HYDRAULIC MODELING OF THE FLOOD AREA IN NORTH-WESTERN KOSOVO THROUGH HEC-RAS SOFTWARE

Flood risk assessment and delineation of flood prone areas are fundamental components of sustainable water resources management, especially in rapidly urbanizing river basins. In north-western Kosovo, the Sitnica River basin has experienced recurrent inundation events, exposing discrepancies between existing regulated design discharges and statistically derived extreme floods. This study develops an integrated hydraulic–legal assessment framework using one-dimensional (1D) and two-dimensional (2D) modeling with HEC-RAS (version 6.3.1) for floodplain delineation and public water asset definition under current national legislation. Extreme value statistical analysis was conducted on a 21-year daily discharge record (1963–1985) at the Nedakoc station. The Gumbel distribution, complemented by comparative Log-Pearson Type III fitting, was used to estimate the 1 % exceedance probability discharge (Q₁%). Results show that the previously adopted design discharge of 239.76 m³/s underestimates the statistically derived Q₁% by approximately 95 % to 110 %, indicating significant hydraulic deficiency in the regulated river reach. Unsteady 2D simulations highlight maximum flood depths up to 3.20 m and velocities up to 2.80 m/s in constrained morphological zones. A sensitivity analysis of roughness coefficients (±20 %) reveals a ±12 % variation in peak depths and ±8 % shift in inundation extent, underscoring model responsiveness to parameter uncertainty. Model calibration and validation against documented flood events (January 2021 and January 2026) yielded a Root Mean Square Error (RMSE) of 0.18 m and a Nash–Sutcliffe Efficiency (NSE) of 0.82, demonstrating good conformity between observed and simulated water levels. The integrated hydraulic modeling approach provides a scientifically defensible basis for more reliable floodplain delineation and public water boundary definition under evolving environmental and regulatory conditions. Limitations include the relatively limited hydrological time series and absence of climate scenario analysis, which future work should address.