Erosive processes in urban areas in the Island of Maranhão - Brazil

Abstract

Urban erosion in Brazil can be related to the lack of a planning that considers the particularities of the environment and the socioeconomic conditions of the urban development. In that sense, the occurrence of erosive processes generally is associated to areas of irregular population settlement, where there is no planning. Along the Island of Maranhão it may be encountered rills and gullies on those areas, putting at risk houses and people's lives. The main factors of superficial and subsurface water flow, that generate rill and gully processes, are the soil properties, rain regime, characteristics of the slopes, soil use and deforestation. In that sense, the environmental situation observed in São Luís is prone to gullying. Rocks of high porosity and low hardness are found. It is one of the most dissected parts of the Island of Maranhão. The annual rain regime is marked by a rainy period and another one with rain deficiency. The soils present, in tactile-appearance identification, high contents of sand and silt and clear colours, which are the evidence of low organic matter content. The original vegetation cover has been cleared intensely. Considering the current conditions, the soils are, in general, very susceptible to the erosive processes, mainly when submitted to human intervention, without planning. Monitoring of the erosive processes carried out since January 2001 demonstrates a recurrence of soil erosion, where the vegetation was removed, on slopes between 5o and 15o, occupied by irregular population settlements, without basic urban infrastructure, especially sanitation, rain pipes and paved roads. The erosion presents itself more intense in those areas of recent demographic expansion, where areas with potential environmental risk can be found, provoking land degradation and silting up of the water bodies, patrimony losses and death risk. Therefore, the understanding of the factors that generate erosive processes, as well as the application of control measures and prevention are fundamental actions to the public safety.