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Sedimentation of high mountain reservoirs: physical scale modelling with sand and lightweight plastic mixtures

Abstract:

High mountain reservoirs receive sediments from sources located in watersheds with scarce vegetation cover, especially during highly erosive events. The sediments entering reservoirs in such regions, are typically composed by a mixture of gravels and sands and to a lesser portion silts and clays. The gravel is transported mainly as bed-load and forms a delta in the upstream end of the reservoir, which slowly migrates towards the dam. The sand is mainly transported in suspension and settles in the vecinity of the dam due to the slower flow velocities. Because both sediment fractions cause an important reduction of the reservoir volume through different morphydynamic mechanisms, both needs to be treated differently in physical scale models. As part of two consultancy projects, reservoir sedimentation was analysed through morphodynamic experiments in physical scale models with the goal to reduce the reservoir sedimentation. Therefore, mixtures of natural sediments -sand or gravel - and lightweight plastic materials were used in the models as similar to the real sediments in the prototype cases. Results show that the deposited reservoir volume can be reduced significantly, applying sediment routing techniques which were optimized through the conducted experiments.