This master’s thesis addresses the flood hazard in the Dreta River basin, a torrential tributary of the Savinja River. Due to its short concentration time and high-intensity rainfall events, floods frequently occur in the Zadrečka Valley, threatening settlements and infrastructure. Within the framework of the national spatial plan, dry detention reservoirs are proposed as a key structural measure to reduce flood peaks. The aim of the thesis was to assess their effectiveness through hydrological and hydraulic modeling. For this purpose, a hydrological model was developed using HEC-HMS and a hydraulic model using HEC-RAS. The hydrological model was calibrated and validated with selected flood events and applied to generate design flows with a 100-year return period, considering climate change impacts. The hydraulic model enabled spatial analyses of flood extent and water depths in the town of Gornji Grad. The results show that dry detention reservoirs can significantly reduce flood peaks. The maximum discharge of the Dreta River in Gornji Grad decreased from 184 m³/s to 124 m³/s, while the flooded area was reduced by approximately 55%. The analysis also revealed that, according to the draft national spatial plan, two of the proposed reservoirs are inappropriately located, as they do not contribute to peak flow reduction. The conclusions confirm that properly sited and dimensioned dry detention reservoirs represent an effective measure to mitigate flood risk. The results provide an important basis for spatial planning, the preparation of the national spatial plan, and the development of adaptation measures to climate change.
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