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.