Beach differentiation along the Rio Grande do Sul coastline (Southern Brazil)

Changes in sediment properties (grain size and composition) associated with shoreline orientation and local hydrodynamics induce beach differentiation along the Rio Grande do Sul coastline between Rio Grande (32 degrees 10' S) and Chui (33 degrees 45' S). Three zones with distinct morphodynamic behavior can be identified: fine sandy beaches near Rio Grande display dissipative characteristics: further south, a 40 km stretch of coast called ''Concheiros'', is composed of shell debris and fine sand, and represent intermediate to reflective beaches; at all other locations beaches show an intermediate stage. Differences in morphodynamic behavior between these regions are characterized by beach face steepness, frequency of secondary morphological features. erosional characteristics and associated hydrodynamics. A seasonal behavior is superimposed on this general morphodynamic pattern, owing to the wave climate regime with a tendency to develop a swell profile, between November and March, and a Storm profile in the remainder of the pear. The ''Concheiros'' area displays low abundance and diversity of the benthic macrofauna and the highest storm-induced subaerial sediment volume change when compared with other beach systems along this area. The combination of distinct morphological features, like well developed beach cusps, scarps and shelly gravel sands provides this area with unique characteristics along the 210 km of coast.