São Marcos Bay is located in “Golfão Maranhense” and it is a pleistocene estuarine system,
that receive hidrosedimentological contribution from Mearim, Pindaré and Grajaú rivers,
being strongly influenced by semi-diurnal macrotides. The main objective of this study was to
perform a multitemporal analysis (25 years - from 1977 to 2002) of the bathymetry and
bottom morphology of this water body in the sector adjacent to Itaqui Port through
quantification and estimation of rates of growth / displacement, identification of areas of
deposition and erosion and characterization of bedforms. The methodology consisted in the
acquisition and georeferencing of bathymetric maps No. 410, issued by the Management
Hydrography and Navigation of Navy of Brazil and the digitization of bathymetric isobath
and quotas. Bathimetric maps were developed from bathymetric contour (scale 1:135.000),
with spacing of 5 meters from the level curves, which allowed, with the bathymetric cross
sections, the analysis of multitemporal quantitative dimensions of the bedforms. The results of
multitemporal analysis of the bathymetric dynamics showed morphological changes both of
order as the depth in the study area, showing the high dynamics in terms of action of
macrotides and reverse flows active in the area. Ten morphological features were identified:
Main Channel and Itacolomi, Almas, Meio, Complexo do Coral, Darlan, Cerca, Cavalos,
Lanzudos and A banks. The sandy banks identified are included in the Perillo´s classification
(1995) as elongated bars of tide, with provision for longitudinal flow of tidal currents in
reverse, and Bank do Meio and da Cerca may still be classified as marginal linear bar the
channels. The banks had orientation and longitudinal displacement and / or growth towards
NE, in displacement rates ranging from 2.9 to 8.2 m / year, showing a more pronounced
action of the ebb currents in the process of reworking the basic features. However, the Darlan
Bank and the lower portion of the longitudinal axis of the Coral do Sul bank, presented
movement to SW, which may be associated with the phenomena of resonance and
amplification of tide occurring in the region. The fact of the São Marcos Bay is located in the
frontal area of the estuary of the Mearim river, means that this bay has a natural tendency to
sandy fill, attested in this study.
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