Natural and antropic geomorphological changes in the inlet of patos lagoon before and after its fixation

Abstract

Comparative analysis of historical records of geocoded charts from the Patos Lagoon inlet between the years of 1883 and 1956 indicates that the shoreline at the south of the west jetty experimented a progradation of the order of 1000 m. This effect was more intense between 1914 and 1971 stabilizing afther this period. During the same period, shoreline progradation to the nort of the structure reached 60 m and 13.4 m respectively at distances of 500 m and 1,000 m of the west jetty. At the inlet, significant changes occurred in the east margin which is extremely dynamic when compared with the west margin. Morphologically, prior to the jetties construction the east point displayed a convex side facing the ocean. Fixation of the east jetty reoriented the point by changing its original form to a concave side facing the ocean. Sediment volume changes between the jetties considering a width of 720 m and a lenght of 4,020 m during distinct years indicated differences between periods of climatic extremes. Natural deppening and silation were respectively associated to a historical flood and a extended drought. The same behavior was identified for the sand bar nucleus which respectively increase and decrease its sediment volume according hydrodynamic changes associated tho the climatic variations.