Hazards and risks associated to coastal processes along the southern Brazilian coastline: A synthesis.

Abstract

Some processes related to hydrodynamics, geomorphology and sediment movement represent coastal hazards and risks along the littoral of Rio Grande do Sul (RS) state in southern Brazil. The hazards imply in coastal erosion, habitat loss and environmental change. The risks are related to serious accidents including fatalities to the coastal users. Shoreface morphology, storms and washouts induce erosion at specific locations of the coastline. Storms and washouts, together with beach morphodynamics and depositional processes both aeolian and hydrodynamic embody latent risks to the physical integrity of people that live in and use this environment. Wave refraction patterns from SE to SW cause erosion in two coastal sectors at the proximities of Conceição Lighthouse and Hermenegildo Beach respectively located at the central and southernmost portion of the RS coastline. In both areas, the high number of washouts amplifies the erosion destroying foredunes and the subaerial beach. In addition, the lowlands of the barrier adjacent to small pocket lagoons in the northern littoral are more susceptible to washout erosion. Both, the refraction patterns and the washouts can be associated with two storms tracks and extra-tropical cyclones which magnify erosion and inundation of the coastal zone. The combination of higher population during summer seasons and intermediate beaches with considerable amounts of medium sand make beaches from the northern littoral and extreme south more risky for bathers. Coastline orientation in relation to the predominant NE wind causes wind-blow sand to invade the coastal plain in the form of transgressive dunes causing several hazards mainly in the northern littoral between Tramandaí and Mostardas. Short-term effects associated with episodic events of mud deposition during heavy storms on Cassino Beach influence the morphodynamics behavior on the sectors affected by the mud deposits creating coastal risks relating to beach usage.