Page - 1035 - in Book of Full Papers - Symposium Hydro Engineering

potentially affecting the powerhouse tailrace – this influence was omitted, which approximately corresponds to the model test trajectories. Fig. 2 Scour patterns at plunge pool for flip bucket options with (left) and without (right) dents The plunge pool forehead general slope including the widths of the berms were such designed to avoid rotational and erosive flow patterns, as e.g. threating Kariba dam in Zambia. In the framework of the Kariba plunge pool scour mitigation studies, a similar adjustment of the forehead slope was recommended as a countermeasure based on physical and numerical modelling [1]. The layout of the pre-excavated plunge pool of NT1 is shown in Fig.3. 6. JETS CHARACTERISTICS BEFORE AND AFTER IMPACTING THE PLUNGE POOL SURFACE A parallel method to assess the nature and hence the erosive potential of a plunging jet has been developed by researchers such as Ervine et al. [2] and Castillo [3, 4] which is based on two major processes (see Fig. 4). First, when travelling through the air the jet develops increasing instability and corresponding turbulent surface disturbances. These gradually reduce the thickness of the solid core of the jet. Beyond the “jet break-up length” Lb the solid 1035