ANALYSIS OF RELIEF ELEMENTS THROUGH THE TOPOGRAPHIC POSITION INDEX (TPI) IN THE ARROIO PUITÃ WATERSHED –RIO GRANDE DO SUL/BRAZIL

Abstract

This study aimed to determine the Topographic Position Index (TPI) classes in the Arroio Puitã watershed. The Arroio Puitã is located in southern Brazil, western portion of the state of Rio Grande do Sul. The altimetric basis for defining the Topographic Position Index, were the radar data from the "Shuttle Radar Topography Mission" (SRTM). The TPI is the basis of the classification system, and is defined as the difference between a cell elevation value and the average elevation of the neighborhood around that cell. Positive values mean that the cell is higher than its surroundings, while negative values mean that it is lower. The scale used to define classes of TPI was 10 pixels, that is, we used a radius of 10 pixels for the neighborhood analysis composing the average altitude and sets the TPI value of the central pixel. TPI classes were so-called: Valleys, Lower Slopes, Gentle Slopes, Steep Slopes, Upper Slopes and Ridges. The area of Gentle Slopes predominates in the watershed with 38.06% of the total area. The areas of Steep Slopes and Lower Slopes, are the second and third in larger areas with 27.15% and 27.11% respectively. The area of the Ridges occupies the smallest area with only 0.44% of the total area. The implementation of the methodology for determining the relief through the Topographic Position Index presented a result that responds well to the major relief features observed in the field, potentializing its application to other areas.