Avaliação de estilos fluviais da bacia hidrográfica do Riacho Grande, Alagoas

Abstract

The researches of fluvial systems of drylands is lower in comparison with the studies developed in humid regions, lacking researches that highlight the particularities of these environments. Thus, the research brought as issue the investigation of the fluvial dynamics of a hydrographic basin of the semi-arid environment of Alagoas through associations between the local and regional physical characteristics, their structural controls, and the interventions resulting from human action. The objective is the characterization of fluvial typologies that exhibit the above-mentioned set of characteristics in order to know in a more detailed way the hydrosedimentological dynamics of the main course of the Riacho Grande watershed. Starting from the hypothesis that the aspects analyzed together can show impacts on the formation and development of depositional features in the Riacho Grande. With this purpose, it was sought to apply the first stage of the theoretical-methodological approach of fluvial styles to the main channel of the basin. It was necessary the application of the Declivity-Extension Ratio (DER) index seeking the plateau ruptures; the mapping of land use and land cover aiming the anthropic interferences; and the mapping of landscape units for the investigation of domains of regional topographic controls. It was revealed that plateau rupturesmay be controlling sedimentation processes along the main course along the three landscape units identified in the basin, being delimited with regions of homogeneous slope and topography. In these units, land use showed an increase in anthropic intervention coverage over a 20-year period. Finally, four fluvial typologies were identified: Unconfined, semi-confined with alluvial bed, confined with mixed rock-aluvial bed, and confined with discontinuous floodplains. Each typology allowed understanding the association of the data obtained and its expression in sediment deposits along the channel (or its absence). The research has proven relevant to the development of studies in tropical drylands. Based on the initial phase of the fluvial styles methodology, the character and behavior of the stretches could be evidenced and correlated in a way that becomes useful for the management and planning of the study area in relation to waterresources.