Coastal morphodynamic processes on the macro-tidal beaches of Pará state under tidally-modulated wave conditions

Abstract

Amazon coast is a vast and complex estuarine–marine system with highly dynamic coastal environments driven by an abundance of sediment reworked by fluvial, tidal and wave processes. The coast of Pará occupies the eastern Amazon Gulf and is more than 2000 km long, with more than 400 sandy beaches. It can be divided into five coastal sectors: the Amazon river-distributary coast; the north coast of Marajó Island; the west and east coasts of Marajó Bay; and the highly indented eastern barrier island coast between Marajó and Gurupi bays. This chapter will examine the eastern Pará coast, between Belém in Marajó Bay and Gurupi Bay, a macro to mega-tidal coast dominated by tide-modified and tide-dominated sand beaches. There is however considerable spatial and temporal variability in beach state, dependent on the amount of nearshore sheltering by inter to sub-tidal sandbanks, with tide-modified beaches (3 < RTR < 15) on the more exposed sections and tide-dominated (RTR > 15) on the more sheltered sections, together with tide-modified beaches at high tide and tide-dominated at low tide. The impact of this tidal modulation on wave energy and beach morphodynamics is examined on three beaches, together with their associated beach hazards. These are then combined with seasonal tourism population to assess the level of risk. The large seasonal beach population coupled with unplanned beach development generates addition hazards including eroding buildings, traffic congestion and accidents on some beaches, and sewerage and litter pollution. Coastal planning and regulation is urgently required for this coast to enable it to develop a safe and sustainable tourist industry and to reduce the beach hazards and risk.