Defining the jet-dissipating components of the flood spillway and minimising the risk of downstream scouring: a fundamental factor in ensuring the stability of the dam.
Flood spillway on the Janneh dam - Country: Lebanon - Client: EBML - Scale: 1:80
The planned Janneh dam, featuring a reservoir with a capacity of 38 Mm3 and located in the Janneh valley on the Nahr Ibrahim river, will provide water for drinking, irrigation and hydropower. The dam is a 350 m long concrete arch structure with a height of approximately 157 m above foundation level.
Contribution of the physical model
The scale-model study aims to validate and, if necessary, optimise the operation of the flood spillway (weir, bridge piers, converging chute, ski jump, stilling basin). In particular, the model provides technical answers regarding:
- checking the hydraulic operation of the weir, converging chute and ski jump,
- determining the precise stage/discharge relation of the weir,
- evaluating the energy dissipation parameters and the risk of scouring in the plunge pool at the downstream toe of the dam,
- proposing and testing modifications to the structures to ensure perfect control of energy dissipation.
The first tests did indeed demonstrate that the combination of a converging chute and a downstream plunge pool length limited by constraints imposed by the civil structures, did not allow satisfactory dissipation of the jet from the ski jump.
After a series of iterations, and by making progressive adjustments, the final configuration of the chute and the ski jump was at last confirmed to be effective and robust: it is made up of a shortened chute with respect to the initial design, a series of bucket blocks in an irregular arrangement on the flip bucket, elongated shapes for the bridge piers, and 4 isolated blocks located above the aerator.
An effective, custom-designed solution which could never even have been conceived without the physical model!