Page - 1082 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 3 Model of the bell-mouth spillway without overflow piers IMPROVEMENTS TO THE BOTTOM END OF THE VERTICAL SHAFT The existing bottom of the vertical shaft has a sharp perpendicular bend (Fig. 4, left). As the water falls vertically to the bottom of the shaft, it forms an aerated turbulent flow cushion that extends downstream to the spillway tunnel. This cushion starts to be significant for 1 in 20 years flow. The rounded bottom of the vertical shaft was proposed (Fig. 4, right). The model revealed that the aerated cushion has diminished significantly. The energy loss is much smaller and the velocity vector is oriented towards the direction of the outlet tunnel. The aerated cushion at the bottom of the shaft was formed for much higher flow exceeding 1 in 100 years return period. 1082