Bedforms controlled by residual current vortices in a subtropical estuarine tidal channel

Abstract

The objective of the present work was to analyze the bottom morphology, the genesis of the bedforms, and the patterns of current and sediment transport of the internal portion of the south mouth in Paranaguá Bay, Paraná - Brazil. This region was used as a laboratory field to study the geomorphology of a dune field on a tide channel, with features of flood delta in the inner portion and ebb delta in the direction of the continental shelf. A sediment hydrodynamic model was used to calculate the direction and magnitude of the sediment transport and the residual current flows. A map of apparent roughness was used in the numerical model, obtained through the soundings of a sidescan sonar (Starfish Sonar) and estimated from the classification of the dune field, so it is possible to obtain simulations with higher correspondence with reality. It was observed two vortices of residual circulations near the shores of Pontal do Sul and Ilha do Mel, with directions towards the continental shelf. The residual circulation vortex is responsible for the triangular shape of the large dunes near the Pontal do Sul margin. In the flood, the sediment material is conducted inward forming small ripples and accumulating sediment material on large dunes. During the ebb, these ripples are supposedly destroyed and attached to the large dunes or to the water column. On the other hand, the bedforms of Saco do Limoeiro are formed due to the effects of the tide when entering the mouth and the confinement of the water mass in the region until the next moment of padding.