Comportamento de análises em superfície planimétrica e modelada frente a representações cartográficas e índices geomorfológicos - Bacia do rio cuiabá - Petrópolis (RJ)

Abstract

There are a number of alternatives to work with the dimensions of the elements of a landscape, such as the use of digital elevation models (DEM), and even then the GIS has a limitation established by not considering the irregularity of the space to be analyzed. In this sense, the analysis in the pattern surface has a greater accuracy regarding the measurements in the landscape, as in the case of geomorphological analysis. In order to provide more subsidy of how different observations in planimetric and modeled surface behave by variations of size and morphological measurements, this work seeks to compare results of geomorphological indices obtained from these two types of observations in the Cuiabá river basin, located in the municipality of Petropolis (RJ). Every study was developed on the scale of 1:10,000 topographic compiled bases provided by the city of Petrópolis (RJ). From this base were built geomorphological indices in planimetric surface. Indexes works are: Topographic Gradient (Tg), drainage density (Dd) and Drainage Efficiency Index (DEI), which were extracted for 41 second order basins of the Cuiabá River basin. The Dd and DEI indices were applied to the surface modeled from a digital elevation model (DEM) that had as its source the planialtimetric data of the cartographic base. In addition to these two indices, it was also considered the hollows for these second order basins, which is part of the surface runoff system together with the hydrography. Results showed a significant increase in modeled surface compared to planimetric, mainly in relation to basin area and drainage length measurements, with an increase of 18.8% and 5.31%, respectively. When the hollows were added to the hydrography, a percentage difference of 8.19% was obtained for the total drainage. These values were decisive for the modification of the results of drainage Density and Drainage Efficiency Index, which had a mean decrease in their respective values of -9.52% and -9.62%. With this, the cartographic representations generated from the observations in the modeled surface presented differentiations in relation to those elaborated with planimetric observations. In addition, the use of the observations on modeled surface was more representative when analyzing the results in relation to the mass movements investigated in the study area. This framework points to new possibilities of morphometric analysis, since these observations can be used in other analyzes or in new geomorphological interpretations, increasing the understanding of the hydrological and erosive dynamics of a landscape.