Dinâmica morfo-sedimentar da praia de Zalala – Quelimane, Zambézia

Abstract

Beach sediments are derived from a wide variety of sources including coastal erosion, rivers, coral reefs and sea shells, and the nature of these sources and the type and intensity of erosion, transport and deposition processes in the coastal region determine the kind of material that forms a beach. In turn the sediment characteristics strongly influence the morphology and the processes that occur in it. The way sediments are worked to remain in this environment involves complex processes and is still a vast science to explore. In this work the morpho-sedimentary dynamics is investigated in detail on the beach of Zalala (Quelimane). A series of sediment samples from different times (rainy and dry) were collected in the area near the surf, while the topographic currents and profiles of different depths were measured. Several satellite maps of different years were also processed to visualize and analyze the impact of these processes on the morphology of Zalala beach. Therefore, the sediment sample was submitted to grain size analysis with emphasis on texture and density, and was based on the Robinson Pipette, Screen and Pycnometer methods respectively. The results showed an abundance of sand (98%) following the clay (3%) and silt (1%) in the beach of Zalala, to this amount of fine sand it is noticed that the beach of Zalala is classified as a dissipative beach; It was observed a variation of the velocities of the chains of 4cm / s-80cm / s, causing in little settling of particles and much removal of the same ones. The topographic profile showed morphology of a more sloping beach (result of erosion) in the dry season and of sandbank (result of deposition) in the rainy season, which is the result of a sedimentary imbalance. While the satellite maps of different years showed that the beach of Zalala significantly altered its geomorphology in the last 56 years, with indices of removal of particles of very high coastal sediments.