TITLE:
Dynamic Evolution of the Joal and Djiffère Spits under the Influence of Atlantic Ocean Activity
AUTHORS:
Madièye Fall, Déthié Sarr, Oustasse A. Sall
KEYWORDS:
Coastline, Mapping, Erosion, Accretion, Morphosedimentary
JOURNAL NAME:
Journal of Environmental Protection,
Vol.16 No.1,
January
31,
2025
ABSTRACT: Changes in the coastline are characterized by accretion and erosion. The aim of this study is to contribute to a better understanding of the dynamics of the coastline and the study areas with a view to mitigating and preventing the risk of coastal erosion in order to propose a coastal occupation model with planned development policies in the future. These phenomena lead to changes in the position of the coastline. After extraction, the satellite images are compiled, then superimposed and processed using Geographic Information Systems (GIS) for statistical calculation of coastline change rates. A morphosedimentary study is carried out using topography and sedimentology. The topographic method is used to calculate sediment volumes using monthly profiles. The sedimentological method is used to determine the granulometric variations in the morphological units by calculating sedimentological indices. With erosion rates of −2.13 m/yr and −2.17 m/yr respectively at Djiffère (Palmarin and Sangomar breccia) and Joal (Joal Fadhiouth and Ngazobil), the EPR index revealed a sediment deficit. Palmarin Ngallou and the island of Fadhiouth are undergoing accretion at rates of +1.43 m/yr and +1.14 m/yr respectively. From a topographical point of view, the respective accumulations of −13.74 m3/m of beach and −8.65 m3/m of beach at Djiffère and Joal respectively point to significant erosion on all the aerial beach units, while for the underwater beaches, accretion was noted with accumulations of +4.00 m3/m of beach and +5.94 m3/m at Djiffère and Joal respectively. As for the sedimentological results, the Mz index shows a decrease in grain size from the high beach to the surf zone. Some points show bimodal deposits, showing the impact of the dune on beach activity, confirmed by the dispersion on the Mz-sigma diagram. The three methods used in this work show that the Djiffère sector in Joal is dominated by erosion, even though accretion points can be noted.