MORPHOLOGICAL DIVERSITY OF THE FRONTAL DUNES ON THE NORTH COAST OF RIO GRANDE DO SUL, BRAZIL

摘要

The formation of beach-dune system is related to beach morphodynamics, sedimentology and the predominant wind direction in relation to the coastline. This work had the objective of identifying the morphological variables and sedimentological responsible for the diversity of beach-front dune system on the North coast of Rio Grande do Sul (RS) and describe the morphology of foredunes. Morphological variables like height of foredunes, azimuth of coast line, width and slope subaerial beach were obtained from references. The percentage of vegetation covered by foredunes was obtained through digital surface models, produced with laser scanning-handling, and high resolution satellite images, classified by maximum likelihood technique. Surface sediment samples were made in foredunes and subaerial beach to determine the percentages of medium sand. Morphological and sedimentological variables were analyzed by statistical techniques, and clustering key components. The percentage of vegetation cover middle of foredunes is 65.2%. In the locker room of the region there is a predominance of silica sands well very well classified. The percentage of sand average is 6.9% (foredunes) and 7.1% (subaerial Beach). Three groups of spas were generated in the statistical analyses. The Group 1 has the lowest percentage of medium sand on the beach (4.3%), subaerial foredunes of lesser height (3.5 m), smaller percentage of vegetation cover (52.2%) and largest azimuth of the coastline (32.8 degrees). The foredunes are erosive stages, have little time and low vegetation cover. The Group 2 presents the greatest percentage of sand dune average (8.3%), lower average width of subaerial beach (48.0 m) and foredunes of 4.1 m of average height. The 3 Group holds the highest percentage of sand beach average (7.6%) subaerial, higher percentage of vegetation cover of foredunes (73.4%), more extensive subaerial beach and foredunes with 3.9 m average height. The same group presents the lowest percentage of sand dune average (5.6%) and lower azimuth of the coastline (25.1 degrees). The foredunes of groups 2 and 3 are in stages of erosion, hummock topography moderates often, due to the action of sangradouros and blowouts that slice up the foredunes. The principal components analysis showed that there is no correlation between morphological variables and sedimentologicas. The only negatively correlated variables are height of foredunes and azimuth of coastline. In the region studied, the coastline encourages the sedimentary transport, allowing the prevailing breeze cover at an angle near 45 degrees on the coast. Some excerpts studied not grouped, therefore they possess unique features like: foredunes of greater height and most vegetated, azimuth coastline near 40 degrees, and high percentages of medium sands studied environments.