Coastline dynamics and its impacts in the northern part of the southern rivers: the case of the northern coastline of Guinea Bissau.

Abstract

ABSTRACT

The objective of this contribution is to analyse the coastline dynamics and its impacts on the northern coastline of Guinea Bissau. The methodology adopted consists in extracting the coastline using multidate Landsat satellite images and analysing the kinematics of the coastline using the DSAS (Digital Shoreline Analysis System) tool under ARGIS. The results of the cartographic processing of the multi-date images show that the sandy beaches of Guinea Bissau are subject to intense erosion phenomena. The first segment analysed, extending from Nhiquim to Bolor, is marked by an alternation of eroding and prograding segments between 1973 and 2018. This part of the Bissau-Guinean coastline is eroding at variable speed. The speed of erosion follows a North-South gradient with 0.21 and 1.8 m/year. The speed of retreat of the coastline is more accentuated in the 1970s on either side of Valera, i.e., 12 m/year in the north and 32.3 m/year in the south. The second segment runs from Mata De Uco to Bote. The highest rate of recession is noted in this part of the coastline studied, particularly during the period 1973-1986. The whole sector is eroding with a speed varying between 53.2 m/year and 0.15 m/year. The average rate of retreat is 19.1 m/year and falls freely between 1986-2003 and 2003-2018. The prograding sectors are in the south with a rate of retreat varying between 2.59 m/year and 8.50 m/year.