UAV-enabled flood damage assessment and recovery monitoring of bridges following Medicane Ianos

Abstract

Strong winds and heavy rainfall hit western and central Greece on 17–18 September 2020 as the Mediterranean Hurricane (Medicane) “Ianos” made its catastrophic passage through the country. Widespread flooding caused landslides and debris flows, while the erosive forces of water washed away foundation supports and earthworks along swelling rivers, impacting buildings, transport infrastructure, and powerlines. The town of Mouzaki, in Central Greece was one of the hotspots of the event. All five bridges that exist in the area, within a radius of 3 km from the town’s center, suffered extensive damage or complete failure, leading to disruption of transportation and month-long isolation of local communities. The paper presents select outcomes of a comprehensive reconnaissance study where aerial photography and mapping by Unmanned Aerial Vehicles (UAVs) were used to enhance conventional field investigation and archival research for damage characterization, assessment and recovery. Three dimensional models of select bridge structures are presented and prominent failure patterns are discussed with reference to key response factors and structural characteristics. The paper provides a kaleidoscopic insight into bridge response to a landmark flood event, where the abundance of perishable data was collected in a timely and systematic manner. A universal inadequacy to withstand this flood is identified, raising concerns over what appears to be a new norm of intense weather events in the western Mediterranean. Although the use of UAV mapping in disaster reconnaissance has been common practice in the past years, this is a unique case study where UAVs were also employed for monitoring of bridge recovery in a multi-hazard environment. Comparison of imagery captured at different stages after the event allowed inspection of restorations with minimum human interactions amid the COVID-19 pandemic. Furthermore, it proved useful for the rapid assessment of the impact of a moderate seismic event that affected the damaged structures only a few months after the Medicane. The approach presented provides an effective solution for transport operators managing assets in an environment of increasingly severe and complex hazards.