Research on the Impact of Extreme Rainfall Events on Torrential Flow

On the night of August 3 to 4, 2023, an extremely intense precipitation event occurred in northwestern and northern Slovenia, exceeding even a 100-year return period. In catchment areas that were already wet due to the rainfall in July, between 150 and 200 mm of rain fell within 6 to 12 h. In the Kamniško-Savinjske Alps, watercourses reached extreme discharges on the morning of August 4, triggering a series of landslides and extreme events in torrents. This resulted in large amounts of material being displaced from the torrent beds. An analysis of the consequences of the extreme discharge on the Konjski Potok torrent is presented. The torrent flows into the Kamniška Bistrica River, which flows through the densely populated Kamnik-Bistriška Plain. An analysis of the geological characteristics of the area shows that the surface is predominantly composed of Triassic limestones. To analyze extreme events, the discharges in the Konjski Potok were calculated using various methods. Different formulas were used to determine the maximum torrential discharge in unmeasured catchments and the results were compared. The critical discharge for triggering the gravel bed movement was also determined. The maximum debris discharge and the volume of displaced material along the Konjski Potok were determined for the selected torrent discharge. The calculated volume of moved material is compared with the volume measured in the field and with the result of the formula for determining the magnitude of the moved material.