On many rivers worldwide, water reservoirs are in operation for multiple purposes. Due to sedimentation, the storage volumes reduce if no countermeasures are taken. Sediment bypass tunnels (SBTs) are an effective countermeasure. They divert sediment-laden water around the dam and allow for re-establishing the natural sediment continuity. However, high-speed sediment-laden flows in SBTs can cause severe invert abrasion, which may reduce their cost-effectiveness and endanger the sustainable use of water and energy supply. Abrasion prediction is essential for design life estimations, selection of adequate lining materials and cost-effectiveness analyses. This project aims at calibrating and enhancing abrasion models. As a prerequisite, sediment transport, hydraulics and hydroabrasion are monitored at three Swiss SBTs. The findings of the present pilot project will contribute to optimization of design and operation of SBTs as well as other hydraulic structures facing hydroabrasion.

Abrasion extended to steel beams initially embedded in concrete at the Val d’Ambra SBT (Photo: Azienda Elettrica Ticinese)