YACYRETA HYDROELECTRIC POWER PLANT

WORKS FOR THE PROTECCION OF THE AGUAPEY STREAM

Introduction

 

The Protection of the Aguapey Stream Basin is one of the main works for the finishing of Yacyreta Reservoir Project. This Project is fundamental since its completion will impede the flooding of vast territories of the Republic of Paraguay thought the elevation of the reservoir storage level to its definitive height of 83 m above sea level.

Main works consist of 64.5 km of land dams which begin in the left margin of the river in Rincon de Santa Maria, cross over the main branch where they reach a maximum height of 43 m. After covering part of Yacyreta Island, cross over Aña Cua branch, then continue through the right margin 25 km, finishing in Paraguay’s San Cosme and Damian cities.

Nearby Damian city is Aguapey Stream, tributary of Parana River, which discharges an average flow of 25 m3 / s over the reservoir at a level of approximately 78 meters.

The Elevation of the Reservoir to its definite storage level of 83 masl would flood Aguapey Stream Valley, generating a sub reservoir of over 450 km2 of which 360 km2 correspond to mainland and wetland, and the remaining 200 km2 corresponding to productive land.

To prevent this situation, Protection Works of Aguapey Stream have been developed consisting of a land dam in the stream mouth to avoid flooding when the reservoir in filled with more than the current storage level and, a drainage channel of 12.5 km long downstream which connects with the collection channel that exists in the dam’s bottom until it reaches the Aña Cua branch.

In this article I will refer to Aguapey I – Aguapey Stream Discharge Channel

 

Aguapey I – Aguapey Stream Discharge Channel

 

The first stage of the construction consisted on a linking channel from Aguapey stream intake position to the station 12+500 in which a junction is made between this one and the channel at the bottom of the dam in order to derive water from the stream to the discharge area in the Aña Cua branch. Construction began in the second part of the year 2005.

The path of the trace was carried out mostly on clay soils, having to go through an important basalt mantle, sandstones and altered rocks between the stations 8+100 and 10+275.

The first excavations in these progressives allowed us to perceive the bedding state of rocky mantles, having as a consequence important alterations that required a demanding and heterogeneous slopes project to meet the safety of all personnel and equipment employed during the process of excavation and also to meet the channel’s medium and long term stability.

For this reason the degree of alteration, the jointing and the RQD of the rock mantle have been entirely analyzed and different sections have been designed to assure proper slope stability.

Due to the alteration of the rock mass, blasting methods were adjusted as regards positioning, separation, depth and drilling load to the effects of making blasting works more efficient.

Taking into account the deep alteration state of the rocks and sandstones present and giving prestige to the integrity of the work in its expected long lifetime, slopes that don’t require injected anchors as a means of support were decided.

 In some cases of deep alteration shotcrete protective paving was done.

Pure soil areas were found with a few little rock outcrops up to the station 8+000.

In almost every section clay soil was found and slopes and lines sections 3H: 1V were design.

In these sections, excavations were done with conventional high performance equipment through traditional methods and intensive dedication.

Slopes protection was done with medium rank rocks up to the berm, which is likely to get into contact with the water flow, and through a vegetable protection and stabilization drainages in superior areas that presented possibility of collapse.

Main data as regards dimensions:

Channel Length: 12.5 km.
Design Flood:   700 m3/ sec
Regular Excavation Volume: 8.640.079 m3
Rock Excavation Volume: 1.863.895 m3
Total Volume of the Excavation: 10.504.000 m3
Channel Maximum Depth:        39.0 m.
Channel Minimum Depth: 8.0 m.
Storage level of the Channel’s Sill: 69.00 masl.

 

The Channel is crossed by many different building works that completed the Project.

One of them is the crossing of the 5B Route in the station 9+400. This route had to be relocated and re-projected and its crossing required a viaduct to bridge the irregularities caused by the channel’s slopes. In the Interjection between the route and the channel a structure was built to control the flow of water.

The viaduct was design with premolded concrete beams that were mounted through the use of launching beams. The total concrete volume was 750 m3.

The central section contains the Channel’s Flow Control Structure, made of four big columns that hold three flat gates set on by hydraulic mechanisms.

These Gates will allow the realization of maintenance procedures downstream.

The Control Structure involved the realization of 2.230 m3 of concrete.

The Channel Crossings are completed by 3 bridges for animal transit and an irrigation bridge with a capacity of 108 m3 to irrigate arable land in Paraguay’s territory.

Aguapey Channel’s Works were successfully completed and in the original deadlines established in December 2007, except for the Irrigation Bridge. Its construction is to be decided by Yacyreta Binational Entity in a near future.

The Final Project, the Inspection, Contract Administration and the Building Work Direction were in charge of the Joint Venture COINTEC-INCONPAR-GCM-ELEPAR-GEIPEX-GCA UTE under the name of ENERYA Consortium.

COINTEC, from The Argentinean Engineering Consultants Chamber (Cámara Argentina de Consultores de Ingeniería) acted as the Argentinean leading company.