Morphodynamics of Embayed Beaches. Case Study in Cape Buzios, Rio de Janeiro, Brazil

Cape Buzios is a balneary touristic county located 180 km east of Rio de Janeiro city, Brazil. The geological site is composed by metassedimentary and metavolcanic rocks originated from a Cambrian and Ordovician (530-490 Ma) collisional event named Buzios Orogeny. The main characteristic of Cape Buzios is distinct structurally controlled beaches. The objective of this paper is to present results of morphodynamics of embayed beaches exposed to distinct wave's directions and relate it to the morphological response of beach profiles. Thirteen different beach profiles were monitored during four years in seven embayed beaches using standard topographic methods, resulting in over 250 beach profile data. Wind and wave data statistics; morphodynamic and embayment scale parameters; equilibrium profiles; closure depth; and planform stability were also calculated. Results led to the identification of three different morphodynamic conditions. The first two are low energy reflective and high energy intermediate beaches that are morphologically stable. In the first case beaches are narrow and equilibrated with their transversal profile. Closure depths vary from 3 to 6 meters. In the second case beaches are overfilled with sediments which even in high energy conditions permit rapid morphological recovery, closure depths are up to 20 meters. The third morphodynamic condition refers to unstable beaches that also have two different characteristics: one group of beaches presents permanently erosional profiles, while the other group presents episodic erosional profiles. The differences were in the range of exposition to higher waves and the volume of nearshore sediments available. Estimated maximum wave heights of 1,3; 2,4 and 5,4 meters can be respectively correlated for each one of the morphodynamic conditions described above.