Técnicas de geoprocessamento para avaliação da evolução do assoreamento no arroio João Dias no município de Caçapava do Sul, RS

Abstract

Pollution of water sources, deforestation, silting of rivers and waterproofing of the soil, among many other actions of modern man, are responsible for the degradation and contamination of water. In hydrographic basins, riparian forest is essential in the creation and maintenance of life in rivers. Its removal, in addition to affecting aquatic life and the entire ecosystem of the region, can accelerate the process of natural erosion and cause the silting up of natural or artificial water resources. Geoprocessing has allowed for better management of large areas quickly and accurately. The studies that seek to understand the factors that contribute to silting up, aim at the analysis of land use, through satellite images and the development of a Geographic Information System (GIS), containing in an integrated way all the information available for a region. Thus, the study sought to evaluate and monitor the main areas of silting occurrence in the riverbed, with the aim of analyzing the causes of the erosion process and verifying the degree of silting present in the João Dias Stream, in the municipality of Caçapava do Sul. used basically covers 6 stages, starting with the temporal analysis of satellite images; acquisition of the rain erosivity map; creation of the soil erodibility map; obtaining the map of the topographic factor and use, management and conservation practices; and map algebra with USLE variables. As a result, the Arroio João Dias Hydrographic Sub-basin presents, in 71.12% of the area, soil losses classified as low (10 ton.ha-1.year-1), mainly due to characteristics such as land use and occupation and geomorphological conditions present in the region. The losses considered to be of high intensity, that is, from 50 to 200 ton.ha-1.year-1, occupy 27.02% of the area and are associated with countryside vegetation. The erosivity classes above 200 ton.ha-1.year-1 represent 1.87% of the sub-basin, being classified as very high erosion. These high levels of erosion correspond to the area located around the open pit copper mine and the tailings dam region, showing a high degree of silting in the João Dias stream bed. With the 34-year temporal analysis in the Minas do Camaquã region, where 11 satellite images were compared over the years, the changes in the vegetation cover were analyzed, observing a 50% reduction in native vegetation from 1984 to 2019, a 35% increase in exposed soil and a 68% increase in countryside vegetation. The possible causes identified for the increase in silting up were the removal of the Permanent Preservation Areas, the construction of the reservoir and the presence of exposed soil on the banks of the stream and in the tailings dam located near the stream.