Perda de solo por escoamento superficial: uma abordagem retrospectiva para uma bacia hidrográfica na região metropolitana da Grande Vitória

Abstract

Soil erosion is a problem which affects mankind harshly and directly impacts the agricultural production, the hydric resources and topographical relief’s configuration. Several mathematic models were developed to forecast and avoid the catastrophic consequences caused by soil loss, aiming to estimate future trends regarding the erosive behavior upon a determined area based on topographic, climatic and land usage and cover parameters. Among these models, one stand outs: The Universal Soil Loss Equation, developed by Wischmeier and Smith in 1978, based on experimental plots observation in the United States and, for being easily replicable and requiring a pretty simple database, is widely accepted as a method of yearly soil loss through hydric erosion estimation in several countries, especially after the rising and wide adoption of Geographic Information Systems (GIS). The parameters for calculating this equation are the rainfall erosivity (R), soil erodibility (K), the slope length (L), slope gradient (S), cropping management factor(C) and the erosion control practice factor (P). When these factors are multiplied, they result in the total of yearly soil loss (A). In this study, the USLE was applied for the entire area of Duas Bocas Watershed, located in the state of Espírito Santo, Brazil, with the objective of identifying the frailest regions to be affected by the hydric erosion, and also, to retrospectively analyze the evolution of the land coverage and usage in this watershed since 1970 and its impacts on soil losses. Moreover, some comparisons were made for the soil’s erodibility factor between the ones registered in previous works with samples collected in situ throughout 39 points using the indirect method proposed by Sharpley and Williams (1990), seeking to check out if this method was adequate for obtaining the soil erodibility on the study area, based exclusively in variables like soil granulometry and percentage of organic carbon in the soil, without texture and the usage of Wischmeier and Smith’s Nomograph.