On-site inspection in monitoring of water flow for the calibration of hydraulic models and the statistical analysis of the hydraulic output. Case study: The river Nileas in North Euboea Greece, before and after the storm Elias in September 2023

North Euboea features elevated topography, expansive wild forests, and numerous small rivers with rainfall patterns similar to the Greek average. Since 2017 a severe disease has affected plane trees (Platanus orientalis), crucial for stabilizing water flow along riverbanks. A devasting wildfire in August 2021 (52,900 hectares burnt areas), further impacted the region significantly. These events induced substantial alterations to the landscape, changing the dynamic of waterflow in watersheds. Our research aims to comprehend, through statistical reasoning, the modifications in water flow and evaluate the collective repercussions on water management. For this purpose, systematic on-site inspections were conducted in April 2023 to map a substream/subriver of the Nileas River and to use water depth for the calibration of the 2D hydraulic model. Also, in September 2023, a devastating storm (“Elias”) caused a dramatic effect in riverbanksdue to the severity of the flood event, and so,in November 2023, we conducted a second systematic on-site inspection to comprehensively assess the situation after the flood event. Hence, a comparative study of Nileas River (before and after the storm) is presented in this study, by emphasizing, through statistical analyses, on the impacts of the landscape changes thoroughlyand to the understanding of the dynamic alterations in the region's watersheds.