Ocorrência de voçorocas (gullies) na rodovia BR 174, trecho Manaus-Presidente Figueiredo (Am): gênese, morfologia e previsão de riscos

Abstract

The analysis of the erosive process is of great importance in maintaining the characteristics of the soil and its environment. Therefore, this work has as main objective to map the gullies of the BR-174 federal highway, in the stretch between Manaus and the municipality of Presidente Figueiredo. Its specific objectives are: characterization of the gully morphometry, description of environmental aspects and degradations in the highway and prediction of the risks of the incisions until reaching the runway. In this regard, the following methodology was used: First, cartographic data collection and literature review, product interpretation (satellite images), field survey and final presentation of the results. Two field surveys were carried out by GPS, tape measure, compass and registration records, observing the aspects regarding the shape, type and eroded volume of the incisions (width, length and depth); characterization of geological formations and geomorphology. When it comes to soil aspects, samples were collected through depths of up to 1.50 meter depth, infiltration and penetration tests and subsequent laboratory analysis of soil physical characteristics. Parameters were used for the elaboration of erosion risk prediction. The results found in the monitoring allowed to affirm that 21 incisions are in the stretch comprised between kilometer 5,3 and 56,1. Located at kilometer 5.3, the gully number 01, registred with the longest length of 159.0 meters, the width of 13.00 meters and depth of 10.00 meters, it is not relatively larger in the 2,067 m² area when compared to the larger incision by area: the gully number 15 in kilometer 45 equivalent to 6,360.31 m². Both are proportionally equal in length, but in terms of area and volume eroded are different. Considering the 21 gullies, 5 presented eroded volume to 999m³; 11 presented eroded volume between 1,000m³ and 9,999m³, classified as small, 3 are medium size, between 10,000m³ and 19,999m³; 3 are large size, between 20,000m³ and 40,000m³. A total of 8 gullies presented medium-term risk and 13 gullies with long-term risk. Several factors corroborate the emergence of erosive incisions: anthropic (road paving, ineffective maintenance of gullies), poorly sized rainfall drainage systems, not taking into account intense periods of precipitation in the study area, causing degradations, such as silting up streams. It was also considered, as regards the highway construction project, the correct technical specification for revegetation of the slopes and the local geomorphology itself, being these potentiators of the erosive process emergence.