Description for La Gogue Dam (Seychelles)

The aims of the assignment are the Design Review and the Supervision of Construction as FIDIC Engineer and Employer’s Representative for the rehabilitation and upgrade of the existing La Gogue dam and the construction of a new water treatment plant for the water supply scheme.

The concept for raising the La Gogue Dam to increase the storage capacity has been under discussion since 1990. Studio Pietrangeli contributed with its remarkable international experience to make it real.

The existing structure, completed in 1979, is a homogeneous earth fill dam with a maximum height of 35 m. The works include the raising of the dam embankment by 6 m with an artificial waterproofing system, which consist in a PVC membrane anchored in a trench excavated in the existing core.

The existing spillway includes a classical free flow sill and a smooth chute located on the right bank. The new optimized layout foresees a side spillway inlet with a channel, a stepped chute and a final stilling basin type II.

The intake tower is located in the left side of the reservoir and by means of a 2 m diameter tunnel crossing the embankment, discharge the water to the Hermitage Treatment Plan. The tower shall be raised in accordance to the new reservoir elevation, while the old footbridge shall be replaced by a new structure in order to ensure access to the intake.

The new water treatment plant, locate downstream the dam, has a capacity of 4’400 m³/day and consists of flocculation and sedimentation, sand filtration, ozone dosing for color and smell removal, and chlorination processes.