Inaccuracies on morphometric characterization of watersheds on GIS ambient

Inaccuracies on morphometric characterization of watersheds on GIS ambient
Vitor Souza Martins1; Demetrius David Da Silva2; Hugo Alexandre Soares Guedes3; Bárbara Batista Porto4

1. Majoring in Agricultural and Environmental Engineering, at Federal University of Viçosa (UFV), scientific initiation scholarship from CNPq. (vitormartins9@hotmail.com)
2.UFV third associate professor; 1A Productivity Research Fellow from CNPq. (demetrius@ufv.br)
3. UFV substitute professor; PhD researcher in Water and Environment Resources. Sponsored by CNPq. (hugo.guedes@ufv.br)
4.Majoring in Environmental Engineering, at Federal University of Viçosa (UFV); scientific initiation scholarship from CNPq. (barbara.porto@ufv.br)

Abstract: The morphometric characterization of watersheds is done, nowadays, with the integration of relief information in Geographic Information System (GIS) interface, extremely applicable on planning and management of water resources. The study objective was to analyze the vegetation and relief influence on the morphometric characterization of “Pedras Negras” stream, at Petróplolis-RJ, comparing the hydrographically conditioned digital elevation models (HCDEMs), generated from sensor VNIR of ASTER (Advanced Spaceborn Thermal Emission and Reflection Radiometer) data, with the model obtained from the processing of IBGE’s topographic maps on the scale of 1:50.000. The study area is characterized for gneissic stone outcrops up to 2263 meters elevation, and surrounded by Atlantic forest, which has full vegetation with trees that reach 40 meters high. The processing and treating of the models had guaranteed the hydrographic conditioning, resulting in models with no spurious depressions, with stream flow originated from riverheads and a detailed and ramified drainage system. The percentage variation of the morphometric data valued by DEMHC ASTER compared with those valued by DEMHC IBGE were superior to 10% for main river length results (22.5%), total length drainage system (24%), watershed contribution area (10.9%), shape factor (-41.3%), drainage density (14.7%) and the river axial length (20.9%). The expressive variations between the models came from the vegetation behavior, which inclines and shadows the river border, causing inaccuracy on the river channel reconnaissance. The DEMHC ASTER presented an average slope variation of (20.9%) compared with IBGE maps, showing a tendency of the models to soothe the relief, loosing curacy on the determination of riverhead points and tributary rivers points also. In a general way, we can see good congruity between DEMHC ASTER and IBGE for hydrologic studies, where the most appropriate on the current study was to work with DEMHC generated from IBGE’s maps.

Keywords: Geographic Information System, Watershed, digital elevation models, morphometric characterization.

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