Page - 588 - in Book of Full Papers - Symposium Hydro Engineering

any means. Block B-6 a has even such a high impact momentum, that prevention of overtopping through a water level reduction it is not possible at all. For the said scenario only an “optimal” lowest water level could be identified which lead to minimal overtopping, which still is 1’126 m³/s. The required reduction would be 50 m. Any further lowering of the reservoir water level again lead to higher overtopping discharges, as the remaining mass of water in the reservoir is not able to damp the impacting momentum (see Table 1). Overtopping heights with the tool from [12] versus the 2D simulation were in general 1 to 45 m (8 to 98 %) higher (see Table 2). By reducing the impact velocity in the range from 8 to 92 % same results as for the 2D simulation can be obtained. Overtopping volumes from the 2D simulation are in general 2 to 6 times higher. Although the impact of the spillway cannot be represented in the pre-assessment tool from [12], it can be said, that mayor impact heights result in increased differences between the tool and the 2D simulation. Table 2 Comparison between results of 2D-Simulation and pre-assessment tool from [12] Comparaison entre les résultats de simulation 2D et l'outil selon [11] 4. DISCUSSION OF THE RESULTS As shown in Fig. 6 (left), overtopping wave heights become more important when the ice block starts to have a significant volume compared to the reservoir volume – threshold for overtopping of the ice block volume is in the order of 50’000 m3 for the investigated situation. Reducing the water level also means to reduce the damping effect of the water mass of the reservoir. As indicated in Fig 7, a reduction of about 40 to 50 meters results to be ineffective regarding the prevention of overtopping. This is also the case, if the volume of the ice block reaches 6 – 10 % of the remaining reservoir volume (Fig. 6 (right)). Of course, not only the block volume and sliding velocity but also the impact location and direction (directly towards the dam or mainly towards a lateral bank) have great Results / Block Nr. CASE 2D 1) Excel 2) 2D 1) Excel 2) 2D 1) Excel 2) 2D 1) Excel 2) 2D 1) Excel 2) 2D 1) Excel 2) Maximal Wave Height - 10 - 11 - 15 - 21 - 10 - 2 [m] Amplitude of the Wave - 8 - 9 - 12 - 17 - 8 - 1 [m] Wave Heigth upstream of the Dam 21 19 7 23 26 33 4 49 18 21 2 3 [m] Wave Height over Dam Crest 14 16 3 19 19 29 1 45 12 17 - - [m] Maximal Discharge 9,703 3,383 606 4,332 14,422 6,457 123 10,158 8,334 3,748 - - [m 3 /s] Overtopping Volume 181 41 13 54 321 83 1 136 193 46 - - [10 3 m 3 ] Volume at Spillway 58 - 8 - 84 - 3 - 58 - 219 - [10 3 m 3 ] Impact Velocity 93 92 71 69 105 105 133 133 97 97 61 61 [m/s] Volume of Ice Block [m 3 ] Altitude of Ice Block [m asl] Impact Height [m] 1) Case 2D: Detailed 2D-Simulation 2) Case Excel: Pre-Assassment based on the Excel-Tool from [11] 297 500 829 1,099 1,629 1,021 18,000 4,791 5,120 5,390 5,920 5,312 4,588 472,500 270,000 526,500 67,000 333,000 B1 B3 B6 B9 B12 B16 588