The Impact of Topographic Resolution on Flood Inundation Extent in Narrow Valley Systems: A Case Study of Karakoçan Stream (Elazığ, Türkiye)

Escalating climate change and unregulated riverbed construction have rendered floods the most devastating hydrometeorological hazards worldwide, posing severe threats to lives and infrastructure. The reliability of hydraulic models in predicting flood risks relies heavily upon the spatial resolution of the Digital Elevation Model (DEM) employed to represent terrain topography. This study investigates the impact of two distinct DEM datasets, featuring 10-m and 25-m spatial resolutions, on flood inundation mapping across the Karakoçan Stream catchment in Elazığ, Türkiye. Hydraulic analyses were performed using the HEC-RAS software, and the simulation outcomes were evaluated based on land use impacts and critical hydraulic parameters. The results revealed that coarsening the DEM resolution from 10 m to 25 m expanded the estimated inundation area from 19.36 km² to 48.75 km², representing an artificial overestimation of approximately 152%. Furthermore, the maximum water depth particularly within residential areas dropped significantly from 9.49 m to 2.82 m. This indicates that low-resolution data fails to capture the vertical depth of the flood volume, erroneously dispersing the water horizontally as a shallow layer. These findings demonstrate that DEM resolution is a critical parameter directly influencing the predictive accuracy of flood hazard models. Consequently, these outcomes underscore the imperative need to meticulously select an optimal DEM resolution, carefully balancing site-specific topographic characteristics with data availability.