Redalyc.Potential Fragility of the Caeté Catchment, Municipality of Alfredo
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Acta Scientiarum. Technology ISSN: 1806-2563 [email protected] Universidade Estadual de Maringá Brasil Redin Vestena, Leandro; Kobiyama, Masato Potential fragility of the Caeté catchment, municipality of Alfredo Wagner, Santa Catarina State, Brazil, to landslides occurrence Acta Scientiarum. Technology, vol. 36, núm. 1, enero-marzo, 2014, pp. 101-109 Universidade Estadual de Maringá Maringá, Brasil Available in: http://www.redalyc.org/articulo.oa?id=303229336015 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Acta Scientiarum http://www.uem.br/acta ISSN printed: 1806-2563 ISSN on-line: 1807-8664 Doi: 10.4025/actascitechnol.v36i1.16047 Potential fragility of the Caeté catchment, municipality of Alfredo Wagner, Santa Catarina State, Brazil, to landslides occurrence Leandro Redin Vestena1* and Masato Kobiyama2 1Departamento de Geografia, Universidade Estadual do Centro-Oeste, Rua Simeão Varela de Sá, 3, 850040-080, Guarapuava, Paraná, Brazil. 2Instituto de Pesquisas Hidráulicas, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil. *Author for correspondence. E-mail: [email protected] ABSTRACT. Natural disasters associated with land mass movements in Brazil have become more frequent in recent years, with significant human loss and material damage. An alternative to reduce such natural disasters will occur when landslides-susceptible areas are mapped, with restrictions or conditions for the occupation of areas with natural fragility to landslide occurrences. Current analysis determines the slopes´ potential degree for the occurrence of landslide susceptibility in the Caeté catchment, municipality of Alfredo Wagner, in the highlands of the state of Santa Catarina, Brazil. The Shallow Stability model (SHALSTAB) identified the slopes´ instability index by hydrological factors, hillside stability and soil. Results revealed areas with high degree of hillside instability and the need for preventive and relieving actions. In fact, areas with very high potential fragility susceptible to the occurrence of mass movement in the Caeté catchment are more than 30% of the basin´s total area. Keywords: SHALSTAB, landslide susceptibility, risk area. Fragilidade potencial das vertentes à ocorrência de deslizamentos na bacia hidrográfica do Caeté, Alfredo Wagner, Estado de Santa Catarina, Brasil RESUMO. Nos últimos anos no Brasil, os desastres naturais associados ao movimento de massa vêm sendo mais frequentes, com maiores danos materiais e humanos. Uma das alternativas de redução deste tipo de desastre natural dar-se-á a partir do mapeamento das áreas suscetíveis a deslizamentos e da determinação de restrições ou de condições para a ocupação de áreas que possuam fragilidade natural à ocorrência a deslizamentos. O presente artigo teve por objetivo determinar o grau de potencialidade das vertentes à ocorrência de deslizamentos na bacia hidrográfica do Caeté, município de Alfredo Wagner, região serrana de Santa Catarina. O modelo SHALSTAB (Shallow Stability) foi empregado para a identificação do índice de instabilidade das vertentes, a partir de fatores hidrológicos, de estabilidade da encosta e do solo. Os resultados demonstram a presença de áreas com elevado grau de instabilidade das encostas e a necessidade de ações preventivas e mitigadoras, uma vez que as áreas com fragilidade potencial muito alta e extremamente alta à ocorrência de movimento de massa na bacia hidrográfica do Caeté compreenderam mais de 30% da área total da bacia. Palavras-chave: SHALSTAB, suscetibilidade a deslizamento, área de risco. Introduction Landslides are notable and significant processes Landslides, continuous natural phenomena that in slope evolution and are characterized by fast form landscapes, are the result of an association of movements (CUNHA, 1991). They may also be hydrogeomorphic, geological and anthropologic intensified by human activities and are similar to factors. According to Guerra (1993), landslides may floods, draughts and other phenomena that cause be defined as soil mass movement on a water- natural disasters. saturated foundation. They depend on several In Brazil, natural disasters associated with land factors, such as the slope angle, rainfall intensity and mass movements have became more and more frequency, vegetation cover, soil consolidation and frequent, especially in the 1990s and 2000s, with 454 others. registered events affecting more than two million The potential fragility to landslides occurrence is people (CEPED, 2012). Natural disasters caused by considered to be a natural vulnerability and depends landslides in Brazil spatially occur in greater on their physical characteristics such as slope, numbers in southeastern and southern Brazil, in the rainfall and soil type. Atlantic Rainforest, and temporally they are Acta Scientiarum. Technology Maringá, v. 36, n. 1, p. 101-109, Jan.