Page - 1034 - in Book of Full Papers - Symposium Hydro Engineering

using a movable bed. With such non-cohesive material good predictive results are expected for the scour depth, but not for its horizontal extents. Therefore the banks were modelled rigid. To minimize the scour depths in the plunge pool, the spillway flip buckets were fitted with dents. The flow patterns for different alternatives of buckets are illustrated Fig.1. Fig. 1 Hydraulic performance of the flip bucket before and after the modification (Q=4,200 m3/s; “baffle blocks” = dents) The dents scatter the jet trajectories. This not only favours the energy dissipation but also better regulates the backward currents, thus reducing the maximum scour and the risk of erosion towards the dam toe. The shape and the depth of the scour holes formed by flows from both buckets alternatives are shown in Fig.2. 5. PLUNGE POOL LAYOUT (OUTLINES & DEPTH) The plunge pool depth design is based on the results of physical model tests and estimates from empirical approaches. Based on this, the excavation level of the plunge pool invert was set at 105.0 m asl which ensures passage of a 100-year flood without any major plunge pool damage. To be on the safe side, the upstream face of the pre-excavation was designed based on jet trajectory calculations that take into account the considerable effect of the air resistance. In contrast for the downstream side – 1034