Remote Sensing with UAVs for Modeling Floods: An Exploratory Approach Based on Three Chilean Rivers

Abstract

The use of unmanned aerial vehicles (UAVs) has been steadily increasing due to their ability to acquire high-precision ground elevation information at a low cost. However, these devices have limitations in estimating elevations of the water surface and submerged terrain (i.e., channel bathymetry). Therefore, the creation of a digital terrain model (DTM) using UAVs in low-water periods means a greater dry channel surface area and thus reduces the lack of information on the wet area not appropriately measured by the UAV. Under such scenarios, UAV-DTM-derived data present an opportunity for practical engineering in estimating floods; however, the accuracy of estimations against current methods of flood estimations and design needs to be measured. The objective of this study is therefore to develop an exploratory analysis for the creation of hydraulic models of river floods using only UAV-derived topographic information. Hydraulic models were constructed based on DTMs created in (i) the traditional manner, considering the bathymetry measured with RTK-GPS and topography, and via (ii) remote sensing, which involves topography measurement with a UAV and assumes a flat bed in the part of the channel covered by water. The 1D steady-state HEC-RAS model v.5.0.3 was used to simulate floods at different return periods. The applied methodology allows a slightly conservative, efficient, economical, and safe approach for the estimation of floods in rivers, with an RMSE of 6.1, 11.8 and 12.6 cm for the Nicodahue, Bellavista and Curanilahue rivers. The approach has important implications for flood studies, as larger areas can be surveyed, and cost- and time-efficient flood estimations can be performed using affordable UAVs. Further research on this topic is necessary to estimate the limitations and precision in rivers with different morphologies and under different geographical contexts.

Remote Sensing with UAVs for Flood Modeling: A Validation with Actual Flood Records

“…Using the aerophotogrammetric information acquired in 2016 and following the methodology developed by Clasing et al [49], a DTM RS was created. During this process, the demarcation between the submerged and exposed portions of the river was determined by analyzing the aerial imagery.…”

“…Following the methodology in Clasing et al [49], a remote sensing hydraulic model, referred to as HM RS , was constructed using DTM RS . To extract geometric data pertaining to the active channel and its floodplain from a digital terrain model (DTM), ArcGIS (version 10.5) and its extension, the Geographic Information System Geo-Spatial River Analysis System (HEC-GeoRAS), were employed.…”

“…This results in a reduction in the uncharted area, making it feasible to create a robust and representative hydraulic model for river flood modeling and design. Consequently, this approach decreases the time and cost associated with gathering topo-bathymetric information [49].…”

“…Clasing et al [49] carried out an exploratory analysis in three rivers of south-central Chile to develop hydraulic models based on remote sensing with UAVs that are representative for flood calculation. To this end, approaches based on aerial images, geometric characterization, and river classification were used.…”

“…Therefore, the objective of this study is to validate a hydraulic model built based on remote sensing using the methodology described by Clasing et al [49], together with actual measurements of a flood. To this end, the Ñuble River flood, which occurred during an extreme event on 24 June 2023, was considered.…”