UAV based High-resolution DEM for 1D Hydrodynamic modeling - A case of Flood Assessment of Sabarmati River, Gujarat, India.

The most frequent catastrophic natural disaster is thought to be flooding. Due to climatic uncertainty, variable rainfall, a lack of river carrying capacity, illegal settlement along river banks, and dense population, flood magnitudes and vulnerabilities increased in the past ten years globally. There are 11,356 records of hydrological and meteorological occurrences from 1900 to 2020, according to the United Office of Disasters Risk Reduction's (UNDRR) International Database, with 8.6 million fatalities and 2600 million US dollars in economic damage. In the current climate, floods cannot be prevented, but their damages can be reduced with a thorough flood assessment. The identification of the flood inundation area, flood arrival time, and flow velocity in flood-prone areas can be accomplished using a variety of hydrodynamic models; however, the limited resolution of DEM (Digital Elevation Model) makes it impossible to determine the actual flooding state. To remedy this shortcoming, we developed a high-resolution DEM from UAV (Unnamed Aerial Vehicle) for this case study, which involves the well-known Sabarmati of Gujarat State, one of India's principal west-flowing rivers with a length of 371 kilometres, which was impacted by a flood in 2006. The 4RTK (Real-Time Kinematic) Phantom, a UAV survey, was used to acquire aerial pictures of a portion of the river Sabarmati. The image was then processed with 75% mosaicking using the Pix4D mapper tool for better accuracy. Later, with the aid of Global Mapper, various DEMs with grid sizes ranging from 0.5 m x 0.5 m to 10 m x 10 m are created with near precision of 3 cm spatial resolution. These generated DEMs are then used as input for the hydrodynamic simulation using Civil Geo-HECRAS. Hence, the hydrological data required for the hydrodynamic model has been assumed from past floods and the geometrical data for the study is derived from the UAV survey with four Manning's roughness coefficients—0.025, 0.030, 0.033, and 0.035 have been assumed for this case study considering the local conditions. The analysis of Manning's roughness value's influence reveals that when roughness increases, discharge reduces, and velocity and Froude's number decrease.

Keywords: Flood, DEM-Digital Elevation Model, UAV-Unnamed Aerial Vehicle, Hydrodynamic modeling, Manning’s roughness