This diploma thesis explores the idea of impounding water from the Paka River in Lake Velenje in the event of a flood wave with a 100-year return period. If such an event were to take place, Šoštanj would once again be subject to substantial material damage. Lake Velenje, which feeds from torrential waters of the Sopota and Lepene hills, is one of the biggest lakes in Slovenia, so it was expected to have substantial capacity for water retention. If the Paka River were impounded in the lake, the Sopota and Lepena waters would have to be impounded as well. It was assumed that the flood waves from Sopota and Lepena would appear prior to the one from Paka, therefore some water from these waves would be drained before the arrival of the Paka wave. To test this assumption, the program HEC-HMS 4.1 was used to create hydrographs for Sopota and Lepena, which show information about peak flow times, maximum flow, and volume. The hydrographs were calculated using data about the timing of maximum daily precipitation with a 100-year return period that was researched and established within the thesis, as well as data on topology, pedology and soil use. The hydrograph for the Paka River was calculated through analysis of changes in water level during major precipitation events over the past two and a half years since automatic data collection was established at the Velenje gauging station. The hydraulic conditions for attenuating the Paka River into Velenje Lake at a scale that would only send as much water through Šoštanj as the existing stream banks can handle were calculated in Excel and visually presented using plotted graphs. It is established that a certain amount of the flood waves from torrential waters can be drained before the arrival of the flood wave from the Paka River and that, in this case, the retentive capacity of the lake is sufficient for the proposed measure. The possibility of implementing the proposed measure is further demonstrated by creating a conceptual design of the mitigating facility. Finally, guidelines are established for possible further phases of the study.