Preliminary Investigation and Assessment of Landslide Dam Occurring in Blumenau, Southern Brazil

Abstract

Following a small landslide, a large landslide or rockslide occurred on the left (western) slope of the Garcia River, southern Blumenau (Santa Catarina state Southern Brazil) at about 2 : 00 am on Friday, October 23, 2015. The landslide appeared to be controlled by the high-intensity rainfall of 80 mm/2 days and duration rainfall of 354 mm/month in addition to unfavorable geological and geomorphologic settings. Landslide debris destroyed 4 houses at the base of landslide slope and completely dammed the Garcia River with a crest height of about 6.0 m above the streambed. Shortly after the landslide dam formed, the dam was filled completely with water and subsequently failed due to overflow and erosion. By the time of our site visit, the Garcia River has been partially blocked with an estimated water level of about 4.5 m above the streambed, creating a small potential for flash flooding and debris flow at the blockage. On December 3 to 4, 2015, Japan International Cooperation Agency (JICA) carried out an on-site survey, in response to the request of the Department of Geology and Natural Risk Analysis of Blumenau Municipality. The objective of the technical survey was to analyze the risk of landslides and provide some geotechnical recommendations for emergency measures and restoration countermeasure works relative to landslide dam.