Estudo do fluxo de sedimentos transportados pela acção do vento na praia de Zalala, Província da Zambézia

Abstract

The present work does mention the study of sediment transport by wind action on the beach of Zalala-Zambézia province, focusing on the main variables that control the dynamics of coastal wind sediments such as tides, winds, temperature, obstacles, diameter of sediments and the availability of sediments. Having main aim to study the flow of sediments transported by action of winds in height. 18 data collection campaigns were carried out, 9 of them in the living tide and 9 in the dead tide on days (07 and 26 July), (02, 26 and 27, August) and (18, 26, 27, 28, 29 and 30 September) from the year 2017. Data were collected through the descriptive sediment aeolian-trap of 160 cm in height and 30 cm in length and width, subdivided into 5 equal parts of 25 cm vertically and with feet of 35 cm in height, which was positioned at a fixed point of the beach (berm) and in a single direction of the wind in a period of 6 hours, that is, from the beginning of the flood or ebb to the end of the same, in both tides (alive and dead). The wind speed was measured at a height of (25, 75 and 125 cm) with an anemometer and the temperature with a thermometer, with a measurement cycle of 10 minutes for 6 hours. The analyzes of the sediments captured by the trap were carried out in the Chemical Laboratory of the ESCMC and the sedimentology in the Department of Geology of the Faculty of Engineering in Maputo where it was weighed and the granulometry was determined. The amount of sediment collected and mean wind speed varied with trap height and wind directions, where the 1st subdivision of the trap recorded the highest amount with 503.38 g, 4.22 m / s or less was recorded in the 5 ° subdivision with 1,07 g to 5,0087 m / s, in the directions to the Northwest had the highest amount with 259,396 g to 5,01 m / s and the lowest was recorded to the West with 78,067 g to 4, 47 m / s. The granulometry of the analyzed sediments presents an average of Phi (3.74 ɸ) that corresponds to the fraction of (fine and very fine sand). It was concluded that the amount of sediment captured and the flow decreases with the height of the trap, where the 1st subdivision presents the highest amount with 503.38 g and 0.0312 g / s * m2 of flow respectively, and that organisms ( nocturnal crabs) has a great influence on the availability of sediments, especially in the living tide.