will be followed by a final stagefor concluding the erection of the electro-mechanicalequipment, finishing of civil works, demobilization oftemporary support installations and environmentallyrecovering the work areas apart from personnel andequipment demobilization.

Construction work on the structures is distributed tobalance the volumes of excavation, earth and rockfillduring the dry seasons, so that the schedule targetsand balancing of the various construction materials canbe met.

The planning of the construction works was done sothat the compacted materials for the dikes and channelslope protections can be used from the excavations thatare necessary for the structures. But even so, some earthmaterials are being sourced at borrow areas for the dikes.

6.5. Balancing Construction MaterialsBecause of the size of the intake circuit structures,

which include the approach channel, the headracechanneland forebay, that connect the head pond withthe tailrace channel downstream from the powerhouse,a large quantity of soil and rock will be generated at thenecessary excavation fronts for the structures, and partwill be used in the dikes, dam shells, aggregate forconcrete, roads, etc.

For stockpiling these materials, areas are to beestablished for use at the work fronts and also for wastematerials. All the excavated materials are to be obtained,as far as possible, inside the area of influence of thejobsite.

Due to the great volume of soil produced in theexcavation work fronts at the jobsite, the use of materialfrom the borrow areas is to be reduced. Only for theconstruction of the side dikes of the headrace channelandthe right bank and for the earthfill for the forebay, intake,substation and powerhouse it is necessary to exploresoils in borrow areas.

Construction sand is obtained by dredging the riverbed in areas by the jobsite and/or on the banks of theriver. These areas have been previously studied. Artificialsand is also being used from the rock crushers and fromthe processing of rock materials for concrete andtransitions for the dikes and channels.

Rock materials for production of rockfill, aggregatefor concrete and transitions are obtained from theexcavation of the initial section of the approach channel,where there is a source of siliceous sandstone.


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7. ENVIRONMENTAL, SOCIAL ANDECONOMICAL ASPECTS

The planning, construction and operation of the projectwere conceived to benefit the region socially,economically and environmentally.

The main social and economical aspects of the supportprograms for the social organization goals, that favorsustainable economical and social development, in themunicipality of Aripuanã, is to create and improvestructures that will be able to act with the newopportunities that arise with the project development.

The participation of the community in the variousstages of the project is motivated by a communicationchannel between the entrepreneur and society, resultingin participative educational actions to capacitate/qualifydifferent social sectors.

The main objective of support in the elaboration theMunicipal Director Plan is to collaborate in defining policiesof planning and territorial administration, guaranteeingthe populations' necessities related to quality of life, socialjustice and development of economical activities. Infurther support of the municipality, help is being done toreinforce management with some institutional instrumentsto face the period when transformations will be fast,because of the construction of Dardanelos powerplantproject. The infrastructure assistance to the municipaltechnical-administrative secretaryships will allow theimplementation of strategic actions by government, andprepare the managers to answer to probable additionaldemands with the project.

Even though the project has no interference withindigenous populations, there is a program to supportFUNAI (The National Indian Foundation) and FUNASA(The National Indian Health Foundation) in the work thatthey are doing in the region. The intention therefore is toreinforce, as collaboration, the plans of these foundations.

The support of basic education is to help face demandsdue to increase of the municipality population.Environmental impacts on the health of the population ofAripunã are being monitored, controlled and avoided.Local activities such as tourism, leisure and culture arealso promoted through specific programs to enhancequality, and integrate the natural attractions anddiversities with the existing infrastructure.

As a solution to help develop the local economy, somemeasures are being taken with the federal and stategovernments to obtain incentives for agriculture and cattleraising, considered the natural vocations in the region,and also of the local markets and the social-cultural profileof the small producers. With these actions, apart fromsatisfying local demand due to increased population anddevelopment because of the project, it will also avoidrural migration to Aripuanã.

Directions were established to orient technical workby construction and erection firms to avoid or reduce

impacts that can degrade public equipment andinfrastructure, and natural areas (vegetation, rivers,conservation areas, among others).

Before construction work started at the jobsite, severalinvestigations and evaluations in the region were carriedout, such as: limnological monitoring and river waterquality tests; geological and spelaean investigations;forest/flora inventory; macrophyte monitoring; seedcollection of forest plants and epiphyte (orchids andbromelias) and implantation of greenhouses/nurseries;monitoring and rescue of fauna; survey and recovery ofarchaeological artifacts. These studies have the purposeof getting to know the local biodiversity, resulting inactions to reduce the impact of the dam project, andacting in an environmentally responsible way.

Before the eradication of the vegetation and forests,work was done to recover epiphytes which were taken togreenhouses for study and species preservation. The florapreservation program started in June 2006.

A plan was worked out so that the compliance withall legal requirements would be completed while the forestwas being eradicated. During all deforestation there wasa constant supervision to minimize actions that couldaffect the environment. Due to these and other alterationscaused by the project, both in the physical and bioticfields, apart from the already degraded aspect of theregion, programs for recovery and environmental controlof the area were created.