-Mar., 2014 102 Vestena and Kobiyama abundant during the summer and late spring, and observed data, Fernandes et al. (2001) obtained especially in December, January and February. 95% efficiency with this model. Furthermore, Their occurrence in the Atlantic Rainforest is mainly Michel et al. (2012) applied this model and conditioned by steep slopes, relief (high altitude) SINMAP to the town of Rio dos Cedros, Santa and proximity to the ocean (more moisture). Catarina State, Brazil, and compared the models’ Further, the summer and late spring periods are performance in terms of identification of susceptive characterized by heavy rainfall events. areas. These authors concluded that SHALSTAB is In the Caeté catchment, municipality of Alfredo more suitable for landslide hazard mapping. Wagner, a mountainous region in the state of Santa In this context, it may be said that SHALSTAB is Catarina, Brazil, agricultural activities have provided highly applicable to Brazilian conditions. The rate of a decrease in water infiltration into the soil especially the stability index calculated by SHALSTAB is in areas with steep slopes and deforested hillsides transformed to the degree of landscape fragility for and riverbanks. There was a subsequent increase in landslides, which may be very useful for the overland flow which sometimes triggered a planning and environmental management. In fact, torrential flow under heavy rain. These factors have the procedure was applied to other mountainous altered soil erosion processes and created favorite region in the state of Santa Catarina. conditions for the destabilization of slopes by Current study determines the potential fragility triggering landslides and mudslides. In fact, the of the Caeté catchment for landslide occurrences by town of Alfredo Wagner has undergone land mass employing the Shallow Landslide Slope Stability movement and floods for a long time Model (SHALSTAB) proposed by Dietrich and (HERRMANN, 2007). Montgomery (1998). The prior knowledge on the most susceptible areas for the occurrence of landslides (hazard areas) Material and methods allows preventive and mitigating actions which may be implemented to reduce physical damage and Study Area human loss. Computer modeling has been of great The Caeté catchment (163 km2) lies in the service in the prevention of disasters. municipality of Alfredo Wagner in the mountainous One of the computational models to predict region of the State of Santa Catarina, between areas susceptible to landslides is the SHALSTAB latitudes 27° 52' 43'' S and 27° 41' 49'' S and longitudes which involves both hydrological (BEVEN; 49° 20' 45'' W and 49° 11' 17'' W (Figure 1). KIRKBY, 1979) and slope stability concepts The catchment is formed by the Caeté and Santo (MONTGOMERY; DIETRICH, 1994) to Anjo rivers with sources at altitudes 1,140 and 1,600 determine the index of slope stability. SHALSTAB m, respectively. Rivers´ densities (1.54 river km-2) has been used successfully in numerous studies and average drainage (1.95 km km-2) of the catchment conducted mainly in the western USA indicate a well-drained area. The waterways have a (GORSEVSKI et al., 2006) and in southern Europe - several small and big waterfalls as well as a large Italy (GULLÀ et al., 2008; MEISINA; number of headwaters (VESTENA et al., 2011). SCARABELLI, 2007), all of which have a temperate The terrain is dissected by steep slopes and climate. structural valleys where inappropriate usage Meisina and Scarabelli (2007) compared the two activities have made the land more susceptible to models SHALSTAB and SINMAP (Stability Index erosion processes. The dissection is represented by Mapping) proposed by Pack et al. (1998), by mountainous steep relief and hills. Alluvial-colluvial applying them to measure data from shallow landslides in an area north of the Alps, Italy. Results deposits lie in the basin, mainly comprised of sandy- obtained by SHALSTAB were more realistic for clay sediments with granules and pebbles with non-extreme events. The authors emphasized that predominantly quartzite lithology deposited in the index of slopes stability shown in both models torrential flow regimes (HERRMANN; ROSA, should not be interpreted as absolute numbers but 1991). The V valleys are characterized by tight an index indicating potentially dangerous areas. drainage system with high runoff velocity and In Brazil, studies with SHALSTAB also gave energy (VESTENA et al., 2011). satisfactory