Spatio-temporal coastline dynamics of the Gambia littoral zone from 1989 to 2019

Coastal erosion and accretion are major challenges that affect socio-economic activities and threatened hotel industries and fisheries which contribute 36% of the GDP in The Gambia. This research aimed to apply geospatial and remote sensing techniques in modelling erosion and accretion on the coastline of The Gambia, West Africa. Multi-temporal satellite data of the years 1989, 2009 and 2019, respectively were collected from Landsat 5 Thematic Mapper (Landsat 5 TM) and Landsat 8 Operational Land Imager and Thermal Infrared Sensor (Landsat 8 OLI TIRS). The collected images were pre-processed and post-processed using ERDAS Imagine 1.2 and ArcGIS 10.3 software. The Modified Normalised Difference Water Index (MNDWI) change detection algorithm was utilised on the images to classify land and water interfaces. Boolean operation classified the images into 0 and 1 as land and water. They were subsequently digitized to create vector layers. Digital Shoreline Analysis System (DSAS) was used to analyse the Spatio-temporal variations on the coastline from 1989 to 2019 and rate of erosion and accretion. The Spatio-temporal analysis for the period 1989 to 2019 found that Cell 1 had an End Point Rate (EPR) of -3.5 ± 3.0 m y−1. Cells 2, 3, 4 and 5 had EPR of -4.7 ± 3.3 m y−1. The remaining cells 5, 6, 7 and 8 shared EPR rate of -1.2 ± 1.1 m y − 1. The rate of erosion in the whole coastline peaked at -2.7 m y−1 and is dominant in Cells 1, 2, 3, 4 and 5, respectively. Accretion also in the whole coastline climaxed to more than +4.5 m y−1 and was mostly dominant in some parts of Cell 2. The inconsistent coastline migration has led to the collapse of some infrastructures in the Tourist Development Area (TDA), loss of agricultural land through salt intrusion and siltation at The Gambia Ports Authority. Hence, this research recommends soft engineering measures in the TDA to avoid disfiguring the recreational sandy beaches and hard engineering measures only between Banjul to Cape Point to protect the Banjul-Serekunda Highway.