The actual erosive phase of the east part of the beaches of Rio de Janeiro State has started during the year of 1997 and, became extreme after March of 1999.
Photographic documentation has been realized from 1997 and compared with pictures and satellite images took before.
The natural anomalies in sedimentary transport cycle and in the sea level are yielding the intense erosion on the littoral of Rio de Janeiro City and others, in the southeast coast of Brazil, classified as an environmental impact. There is erosion beyond the foundations of life-guard spot houses N. 8 at Ipanema beach and N. 13 at S. Conrado beach, where the seawall protections and the walkways breakdown. In these beaches, the berm sands get out, the sea acts directly on the seawall and at Arpoador beach occurred a rupture connected with the destruction of the last ramp access to this beach, where escape the soil material and the walkway gone under. In Ipanema beach, a layer of gross material of artificial embankment, the tubes of submarine sewage outfall and dangerous steel planks have been exposed. The quality of these beaches, as resort, deteriorated.
During the year 1997, erosive phases seemed to have been caused by natural anomalies on the alongshore transport, that are added to the intense erosive phase started in the middle of March of 1999. This erosion, specially strong between 18 and 19 of April of 1999, was caused mainly by the high waves associated with the rising of sea level, basically a storm surge. This surge has commonly components of wave set-up, wind set-up and the rise of sea level as a result of an atmospheric cyclone low pressure area, that moves against the coast, surrounded by high pressure areas offshore, that yields a hump in the sea surface. The coincidence with a phase of high water spring level occurred.
Other possible component of erosion cause must be the out of phase of the normal storm season in relation with the monthly sea level distribution along the year. The normal storm's season is mainly during July and August, the minimum monthly normal sea level is during August to September and the peak of maximum monthly normal sea level is during May in the southeast Brazilian coast. The time lag is probably connected with large-scale phenomena like El Nino in 1997 and La Nina in 1999, when strongest annual storms occurred in the end of May.
The history of the city remembers us, in the past recent, some inclination of buildings on the coast, function of static and dynamic pressures in the soil, due respectively to the rise of sea level and to the waves, that communicate indirectly its hydraulic loads through the beach ridge, where the buildings lie.