Debris flows are common phenomena along the “Serra do Mar”, a mountain range of about 800 to 1000 m high, running along the Southern Brazilian coastal area. This paper deals with the “Sabo Works”, i.e., structures to control debris-flows, proposed for an area of the “Serra do Mar”, in Cubatão, São Paulo-Brazil. The Brazil-Japan cooperation in the mid-1980 is described, followed by a brief history of past events that affected a PETROBRAS large oil refinery located in the area. A description of the phenomenon and the conditions for its occurrence are presented. The concepts and functions of the proposed “sabo works” are pointed out, stressing that they intended to protect the refinery installations and to preserve the environment.
Debris flows are a singular type of mass movement with high impact and great destructive power. They occur in small catchments with high relief. Debris flows are generated by landslide nucleation in steep initiation zones. The understanding of geological and geotechnical behavior of the regolith and colluvium in these areas is very important to understand debris flows generation and runoff. The present study analyzes a 2.5 m thick regolith profile in a granite saprolite, located in a large scar slip (4.3 km2 area) in the Gigante's Creek catchment in the Serra do Mar range, southern Brazil. Six samples were taken, corresponding to (1) Fresh rock ; (2) Slightly weathered rock ; (3) Soft weathered rock II ; (4) Soft weathered rock I ; (5) Transition zone material and (6) Homogeneous saprolite. Quartz is the most common mineral occurring throughout the profile, while biotite only occurs in deeper horizons. Illite, halloysite, gibbsite, and kaolinite are the secondary minerals at the intermediary zones of the profile, while kaolinite and gibbsite dominate the top of the profile. The proportion of texturally sandy material increases from top to bottom of the profile. The transition zone material, sampled at intermediate portions, have the same textural behavior as the catchment's colluvial materials. The physical indexes show that specific weight of solids (γ s) increase with depth, with the less dense newly formed phase in the upper portions of the regolith. The differences in the voids ratio ( e ) and soil moisture ( W ) show variations within the profile, and that coincides with the kaolin minerals formation and major landslide disruption zones observed in the field. The understanding of these phenomena will help in defining the initiation zones of landslides with the potential to set off debris flows generated by translational landslides.
The translational landslides result from the combination of favorable conditions when one assumes the existence of functional relations between the spatial distribution of determining factors and processes. Thus, it is possible calculating the probability of occurring these landslides, as well as generating organized maps of susceptibility classes based on the inventory of slip scars and on the variables able to influence their occurrence. Accordingly, the aim of the present study is to analyze the spatial relations between the occurred landslides and a set of potential determining factors, as well as to propose and test susceptibility models based on this analysis. The application of Bayes' theorem of conditional probability using the weights-of-evidence technique allowed analyzing the spatial relations between a set of potential determining factors (geological, geomorphological and soil use and cover factors) and 294 translational landslides in 2008 in the study area. Fifteen different integration schemes of the weighted values, able to reflect the spatial association of each factor in relation to the landslides, were elaborated. The adjustment concerning the spatial independence between the themes and the classification and prediction efficiency of each scheme were analyzed. Three models have met the conditional independence requirements. It was possible identifying that the high-to-very-high susceptibility conditions have varied from 15% (in the model integrating the values of themes such as slope, plan curvature and distance to lineament) to 28% (in the model integrating values of themes such as slope and profile curvature) in Blumenau County－Santa Catarina State, based on the selected models.
The rapid growth of urban areas and their inadequate expansion on slopes and flood plains made sediment disasters more frequent in Brazil. After the succession of disasters that caused major damage between 2008 and 2011, the Brazilian government reformulated its strategy and policies related to disaster risk management. Within this strategy, the Brazilian government has proposed a cooperation agreement with the Government of Japan, resulting in GIDES Project, which has as its main objective the strengthening of the national strategy for natural disaster risk management. Regarding actions related to the monitoring and early warning of sediment disasters, three Brazilian Municipalities were chosen as Pilot Implementations for GIDES, aiming to allow the discussion of new methodologies, adapting content and language of the alerts, the establishment of shared and unified information flows and records, and the establishment of common protocols, in experimental scale. This article aims to draw the major aspects in Brazilian risk management context, outline the main challenges faced so far and the Project's contribution perspectives for the improvement of sediment disaster risk management in Brazil, especially on issues related to monitoring and early warning.
By presenting some legal aspects related to disaster management in Brazil, the present work showed that the Brazilian classification of natural disasters is not well established. In the focus on an analysis of the historical views of debris flow disaster management in Brazil, technical-scientific studies about large disaster with debris flows which occurred only in Brazil during the period 1900-2014 were searched mainly through a Web-based survey. The searching result shows that most of bibliographies are proceedings papers and that the papers in scientific journals are only 13% of all the publications. The historical analysis suggests five urgent actions to Brazilian organizations : (i) establishment of correct and uniform terminology about debris flow ; (ii) systematization of hydrometeorological monitoring, its forecasting and topographic survey ; (iii) occurrence registration and database construction ; (iv) debris flow hazard mapping ; and (v) woody-debris flow researches. Based on the Brazilian current situation, the present work proposes comprehensive measures to reduce debris flow disasters, by constructing and using school catchments which are defined as experimental catchments that are used for scientific researches and environmental education for local people.
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.