Tropical sandy beaches of Pernambuco state

Abstract

Pernambuco state is located in the Northeast region of Brazil and has a 187 km long coastline containing a range of coastal environments including beaches, estuaries, reefs and headlands all with varying degrees of preservation and occupation. The coast of which 156 km (83 %), is sandy beaches, can be divided into three physiographic sectors. Sand deposits are limited to a narrow strip of the Holocene beach area, deposited between the low-water line and the Holocene terraces. They are predominately quartz, with some beaches containing heavy minerals. The shoreface and the inner shelf has a highly complex underwater topography owing to the presence of beachrock, coral and algae reefs structures at several different depths, as well as paleochannels and other features. The coast has three well defined zonation in terms of wave energy: (1) Goiana to Paulista city, has a high wave convergence zone offshore with a high dissipation/diffraction rates across the inner shelf due to its wide reefs and shallow shelf resulting in low waves at the shore; (2) Paulista to Cabo city, an intermediate wave convergence zone marked by few divergence zones at low tide; (3) Ipojuca to São José da Coroa Grande city there are fewer convergence zones but the inner shelf has numerous discontinuous reefs inducing refraction and diffraction patterns. This pattern is controls the shoreline morphology and beach morphodynamic behavior. Based on this the beaches can be divided into three sectors: with the reef protected northern beaches are tide-modified; the exposed southern beaches are wave-dominated; and the middle sector beaches where the beachrock reefs controls the relation between wave and tide are geomorphologically controlled.