Hydrologic-hydraulic modelling and flood hazard mapping for infrastructure resilience in a small mountainous catchment on Northern Greece

Flood-prone small mountainous catchments hosting critical infrastructure, such as bridges and transport networks, require integrated hydrologic–hydraulic analyses to ensure long-term resilience under changing climatic and land-use conditions. This study develops a coupled HEC-HMS–HEC-RAS modelling framework to quantify design discharges, inundation patterns and local hydraulic controls for the torrential stream crossing the settlement of Kato Nevrokopi in Northern Greece. Using high-resolution topographic data (DEM), GIS-based basin delineation and long-term rainfall records, design storms for multiple return periods are derived and transformed into flood hydrographs at the catchment outlet. These hydrographs force 1D steady-flow simulations in HEC-RAS, explicitly representing bridges, piers and local constrictions that act as morphodynamic bottlenecks and potential failure points under extreme flows. Model results are used to generate flood extent and water-depth maps for events up to the 1,000-year return period, identify critical cross-sections where afflux and backwater effects are most pronounced, and assess the effectiveness of alternative layout and channel-training configurations. The analysis is framed within the current EU Floods Directive 2007/60/EC and Greek legislation for stream delineation, linking quantitative hazard metrics to planning constraints and infrastructure design requirements. The work highlights how relatively simple, openly available tools, when combined with detailed geometric representation of bridges and channel morphology, can support evidence-based decisions on flood protection works, minimise over-engineering, and improve the adaptive management of critical infrastructure in steep, data-scarce basins.