Caracterização preliminar da bacia de drenagem do rio Marapanim

Abstract

The coast of Pará stands out in the Brazilian context for the uniqueness of its morphology: it is an extremely jagged coast, composed of alternating tapered bays and sandy tips that, in reality, are indicators of a complex past evolution. Although extremely interesting from a scientific point of view, this type of coast has been relatively little studied in the north of Brazil, where there is a real lack of basic data, especially cartography. The objective of the present work is to contribute to fill this gap through the characterization of the Marapanim river basin and the elaboration of a detailed drainage map, by means of the analysis and interpretation of aerial photographs in 1:70,000 scale, subsidized by a field control, taking into consideration the parameters established by Howard (1967), Soares & Fiori (1976) and Summerfield (1991) for drainage network analysis. In terms of general characterization, the Marapanim River, whose sources are located in the municipality of Castanhal, presents an alluvial channel of the meandering type, except when it reaches the "bay" of Marapanim and acquires a tapering configuration. Its drainage basin is elongated, asymmetric and constituted by a series of sub-basins. The basic drainage pattern is of dendritic to sub-dentritic type, with several modified sub-patterns and associated anomalous forms (arch, elbow, etc ...), probably related to the interactions of geological geomorphological factors, nature of the sediments, terrain permeability, among others. At the drainage texture level, two main types were identified: fine texture, developed in the fluvio-estuarine plain, and characterized by a dense drainage network, quite branched and disordered (multidirectional); coarse texture, which develops in the coastal plateau domain, on the contrary, exhibits a low degree of branching and more spaced waterways.