Automated analysis of landforms of the Paraguaçu River Basin / Bahia

, no estado


Introduction
The spatial arrangement of homogeneous landforms, landform elements and slopes shape are the result of the action of the tectonic forces, that provokes uplifts and relegation, and agents of the terrestrial surface that act in the rocky materials decomposing and disaggregating that over time develop different features and forms.
The development of geoprocessing methods mainly GIS makes it's possible to represent the terrestrial surface as digital models (DEM). Which allow the topographic analysis of a zone of interest, as well as the automated calculation of a series of related variable measurements using equations applied to numeric models of altimetric

Study Area
The Paraguaçu River Basin (Figure 1) is located in the central-eastern region of the state of Bahia, geographically limited by the coordinates 11 ° 00 'S and 14' 00 ° S and 38 ° 00'W and 42 ° 00 'W.

Methodology
The Paraguaçu River basin had its digital relief parameters, mapped and quantified with the GIS and the cartographic base consisting in data from codified hydrographic basins of (ANA -AGÊNCIA NACIONAL DE ÁGUAS, 2018), for spatial delimitation and definition of the rivers that constitute the basin.
It was carried out an analysis of morphometric parameters related to the hydrographic network and the Digital processing as well as the database was organized and managed with ArcGIS 10.3®, by spatial analysis and three-dimensional analysis tools. The hydrographic hierarchy of the channels net stands out, where the watercourses was classified and quantified according the proposal of Strahler (1952). The relief was characterized by the altitudes and amplitudes present of the basin and the its declivity, according to the classes proposed by Ponçano et al. (1981) and adapted by Trentin and Robaina (2005) (Table 1). The amplitudes are defined using the Focal Statistics tool that analyzes the difference in altitude in a circular mobile window with a two pixel radius and the declivity is calculated in percentage using the Slope tool that defines the slope between the pixels in a 3x3 pixel moving window over the DEM. For the determination of the relief elements the proceeding is based on the proposal of Jasiewicz e Stepinski

Results
The     The information and data of lithological and morphological was evaluated allowed to determine 10 Landforms Units ( Figure 8) and ( Table 2). Some of the main landforms units that make up the landscapes of the Paraguaçu River basin, are represent in (Figure 9).   In this type of landforms, the elements of the peak and pit are relatively important.
Included in this landforms unit occur a very peculiar shape, marked by the oriented ridge and wide slopes, associated with the exposure of an intrusion of metabasite Paleoproterozoic that constitutes the Orobó Saw (Serra do Orobó) ( Figure 10D).
In the extreme south, truncated by the main channel of the Paraguaçu River, it develops in a landforms of slightly undulations hills, defined by landforms unit 2, which constitutes the Middle Paraguaçu Pediplane   Figure 10F) characterized by undulated hills with narrow slope elements and ridge elements, spur and associated short valleys.
In the Iguapé Bay ( Figure 10I), the contact of these lands with the basement occurs through a rupture of the relief.
This coincides with the fault that delimits the eastern edge of the Recôncavo basin with Cretaceous age, where there is a transition from landforms undulating hills to slightly undulations hills and flat areas (unit 2) next to Todos os Santos Bay with sandy and mangroves.

Conclusion
This work confirms that landforms can be described and quantified into simple relief elements by parameterization of digital elevation model (DEM). In this research, the investigation of the morphometric parameters using equations applied to numeric models to characterize elemental forms associated with landforms, provide an input for pattern-based query tool capable of identifying all local landscapes similar to a given reference.
In this sense, associating the geomorphons elements and landforms with the nature of the lithologies and diverse structural was possible to describe and analyze the relief in 1 to 10 distributed from the upper course of the Paraguaçu River represented by the high plateau named Chapada Diamantina and the plane areas successively placed to downstream and characterized by slightly undulations each with specific elements.
The combination of different mapping techniques combined with increasingly modern and accessible digital mapping methodologies makes it possible to enrich the descriptions and expand the discussions on mapping in river basins, while using traditional mapping works in Brazil. The Paraguaçu River basin has a complex morphology and the combination of these different mappings and methods allowed the definition of ten landforms units.
This results expand the discussion on the use the digital relief-modeling theme to describe and assist in the construction of more detailed systematized geomorphological maps.