Abstract
Abstract Wave-dominated embayed beaches on irregular rocky coastlines are highly appreciated for their landscapes and tourism potential. Yet our understanding about the interaction of the oceanographic processes with the geological inheritance in this type of beaches still needs further investigation to better understand their natural balance. In this study, we apply the classical approach of morphodynamics to describe for the first time the variations in the Boiçucanga beach morphology, an embayed beach located in São Sebastião City on an irregular rocky coastline that is well known for its beautiful beaches embedded in the valleys of Serra do Mar. Field surveys were performed over 15 months, between April 2008 and September 2009, seeking to evaluate the interactions among the morphology, sediments and hydrodynamic characteristics at Boiçucanga. All data generated during the field surveys have supported the application of the following morphodynamic models: Classification of morphological beach stages [O]; Number of nearshore sandbars [B*]; Relative tide range [RTR]; Beach exposure on embayed coasts [Ro/a and ß]; and Embayment beach scaling parameter [d] to determine the geomorphological behavior of the beach on monthly and annual time scales. From these models, Boiçucanga is classified as a deep embayed beach exposed to high-energy waves, with a predominant reflective profile, which favors the development of beach cusps and topographically controlled rip currents. The combined results of the field observations and applied models allowed us to better understand the role of geological heritage in the two morphodynamic signatures found at the same beach arch. For future studies, we will focus on numerical models to increase the understanding of the hydrodynamic processes that govern the sediment transport in Boiçucanga.
Highlights
Beach morphodynamics refers to the dynamic interactions between hydrodynamic processes and sediments disposed on the beach profile (Short and Jackson, 2013). Short (1999a) suggests the following five major parameters to describe beach systems: 1 - tidal range, 2 - wave height, 3 - wave period, 4 - sediment grain size/shape and 5 - beach length/embayment
The Google Earth images from 10/01/2009, 20/06/2015 and 12/06/2016 show a suspended plume of sediments crossing the western limit of Boiçucanga. This process of sediment bypass indicates that Boiçucanga is not a closed system regarding coastal circulation cells and sediment transport
The Silvester and Hsu (1997) model was applied to Boiçucanga, and the existence of topographically controlled rip currents and beach cusps indicated a large influence of the surrounding headlands on the coastal circulation and approaching waves
Summary
Beach morphodynamics refers to the dynamic interactions between hydrodynamic processes and sediments disposed on the beach profile (Short and Jackson, 2013). Short (1999a) suggests the following five major parameters to describe beach systems: 1 - tidal range, 2 - wave height, 3 - wave period, 4 - sediment grain size/shape and 5 - beach length/embayment. The classification of morphological beach stages [Ω] (Wright and Short, 1984), the numbers of nearshore sandbars [B*] (Short and Aagaard, 1993), the relative tide range [RTR] (Masselink and Short, 1993), the beach exposure in embayed coasts [Ro/a and β] (Silvester and Hsu, 1997) and the embayment beach scaling parameter [δ], modified after Short and Masselink (1999b) by Castelle and Coco (2012), are among the most representative models of the classical morphodynamics approach, all widely cited in the specialized literature These specific models were chosen for this study because they are complementary to each other, forming a very important set of tools for integrated analysis of beach systems, when applied jointly. We have applied the above mentioned models to describe, for the first time, the dynamic morphology of Boiçucanga, an embayed beach located on the north shore of São Paulo, Brazil; a wellknown region for its natural beauties and its role as an important tourist location in the local economy
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