SOME COASTAL IMPACTS RELATED TO WIND WAVE CHANGES IN SOUTH-EASTERN SOUTH AMERICAN CONTINENTAL SHELF

WALTER C. DRAGANI, JORGE O. CODIGNOTTO, PAULA B. MARTIN, MARÍA I. CAMPOS, GUADALUPE ALONSO, CLAUDIA G. SIMIONATO AND RUBÉN A. MEDINA

Southern Ocean: Oceanography and Climatic Impact

Nova Sciences publishers

Lugar: New York; Año: 2012; p. 161 - 177

Coastal impacts (especially erosion) related to a possible wind wave height increase in the South-eastern South American Continental Shelf are reported in this work. Several papers presented evidence about a possible change on the low atmospheric circulation in this region of the Southern Hemisphere. Consequently, a weak increase in wave height might be occurring which would be hard to quantify due to shortness and insufficiency of available observations. In order to study a possible trend in mean annual wind wave heights, Simulating Waves Nearshore (SWAN) model forced with NCEP/NCAR surface wind was implemented in a regional domain for the period 1971-2005. The annual root-mean-square heights of the simulated wave show significant trends at several locations of the inner continental shelf and the adjacent ocean. The most significant increase is observed between 1991-2000 and 1981-1990 decades. The largest difference (0.20 m, 9%) occurs around 34°S-48°W. Wave height increase is somewhat lower, 7%, in the continental shelf and in the Río de la Plata estuary. The coastal area of Samborombón Bay (located at the outer Río de la Plata) ends in a micro cliff which, during the last decades, has been undergoing increasing retrogression (8.2 m/decade). Positive trends in frequencies (10 ± 6 and 7 ± 6 cases/decade) and heights (0.04 ± 0.02 and 0.02 ± 0.02 m/decade) of waves propagating from the E and ESE directions were obtained as a result of this numerical study. In addition, significant variations in the net alongshore wave energy flux were inferred at the north eastern Buenos Aires Province, which could be responsible for the substantial retrogression observed at Punta Rasa, a sand spit located at the northernmost extreme of the Buenos Aires Atlantic coast. Finally, some previous papers have reported a rise in the frequency, height and duration of storm surges in the Río de la Plata and an increase in the mean sea level in the region. The joint effect of those processes on coastal erosion is discussed and it is concluded that the combination of these different factors constitutes a powerful and effective mechanism which is likely responsible for the observed changes in this region of South America.