Estimated volume of sedimentary deposits in river Araguaia, State of Goiás – Brazil, through Remotely Piloted Aircraft System (RPAS)

The Araguaia river basin covers an area of 386,000 km², with an average flow of 6,420 m3/s, being one of the main priority areas for the conservation of the Cerrado (Brazilian savannah) and water resources in Brazil. However, in the last five decades (since 1970), large extensions of this hydrographic region have been the object of an intense process of transformation associated with the advance of the agricultural frontier, particularly by monocultures of pastures, soybeans, corn, sugarcane and livestock. As a consequence of these processes of land use and occupation, the Araguaia river basin presents high levels of anthropization, mainly the emergence and acceleration of erosion and silting processes present in various sectors of the basin. There is also an intensification of channel silting, changes in water quality and negative impacts on aquatic ecosystems, as well as on the geomorphological and ecological processes of the alluvial plain, which represents a rapid response of the Araguaia river system to the changes that occurred in this historical period, shaping the middle section of this river system, in one of the areas with the greatest storage and transport of sediments in the Cerrado and in Brazil. In this article, using aerophotogrammetry techniques and three-dimensional models of the landscape, combined with the use of an RPAS, the objective was to quantify the volume of sediments deposited and/or stored at the confluence of the Araguaia River with the Vermelho River, in Aruanã, State of Goiás. The methodology was based on a set of aerial photos obtained with multi-rotor, DJI/Phantom4, low-cost and easy-to-operate RPAS, processed in PIX4D Mapper, allowing the elaboration of Digital Surface Models (DSM), and high-quality mosaics. spatial resolution, as well as the granulometric and sedimentological characteristics in the study area (sandy bars in the middle channel of the Araguaia River). In addition to geoprocessing tools and the use of satellite images (SENTINEL 2) to assist in the interpretation of sedimentary dynamics. With aerial records, modeling and sedimentological characteristics, the technique proved to be quite efficient in the quantification of sediments deposited/stored in the channel, allowing the identification of an area of 1.15 km2 and a volume of ~1318312.63 tons, in an extension 2 km from the middle section of the Araguaia River, with a hydrological quota of 163 cm. It was also identified that the Araguaia river in this stretch has a width of 300 to 500 meters, covering a large number of fluvial geoforms, with emphasis on the accumulation of sedimentary deposits, lateral and central bars, with the intercalation of coarse and medium sands, with fine sediments that mark changes in the hydrological cycles, different levels of connectivity with the river channel and the process of vegetation consolidation between the annual hydrological cycles.