Classification of the Southern Brazilian Coast According to Storm Wave Patterns and Geomorphologic Evidence of Coastal Erosion

An attempt was made to classify the Gaucha coastal zone (southern Brazil) on the base of wave refraction patterns and its relationship with first order coastal processes such as erosion an accretion. The full extension of the coastal zone was analyzed (640 Km). Relatively long waves (period greater than 9s) were under consideration. Refraction diagrams constructed with wave period and direction increments of 1 s and 10 degrees respectively, reveal four types of storm processes: convergent or focus, divergent, variable and without refraction. All of them demonstrate definite stability in relation to changeable wave period and direction of propagation in the open sea. The classification itself is made in the form of a chart. As a result a strong relation was found between the location of wave focus spots and beach erosion localities. Such evidences are related to Conceicao lighthouse area and Hermenegildo beach. The areas are of extension of 30 Km to 55 Km, and the coastal retreat rate is 0.5 m/year in Hermenegildo and up to 3.6 m/year in Conceicao lighthouse correspondingly to five years monitoring. At the same time no clear relations have been found between divergent and variable patterns and coastal events. Moreover this approach is not able to explicate the cause of coastal erosion of the scale of 1 Km (Lagamarzinho beach). The role of relatively short waves (period less than 9 s) is unclear as well.