Post Flash Flood Disaster Analysis Utilizing UAV Photogrammetry and GIS. Case Study: Maldevta, Dehradun

Post-disaster damage assessment is essential for estimating losses and planning effective response, recovery, and mitigation strategies. However, field-based surveys and satellite image interpretation often face challenges during emergencies. Field surveys may be hindered by physical accessibility, while satellite imagery can be affected by cloud cover, long revisit times, and the high cost of high-resolution images. To address these challenges, a nano-category UAV was employed to document flood-impacted areas in response to a flash flood event that turned into a disaster, resulting in loss of lives during the 2022 flood, and significant property damage and economic losses from both the 2022 and 2023 floods. The DJI Mini 3 Pro captured high-resolution imagery at two locations during the flood on 16 August 2023, and at one location post-event on 2 September 2023. The collected data was processed using Agisoft Metashape, generating detailed orthomosaic maps and 3D models of the affected regions. This UAV data acquisition provided high-resolution orthomosaics with a ground sampling distance of 3.01 cm/pixel and digital elevation models at 6.14 cm/pixel. The imagery and models were instrumental for rescue and relief operations, logistical planning, and recovery efforts. This study highlights the effectiveness of nano-category UAVs in post-flash flood damage assessment in the Maldevta region, Dehradun, Uttarakhand, demonstrating their potential for quick and reliable data collection and analysis in disaster scenarios.