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(see [13]) fell from the Hualcan glacier into the reservoir 513. The generated wave height over the natural dam of this event was estimated between 5 and 6 m causing downstream inundations and small damages (see [13] and [14]). According to [13], this event occurred when the reservoir had a free board of 20.0 m. According to the model, the 18 selected blocks generate wave heights above the dam crest between 0 and 45 m. The simulated detachment of an entire group of ice blocks resulted in similar wave heights as for individual blocks. Although block B-16 does not to generate a overtopping, this block also was considered in the detailed simulation due to its proximity to the reservoir. Based on this pre-assessment, 6 most important individual blocks were investigated in more detail (Fig. 5 – blocks marked red). Fig. 5 Wave height above the dam crest applying tool from [12] Hauteur des vagues au-dessus de crête du barrage avec l’outil selon [11] 3.2. APPLIED MODEL & DETAILED SIMULATION PROCEDURE For the detailed investigation, a 2D numerical simulation was applied with different scenarios to maintain the operation of the reservoir and at the same time to mitigate the risk of downstream damages due to a glacier block impact and resulting GLOF. The complete process chain of the impact events based on the crated DEM (satellite-, bathymetric- and drone topography) was simulated with a 2-dimensional hydrodynamic model (HYDRO_AS-2D (Hydrotec, Germany)), which is based on the shallow-water equations (depth-averaged) for free surface flow using the Finite-Volume-Discretization. For each selected ice block, (see Fig. 5) the simulation was carried out following a 3-step approach: (Step 1) Pre-simulations to model the sliding phase, (Step 2) Main simulation to model the impact phase, the wave propagation in the reservoir and the wave run-up at the dam, and (Step 3) Iterative simulations to estimate the required reduction of the reservoir water level to prevent overtopping including a variation of the block volumes Sliding path, impact velocity and impact direction were determined in the pre-simulation (Step 1). To be on the conservative side, the main simulation 586