Page - 1084 - in Book of Full Papers - Symposium Hydro Engineering

EFFECTS ON SPILLWAY CAPACITY Rating curve was derived for the existing design (Var 1), on the improved design after the removal of the existing overflow piers (Var 2) and on the improved design with the rounded bottom end of the spillway shaft (Var 3). The comparison of rating curves representing the three modelled cases as well as the existing rating curve that is present in the operating manual can be seen in Fig. 6. Fig. 6 Rating curve comparison Curves derived by the physical model do not differ significantly; however, the plot shows the significant difference between the operating manual rating curve (labelled MR) and the models. As the very small difference between the modelled rating curves suggests, the proposed design improvements do not affect the capacity of the structure significantly. However, it was proved by the physical model that the removal of the overflow piers improve water supply conditions at the vertical shaft and partly eliminate pulsations and decrease the hydraulic load on the structure, while the rounded bottom end of the vertical shaft prevents the existence of the extremely turbulent flow in the spillway tunnel downstream of the bend. The original capacity of the Jirkov Dam spillway prior the reaching the undesired hydraulic conditions regime was assessed to be 95 m3.s-1, while the improved design capacity is 124,6 m3.s-1. This capacity is higher than 1 in 10 000 years flow which meets the Czech national standards for dam safety. 1084