Mapeamento geomorfológico aplicado na análise de impactos ambientais urbanos: contribuições ao (re)conhecimento de morfologias, morfocronogêneses e morfodinâmicas do relevo da bacia hidrográfica do Arroio Feijó - RS / Geomorphologic mapping applied to the analysis of urban environmental impacts: contributions to the (re) cognition of morphology, morphochronogenesis, and morphodynamics of the Feijó/ RS stream basin relief

Moisés Ortemar Rehbein

Urban environmental impacts generate various social disorders. In many cases, the analysis of environmental impacts should be the agenda for everyday discussion, included in urban planning policies. As support to these policies of urban planning in a perspective of applicability of geomorphologic knowledge we highlight the thematic mappings in geomorphology.This research, at large, aims at the analysis of urban environmental impacts in the Feijó stream hydrographic basin, using geomorphologic mapping detail as a reference tool, demarcation, and synthesis of these analyses. Ab\ Saber (1969), Ross (1992), and Fujimoto (2001) are presented in the theoretical and methodological research done. Highlighted as operating modes are the activities of research in literature, elaboration of cartographic documents, field work, and based on these activities, the analyses. Understanding urban environmental impacts requires the recognition of the processes that generated them and that, in their own movement, transformed them. Urban environmental impacts form, along the historical process, by judgments of value of significance of disruptive effects, of genesis or anthropogenic consequences, in the urban city or beyond, in the environment, which, in promotion of ecological and/or social changes, questions states of selforganization and/or of relative environmental stability. The apprehension of urban environmental impacts stands out by understanding environmental processes through the most possibly articulated multidimensional analysis. Guidelines for structuring geomorphologic detail mapping, highlighting the elements of approach agreed upon by the Committee of Geomorphologic Mapping Research of the International Geographical Union (IGU), morphographic, morphometric, and morphocronogenetic data of the relief, when the morphodynamic readings of the relief are added, is believed, in the case of the Feijó stream hydrographic basin, to well underlie analysis of environmental impacts. Hydrographic, geological, pedological, pluviometric, socio-historical, and socio-economical data approaches contribute to the structure of the geomorphologic mapping of the Feijó stream hydrographic basin and, from this, the recognition of outstanding environmental impacts in the urban hydrographic basin concerned. In the context of the geomorphologic mapping standards, units and geometries of sections of the Feijó hydrographic basin relief are recognized, as well as forms of current processes, pedological aspects and areas of relatively recent morphogenetic indications of the relief are also recognized which, significantly altered in the process of human occupation of the hydrographic basin: there is an increased flow by land and a consequent reduction of infiltration. Change in the hydrological system of the slope is verified, and consequently of the course of the river. With intense alteration of the morphogenetic processes, marked by the increase in superficial flows, there is a collapse in the functionality of the canals, with the undermining of the banks, silting, and their flooding. Aiming at mitigating the problems arising from these situations, among other practices, the process of rectification of river courses is used, which becomes permanent. Thus, the search for the genesis, functions, and relations are imposed, for a better understanding of environmental impacts. One should consider this as a constant search among the variables of environmental dynamics, among which, the morphodynamics of the relief of the Feijó stream hydrographic basin is indicated.

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