Hydrologic-Hydraulic Modelling of the Gogna River at Schio: fixed and mobile bed formulations

Flood hazards are one of the most important natural risks in mountainous environments, where steep slopes, intense rainfall, and rapid runoff can lead to flooding, ground instability, and severe impacts on urban areas. The evaluation of flood-prone areas is significant for risk mitigation and management, especially in small basins where observational data are often limited or unavailable. This thesis focuses on the assessment of flood hazard in the Gogna river basin, located in the municipality of Schio (Italy), an alluvial fan system with high sediment transport rate and torrent-like hydraulic characteristics. The assessment was carried out through the integration of hydrologic and hydraulic modelling, implemented using HEC-HMS 4.12 and HEC-RAS 6.6, respectively. The hydrologic model was implemented to estimate the design flood hydrographs at the apex of the alluvial fan, which were then used as upstream boundary conditions for a hydraulic model. Subsequently, a 2D hydraulic model was developed, explicitly incorporating sediment transport and sediment erosion and deposition, in accordance with the guidelines of the Piano di Gestione del Rischio di Alluvioni (PGRA). The model implemented within HEC-RAS allows the interaction between channel morphology and the flow dynamics to be represented during a flood event. As per the PGRA guidelines, model parameters were estimated using values from the literature and basin physical characteristics, due to the absence of observed hydrometric data. Flood hazard was evaluated based on the maximum water depth, flow velocity, and their combined effect, as prescribed by the PGRA. The resulting hazard maps provide a detailed representation of areas exposed to different levels of flood hazard and are useful tools for flood risk management and territorial planning.