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(Step 2) starts with a fluid body right before its impact, which has exactly the shape of the ice block as predefined by the glaciologist (in the pre-simulation the sliding fluid body disintegrates somewhat which decreases the impact momentum). The comparison of the results from Step 1 to outcomes from [12] showed minor differences from -9.0 to +5.0% (mean -0.9 %) for the mean impact velocity. Nevertheless, velocities from the pre-simulation (Step 1) are spatially distributed with lower magnitudes at the edges of the impacting fluid body, which decreases the impact momentum. The resulting overtopping wave heights would be in average 22% and the overflow discharges 33% lower. Therefore and to assure a conservative approach, the initial velocity magnitude of the impacting fluid bodies was set constant for the entire fluid body in the main simulations based on the theoretical approach according to Körner [12]. As indicated in Step 3, additional to the 6 base cases, 17 simulations with different ice block volumes maintaining their locations and different reservoir levels were executed to cover the most important conditions and detect the minimal water levels in the reservoir which would prevent overtopping. 3.3. SIMULATION RESULTS The simulation results show that in five of the six base cases (-a marked red) overtopping occurs when the operational water level is at the actual altitude of 4290.88 m a.s.l. Table 1 Results of 2D-Simulation Resultáts de la Simulacion 2D Overtopping heights between 1 and 19 m were obtained based on impact heights between 300 and 1’600 m and volumes between 18’000 and 526’500 m3. Only in one case (B16-a) no overtopping occurred due to the low volume and impact height. To prevent overtopping at the dam, the water level in the lagoon has to be reduced between 2 and 40 m. Correspondingly, the actual water volume of the lagoon (29 Mio.m3) is reduced down to 5 Mio.m3, which represents a reduction of 82 % and would mean to abandon the operation of the lagoon for Case a b c d e a b c d a b c d a b c a b c d a b c Block Volume 50,000 40,000 18,000 [m3] Altitude [m asl] Impact Height 500 545 500 520 500 829 835 829 832 1,099 1,149 1,099 1,129 1,629 1,631 1,629 1,021 1,066 1,021 1,041 297 297 305 [m] Reduction of FSL - 45 - 20 - - 6 - 3 - 50 - 30 - 2 - - 45 - 20 - - 8 [m] Wave Heigth 14 - 6 - - 3 - 1 - 19 3 11 - 1 - - 12 - 9 - - 4 - [m] Reservoir Volume 29 7 29 17 29 29 25 29 27 29 5 29 13 29 28 29 29 7 29 17 29 29 24 [Mio. m3] 4,588 BLOCK B-1 BLOCK B-3 BLOCK B-6 BLOCK B-9 BLOCK B-12 BLOCK B-16 4,791 5,120 5,390 5,920 5,312 67,000 333,000 200,000 80,000472,500 220,000 270,000 150,000 526,500 250,000 587