FLOOD MAGNITUDE AND DYNAMICS IN THE UNGAUGED VELABISHT RIVER BASIN, ALBANIA, BASED ON RAINFALL-RUNOFF MODELING

Reliable estimation of flood magnitudes is a fundamental requirement for the design of hydraulic infrastructure, flood risk management, and the mitigation of flood-related impacts. In ungauged river basins, where discharge observations are unavailable, this task becomes particularly challenging and is associated with considerable uncertainty. This study presents a comprehensive assessment of flood hydrographs in the ungauged Velabisht River basin, which forms part of the Osumi river system in Albania. Flood simulation was performed using the semi-distributed Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS). Six independent meteorological scenarios were developed on the basis of precipitation data collected from stations located within and in the vicinity of the basin. A frequency analysis of annual maximum daily precipitation was conducted, resulting in depth duration frequency (DDF) relationships for each scenario. Design storm hyetographs were constructed using regional rainfall characteristics and the alternating block method. Precipitation losses were estimated using the Curve Number method, with spatially distributed curve numbers derived through Geographic Information System (GIS) analysis under average antecedent moisture conditions. Surface runoff hydrographs were generated using the synthetic unit hydrograph recommended by the Natural Resources Conservation Service, while baseflow was represented by an exponential recession approach. Flood routing along the river network was simulated using the Muskingum Cunge method.