The latest relevant debris flow event in Portugal occurred in Madeira Island on 20th February 2010, with a death toll of 48 people and severe property damage, valuated in more than 1000 million €[1]. Although uncommon[2], debris flows are among natural hazards which more human casualties and overall damage have made in Madeira.
According to (EARAM, 2010), the February 2010 event was mainly triggered by high intensity rainfall conditions resulting in flood peaks with high transport capacity and susceptible to transport large boulders (which in several cases exceed 2 m in diameter). This event had an estimated return period of 100 years and severely encroached few southern Madeira districts, particularly Funchal and Ribeira Brava.
One of the major impacts of occurred debris flow events was the overall clogging by sediments on the main rivers and streams, especially on lower gradient areas which usually corresponded to urban settlements. Consequently, the rivers cross sections were significantly reduced as well as discharge capacity, resulting in widespread overtopping and extreme flash floods events responsible for several damages and casualties, especially in Funchal city.
[1] Source: sicnoticias.sapo.pt
[2] According (EARAM, 2010), there were 10 debris flow records since 1803 which was the year when the most destructive debris flow occured in Madeira island.