Dinâmica do uso e cobertura da terra e a ocorrência de inundações no médio curso da bacia hidrográfica do Rio Santo Antônio, ilha do Maranhão

Abstract

The purpose of the urbanization process is to search for better living conditions and professional opportunities. With the saturation of large urban centers, the population settles in areas considered unsuitable, such as on slopes, on the banks of river channels and in other morphologies, which are altered and consequently water pollution occurs, vegetation removal, silting of the river beds, dumping of effluents in channels and others. It is in the rainy season that the effects of human activities in the channels are notorious, with the rise in the water levei of the rivers, the phenomenon of flooding occurs, which consequently affects the population in its surroundings. The study area of the research is the middle course of the Santo Antônio river basin, being located in the northeast portion of the Maranhão Island; covers the municipalities of São José de Ribamar and Paço do Lumiar, with an area of 19.25 km2. The general objective of the research is to analyze the dynamics of land use and cover and the oecurrence of floods in the middle course of the Santo Antônio river basin, Ilha do Maranhão. The specific objectives are to assess the types of land use and land cover in the study area; to identify the areas with oecurrence of floods and to characterize the alterations that occurred in the middle course of the river basin of Santo Antônio, Uha do Maranhão. For research, bibliographic surveys were canied out. For the characterization of the watershed, a morphological analysis was performed using factors such as slope, relief units, surface curvature, hypsometry and fluvial hierarchy. As a result, it appears that the study area has a moderate slope, with a gently undulating relief, as there is a predominance of sparse hills. The curvature of the surface indicated that 95.71% of the slopes in the area are straight, which provides greater speed in surface runoff and facilitates urban occupations close to the channels. Altimetrically, the basin had the highest percentage in the variation of classes between 15 and 40 meters, with the presence of boards in the locality being not very expressive. Regarding the hierarchy of the channels, the médium course has 18 first-order channels, 5 second-order channels, 2 third-order channels, and the main channel is defined as fourth-order. As for the use and land cover, there are 3 classes, namely, exposed soil with an area of 31.28% of the total; urban area with 21.65% of the total; and vegetation, with 47.04% of the total area. A comparison of the drainage of the channels of the 1980s with those of the 2020s was carried out and the silting and channeling of the fírst order channels was observed, with a significant loss of drainage channels in a time interval of 40 years. A map of the location of the flooding phenomenon was prepared with the main points of oecurrence of the phenomenon. Interviews were carried out with residents in Mercês and Cidade Verde, where all reported that they witnessed the phenomenon studied and the year with the highest oecurrence was 2021, with rapid and intense rains. As a characterization of the changes in the study area, the models of Rapid River Assessment Protocol, by the authors Carvalho (2010) and Lobo (2011) were applied at 5 points in the middle course of Santo Antônio, analyzing each parameter. It is stated that all analyzed points are altered. In the middle course of the Santo Antônio hydrographic basin, alterations were identified in its channels, such as irregular disposal of solid waste, suppression of vegetation, occupation of river beds, erosive processes on the banks of the channel, silting and impermeable areas, factors that cause disturbances to the population in the rainy season with the oecurrence of floods in the hydrographic basin