Song Loulou Hydroelectric Power Plant

Name of Project:
Song Loulou Hydroelectric Power Plant


Country:
Camerun

Client:
Société Nationale d’Electricité du Cameroun (SONEL)

Construction period:
First Phase: 1976 - 1981 - Expansion: 1984 - 1987

The Song Loulou hydroelectric power plant is located on the most important river in Cameroon, the Sanaga, 55 km upstream of Edea, in the middle of tropical forest but close to major urban centers such as Douala (150 km), Edea, and Yaoundé.
Between the right bank and left bank of the river, the various works that form the reservoir are:

  • Main dam made of earth and rock
  • Secondary dam;
  • Spillway;
  • Intake structure.

The intake structure and the power plant were designed to accommodate and house up to eight generator units; the first phase called for the installation of 4 turbines.

The main dam, which is 328 m long and reaches a maximum height of 20 m, is made of laterite and rock with a core of compacted clay. The embankment volume is 240,000 m³. The rocky foundation layer, which is practically horizontal, was consolidated with concrete and made waterproof with a grout curtain of up to 20 m deep. On the upstream side, a rip-rap of large boulders provides adequate protection against wave movement from the water of the reservoir.

The spillway, measuring 133 m long and 21.50 m high on average, allows excess water to pass. Indeed, it was designed to withstand an exceptional design flooding of 10,000 m³/sec with the plant closed. The spillway consists of seven 14 m-wide openings separated by 4.50-m-thick piles set in rock. The volume of concrete was 76,000 m³. The depth of the grout curtain was 20 m.

A platform poured on the piles allows for driving on the crest over all the dam structures. The openings are equipped with sector gates measuring 14 m wide and 17 m high which are controlled by winches.

The intake structure, which is 240 m long and an average of 27 m high, reaches the left shoulder and connects to the spillway through two transition blocks. Eight identical monolithic buttress blocks measuring 18.5 m and made of reinforced concrete, made impermeable at contact points with joints Waterstop joints, form the intake structure for the eight generator units planned for the plant. The volume of concrete was of 86,500 m³. The uncontrolled intake structures are protected by temporary masonry vaults. The inlet cross-section of 13.5 x 13.5 m. is protected by a grid with its trash rack rake.
The four penstocks are all identical, with a constant circular cross-section of 6.40 m; the total length is 51 m.

The power plant, which is completely separate from the intake and damming structures, is of the conventional type. The spacing between the units is identical to that of the penstocks, i.e., 18.50 m.
In the first phase, the plant facilities were limited to four vertical-axis Francis turbines having a nominal power rating of 49.5 MW each. The dimensions of the power plant are: 109 m long, 33.3 m wide, and 45 m high. Construction of the plant required 83,000 m³ of excavation and 38,000 m³ of concrete.

Upon exiting the plant, the water is returned to the Sanaga River via an outlet channel excavated in rock measuring 1,100 m long, which follows the run of the river's secondary branch.
In the typical cross-section, the width at the base is 23 m while the average crest width is 35 m.
The maximum height is about 25 m. The material removed (670,000 m³) was used to make the aggregate and for the rockfill embankments of the main dam and cofferdams.

The substation is located on the left bank of the outlet channel and was made for the final phase with 8 generator units.

The secondary dam is a concrete structure (12,300 m³) located on the secondary branch of the river, with an uncontrolled spillway; it has an average height of 8.50 m and is 528 m long. In order to access the dam area, 6 km of road on the right bank and 2.5 km of road on the left bank had to be opened, and a 275-m-long bridge had to be built.

The bridge, with a total length of 275 m and five 55-m-long spans, rests on the two shoulders and on four pillars in the riverbed. The pillars are 1.20 m in diameter and rise to a maximum height of 18 m; they are anchored in rock and secured with injected anchors.

 

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Last update: 24/09/2014