Short-term morphological characterization of beaches in Caucaia and São Gonçalo do Amarante counties, Ceará State, Brazil

Abstract

The research was developed in the beaches of Caucaia and São Gonçalo of Amarante counties, located between Rio Ceará’s outlet and Pecém, Ceará State, Brazil. The study has as objective to define and quantify the coastal processes that account for the erosion observed in the area, causing damages to the environment and highlighting the agents that interfere directly on those modifications: winds, waves, tides and longitudinal currents, as well as, instability generated by human action. The waves that reach the coastlline are of the types: sea, irregular waves with the period varying between 4 and 9 s, with a mean height of 1.10 m and approaching direction ESSE; and swell, waves that are more regular, with height of about 1.0 m, period above 10 s and approaching direction N-NE. The tides are semidiurnal(12 hour periods) and a 160 cm range. The superficial currents presented speeds in dry period from 0.22 and 0.68m/s and approaching direction N-NW. The used methodology consisted of a critical analysis of the previous works, definition of short-term variations of the coastline, the visualization proceeded for the observation of eight pre-established profiles, for 27 months, together with sampling of the sediments. The quota of those profiles was reduced to the hydrographic zero by Brazil’s Hydrography and Navigation Directory (DHN). The study of the profiles identified areas of erosive tendencies with rates from -48m³/m.yr. to -16,8m³/m.yr., deposition point of sediments with +37m³/m.yr. to +26,4m³/m.yr., as well as places where the coastal zone is in balance. The sediments presented a predominance of medium sand, rich in quartz, with polished and sub-round grains.