Vulnerability of the coastal zone of The Gambia to sea level rise and development of response strategies and adaptation options

摘要

The coastal zone of The Gambia consists of 70 km open ocean coast and 200 km sheltered coast. Only about 20 km of the open coastline is significantly developed and this includes Banjul (the capital city), Bakau and Cape St. Mary, Fajara and the Tourism Development Area (TDA). Tourism is the most important economic sector in the coastal zone and contributes about 10% of the government revenue. Fisheries and agriculture are also important coastal industries. In this study the Aerial Videotape-assisted Vulnerability Analysis (AVVA) technique has been used to provide a detailed analysis of vulnerability to sea level rise, and adaptation strategies have been identified. The data used includes a video recording of the coastline, color infrared and black and white aerial photography, topographic maps, bathymetric maps, a geological map of The Gambia and still photographs. The data have been used to characterize the coastal zone into 9 geomorphological units, wherein the cultural and heritage sites of economic importance have been delineated and characterized according to their biophysical and economic importance. Future erosion rates have been projected by applying the Bruun Rule, and future total land loss due to inundation in response to global warming and accelerated sea level rise has been determined. The sea level rise scenarios considered are 0.2 m, 0.5 m, and 1.0 m per century. Inundation is estimated to be about 92.32 x 106 m2 for a 1.0 m sea level rise, 45.89 x 106 m2 for a 0.5 m sea level rise and 4.96 x 106 m2 for a 0.2 m sea level rise. The greater part of this area lost will be wetlands and mangrove systems important for fish spawning areas and habitats for wildlife. Shoreline retreat is estimated to vary between about 6.8 m in cliffy areas to about 880 m for more flat and sandy areas based on the Bruun Rule. Population and physical structures at risk have been determined. Attempts have been made to report this loss in monetary terms, but firm figures are not yet available. Only one unit of the coastal zone has been evaluated. In this unit, it is expected that the capital city will be completely lost through both erosion and inundation within 50 to 60 yr with a total of 42000 persons displaced. Lands and physical structures to be lost are estimated at US$ 217 million. Response strategies and adaptation options identified include: innovative sand management, building and rehabilitation of groins, construction of revetments to protect important areas, construction of sea-walls/bulkheads, public outreach and awareness, building regulations and urban growth planning, wetland preservation and mitigation, and development of a coastal zone management plan.