Multitemporal Variability in the Morphodynamics of a River-Estuarine Island

Abstract

Lobo, F.C.; Peixoto, H.J.C.; Borba, T.A.; Monteiro, S.M., and Rollnic, M., 2020. Multitemporal variability in a river-estuarine island. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 865–869. Coconut Creek (Florida), ISSN 0749-0208.Cotijuba Island, in Northern Brazil (1°14.249′S, 48°32.806′W), has typical characteristics of Amazon lowlands, such as low and smooth topography and the presence of cliffs surrounding its river-estuarine beaches. The beach environment on this island has morphological variations determined by hydrodynamics of the Para River estuary (mesotides and mean annual outflow of 104 m3s-1), climatic seasonality in the region, and anthropogenic changes. Thus, it was investigated how coastal morphological changes occur on the beaches of Cotijuba Island at different temporal scales, considering regional seasonality. The polygons methodology was used based on Landsat satellite images taken in 1987, 1998, 2008, and 2017, and on in situ measurements of morphological variations of the beaches in 2018 using topographic profiles taken with a digital level GEOMAX ZDL 700, covering 8.7 km of beaches that are bathed by the Para River estuary. Cotijuba Island seems to have little or no influence from long-term climatic conditions, as the ENSO phenomena. Although climatic influence is evident at short-term temporal scales, it is worth emphasizing that the physiographic features of the beaches, such as the presence of perennial and temporary channels, and of rocky outcrops, also affect morphodynamic changes on the beaches, especially at a small temporal scale.