The program for monitoring the avifauna consists ofthree big activities: monitoring swallows that live in thefalls, monitoring migratory birds, especially kingfishers,and monitoring birds in the forest. The two first activitiesstarted in September 2006 and are already producingresults and interaction with the population that live in theregion.

The program for monitoring the herpeto-fauna startedin February 2005 and had the purpose of continuing theinventory of amphibious animals and reptile species thatlive in rock habitats and ecosystems, and to obtaininformation that will permit dealing with and conservationof these species as well as other programs related tothe environment.

With the necessity of knowing in details the fish thatlive around the rocks in the river area of the project, aprogram was started to monitor the ichthyo-fauna in June2006. Reports are being elaborated about the behavior offish during various periods of the year, to find out howthey use the rock habitats and the reproduction of thespecies. This has also helped in the regulation of fishingactivities in the municipality.

8. DAM INSTRUMENTATION ANDMONITORING

The project is in the initial construction stage, andthe instruments for monitoring the structural behavior have


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still not been installed. Because of the configuration, therun of river powerplant with no high dam and reservoir,the only planned geotechnical instruments areCasagrande piezometers and bench marks to controlthe intake side dike settlements. In the concretestructures the installation of thermometers or thermo-couples is being planned to check concrete temperaturevariations.

9. TECHNICAL FEATURES

GeneralLocalization Aripuanã-Mato Grosso, MT

Long. 59°27'51" W - Lat. 10º09'48" S

PowerplantStart of Construction 2007Completion 2010Owner Energética Águas da Pedra S/AFinal Design PCE - Projetos e Consultorias de

Engenharia Ltda.Construction Construtora Norberto Odebrecht S/A.Electro-Mechanical Equipment Indústrias

Metalúrgicas Pescarmona S.A.I.C. y F.230 kV Transmission Line Tabocas

Participações Empreendimentos S/A.

Basic DataHydrographic basin area 146,257 km2

Annual mean precipitation 1,920 mmAnnual mean temperature 25 °C

Reservoir/HeadpondSurface area at maximum normal elevation 0.24 km2

Total volume 0.12 x 106 m3

Active volume 0.12 x 106 m3

Maximum Normal Level 213.50 mMaximum Flood Level 215.30 mMinimum normal level 213.50 m

Tailrace ChannelMaximum Normal Level 114.34 mMaximum Flood Level 124.35 mMinimum Normal Level 112.80 m

FlowsMean inflow 318 m3/sMaximum recorded inflow 1,482.00 m3/sMinimum daily average 9.08 m3/sMaximum diversion flow and recurrence 1,845 m3/s

Tr = 50 yearsDesign flood - 10,000 year 2,880 m3/s

SpillwayType Free Overflow SurfaceLength 944.50 mCapacity 2,880 m3/sMaximum specific discharge 3.31 m3/s/m

IntakeType GravityLength 34.00 mMaximum height 13.80 m

Intake GatesType Stoplogs and Wheeled GateQuantity 5 eachDimensionsWidth 4 x 4.20 m + 1 x 3.20 mHeight 4 x 4.20 m + 1 x 3.20 mManufacturer IMPSA

DiversionType ChannelDiversion structureHeight 2.50 mLength 2.5 m

PenstocksType Steel (SAR-50A)Quantity 5Inside Diameter 4 x 4.20 + 1 x 3.20 mLength 430 m (mean)Manufacturer IMPSA

PowerhouseType IndoorHeight 37.8 mLength 109.0 mCapacity 261 MW

TurbineType Francis Vertical AxisNumber of units 5Rated capacity 4 x 58.88 MW and 1 x 29.59 MWRated head 95.6 mMaximum unit discharge

4 x 67.22 m3/s e 1 x 33.96 m3/sRated Velocity 4,85 m/s & 4,22 m/sManufacturer IMPSA

GeneratorsType Vertical Axis, Synchronous, Three PhaseNominal rating 4 x 61.00 MVA + 1 x 30.50 MVAVoltage 13.8 kVFrequency 60 HzSpeed 276.90 / 400.00 r.p.m.Manufacturer IMPSA


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High Voltage TransformersQuantity 5Type 3 PhaseNominal rating 4 x 61.0 MVA + 1 x 30.5 MVAVoltage 13.8 kV x 230 kV (+/- 2 x 2,5%)Manufacturer WEG

QuantitiesSoil excavation 691,000 m3

Rock excavation 985,000 m3

Compacted clay 140,000 m3

Rockfill 41,000 m3

Concrete 84,000 m3 (conventional and gunite)Rebars 4,200 t

10. BIBLIOGRAPHY

[1] CONSTRUTORA NORBERTO ODEBRECHT S.A.et al. Projeto Básico do AHE Dardanelos - Volume I.Cuiabá: 2007.

[2] CONSTRUTORA NORBERTO ODEBRECHT S.A.et al. Relatório Mensal de Progresso - Novembro/2007.Aripuanã: 2007.

[3] ENERGÉTICA ÁGUAS DA PEDRA S.A.Energética Águas da Pedra Informativo - Volume I.Cuiabá: 2007.

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