Comportamento Morfodinâmico da Praia da Taíba, Nordeste do Brasil

Abstract

Beach morphodynamics is a study method that integrates morphological and dynamic in a more complete description of the beach and surf zone. Morphodynamic aspects of Taiba beach were characterized from June 2006 to August 2007. Wave height and period and beach particle size were recorded. Beach profiles, dimensionless parameters of Dean (Ω), surf-scalling parameter (Σ), Beach Index (BI) and Relative Tide Range Parameter (RTR) were calculated in order to compare different classifications that describe the beach morphodynamics. Sediment samples were collected in two beach zones: 1 (0-30m) and 2 (30-60m) from the swash zone. Wave heights ranged from 0.40 m to 0.60 m and the period of 5.93 s to 8.31 s, classifying Taíba as moderate wave energy beach. The average rating of the sediment was composed of fine or very fine sand, presenting, however, in some months, samples of medium sand in zone 2, probably due to wave action that breaks the selected area of the sediment, moving finer particles. The parameter values of Dean (Ω) and BI ranked Taíba as intermediate beach, providing, however, a few months in reflective mode characteristics. The surf-scaling parameter indicated wave dissipation, with spilling waves by the coefficient of surf, RTR and indicated that the tidal action is principal modifier of beach profiles. The beach had moderate wave energy, with low variability in height and wave period in the surf zone. In most months there were large tidal ranges, with more than 80m in length. The profiles presented angles between 1/16 to 1/35 and could be characterized as a low tide terrace. The surf zone was well-defined, relatively long, between 50 and 100m, with frequent occurrence of more than one line break waves. There are different proposals for the classification morphodynamics but for meso and macrotidal environments, such as the Taíba beach, the application of Dean parameter is not enough to characterize the morphodynamic behavior, it is necessary to incorporate factor variation of tidal range to obtain a more satisfactory classification. Therefore, the intermediate morphodynamic state of Taiba beach can be considering from two different indexes, with a complete description by use of the Beach Index and the Relative Tide Range Parameter. Understanding of the processes responsible for the morphodynamics of coastal environments is necessary, given that such processes play an important role in the formation and stabilization of the beach environment, and is the first step towards a management of these spaces in a sustainable manner.