Mar do Ararapira is an unusual estuary located at the border of Paraná and São Paulo states, in a relevant area of ecological interest and where an opening of a new inlet occurred in August 2018. Differing from classical estuarine models Mar do Ararapira has three inlets, one with open sea and two with the estuarine systems of Baía de Trapandé and Baía dos Pinheiros, the latter through an artificial channel named Canal do Varadouro. Mar do Ararapira also has multiple riverine inputs and the estuary head is not well defined. This paper presents: (a) Mar do Ararapira watershed characteristics, (b) an update of coastline shift close to the inlet and (c) a characterization of the estuarine bathymetry, bottom sediments and bedforms in 2009 and 2011. Comparison of parameters before and after an opening of a new inlet will help both the management of the estuary`s natural resources and the lives of the people inhabiting the surroundings. It is concluded that Mar do Ararapira corresponds to the lower part of an estuary. Its watershed extends 221.6 km 2 and is composed by three different morphologic sectors, which drains mountains and coastal plains. It presents a significant fresh-water input, estimated to range from 6.6 to 9.1 m 3 /s, and weak connectivity with its neighbor estuarine complexes. It is a shallow water body, with a mean depth of 4 m, where a deep main channel suggests intense bottom erosion by tidal currents. The ocean inlet migrates southwestward, mainly under the influence of high energy events. Prevailing bottom sediments are sand and muddysand. Subaqueous-sand-dunes and plane-beds are the most common bedforms at Mar do Ararapira. Three estuarine dynamically different sectors were recognized: (a) an inner sector with low tidal-current velocities and finer sediments; (b) a middle sector similar to a fluvial meander in dynamics, with higher tidal-current velocities and sandy sediments, where concave coasts are continuously eroded and convex coasts are silted; and (c) an outer sector, in which tidal-currents are segregated.
This study examines surficial sediment distribution patterns, slope and morphological characteristics of the Paraná inner continental shelf. Paraná inner continental shelf is located on the southern Brazilian continental shelf, a wide and low gradient shelf, in the vicinity of two large unfilled estuaries and the Serra do Mar mountain range. It is characterized as a wave/storm dominated continental shelf with microtidal, semidiurnal regime and a small supply of recent continental sediments. We analyzed grainsize parameters and sediment composition of 875 grab samples and investigated the inner continental shelf morphology and slope through a digital bathymetric model built from regional nautical charts. We combined and evaluated the characteristics of grain-size curves, the spatial distribution of sediments, and the morphology and slope of the inner continental shelf to identify different sedimentary facies. Sediment distribution patterns change from the coast seaward and between three defined sectors along the coastline: south, central and north inner continental shelf. This variation seems to be related to recent sediment sources and to the presence of deposits from ancient coastal plain and inner continental shelf environments formed before the last Holocene sea-level highstand. Sediments with mean diameter of fine to very fine sands prevail at all depths. Deposits of sediments with mean diameter of silt and medium to coarse sands are significant in particular areas, generally associated with steep slopes, troughs, and sand ridges. Possible causes of sedimentary patchiness are the outcropping of medium to coarse sand and the supply of recent estuarine muddy sediments provided by large estuarine complexes to the Paraná inner continental shelf. The results obtained contribute to the knowledge about the sediment dynamics of Paraná inner continental shelf.
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