Relação entre feições doliniformes e a evolução de uma voçoroca em cabeceira de drenagem na Bacia Hidrográfica do Arroio Sarandi, municípios de Santa Maria e Dilermando de Aguiar-RS

Abstract

This paper analyzes the contribution of doline type depressions for the evolution of a gully located on the watershed of Sarandi Stream, in Santa Maria and Dilermando de Aguiar/RS. In order to do that, physical characterization and evaluation of erodibility tests with the use of indirect methods were performed on the materials composing the said gully. The results of the tests indicated that sandstone, which is in the basis of gully, is more erodible than the horizon A/B of the soil located above it, a fact which can be related to the loss of resistance due to suction and the apparent fragility of the cementing agent between the particles. The difference in erodibility between the sandstone and the soil could partly explain the genesis of karst features, because water percolation along the sandstone would result in ducts originated from the entrainment of particles and/or from the dissolution of the cement, thus provoking the collapse of the material above them (surface layers). This process occurs more easily in the surroundings of structural lineaments. Once established on the landscape, dolineform depressions tend to join due to surface flow, evolving into incised channels that deepen and promote the advance of the gully upstream.