Distribuição das formas de fundo e padrões sedimentares no porto do Mucuripe, Fortaleza-Ceará

Abstract

Mucuripe headland presents constant morphological changes in the subaerial and subaqueous areas since the 1930s. This study focuses on the adjacent submarine area of the Mucuripe Harbour in Fortaleza. It was performed an analysis of the substrate acoustic responses associated to constant interventions for port management. The submerse morphology of the Mucuripe Harbour was classifi ed taking into account the integrated view of environmental conditions (processes, forms, and human intervention) in the construction of the underwater landscape. It has been used high resolution seismic and sonography, and compilation of sedimentological data. The acoustic responses resulting from sedimentation patterns and submerged forms constituted the echofacies. The echofacies I is associated to muddy substrates (mainly fl uid mud) and subsurface refl ectors, mainly related to the evolution basin, and to port access canal (areas sheltered by the Titã jetty). The echofacies II has subsurface layers and compact compartment, where the refl ectors are not clearly observed, it is associated to the evolution of the echofacies I and consequent compaction, also located in sheltered sectors. These two echofacies show the fl at bottom morphological pattern as dominant, being interrupted only in sectors with dredging marks – micro-canals. The echofacies III shows high refl ection coeffi cient, substrate related to sand ripples and subaqueous dunes, associated predominantly to the jetty out of the sheltered sectors. The echofacies IV is associated to rocky substrates and it has a high backscattering, located near the Pier. As morphological patterns, it was verifi ed features products of the dredges in the port access canal and basin of evolution – slopes, micro-canals, and mounds. The grain size contrast between the canal and its surroundings was evidenced, in the area out of the sheltered sector the predominance of sandy bottoms was observed, with micro-features – sand ripples and macro-features – bank/dunes and in the sheltered area the predominance of fi ne sediments occurred. There is an outstanding feature possibly associated to a small boat sunk near the pier. The presence of fl uid mud, mainly within the canal (evolution basin) is due to the deposition of fi ne sediments (<0.062 mm) and to low hydrodynamic (“shadow” eff ect of the Titan). The constant silting in the sheltered sector imposes the mapping of sectors with fl uid mud. This fact is of crucial importance to the management of the places where the dredging is necessary to ensure safe depths for navigation.