The September 18-20 2020 Medicane Ianos Impact on Greece Phase I Reconnaissance Report

Abstract

On September 17-20 2020 Medicane Ianos impacted Greece. The Medicane caused significant wind damage, and precipitation related impacts. The amount of precipitation during a duration of about ~48 hrs was among the highest recorded and exceeded, in certain areas, the mean annual precipitation. The extent of the affected area was very large and encompassed the western, central and southern Greece, all the way south to the island of Crete. The Ionian islands and the areas around Karditsa and Lamia in Central Greece were particularly affected. Field deployments to collect perishable field performance data were supported by remote sensing tools and geospatial data analysis. The GEER team used optical and radar satellite imagery to generate a broad assessment of the conditions, as well as data-mined social media to identify sites of particular interest. On the ground, conventional site characterization tools were supplemented by Unmanned Aerial Vehicles to generate three dimensional models of target areas and sites. During field deployment, data collected in the field were uploaded on a shared Box folder and were projected on a web-based GIS map the next morning to facilitate collaboration among teams. The amount of precipitation resulted in a wide variety of landsliding that included (a) landslides involving soils and fractured and weathered rocks, (b) rockslides, rockfalls and structurally controlled rock failures, as well as (c) debris flows. Just in the areas to the west of Karditsa, around Lake Plastiras, more than 1,400 landslides were mapped using satellite imagery, and some of them were documented in the field, although access in the mountainous areas affected data collection. In Cephalonia, one of a few major debris flows, a rare occurrence on the island, devastated the community of Assos. Extensive flooding was also observed throughout the affected areas nationwide. Lower-elevation areas were flooded, and portions of the town of Karditsa and surrounding communities became completely submerged. The amount of water compromised, in numerous areas, the road and railroad network by washing out roads or railroad lines, damaging the embankments that supported the pavements, or disrupting their functionality by landslide debris. Particularly pronounced was the damage to many bridges, ranging from minor damages (such as movement) to complete collapse due to foundation scour, or lateral loads by water and debris. Riverbanks and levees were also overtopped and scoured. The extent of the affected area by Medicane Ianos far exceeds the extent of affected areas by other natural disasters, such as earthquakes or precipitation events. The diversity of damage observed also raises the need for community-level resiliency considerations, particularly in light of what appears to be a potentially new “norm” of more intense and larger precipitation events, such as this medicane. To that end, this report contributes to the condition assessment and perishable data collection from Medicane Ianos that can support engineers and community leaders in being prepared for future events. It also forms the basis for subsequent phases of investigation to better understand the causes of the recorded damage and the contributing factors.