Delimitação e caracterização morfométrica da sub-bacia do Rio Gurjaú com o uso de geotecnologias

Abstract

The study of the characteristics of a river basin allows one to understand its dynamics and to carry out an adequate management of its resources. With this in view, the present work aimed to characterize morphometrically the sub-basin of the Gurjaú River, in the Metropolitan Region of Recife -PE, through geotechnologies. In this study, a shapefile of the municipalities of Pernambuco was used, which assisted as a visual reference to locate the water course, and an SRTM image of spatial resolution of 30 mx 30 m, referring to the study area, provided by the National Institute of Space Research (INPE). Using Google Earth Pro, the Gurjaú River was identified. The image was imported into the free software Spring 5.5.4 ̧ where the isolines, the water flow directionmatrix and the flow matrix accumulated in each cell were generated, which were used to delimit the sub-basin. The area and perimeter of the basin were measured and the water flowswere vectored. The altitude was rated 30 by 30 meters. The gradient grid was generated, and the maps of hypsometry and slope were elaborated. The following morphometric parameters were calculated: compaction coefficient (Kc), circularity index (Ic), shape factor (Kf), elongation ratio (Re), drainage network, drainage hierarchy, drainage density (Dd) (Dh), torrentiality coefficient (Ct), maintenance coefficient (Cm), roughness index (HD) and relief ratio (Rr). The minimum altitude found in the sub-basin was 0 m, and the maximum altitude was 370 m. The most representative altitude class along the sub-basin was between 90 and 120 m, while the least representative was between 360 and 390 m. The minimum slope was 0% and the maximum found was 181.57%. The relief of the region is mostly wavy, presenting between 8% and 20% of slope. The area found was 148,115 km², the perimeter was 68,948 km and the axial length of the sub-basin was 22,723 km. The values obtained for the morphometric characteristics were: Kc = 1.586; Ic =, 392; Kf = 0.287; RL = 0.604; total length of watercourses = 110,226 km; hierarchy of channels = 4th order; Dd = 0.744 km.-2; Dh = 0.317; Ct = 0.235; Cm = 1344.09 m².m-1; HD = 0.277; Rf = 16.28. It was possible to notice that the sub-basin of the Gurjaú River has an elongated form, with slopes not very steep, and therefore is not subject to floods.