Mudanças morfológicas da extremidade NE da Ilha Comprida (SP) nos últimos dois séculos

Abstract

Ilha Comprida, a Holocene barrier built by alignments of littoral ridges, underwent intense morphologic changes in the past 200 years, mainly in its NE extremity. These changes includes northward shifting of the Icapara inlet, local variation of the width of the island, the formation of a small transgressive dunefield, an increase in the width of the Valo Grande artificial channel, and appearance and disappearance of ephemeral features such as a coastline prominence and a lagoonal embayment. The morphodynamics of the northeastern extremity of the island results from the interaction between littoral drift currents, tides, and fluvial sedimentary supply from the Ribeira de Iguape River. The remarkable northeastwards littoral drift, inferred by sedimentological analysis, is the main factor of the shifting of the Icapara channel in this direction, added to a “meandering effect” of the channel. This effect would be generated by interaction between the tidal regime and the fluvial sedimentary supply, such that the northward margin of the channel (Iguape) acts like a erosional levee, and the southward margin (Ilha Comprida) acts like a point bar. In this way, sand is removed at Iguape and deposited at the tip of Ilha Comprida. Even though the northeasterly growth of the barrier occurred over thousands of years its speed increased significantly after the opening of Valo Grande in 1852, which became factor influencing the sedimentary input at the Icapara inlet.