Bridge foundation scour is the most common cause for the failure of highway bridges. The assessment of local scouring mechanism around bridge piers provides information for decision-making regarding the pile footing design, predicting the safety of bridges under critical scoured conditions, and as a result, may help prevent unnecessary loses. Since scour in bridges is the water-induced erosion of soil particles around bridge foundations, the loss of lateral load capacity at bridge foundations may induce bridges to become highly vulnerable to failure when the effects of scour and floods are combined. In this study, high definition 3D models of the flood plain and the amount of current scour in bridge piles were acquired by Unmanned aerial vehicle (UAV) based measurements which provide a practical approach and bring high precision solutions considering traditional measurement systems. The present study evaluated the performance of bridges with reinforced concrete (RC) pile foundations under the effects of local scour and flood. Thus, a RC bridge constructed over Boğaçayı in Antalya, Turkey was selected as the case study. The vulnerability of the bridge was assessed under flood loading considering the predicted scour amount. The maximum flood loads according to different return periods (5, 20, 50, 100 and 500 years) and the corresponding maximum scour depths were determined by HEC-RAS software. As a result, the outputs were regarded as input parameters for the evaluation of lateral behavior of the bridge under consideration. The soil-pile foundation-structure interaction was implemented in the finite element models of pile groups. The multi-hazard performance of the bridge was evaluated under the maximum predicted scour depth and corresponding flood load. In conclusion, as the scour depth increased the fundamental periods, shear forces and the bending moments were observed to increase while the pile lateral load capacities diminished. Therefore, it was ascertained that the scour substantially deteriorated the performance of the bridge under multi-hazard environment.

Unmanned Aerial Vehicle (UAV) based Structure-from-Motion (SfM) techniques have renovated 3D topographic monitoring of earth surface, offering low-cost, rapid and reliable data acquisition and processing. Multi-temporal models of the river environment can be produced by autonomous operation in order to determine erosion, subsidence, landslide, soil transport and surface deformation in the riverbeds. Herein, the acquisition of repeated topographic surveys helps us to characterize the flow regime and to monitor the sediment dynamics. This study presents the hydromorphological changes of the meandering structures by using UAV-generated point clouds and Digital Surface Models (DSMs) produced by SfM at different times in the Büyük Menderes Basin located in the western part of Turkey. The processing of the data obtained with the flights were made in January and June 2018 at selected three meander locations with the highest visible changes according to the long-term satellite imageries. Especially, riverbank erosion along the river was determined by digitizing the edges and volumetric calculations of the eroded/deposited sediments derived from UAV-based measurements. In addition to the periodic volumetric differences of the meander structures, the differences in volumetric comparison methods for the same meander structures have been evaluated. Ultimately, the sediment profiles were extracted along the river banks at the selected part of the meanders and the amount of deposited sediments were determined to increase in a range between 1.5% and 3.3% of the total sediment. In conclusion, it is estimated that UAVs will be used instead of conventional photogrammetry aircraft in many future projects, considering the data production times and costs in large areas. Further, various digital cameras and sensors can be mounted on UAVs in order for examining the sediment effect on the health and productivity of plants in agricultural areas around the meanders.